Systems and methods for measuring mechanical impedance of the respiratory system

Abstract

1. A system for measuring the mechanical impedance of a patient's respiratory system during spontaneous breathing activities, comprising: a fan; and a motor for driving said fan, said motor and said fan being disposed within a cavity, said cavity being divided into two sub-cavities separated from each other so as to prevent the passage of air, one of said two sub-cavities housing the motor and the other housing the fan, both having a beginning end and an end with access to the outside.

Description

[Technical Field]

[0001] The present invention relates to a system and method for measuring the mechanical impedance of an individual's (e.g., a patient's) respiratory system during spontaneous breathing activity using forced oscillation techniques (FOT or oscillometry). [Background technology]

[0002] Oscillometry is a method for measuring the mechanical properties of the airways and lungs based on the analysis of airflow resulting from the application of small-amplitude pressure stimuli oscillating at frequencies exceeding those of spontaneous breathing. First proposed in 1956 by American physiologist Arthur Dubois (Journal of Applied Physiology, May 1956, Vol. 8, No. 6, pp. 587-594), this method has attracted increasing interest in recent years from the clinical community as a potential new, noninvasive, and easy-to-use means for diagnosing and monitoring respiratory system dysfunction.

[0003] This, together with the emergence on the market of new devices utilizing this method, has recently prompted the European Respiratory Society to publish a technical standards document to support the widespread adoption of such devices in clinical practice (Eur Respir J 2020;55:1900753).

[0004] During oscillometric measurements, the respiratory system is subjected to small amplitude oscillatory mechanical stimuli generated by an external actuator. The difficulty of eliciting the subsequent movement of air through the respiratory system from the stimulus is quantified by calculating the mechanical impedance (Z), which is obtained from the complex ratio between pressure (P m) and flow (V m) measured at the entrance to the airways for any or all of the stimulus's frequency components (f).

[0005]

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[0006] Mechanical impedance is a complex number, whose real part, called resistance (R(f)), is an indicator of the airway caliber and / or their patency, and whose imaginary part, called reactance (X(f)), summarizes the system's ability to store energy and is therefore determined by both the elastic and inertial properties of the respiratory system.

[0007] A variety of oscillometric measurement systems have been reported in the scientific and technical literature, characterized by the use of different stimulus generation systems.

[0008] When first used, the stimulus generator consisted of a cylinder coupled to a piston, an outlet from this cylinder connected directly to the airway opening (nose or mouth), and a set of sensors for measuring flow and pressure (Journal of Applied Physiology, May 1956, vol. 8, no. 6, pp. 587-594; U.S. Pat. No. 3,713,436, filed October 23, 1970). These bulky and complex systems could not be used for measurements during spontaneous breathing, but could only be used for measurements during short periods of apnea.

[0009] Subsequently, beginning in the late 1960s, oscillometric measurement systems consisting of a vibration-generating loudspeaker connected to a set of pressure and flow sensors in direct contact with an individual's airway opening, in parallel with a high-inertance path consisting of tubing and / or resistance of sufficient diameter and length, began to be more widely used to enable measurements during spontaneous breathing (The Journal of Clinical Investigation, November 1975, vol. 56, pp. 1210-1230; U.S. Pat. No. 4,333,476; EP 1551293). However, the presence of high-inertance tubing significantly increased dead space in the respiratory system and necessitated the use of additional flow generators to refresh the air, which increased the size and complexity of the overall system.

[0010] Smaller mechanisms that use actuators to partially or totally occlude the airway during spontaneous breathing have been constructed to create a pressure disturbance in the circuit where stimulation energy is generated by the respiratory muscles, as described in U.S. Pat. Nos. 4,220,161 and 6,066,101.

[0011] Devices in the latter category are cheaper and less bulky, but do not work at low inspiratory and expiratory flows (e.g., at the end of inspiration and end of expiration) and are not suitable for measuring reactance.

