Device and method for measuring at least one physiological parameter

Abstract

The invention relates to a measurement device (100) for measuring at least one physiological parameter, the measurement device (100) comprising a housing (101) which has: - a measurement chamber (104), which has an internal volume filled with a gas, - a sensitive cell (105) permitting measurement of at least a first physiological parameter, the sensitive cell (105) being disposed in contact with the gas contained in the internal volume of the measurement chamber (104), and - an inlet (107) for a physiological liquid of a patient, the inlet (107) being disposed in such a way that the physiological liquid comes into contact with the gas, and the gas remains interposed between the sensitive cell (105) and the physiological liquid of the patient in such a way as to generate an interface between the gas, contained in the internal volume, and the physiological liquid. The invention further relates to a method for measuring at least one physiological parameter.

Description

Description Title of the invention: Device and method for measuring at least one physiological parameter [Technical field]

[0001] The invention relates to a device and a method for measuring at least one physiological parameter. The invention applies in particular to measuring the pressure of a physiological fluid punctured inside a patient's body. In particular, the invention relates to a device and a method for measuring the pressure of a physiological fluid which is in contact with the central nervous system. More particularly, the invention measures the pressure of the cerebrospinal fluid (CSF) punctured, for example, by means of a lumbar puncture.

[0002] Intracranial pressure is the pressure of the CSF present inside the skull, which bathes the central nervous system. Access to CSF ​​by lumbar puncture was described by Quincke in 1891. CSF pressure measured by lumbar puncture is also a measure of intracranial pressure [Lenfeldt N, Koskinen LO, Bergenheim AT, Malm J, Eklund A. CSF pressure assessed by lumbar puncture agrees with intracranial pressure. Neurology. 2007; vol 68, no2, p.155-158]. The measurement of intracranial pressure by lumbar puncture marks an important advance in neurology in the understanding and especially the identification of intracranial hypertension threatening the central nervous system.

[0003] CSF pressure can be measured either statically or dynamically. The static or hydrostatic approach involves measuring the steady-state pressure and pulsatility of the CSF secondary to cyclic cardiac and respiratory oscillations; whereas the dynamic or hydrodynamic approach involves applying a known stress to the intracranial fluid system, called a perfusion test, and analyzing the system's response to this stress. [Czosnyka M, Pickard JD. Monitoring and interpretation of intracranial pressure. Journal of Neurology, Neurosurgery & Psychiatry, 2004, vol. 75, no. 6, p. 813-821],

[0004] The hydrostatic approach allows the measurement of fluid pressure inside the skull and the identification of normal pressure and increased pressure known as intracranial hypertension. This can manifest as headaches, nausea or vomiting, cognitive impairment, and even coma in the most severe forms.

[0005] The causes of intracranial hypertension syndromes can be multiple: expansive pathology such as a tumor, an intracerebral hematoma or a hydrocephalus, but also a blockage of the venous drainage system by thrombophlebitis, ...).

[0006] There are also so-called "secondary" causes of intracranial hypertension such as endocrinopathies (Addisson's disease, Cushing's disease, hypothyroidism, hyperparathyroidism), a vitamin A deficiency altering the structure of the arachnoid villi, during drug intake (hormonal, antibiotic, lithium or cimetidine), and various other pathologies (sleep apnea syndrome, chronic renal failure, iron deficiency anemia).

[0007] The hydrodynamic approach can be achieved by injecting saline into the CSF using the access provided by lumbar puncture. This saline injection applies stress to the intracranial fluid system. The response of the intracranial system following the perfusion test allows for the extraction of various relevant measurements, including the measurement of CSF flow within the skull. The increase in flow resistance is an important parameter in clinical practice, as it allows for the demonstration of an objective alteration in CSF circulation that indicates hydrocephalus.

[0008] [Prior art]

[0009] In the 1930s, Professor Henri Claude developed a manometer that included a hose that connected directly to a lumbar puncture needle. The concept behind the Claude Manometer was to place the cerebrospinal fluid directly in contact with the manometer's measuring area. Today, the Claude Manometer is banned for health reasons. Furthermore, the Claude Manometer also cannot measure the pulsatility of intracranial pressure.

[0010] Currently, there is no simple and reliable device on the market to quantify intracranial pressure by measuring CSF pressure. Thus, in 2022, practitioners still measure cerebrospinal fluid pressure by measuring a water column, as described by QUINCKE in 1891. For this, practitioners use a seamstress's tape measure manually placed along the flexible, sterile, single-use tube. In practice, the flexible tube is connected to the lumbar puncture needle. Although this rudimentary method may be sufficient to approximately measure a stationary intracranial hydrostatic pressure, it does not allow for precise measurement of the mean value and pulsatility of the intracranial pressure, nor for recording the signal, nor for performing a hydrodynamic exploration.

[0011] However, more complex solutions exist, notably using a piezoelectric sensor. The piezoelectric sensor converts liquid pressure into an electrical signal; the electrical signal must then be amplified and digitized to be processed by specific software. In practice, the sensitive cell of the piezoelectric sensor is placed directly in contact with the CSF in order to measure its pressure using an approach that can be hydrostatic or hydrodynamic.

[0012] Generally speaking, the CSF pressure measured by the sensitive cell of the piezoelectric sensor is the summation of two forces per unit area: the pressure transmitted by the fluid, and the pressure related to the displacement of the mass of the fluid. Indeed, this mass undergoes accelerations either direct or due to gravity. In fact, the piezoelectric sensor measures the pressure transmitted by the CSF but also the accelerations of the liquid mass which constitute artifacts and deteriorate the quality of the CSF pressure signal. Thus a liquid pressure sensor measures all physical accelerations related to the medical environment in which the pressure measurement is carried out. For example, vibrations of medical equipment will generate an artifact within the signal measured by the pressure sensor, this is also the case of a shock which occurs on the patient's bed etc.These vibrations and other artifacts disrupt fine measurements such as the pulsatility of intracranial pressure.

[0013] The system known as "ICM+"® was developed by the University of Cambridge (UK) to enable intracranial multi-monitoring. This software allows, among other things, the measurement of CSF pressure in order to perform both static and dynamic analysis of intracranial pressure. The ICM+ system allows for reliable measurement of intracranial pressure at the patient's bedside. However, this software is dedicated to clinical research, and is not easily accessible to a majority of practitioners at the patient's bedside. In particular, no specific sensor is designed for the "ICM+"® system.

[0014] Document US 4,858,619 describes a system that measures variations in CSF pressure and allows its drainage. This system allows CSF pressure to be measured remotely, whether the puncture site is lumbar or cranial. In this document, the pressure sensor transforms the fluid pressure that it measures into an electrical signal. For this purpose, the sensitive cell of a pressure sensor is placed in a measuring chamber that is first emptied of its air and filled with physiological saline by a purging operation. The CSF is then in fluid communication with the measuring chamber filled with physiological saline. On the one hand, the sensitive cell measures physical acceleration artifacts that the pressure sensor undergoes but also accelerations of the mass of the physiological liquid, and on the other hand, this system does not allow measurement of CSF pressure pulsatility using a hydrodynamic approach.

[0015] Document CN 105641758 describes another CSF drainage system where it is punctured directly from the patient's skull. A tube drains the punctured CSF to a first lower end of a vertically oriented bulb in which a float is placed. The bulb has a second upper end connected to a guide tube which is equipped with a pressure sensor. The guide tube is filled with a gas. The float thus constitutes a membrane which aims to separate the CSF located under the float and the gas located above the float and in the guide tube. The objective of this system is to prevent the liquid from coming into contact with the pressure sensor, which would thus not have to be sterilized. The system thus measures the pressure of the CSF through the gas contained in the guide tube. When the pressure of the CSF increases above a certain threshold, a solenoid valve allows the drainage of the CSF into a collection bag.However, monitoring CSF pressure variations is unreliable. Indeed, CSF pressure variations are measured by measuring the pressure of the gas contained in the guide tube even though the gas is not in direct contact with the CSF. In addition, the float that separates the gas from the CSF is likely to disrupt the measurements by damping CSF pressure variations but also by the accelerations that the float may undergo in the event of movement of the tubing or the bulb.

[0016] The invention aims to overcome all or part of the aforementioned drawbacks. [Statement of the invention]

[0017] The invention aims to provide a reliable and cost-effective solution for measuring at least one physiological parameter such as CSF pressure by lumbar puncture.

[0018] The invention aims to reliably measure at least one physiological parameter at the patient's bedside.

[0019] In particular, the invention aims to provide a technical solution for reliably measuring variations in CSF pressure over time.

[0020] The invention aims in particular to reliably measure the stationary pressure or the pulsatile pressure of the CSF.

[0021] To this end, a first aspect of the invention relates to a device for measuring at least one physiological parameter. The measuring device comprises a housing which extends longitudinally between a first end and a second end opposite the first end. The housing comprises three parts: a measuring chamber which is arranged in the housing, the measuring chamber having an internal volume which is filled with gas, a sensitive cell making it possible to measure at least a first physiological parameter, the sensitive cell being arranged in contact with the gas contained in the internal volume of the measuring chamber, and an inlet of a physiological liquid of the patient into the measuring chamber, the inlet being arranged so that the physiological liquid comes into contact with gas and the volume of gas remains interposed between the sensitive cell and the physiological liquid of the patient.

[0022] According to the invention, the measuring chamber makes it possible to generate two interfaces: a first interface between the gas contained in the internal volume and the physiological liquid of the patient which enters through the inlet, a second interface between the gas contained in the measuring chamber and the sensitive cell.

[0023] The measuring device according to the invention makes it possible to reliably measure a physiological fluid parameter such as CSF pressure. Indeed, in a fluid, according to Pascal's principle, pressure variations at one point are transmitted in full to all points of this fluid. The pressure variations of the physiological liquid are therefore transmitted to the sensitive cell of the sensor via a gas bubble, which corresponds to a "hydropneumatic transmission interface" or a liquid-gas interface.

[0024] Furthermore, the device according to the invention makes it possible to reduce artifacts due to vibrations of the sensor.

[0025] In embodiments of the first aspect of the invention, the measuring chamber may have an internal volume that is non-zero and less than or equal to 1 ml, in particular, the internal volume must be strictly less than 1 ml, preferably less than 0.7 ml. The internal volume of the measuring chamber may thus contain a volume of gas making it possible to control the damping of the pulsatility of the pressure of the physiological liquid. This is so that the damping of the pulsatility is acceptable in clinical practice.

[0026] In embodiments, the gas contained in the internal volume of the measuring chamber may correspond to atmospheric air. Indeed, the manufacturing process of the measuring device, for example by plastic injection, not being carried out under vacuum, the measuring chamber is naturally filled with atmospheric air.

[0027] In embodiments of the first aspect of the invention the measuring chamber may have an internal volume of between 0.2 ml and 0.5 ml.

[0028] In embodiments of the first aspect of the invention, the sensitive cell may be a piezoelectric cell of a pressure sensor. The liquid-gas interface also makes it possible to dampen the physical accelerations experienced by the pressure sensor. This improves the reliability of the measurements.

[0029] In embodiments of the first aspect of the invention, the housing may comprise a sealing membrane which is interposed between the sensitive cell and the internal volume of the measuring chamber, the sealing membrane protecting the sensitive cell. The sensitive cell of the sensor may be, for example, a piezoelectric cell of a pressure sensor. The sealing membrane makes it possible to isolate the CSF and, more broadly, the patient's biological tissue from the highly toxic electronic components that a piezoelectric type sensitive cell may contain.

[0030] In embodiments of the first aspect of the invention, the internal volume of the measuring chamber may be cylindrical. A cylindrical shape allows a liquid-gas interface to be formed when physiological liquid enters the measuring chamber.

[0031] In embodiments of the first aspect of the invention, the measuring device may comprise a connector disposed at the inlet of the housing, this connector sealingly connecting the measuring chamber to a physiological fluid connection device of the patient. The physiological fluid connection device may be a lumbar puncture needle. Preferably, the lumbar puncture needle is connected directly to the connector of the measuring device.

[0032] In embodiments of the first aspect of the invention, the inlet may be openable and closable to control the entry of physiological fluid into the measuring chamber.

[0033] In embodiments of the first aspect of the invention, the measuring device may comprise means for transmitting measurements of the first physiological parameter to a remote digital terminal.

[0034] In embodiments of the first aspect of the invention, the sensitive cell may be disposed at the first end of the housing, while the inlet is disposed at the second end of the housing.

[0035] A second aspect of the invention relates to a method for measuring at least one physiological parameter of a patient. According to the invention, the method comprises: a step of connecting the measuring chamber to the physiological fluid of a patient, the measuring chamber being filled with gas and comprising a sensitive cell making it possible to measure at least one physiological parameter, a step of generating a first interface between the gas present in the measuring chamber and the physiological fluid coming from the patient, the gas remaining interposed between the physiological fluid and the sensitive cell so as to form a second interface between the gas and the sensitive cell, a step of measuring at least one first physiological parameter, the measurement being carried out by the sensitive cell through the gas interposed between the physiological fluid and the sensitive cell.

[0036] The measuring process follows the same technical principle as the measuring device; it generates a liquid / gas interface at which the physiological liquid comes into contact with the gas contained in the measuring chamber. The physiological liquid then transmits the pressure of the CSF to the gas, which in turn transmits this pressure to the sensitive cell of the measuring sensor.