[0012] A small, potentially portable respiratory impedance measurement system is described in patent application ITBG20100042 by the owner of the present patent application. The system comprises a cavity through which the individual being measured breathes, the cavity housing a motor connected to a fan, the appropriately controlled movement of which is capable of generating the pressure oscillations required for stimulating the respiratory system and measuring respiratory impedance.

[0013] It is an object of the present invention to provide a system and method for mechanical measurements of the respiratory system that at least partially overcomes the shortcomings of existing systems or improves their performance.

[0014] A primary object of the present invention is to provide a system and method for measuring respiratory impedance that reduces the drawbacks of known techniques. Summary of the Invention

[0015] According to the present invention, this result is achieved through the construction of a portable system for measuring the mechanical impedance of a patient's respiratory system during spontaneous breathing, comprising: a system comprising a motor and a fan for generating a pressure stimulus capable of producing small fluctuations in pressure and / or flow at an opening to the airway; a detection system capable of measuring the pressure and flow values ​​generated by the stimulus and by the patient's spontaneous breathing activity; and a microprocessor capable of controlling the system for generating the pressure stimulus, receiving the data measured by the detection system, and calculating a measurement of the mechanical impedance of the patient's respiratory system based on the values ​​measured by the detection system, wherein the portable system comprises a first chamber housing the motor and a second chamber housing the fan, the first and second chambers being separate from each other so that there is no passage of air between them, and the second chamber having a rear opening capable of taking in air from the external environment and a front opening in contact with the patient and capable of receiving the patient's inspiratory and expiratory flows.

[0016] The detection system preferably comprises at least one pressure sensor. According to a preferred embodiment, the detection system also comprises a flow meter for measuring the flow rate generated by the patient's spontaneous breathing activity, or the flow rate generated by the patient's spontaneous breathing activity is estimated by the microprocessor based on one or more of the following data: fan rotation speed, motor power consumption, pressure, temperature, and humidity.

[0017] In a preferred embodiment, the microprocessor is configured to modulate the pressure stimulus such that the rotational speed is reduced during the initial measurement phase compared to the steady-state measurement phase. The fan speed during the initial phase may be controlled by the microprocessor to produce a pressure stimulus whose peak-to-peak amplitude increases linearly until a predetermined target value is reached. According to a possible alternative embodiment, the fan speed during the initial phase may be controlled by the microprocessor to produce a pressure stimulus whose peak-to-peak amplitude increases exponentially until a predetermined target value is reached. According to a preferred embodiment, the fan speed during the steady-state measurement phase (i.e., after the acclimation phase) is controlled by a closed-loop control system to maintain a constant peak-to-peak amplitude and produce a pressure stimulus equal to a value determined based on one or more of the patient's pressure, flow, impedance, resistance, and reactance values ​​measured during the initial measurement phase.

[0018] According to another aspect of the present invention, there is provided a method for operating the portable system described above, comprising the steps of generating a pressure stimulus that produces small pressure fluctuations, measuring pressure and flow values ​​produced by the stimulus and the patient's spontaneous breathing activity, receiving data measured by the sensing system from a microprocessor, and calculating a measure of the mechanical impedance of the patient's respiratory system based on the values ​​measured by the sensing system.

[0019] There is also provided a computer program which, when executed by a microprocessor, carries out the above-described method.

[0020] According to a further aspect of the present invention, there is provided a kit for measuring the mechanical impedance of a patient's respiratory system during spontaneous breathing, the kit comprising the system described above and a test and calibration apparatus comprising a hollow conduit having two generally frusto-conical opposing ends with smaller cross-sections converging inward, the two frusto-conical ends being joined together by a generally cylindrical central portion, the test and calibration apparatus having a known, predetermined impedance value.

[0021] The present invention allows for the development of a compact, portable device that can be used on different individuals, is easy to clean, and maximizes patient comfort during measurements.

[0022] Among the advantages that can be obtained from devices made in accordance with embodiments of the present invention are the following:

[0023] The separation between the chamber housing the motor and the chamber housing the fan allows the motor to be isolated from the patient's inhaled and exhaled air, preventing inhalation of dust accidentally generated during motor operation and preventing moisture and saliva produced during breathing from damaging the motor's circuitry and electrical connections.