[0037] In embodiments of the second aspect of the invention, the volume of gas interposed between the sensitive cell and the physiological liquid of the patient may be non-zero and less than or equal to 1 ml, in particular, said volume of gas may be strictly less than 1 ml, preferably, said volume of gas may be less than 0.7 ml. This volume of gas interposed between the sensitive cell and the physiological liquid of the patient makes it possible to control the damping of the pulsatility of the pressure of the physiological liquid. This is so that the damping of the pulsatility is acceptable in clinical practice.

[0038] In embodiments of the second aspect of the invention, the measuring chamber may be connected to a physiological fluid sampling device which may be the patient's cerebrospinal fluid. In particular, the connecting device may be a lumbar puncture needle. Preferably, the lumbar puncture needle is connected directly to the measuring chamber.

[0039] In embodiments of the second aspect of the invention, the first physiological parameter may correspond to a stationary pressure or a dynamic pressure of the physiological fluid of the patient.

[0040] In embodiments of the second aspect of the invention, the measurement method may comprise a step of determining at least one second physiological parameter through the measurement of the first physiological parameter. [Description of the drawings]

[0041] Other characteristics and advantages of the invention will become apparent from reading the description which follows. This description is purely illustrative and must be read in conjunction with the appended drawings in which:

[0042] [Fig. 1] is a schematic representation of a longitudinal section of a measuring device according to the invention, the measuring device being connected to a lumbar puncture needle.

[0043] [Fig. 2] is a schematic representation of the measuring device of Figure 1 and its medical-technical interactions.

[0044] [Fig. 3] is a schematic representation of a measuring device according to the invention.

[0045] [Fig. 4] is a representation of a flowchart schematically illustrating a measuring method according to the invention.

[0046] [Fig. 5] is a schematic representation of an experimental setup for conducting a comparative study of hydrostatic pressure measurements made by a liquid interface sensor and a liquid / air interface sensor.

[0047] [Fig. 6] is a representation of a graphical record of the hydrostatic pressure signals measured during Experiment 1, the signals being measured by a liquid interface sensor and a liquid / air interface sensor according to the setup of Figure 5.

[0048] [Fig. 7] is a representation of a magnification of the recording of Figure 6.

[0049] [Fig. 8] is a representation of a graphical recording of the hydrostatic pressure signals measured during Experiment 2 in which the signals are measured by a liquid interface sensor and a liquid / air interface sensor according to the setup of Figure 5.

[0050] [Fig. 9] is a representation of an enlargement of cycle C7 of the graph of the record of Figure 8.

[0051] [Fig. 10] is a representation of a Bland Altman plot constructed with data from Experiment 2.

[0052] [Fig. 11] is a representation of a graphical recording of the pressure signals measured during an experiment 3 in which the pressure is pulsatile, the signals being measured by a liquid interface sensor and a liquid / air interface sensor according to the setup of Figure 5.

[0053] [Fig. 12] is a representation of an enlargement of cycle C1 of the graph of the recording of Figure 11.

[0054] [Fig. 13] is a representation of an enlargement of cycle C7 of the graph of the record of Figure 11.

[0055] [Fig. 14] is a representation of a results diagram of an experiment 4 conducted using the setup of Figure 5, the diagram representing the evolution of the pressure pulsatility measured by the liquid / air interface sensor and the liquid interface sensor as a function of the air volume of the liquid / air interface.

[0056] [Fig. 15] is a representation of a diagram illustrating a constitutive law of the damping of the pulsatility of the pressure measured by the liquid / air interface sensor as a function of the air volume of the liquid / air interface. [Description of embodiments]

[0057] With reference to Figures 1 to 3, the invention relates to a measuring device 100 for at least one physiological parameter. More particularly, the measuring device 100 is configured to measure the pressure of the physiological liquid punctured from the body of a patient. For example, the invention relates to a measuring device 100 CSF pressure which is an indirect measure of a patient's intracranial pressure.

[0058] As illustrated in Figures 1-3, the measuring device 100 comprises a housing 101. The housing 101 defines the outer casing of the measuring device 100. The housing 101 extends longitudinally between a first end 102 and a second end 103 opposite the first end 102. The housing 101 has a measuring chamber 104. The measuring chamber 104 extends inside the housing 101. In this example, the measuring chamber 104 extends between the first end 102 and the second end 103 of the housing 101. The measuring chamber 104 is filled by default with a gas G. For example, the measuring chamber 104 can be filled with air. However, it is also possible to fill the measuring chamber 104 with another gas.

[0059] In this example, the measuring chamber 104 has a non-zero volume less than or equal to 1 ml. In particular, the internal volume of the measuring chamber 104 may be less than 1 ml. Preferably, the internal volume of the measuring chamber 104 is less than 0.7 ml.

[0060] According to one embodiment of the invention, the internal volume of the measuring chamber 104 can be between 0.2 ml and 0.5 ml. However, the internal volume can also be between 0.3 ml and 0.4 ml.

[0061] Here, the internal volume of the measuring chamber 104 is cylindrical. The internal volume is delimited by the internal walls of the housing 101.

[0062] As illustrated in Figures 1 to 3, the housing 101 comprises a sensitive cell 105 for measuring at least one physiological parameter. The sensitive cell 105 is arranged in contact with the gas G contained in the internal volume of the measuring chamber 104. In this example, the sensitive cell 105 is arranged at the first end 102 of the housing 101. In particular, the sensitive cell 105 could be of the piezoelectric type. A sensitive cell of the piezoelectric type makes it possible to transform a pressure measurement into an electrical signal.

[0063] As illustrated in Figures 1 to 3, the housing 101 comprises a sealing membrane 106. The sealing membrane 106 is interposed between the sensitive cell 105 and the gas G contained in the internal volume of the measuring chamber 104. In this example, the sealing membrane 106 is arranged at the first end 102 of the housing 101. The sealing membrane 106 isolates the sensitive cell 105. The sealing membrane 106 improves the safety of the device, keeping the electronic components isolated from the internal volume of the measuring chamber 104. The sealing membrane can be made of a medical polymeric material impermeable to air and water such as silicone or polyurethane.

[0064] In the example of Figures 1 to 3, the housing 101 comprises an inlet 107 for a physiological liquid LP of a patient. Preferably, the housing 101 comprises only one inlet 107. Indeed, unlike the prior art, no attempt is made to eliminate the gas present in the measuring chamber 104. Conventionally in clinical practice, it is avoided to bring air into contact with a physiological fluid, in fact, the injection of a small volume of air into the blood system exposes to an embolism which can have serious consequences. However, the injection of the same small volume of air into the nervous system will have no consequences. Therefore, a single inlet 107 makes it possible to control the formation of a liquid / gas interface within the measuring chamber 104. The inlet 107 is arranged so that the physiological liquid LP comes into contact with the gas G. The gas G then remains interposed between the sensitive cell 105 and the physiological liquid LP of the patient.For this purpose, the inlet 107 can be arranged on the housing 101 opposite the sensitive cell 105. In the example of FIGS. 1 to 3, the inlet 107 is arranged at the second end 103 of the housing 101 while the sensitive cell 105 is arranged at the first end 102 of the housing 101. Here, the inlet 107 is constituted by an opening in the housing 101, the outline of the inlet 107 being shown in dotted lines in FIGS. 1 to 3. Nevertheless, other configurations and other shapes of housing are conceivable to allow the gas G to remain interposed between the physiological liquid LP and the sensitive cell 105.

[0065] As illustrated in Figures 1 to 3, the measuring device 100 comprises a connector 108. The connector 108 is arranged at the inlet 107 of the housing 101. In this example, the connector 108 sealingly connects the measuring chamber 104 to a connection device 200 for the patient's physiological liquid LP. In this example, the connector 108 is in the form of a male conical portion which is configured to connect with a female conical tip 109 of the connection device 200.

[0066] In the example of Figures 1 and 3, the female conical tip 109 of the connection device 200 connects directly to the conical connector 108 of the housing 101. As illustrated in Figures 1 and 3, the connection device 200 comprises a lumbar puncture needle 201.

[0067] Preferably, the connection device 200 consists of a lumbar puncture needle 201. According to this configuration, the measuring device 100 is directly connected to the lumbar puncture needle 201. This makes it possible to simplify the use of the measuring device 100 for practitioners.

[0068] Alternatively, the connector 108 may be connected via a three-way tap to the tapered tip 109 of the lumbar puncture needle 201.

[0069] According to another alternative use of the invention, not illustrated, the connector 108 can be connected to a tube inserted between the measuring device 100 and the lumbar puncture needle 201.

[0070] A lumbar puncture involves inserting a needle through the patient's skin into the lumbar sac to access the CSF. Typically, a lumbar puncture is used to collect CSF and allow for biochemical or biological analysis. A lumbar puncture is therefore commonly used in cases of suspected meningitis, inflammatory neurological disease, or neurodegenerative disease.

[0071] In addition to the biochemical analysis window open to the nervous system, the lumbar puncture also offers a window for biomechanical analysis of the nervous system through the measurement of CSF pressure. The lumbar puncture currently constitutes the least traumatic access technique for accessing the cerebrospinal fluid. In fact, in the context of the present invention, the lumbar puncture constitutes a preferred means for accessing the CSF which constitutes the physiological LP liquid within the meaning of the invention. It is then possible to measure, through the CSF pressure, the intracranial pressure. Nevertheless, the measuring device 100 can also operate with other methods of accessing the CSF such as an intraventricular drain.

[0072] According to one embodiment of the invention, the inlet 107 can be openable and closable. For this purpose, the inlet 107 can be connected by the connector 108 to a tap with at least two ways.

[0073] As illustrated in Figures 1 to 3, the measuring chamber 104 according to the invention makes it possible to generate a first interface between the gas G which is contained in the internal volume of the measuring chamber 04, and the physiological liquid LP of the patient which enters the measuring chamber 104 through the inlet 107. When the physiological liquid LP enters the measuring chamber 104, the gas G remains interposed between the sensitive cell 105 and the physiological liquid LP of the patient which generates a second interface between the gas G and the sensitive cell 105. The formation of the liquid-gas interface and the gas-sensitive cell interface 105 is due to the conformation of the measuring chamber 104. However, the arrangement of the sensitive cell 105 relative to the inlet 107 can also contribute to generating said interfaces.In the example illustrated in Figures 1 to 3, the liquid-gas interface has a meniscal conformation, this is partly due to the cylindrical shape of the measuring chamber 104. However, the physicochemical properties of the gas G and the physiological liquid LP also participate in establishing a particular shape of the meniscus at the measuring interface.

[0074] As illustrated in Figures 1 to 3, the measuring device 100 comprises transmission means 110. The transmission means 110 transmit the measurements of the physiological parameter to a digital terminal 300 remote from the measuring device 100.

[0075] In the example of figures 1 and 2, the transmission means 110 are arranged in an electronic compartment 111 arranged in the extension of the first end 102 of the housing 101. The electronic compartment 111 comprises an electronic card 112 connected, on the one hand, to the transmission means 110, and on the other hand, to the sensitive cell 105. The data measured by the sensitive cell 105 are transmitted to the transmission means 110 which relay them to the remote digital terminal 300. In the case of a piezoelectric sensitive cell of a pressure sensor, the measured data are transmitted to the transmission means in the form of an electrical signal.

[0076] In the example of Figures 1 to 3, the transmission means 110 are wireless. For example, the transmission means 110 may consist of a transmitter / receiver of electromagnetic waves such as radio waves, Bluetooth, WIFI, etc. Under certain particular conditions, the transmission means 110 may be wired.

[0077] The electronic compartment 111 may also include a battery that supplies power to the electronic board 112 and the electronic components to which the electronic board 112 is connected. The battery may be rechargeable or single-use.

[0078] In the example of Figure 3, the electronic compartment 111 is separated from the housing 101. In this configuration, the measuring device 100 comprises an electrical cable 113 exterior which detachably connects the sensitive cell 105 to the electronic card 112. For hygiene reasons, the housing 101 is for single use, thus an electronic compartment 111 separated from the housing 101 allows the electronic compartment 111 to be reused for several patients.

[0079] The digital terminal 300 may be a smartphone, a tablet, a computer or any other device capable of receiving data and analyzing it using an algorithm stored in its memory or a remote server accessible via a telecommunications network.

[0080] As illustrated in Figure 4, the invention also relates to a method 400 for measuring at least one physiological parameter of a patient.

[0081] The measuring method 400 comprises a step 401 of connecting a measuring chamber to the physiological fluid of a patient. For example, the measuring chamber can be connected to the physiological fluid of the patient through a connection device 200. The connection device 200 can comprise a lumbar puncture needle. This allows access to the cerebrospinal fluid to measure intracranial pressure.

[0082] In the example illustrated in Figure 2, the lumbar puncture needle 201 which is connected to the patient, can also be connected to a tubing using a three-way tap, for injection in order to carry out dynamic tests.

[0083] According to the invention, during the connection step 401, the measuring chamber is filled by default with a gas G and comprises a sensitive cell making it possible to measure at least one physiological parameter. For example, the housing comprises a sensitive cell of the piezoelectric type in order to measure the pressure of the CSF.