[0024] Said separation also allows for replacement of only the breathing chamber and the fan therein in the event of contamination, allowing for the possibility of using the device on different patients without having to replace the entire device.

[0025] As provided in one optional embodiment of the present invention, the generation of gradually increasing stimuli during the acclimation phase of the measurement helps the individual become accustomed to the presence of the stimulating vibrations, increasing acceptance of the test.

[0026] The generation of stimuli whose amplitude is adjusted based on the amplitude of the resulting flow oscillations, as provided by possible embodiments of the present invention, optimizes the signal-to-noise ratio and allows the use of reduced amplitude pressure stimuli in individuals with low respiratory impedance, increasing comfort during measurements.

[0027] These and further advantages, objects and features of the present invention will be better understood by those skilled in the art from the following description and accompanying drawings, which relate to examples of embodiments of an illustrative nature, but which should not be understood in a limiting sense. [Brief explanation of the drawings]

[0028] [Figure 1] 1 is a schematic diagram of a system for measuring mechanical impedance of the respiratory system, in accordance with a preferred embodiment of the present invention; [Figure 2] 1A-1C are diagrams illustrating pressure patterns in a patient's mouth during the adaptation and measurement phases, in accordance with a preferred embodiment of the present invention; [Figure 3] FIG. 1 shows a mechanical device for calibrating a system according to the invention and for automatically checking correct system function. DETAILED DESCRIPTION OF THE INVENTION

[0029] With reference to the accompanying drawings, and in particular to FIG. 1, a system for measuring the mechanical impedance of the respiratory system, according to a preferred embodiment of the present invention, comprises a motor 3 connected to a centrifugal fan 4 .

[0030] The motor 3 is located within a first chamber 1 that is not in communication with the patient's inhaled and exhaled gases. The fan 4 is located within a second chamber 2 (the "breathing chamber") that has a beginning end 7 and a terminal end 6, both with an opening to the outside. The first and second chambers are placed in communication with each other to transfer mechanical motion from the motor to the fan but not allow air to pass between the two chambers.

[0031] The chamber 1 housing the motor and the breathing chamber 2 may be housed in the same chamber (or cavity), from which two separate sub-chambers (or sub-cavities) are obtained, for example by a partition that allows mechanical communication (e.g. the motor shaft that rotates the fan) but prevents the passage of air, so that the air inhaled by the user (patient) does not contain harmful dust generated by the motor. This is one of the advantages offered by the system according to the invention over the system described, for example, in patent application ITBG20100042.

[0032] The starting end 7 is designed to be connected to a mouthpiece or other interface with the patient and is preferably about 2-4 cm in diameter.

[0033] In an alternative embodiment, the chamber 2 may house a fan 4 of the axial type.

[0034] The distance travelled by the air within the chamber is less than 25 cm, preferably about 15 cm, allowing the device to be easily transported.

[0035] If the volume of the breathing chamber 2 is greater than 50 ml, the breathing chamber 2 preferably includes one or more vents located approximately midway between the starting end 7 and the sampling port 11 for pressure and flow signals; the vents are needed to ensure that exhaled air diffuses to the outside.

[0036] According to one possible embodiment, the breathing chamber includes a flow meter 8 with a resistive element capable of producing a pressure drop that can produce a known change in the pressure and effect of the airflow through the breathing chamber. In alternative embodiments, flow measurement at the airway opening can be performed without a resistive element, using an ultrasonic or hot wire type sensor.

[0037] In further embodiments, the flow rate may be estimated from rotational speed and / or power consumption and / or pressure values ​​measured in the chamber 2 and in the environment.

[0038] According to a possible embodiment, the chamber 1 also comprises a pressure sensor 9 (Pm) and a flow sensor 10 (V·_m) arranged in communication with the breathing chamber 2 via a pneumatic connection 11 .