[0084] As illustrated in Figure 4, the measuring method 400 comprises a step 402 of generating a first interface between the gas present in the measuring chamber and the physiological liquid coming from the patient. As illustrated in Figures 1 to 3, the gas is interposed between the physiological liquid of the patient and the sensitive cell so as to form a second interface between the gas and the sensitive cell. For this purpose, the measuring chamber can be placed in fluidic connection directly with a connection device 200 consisting of a lumbar puncture needle 201.

[0085] The measuring chamber can be connected to the 201 lumbar puncture needle and tubing to perform dynamic tests.

[0086] In this example, the gas interposed between the sensitive cell 105 and the patient's physiological liquid has a non-zero volume less than or equal to 1 ml. The volume of gas interposed between the physiological liquid and the sensitive cell may also be less than 1 ml. In particular, the volume of gas interposed between the physiological liquid and the sensitive cell 105 may be less than 0.7 ml.

[0087] According to one embodiment of the invention, the volume of gas interposed between the physiological liquid and the sensitive cell may be between 0.2 ml and 0.5 ml. However, the volume of gas interposed between the physiological liquid and the sensitive cell 105 may also be between 0.3 ml and 0.4 ml.

[0088] Thus, the sensitive cell 105 performs a measurement through a hydropneumatic interface. The hydropneumatic interface has the advantage of damping the physical accelerations undergone by the sensitive cell 105 such as the movements of the patient or the vibrations induced by the medical environment (monitoring equipment, etc.), while allowing a more reliable measurement of the pressure or pulsatility of the CSF.

[0089] As illustrated in Figure 4, the measuring method 400 comprises a step 403 of measuring at least a first physiological parameter. The measurement of the first physiological parameter is carried out using a sensitive cell while the gas G contained in the measuring chamber is interposed between the physiological liquid and the sensitive cell. For example, the CSF pressure is a physiological parameter that can be measured by the measuring method 400, in this case the CSF pressure can constitute the first physiological parameter. A sensitive cell of the piezoelectric type can be used to carry out the measurement of the stationary hydrostatic pressure or the pulsatile pressure of the CSF.

[0090] In the example of figure 4, the measurement method 400 can comprise a step 404 of determining at least one second physiological parameter through the measurement of the first physiological parameter.

[0091] In a first example, an average value of the patient's intracranial pressure can be determined. The average value of the intracranial pressure then constitutes the second physiological parameter.

[0092] In a second example, the patient's intracranial pressure can be determined by pulsatility. The value of intracranial pulsatility then constitutes the third physiological parameter.

[0093] Within the framework of a hydrodynamic approach, the method according to the invention makes it possible to determine other physiological parameters such as the frequency of the respiratory cycle, cerebral compliance or resistance to CSF ​​flow.

[0094] As illustrated in Figures 3 and 4, the measurement method 400 may comprise a step 405 of transmitting the data measured by the sensitive cell to a digital terminal 300 remote from the sensitive cell. The transmission step 405 may be carried out according to a Bluetooth or WIFI type protocol or even in an analog manner via a wired connection.

[0095] Upon receipt of the measured data, the digital terminal 300 may execute step 404 and process the signal to extract at least one physiological parameter. The patient's intracranial pressure is a parameter that can be determined directly by measuring the CSF pressure.

[0096] According to the invention, the measuring device 100 is particularly suitable for implementing the measuring method 400.

[0097] The measuring device 100 and the measuring method 400 make it possible to reliably and accurately measure the CSF pressure in both a hydrostatic and a hydrodynamic approach. The hydrostatic approach consists of measuring the stationary pressure or the pulsatile pressure of the CSF secondary to cardiac and respiratory cyclic oscillations. The hydrodynamic approach consists of applying a known stress to the intracranial fluid system, called a perfusion test, and analyzing the system's response to this stress.

[0098] To explore the hydrostatic component of CSF pressure, the measuring chamber 104 is connected to a connection device 200 which is fluidically connected to the nervous system, for example, via a lumbar puncture. Variations in the signal electrical measured by the sensitive cell 105 translate the variations in CSF pressure.

[0099] To explore the hydrodynamic component of CSF pressure, a fluidic constraint is applied to the CSF by injecting physiological serum at a constant flow rate through an inlet port at the lumbar puncture. This perfusion test is carried out through an inlet port made in parallel with the first port to which the connection device 200 is connected and which places the measuring device 100 in fluidic contact with the CSF. [Experimental results]

[0100] In order to address the technical problems set out in this document, the inventors conducted a comparative experimental study between the pressure measurements obtained by a sensor with a liquid / sensitive cell interface called a “water sensor” 501 and the pressure measurements obtained by a sensor with two liquid / gas / sensitive cell interfaces called a “hydropneumatic sensor” 502. This work was carried out within the same experimental setup 500 which uses a physiological serum S replacing the patient's physiological liquid.

[0101] Figure 5 schematically represents the experimental setup 500. The two sensors 501, 502 are of the piezoelectric type of the brand “Transpac™” marketed by the company ICUMED for measuring invasive arterial pressure. This pressure measuring device comprises a measuring chamber 503 whose internal volume is 0.2 ml. Furthermore, this measuring device comprises a fluid inlet 504 which is connected to a tube 600 filled with physiological saline S. The fluid inlet 504 is equipped with a three-way tap 504 to control the connection or disconnection of the sensor with the physiological saline S. The measuring device used comprises, opposite the inlet 504, a bottom wall constituted by the sensitive cell of the piezoelectric sensor 505.Near the piezoelectric sensor 505, the side wall of the measuring chamber 503 comprises a purge opening 506 whose opening and closing are controlled by a tap or a manual valve. The piezoelectric sensor 505 of this measuring device has a sensitivity of plus or minus one percent and a linearity of 1%, finally this piezoelectric sensor is designed to measure pressure variations between -20 mmHg and 300 mmHg.

[0102] In the experimental setup 500 illustrated in Figure 5, the two sensors 501 and 502 are mounted on a support and held horizontally in the same plane. Here, the two sensors 501, 502 are connected to a tube 600 in a parallel arrangement. The tube 600 comprises a three-way valve 601 at each junction point with a connection tube 602 connecting the tube 600 to the sensors 501 and 502.

[0103] The sensitive cell of each piezoelectric sensor 501 and 502 is connected by an electric cable 507 independently to an amplifier then a converter before being recorded on a computer using the “ICM+®” software.

[0104] In the experimental setup 500 of Figure 5, the purge opening 506 of the hydropneumatic sensor 502 is connected to a syringe 508 containing air. The syringe 508 is graduated and makes it possible to control the volume of air in the measuring chamber 503, that is to say, the volume of air interposed between the sensitive cell of the piezoelectric sensor 505 and the physiological serum S.

[0105] The experimental setup 500 also includes a graduated column 603 which is held vertically. The graduated column 603 has a fluid connection at its lower end. The graduated column 603 allows the inventors to visualize the pressure applied to the sensors 501, 502 by measuring the water column within the graduated column 603. For this purpose, the sensors 501, 502 are positioned such that their piezoelectric sensitive cells 505 are located in a horizontal plane P passing through the zero level defined on the graduated column. In the example of Figure 5, the graduated column 603 is arranged at one end of a first branch of the tubing 600. The second branch of the tubing 600 is mounted in parallel with the first branch and supplies the sensors 501, 502 through connection taps 601 which are arranged at each junction point with a connection tube 602.

[0106] The tubing 600 filled with physiological serum S is connected to an electric syringe pump 604. This syringe pump 607 is configured to apply static pressures in successive stages between -20 mmHg and 50 mmHg. These values ​​correspond to the CSF pressures that can be measured in a patient in both physiology and pathology. The electric syringe pump 604 used in this experiment is of the FRESENIUS® type.

[0107] The connection tap 601 allows to connect, if necessary with the tubing 604, an oscillatory generator 605 in order to create dynamic wave pressures with a frequency of 1 Hz and amplitudes adjustable between 0.1 and 10 mmHg. These amplitude values ​​correspond to those of the intracranial pressure in a patient both in physiology and in pathology. The oscillatory pressure generator 605 used during this experiment is of the RADOMEDIC® type.

[0108] It should be noted that the sensors 501 and 502 when delivered naturally contain air in their measuring chambers 503.

[0109] For the water sensor 501, an air purge is carried out through the opening 506 of the measuring chamber 503 and by filling it with physiological serum. Thus the sensitive cell is in direct contact with the fluid in the chamber measurement. This air purge protocol is the usual recommended operating procedure for measuring water pressure with this type of sensor in clinical practice. In particular for invasive measurement of arterial or venous blood pressure.

[0110] Once the water sensor 501 is purged of air, it is in fluid connection with the physiological serum S.

[0111] For the hydropneumatic sensor 502, no air purge is performed. The measuring chamber 503 having a volume of 0.2 ml, it will thus contain 0.2 ml of air. This volume of air will therefore be interposed between the sensitive cell 505 and the inlet 504. The hydropneumatic sensor will then be connected to the physiological serum by the connection 602. A controlled volume of air will thus be added between the piezoelectric sensor 505 and the physiological serum S. The inventors thus generate a liquid / gas measurement interface within the measuring chamber in accordance with the present invention, corresponding to the hydropneumatic principle.

[0112] The two water sensors 501 and hydropneumatic 502 are in fluidic connection thanks to the physiological serum S to the graduated column 603, to the electric syringe pump 604 and to the dynamic pressure generator 605. [Experiment 1]

[0113] Experiment 1 consists of recording, using the “ICM+®” software, the pressure measurements made by the water sensor 501 and the pressure measurements made by the hydropneumatic sensor 502 simultaneously. As a reminder, the volume of air in the hydropneumatic sensor 502 is that of the internal volume of the measuring chamber 503, i.e. 0.2 ml.

[0114] An acquisition of stationary hydrostatic pressure measurements was carried out at 100 Hz for a recording time of 5 minutes. Thanks to the injection of physiological saline, the hydrostatic pressure could be gradually increased in the two sensors 501 and 502. Figure 6 corresponds to the recording of this experiment. In this figure, the gray signal corresponds to the water sensor 501 and the black signal corresponds to the hydropneumatic sensor 502.

[0115] In experiment 1, the electric syringe pump 607 rests on the table top on which the experimental setup 500 is placed. In the basal state, the values ​​measured by the water sensor 501 and by the hydropneumatic sensor 502 are identical: the two traces of the two sensors are superimposed in figure 6. Arrow D indicates the switching on of the electric syringe pump 604 at time 16h 53 min and 30 sec. As soon as it is switched on, a progressive increase in pressure is observed from 0 mmHg to approximately 25 mmHg at the recording time 16 h 56 min and 18 sec where the electric syringe pump 604 is stopped (arrow ST).

[0116] The electrical cables of the sensors 501 and 502 are connected separately to the computer running the “ICM+” software; therefore the inventors were able to study and compare the signals from the water sensor 501 and those from the hydropneumatic sensor 502. This is also the case in the following experiments.

[0117] In the recording of Figure 6, the inventors noted that the signals of the two sensors 501, 502 were superimposed until the electric syringe pump 604 was switched on D. The two signals being superimposed, only the black signal is visible. When the electric syringe pump was switched on D, on the one hand, an increase in the hydrostatic pressure of the two signals is observed according to a similar curve, and on the other hand, an oscillation of the gray signal recorded by the water sensor 501. Figure 7 is an enlargement of Figure 6, it shows that the signal from the hydropneumatic sensor 502 (in black) also exhibits an oscillation, however its amplitude is much less than that of the water sensor 501 (in gray). As soon as the electric syringe pump 604 stops ST, the oscillation disappears; the two signals from the two water sensors 501 and hydropneumatic 502 are then superimposable.

[0118] This oscillation is not induced by the pulse generator 607 which is switched off. This oscillation appeared as soon as the electric syringe pump 604 was switched on, and ceased as soon as it was switched off. The inventors thus concluded that the mechanical vibrations of the electric syringe pump 604 resting on the table are transmitted to the water sensor 501, while the hydropneumatic sensor 502 dampens them. The density of air is 1.29 kg / m 3 while that of a liquid like water is 1000 kg / m 3. Water therefore has a density approximately 1000 times greater than that of air. The 0.2 ml measuring chamber of the water sensor therefore has a mass of -0.2 g; whereas the 0.2 ml measuring chamber of the hydropneumatic sensor has a mass of only -0.26 pg. During acceleration of the water sensor induced by a vibration wave, the mass of water in the measuring chamber (-0.2 g) creates a mechanical stress on the sensitive cell 505 which results in a measurement artifact. Whereas in the measuring chamber of a hydropneumatic sensor the low mass of air (-0.26 pg) only creates a very low mechanical stress on the sensitive cell, thus damping the vibration wave.

[0119] This experiment shows that the 502 hydropneumatic sensor dampens the physical accelerations that are transmitted during vibration to the measuring device. From a practical point of view, this results in an increase in the accuracy of CSF pressure measurement.

[0120] In this experiment 1, we also compared the two sensors from the arithmetic point of view. The mean value ± standard deviation of the difference absolute difference between the water sensor and the hydropneumatic sensor is 0.19 ± 0.21 mmHg, and the 95% confidence interval of the absolute difference is 0.41 mmHg. That is, 95% of the difference values ​​between the water sensor and the hydropneumatic sensor are within an interval of ± 0.41 mmHg.

[0121] During experiments 2, 3 and 4, the electric syringe pump 604 is moved away from the manipulation table so that the physical vibrations it generates are not transmitted directly to the sensors and do not create an artifact. [Experiment 2]

[0122] Experiment 2 implements setup 500 to study the impact of the air volume of the measuring chamber on the accuracy of the static pressure measurement of the hydropneumatic sensor.