[0039] Associated with the chamber 1 is a mains or battery powered microprocessor based processing and control system 5 which receives signals from the sensors 9 and 10, stores them in its memory and performs the necessary processing to calculate the mechanical impedance of the respiratory system. The processing system also includes motor drive circuitry 3 and modules for communicating with the outside world to take measurements and send / receive commands to / from the microprocessor.

[0040] According to one embodiment, the processing and control device 5, which manages the acquired measurements, comprises a memory and an electronic interface for data retrieval. In another embodiment, the processing and control device 5 comprises a data processing system in addition to the memory, and thus provides directly the previously processed data.

[0041] In another embodiment, an apparatus includes a system for transmitting wireless data.

[0042] In another embodiment, the device includes a system for transmitting data over the Internet to an external processing and storage system.

[0043] In another embodiment, the device may include sensors for measuring blood saturation and / or heart rate.

[0044] In another embodiment, the device may include a display that shows measured values ​​and system information.

[0045] In another embodiment, the device may include an input system, such as buttons or a touch screen, for entering patient information and changing system settings.

[0046] The rotational speed of the motor 3 is controlled by a microprocessor to force ambient air into the breathing chamber 2 to produce pressure fluctuations of a predetermined shape, typically a sine wave or a sum of sine waves with a frequency greater than 2 Hz, and of a maximum peak-to-peak amplitude of 5 cmH2O, with an average pressure value near the starting end 7 of no more than 2.5 cmH2O.

[0047] In a preferred embodiment, the mean pressure value is between 0.75 and 1 cmH2O, and therefore the peak-to-peak pressure value is between 1.5 and 2 cmH2O.

[0048] In one embodiment, the movement of the fan 4 is activated only when the individual exhibits respiratory activity.

[0049] Vibrations caused by fan rotation can cause discomfort to the patient. To overcome this problem, in a preferred embodiment of the present invention, during an initial stage of fan operation, called the acclimation stage, the rotational speed of fan 4 is controlled to produce a pressure stimulus whose peak-to-peak amplitude increases linearly up to a predetermined target value.

[0050] In another embodiment, during the adaptation phase, the rotational speed of the fan 4 is controlled to produce a pressure stimulus whose peak-to-peak amplitude increases exponentially until it reaches a predetermined target value, for example 2 cmH2O.

[0051] In a further embodiment, during the adaptation phase, the rotational speed of the fan 4 is controlled to produce a pressure stimulus whose peak-to-peak amplitude increases according to a curve of a predetermined shape until it reaches a predetermined target value, for example 2 cmH2O.

[0052] According to yet another embodiment, during the measurement phase, the rotational speed of the fan 4 is modulated by the closed-loop control system to produce a pressure stimulus whose ideal peak-to-peak amplitude is kept constant and equal to a preset value or a value determined based on one or more of the patient's pressure, flow, impedance, resistance and reactance values ​​measured during the acclimation phase.

[0053] In another embodiment, during the measurement phase, the rotational speed of the fan 4 is modulated according to a series of values ​​to produce a pressure stimulus whose peak-to-peak amplitude is equal to a preset value or is determined based on the patient's impedance, resistance and reactance values ​​measured during the acclimation phase.

[0054] In another embodiment, during the measurement phase, the rotational speed of the fan 4 is controlled to generate flow oscillations above a predetermined value or to produce a pressure stimulus determined based on the patient's impedance, resistance and reactance values ​​measured during the acclimation phase.

[0055] One problem that can arise when using the system of the present invention is maintaining the correct calibration of the pressure and flow sensors for impedance measurements. Figure 3 shows a test fixture in the shape of two cones connected by one or more cylindrical ducts. By dimensioning the area and length of the cylindrical ducts, it is possible to create a test object characterized by a time-stable mechanical impedance value that can be used to both automatically check the calibration status of sensors in the system of the present invention and, in some cases, to calibrate those sensors. The test fixture can be supplied in a kit with the system of the present invention to allow the end user to perform calibration checks on the system and, if necessary, calibrate it.

[0056] In another embodiment, the breathing chamber 2 and fan 4 may be removed and replaced.