[0123] The pressure of the physiological serum is increased in successive static steps of about ten seconds then a return to zero. The signals from the hydric 501 and hydropneumatic 502 sensors are recorded simultaneously at 100 Hz. Several pressure increase cycles are carried out with different volumes of air in the measuring chamber of the hydropneumatic sensor by adding air with the syringe 508, at room temperature and atmospheric pressure. Figure 8 reproduces the recording which lasts 23 minutes. The first cycle C0 of pressure increase is carried out without adding air; the volume of air in the measuring chamber is therefore 0.2 ml. The two curves are perfectly superimposable. Then 0.1 ml of air is added to the measuring chamber of the hydropneumatic sensor. Cycle C1 corresponds to the different pressure steps with an addition of 0.1 ml of air. The two curves are perfectly superimposable.Cycles C0 to C8 are performed with increasing air volumes, described in Table 1. Table 1

[0124] By observing the curve in the different cycles, we see that whatever the volume of air interposed between the sensitive cell of the piezoelectric sensor 505 and the physiological serum S, the signals measured by the water sensor 501 and by the hydropneumatic sensor 502 are superimposed.

[0125] Figure 9 is an enlargement of the graph of cycle C8 of the experiment, that is, the cycle for which a volume of 64 ml of air is interposed between the sensitive cell of the piezoelectric sensor 505 and the physiological serum S. The air volume of 64 ml is maximal in the context of experiment 2. On this graph we can distinguish the two signals of the water sensor 501 in gray and of the sensor hydropneumatic 502 in black. The two signals overlap perfectly for most of the recording.

[0126] Figure 10 is a Bland-Altman plot produced from the experimental data of Experiment 2. The X axis of the plot corresponds to the mean value of the 501 water and 502 hydropneumatic pressure measurements expressed in mmHg. The Y axis of the plot corresponds to the difference between the 501 water and 502 hydropneumatic pressure measurements expressed in mmHg. A linear regression is then performed.

[0127] The mean value ± standard deviation of the absolute difference between the water sensor and the hydropneumatic sensor is 0.24 mmHg ± 0.17 mmHg; the 95% confidence interval of the absolute difference is 0.33 mmHg. That is, 95% of the difference values ​​between the water sensor and the hydropneumatic sensor are within an interval of ± 0.33 mmHg.

[0128] In Experiment 2, the pressure varied between -10 and +30 mmHg, which corresponds to the values ​​found in clinical practice. 0.33 mmHg represents at most ~1% of the pressure measurement value. This measurement variation is acceptable in clinical practice. It should also be noted that 1% also corresponds to the sensitivity of the sensor.

[0129] Scientific literature specifies that a blood pressure sensor is reliable when it offers a percentage error of 5% of the measurement compared to the patient's actual blood pressure.

[0130] Experiment 2 shows that a volume of air between 0.2 ml and 64 ml inserted in the measuring chamber of a hydropneumatic sensor 502 allows a reliable measurement of the pressure, in comparison with that of a water sensor 501. [Experiment 3]

[0131] Experiment 3 implements setup 500 to study the impact of the air volume of the measuring chamber on the accuracy of the dynamic pressure measurement of the hydropneumatic sensor 502.

[0132] For this purpose, the oscillatory generator 605 allows the creation of dynamic wave pressures with a frequency of 1 Hz and adjustable amplitudes between 0.1 and 10 mmHg. The signals from the hydric 501 and hydropneumatic 502 sensors are recorded simultaneously at 100 Hz. The recording duration is 8 minutes.

[0133] For this experiment, the static pressure is stable, with no variation in the average pressure. Only the dynamic pressure is modified thanks to the oscillatory generator 605, with study of the impact of the air volume on the pulsatility of the pressure measured by the hydropneumatic sensor 502. Several recordings are made at different levels of pulsatility. For each level of pulsatility, the volume of air in The measuring chamber of the hydropneumatic sensor is gradually increased by adding air using the syringe 508. Figure 11 reproduces one of the recordings. The black trace corresponds to the hydropneumatic sensor 502 showing the damping at each cycle of increasing the air volume. On the other hand, the gray trace corresponding to the water sensor 501 remains unchanged between cycles. Cycles C1 to C7 are carried out with increasing air volumes, described in Table 2. Table 2

[0134] Each time air is added to the measuring chamber, the pulsatility of the signal measured by the hydropneumatic sensor 502 decreases proportionally with a damping phenomenon.

[0135] Figure 12 is an enlargement of cycle C1. In this recording, the gray signal from the water sensor 502 cannot be seen, which is superimposed on the black signal from the hydropneumatic sensor 501. With a very low air volume, the signal damping is minimal.

[0136] Figure 13 is an enlargement of cycle C7. At the beginning of this recording, the gray signal from the water sensor 502 shows the pulsatility produced by the wave generator 605. As soon as the hydropneumatic sensor is connected with 20ml of air, we immediately note the damping of the gray signal from the water sensor (502) synchronous with the black signal from the hydropneumatic sensor 501; these two sensors being connected in parallel.

[0137] Experiment 3 shows that in the case of pulsatile pressure, the air volume of the hydropneumatic sensor 501 modifies the dynamic measurement of the pressure and consequently influences the precision of the measurement. [Experiment 4]

[0138] Experiment 4 aims to determine the air volume of the measuring chamber of the hydropneumatic sensor 502 in order to provide an accurate and clinically acceptable measurement of pulsatility.

[0139] Experiment 4 consists of carrying out a series of 8 manipulations at different levels of pulsatility during which the air volume of the hydropneumatic sensor 502 is gradually increased by adding air at room temperature and atmospheric pressure using the syringe 508. The experiment is carried out over a period of 10 minutes with a pulsatility of 1 Hz produced by the generator 605 whose oscillation is adjustable. The recording is carried out with the “ICM+®” software and an acquisition at 100 Hz. For each volume of air (cycles C1 to C7), the pulsatility is not calculated by the difference between maximum and minimum, but with a Fourier transform by measuring the power of the fundamental harmonic in the frequency range of the signal pulsation. We thus obtain a numerical value of the pulsatility for each volume of air from 0.2 ml to 20 ml. A graphical representation is obtained with the XL software characterizing the damping of the pulsatility. An exponential regression analysis is carried out with obtaining its mathematical equation and the Pearson coefficient. For each oscillatory condition, it is thus possible to obtain an exponential curve describing the behavior law of the pulsatility damping as a function of the air volume.

[0140] Figure 14 illustrates the 8 experiments. Each point corresponds to a pulsatility value for different air volumes of the hydropneumatic sensor 502. Each curve corresponds to the evolution of the pulsatility value measured during the different manipulations. The transfer of the data to this same graph allowed the inventors to plot the exponential regression curves of each manipulation.

[0141] From the exponential regression equations of the data from the 8 manipulations of experiment 4, the inventors calculated the theoretical variation of pulsatility damping (Apulsatility) induced for each addition of an elementary volume of 0.1 ml of air at the hydropneumatic sensor 502. The results are expressed as a percentage of pulsatility damping per elementary volume of air. These results make it possible to establish the average values ​​and the standard deviation of the pulsatility damping of the hydropneumatic sensor 502 as a function of the volume of air in the measuring chamber. The results are described in Table 3 below. Table 3

[0142] As shown in Table 3, the average pulsatility damping of a hydropneumatic sensor 502 is less than 6.55% for an air volume of less than 1 ml. Therefore, taking the accuracy of blood pressure measurement as a reference, the inventors concluded that the air volume of the sensor hydropneumatic must be less than 0.7 ml to ensure reliable (<5%) measurements of CSF pulsatility.

[0143] The inventors have determined a behavior law allowing to determine the percentage of damping of the pulsatility AP as a function of the volume of air Vair (in ml). This law is expressed according to the following equation: Ap = 0.0652*Vair + 0.0006

[0144] This linear law, as illustrated in Figure 15, makes it possible to define that a volume of air strictly less than 0.7 ml makes it possible to measure the pulsatility of the pressure of a physiological liquid such as CSF with a hydropneumatic sensor, with a measurement variability of less than 5%.

[0145] According to these experimental results, it is thus possible to determine the volume of the measuring chamber of the measuring device as non-zero and less than 1 ml. In the case of CSF, when establishing the liquid / gas interface, the physiological values ​​that the CSF pressure can take are likely to cause only a slight variation in the volume of gas initially contained at atmospheric pressure in the measuring chamber such that the gas initially contained at atmospheric pressure in the measuring chamber retains a non-zero volume and less than or equal to 1 ml.

[0146] This observation applies to the volume of gas interposed between the CSF and the sensitive cell within the framework of the measuring method defined according to the invention.

[0147] These experimental results show that it is possible to measure the pressure, whether stationary or pulsatile, of a biological fluid through a hydropneumatic interface. The invention can thus be used to measure other physiological parameters such as bladder pressure, arterial pressure, venous pressure, interstitial tissue pressure in the context of compartment syndrome, ocular pressure, pressure in the upper airways, pressure in the digestive tract and any other pressure of bodily biological fluid. For each of these applications, the biological fluid of interest is placed in contact with the measuring device 100 as described above, in a known manner, the biological fluid of interest can be probed or punctured depending on its nature.

Claims

Demands

1. A measuring device (100) for at least one physiological parameter, the measuring device (100) comprising a housing (101) extending longitudinally between a first end (102) and a second end (103) opposite the first end (102), the housing (101) comprising: a measuring chamber (104) disposed within the housing (101), the measuring chamber (104) having an internal volume filled with gas, a sensing cell (105) for measuring at least one first physiological parameter, the sensing cell (105) being disposed in contact with the gas contained in the internal volume of the measuring chamber (104), and an inlet (107) for a patient's physiological fluid into the measuring chamber (104), characterized in that the inlet (107) is disposed such that the physiological fluid comes into contact with the gas and the gas remains intercalated between the sensing cell (105) and the patient's physiological fluidThe measuring chamber (104) allows for the generation of two interfaces: a first interface between the gas contained in the internal volume and the patient's physiological fluid which enters the measuring chamber (101) through the inlet (107), and a second interface between the gas contained in the measuring chamber (104) and the sensitive cell (105).

2. Measuring device (100) according to claim 1, wherein the measuring chamber (104) has an internal volume that is non-zero and less than or equal to 1 ml, in particular, the internal volume is strictly less than 1 ml, preferably, the internal volume is less than 0.7 ml.

3. Measuring device (100) according to any one of claims 1 and 2, wherein the measuring chamber (104) has an internal volume between 0.2 ml and 0.5 ml.

4. Measuring device (100) according to any one of claims 1 to 3, wherein the sensitive cell (105) is a piezoelectric cell of a pressure sensor.

5. Measuring device (100) according to any one of claims 1 to 4, wherein the housing (101) includes a sealing membrane (106) which is interposed between the sensitive cell (105) and the internal volume of the measuring chamber (104), the sealing membrane (106) protecting the sensitive cell (105).

6. Measuring device (100) according to any one of claims 1 to 5, wherein the internal volume of the measuring chamber (104) is cylindrical.

7. Measuring device (100) according to any one of claims 1 to 6, comprising a connector (108) disposed at the inlet (107) of the housing (101), the connector (108) sealingly connecting the measuring chamber (104) to a connection device (200) to the patient's physiological fluid.

8. Measuring device (100) according to any one of claims 1 to 7, wherein the inlet (107) is openable and recloseable.

9. A measuring device (100) according to any one of claims 1 to 8, comprising transmission means (110) which transmit the measurements of the first physiological parameter to a remote digital terminal.

10. Measuring device (100) according to any one of claims 1 to 9, wherein the gas in the measuring chamber (104) consists of atmospheric air.

11. Measuring device (100) according to any one of claims 1 to 10, wherein the sensitive cell (105) is disposed at the first end (102) of the housing (101), while the inlet (107) is disposed at the second end (103) of the housing (101).

12. A method for measuring (400) at least one physiological parameter of a patient, characterized in that the method comprises: a step of connecting (401) a measuring chamber to a patient's physiological fluid, the measuring chamber being filled with gas and comprising a sensitive cell for measuring at least one physiological parameter, a step of generating (402) a first interface between the gas present in the measuring chamber and the physiological fluid from the patient, the gas remaining intercalated between the physiological fluid and the sensitive cell so as to form a second interface between the gas and the sensitive cell, and a step of measuring (403) at least one first physiological parameter, the measurement being carried out by the sensitive cell through the gas intercalated between the physiological fluid and the sensitive cell.

13. A measurement method (400) according to claim 12, wherein the gas intercalated between the sensitive cell and the patient's physiological fluid has a non-zero volume less than or equal to 1 ml, in particular, said volume of gas is strictly less than 1 ml, preferably, said volume of gas is less than 0.7 ml.

14. A measuring method (400) according to any one of claims 12 and 13, wherein the measuring chamber is connected to a physiological fluid connection device which consists of the cerebrospinal fluid of a patient.

15. A measurement method (400) according to any one of claims 12 to 14, wherein the first physiological parameter corresponds to a pressure of the patient's physiological fluid.

16. A measurement method (400) according to any one of claims 12 to 15, comprising a step of determining (404) at least one second physiological parameter through the measurement of the first physiological parameter.

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