[0057] To allow the patient to breathe spontaneously through the circuit with minimal effort, the dimensions of the breathing chamber 2, and the air inlet and outlet areas near the beginning 7 and end 6, are preferably dimensioned to have a maximum impedance of 1 cmH2O / L / s at normal breathing frequencies, thus measured in the range of 0-1 Hz.

[0058] A possible procedure for measuring the mechanical impedance of the respiratory system using the system described herein is described below. When switched on, the system may prompt the user to check for correct function using the provided test equipment. The patient is then induced to breathe through the connection interface (filter, mouthpiece) connected to the starting end 7. After the sensors identify the presence of respiratory activity, the system activates the motor 3 and fan 4 and initiates an acclimation phase during which impedance, resistance, and reactance values ​​are determined and continuously updated by the system based on the pressure and flow values ​​read by sensors 9 and 10. At the end of the acclimation phase, the system automatically switches to a measurement phase of predetermined duration, at which point the measurements are stored.

[0059] Respiratory impedance can be calculated using any impedance calculation algorithm, such as the least-squares optimization-based algorithm reported by Horowitz (Comput Biomed Res 1983 Dec; 16(6):499-521) and Kackza (Ann Biomed Eng 1999 May; 27(3):340-55) and recently improved by Dellaca et al. (EP 1551293). This algorithm is based on decomposing pressure and flow signals into their components resulting from normal respiratory activity and those resulting from external stimuli. The latter are then decomposed into their constituent harmonics, each of which is subjected to an iterative calculation procedure to identify their respective phase coefficients within a time window of predetermined length W.

[0060] The phase coefficients of the pressure and flow signals determined for each of the harmonics (f) are calculated over the time window Z w yields the impedance Z(f) with respect to the data present in (f).

[0061]

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[0062] This calculation is then repeated, shifting the time window forward by one or more samples to obtain a calculation of Z(f) for all measured data.

[0063] The Z(f), R(f), X(f), pressure and flow values ​​are then analyzed using both thresholding and statistical outlier identification methods to identify and exclude portions of the measured data that are due to measurement artifacts, such as glottal closure, swallowing, coughing, phonation, or leaks in the mouthpiece / filter used for the measurements. Finally, the measured results are obtained by calculating one or more parameters derived from the Z(f), R(f), X(f), pressure and flow values ​​for the portions of the free data that do not contain artifacts.

Claims

1. a system for generating a pressure signal capable of producing small changes in pressure and / or flow at the opening to the airway, the system including a motor and a fan; a detection system capable of measuring pressure and flow values ​​produced by the stimulus and by the individual's spontaneous breathing activity; controlling the system to generate a pressure signal; receiving data measured by the detection system; calculating a measure of the mechanical impedance of the individual's respiratory system based on the values ​​measured by the detection system; A microprocessor capable of 1. A portable system for measuring mechanical impedance of an individual's respiratory system during spontaneous breathing, comprising:

10. The portable system of claim 9, wherein the portable system comprises a first chamber housing the motor and a second chamber housing the fan, the first chamber and the second chamber being separate from one another such that there is no passage of air between the first chamber and the second chamber, and the second chamber having a rear opening capable of exchanging air with an external environment and a front opening in contact with the individual and capable of receiving the individual's inspiratory and expiratory air flows.

2. 10. The portable system of claim 1, wherein the detection system comprises one or more of at least one pressure sensor and at least one flow meter for measuring the flow rate caused by the individual's spontaneous breathing activity.

3. 3. The portable system of claim 1, wherein the flow rate generated by the spontaneous breathing activity of the individual is estimated by the microprocessor based on one or more of the following data: fan rotation speed, power consumption value of the motor, and pressure, temperature, and humidity of the air.

4. 4. The portable system of claim 1, further characterized in that the microprocessor is configured to modulate the pressure signal such that during an initial measurement phase, the rotational speed is reduced relative to a steady-state measurement phase.

5. 5. The portable system of claim 4, wherein during the initial stage, the rotational speed of the fan is controlled by the microprocessor to produce a pressure signal whose peak-to-peak amplitude increases linearly until it reaches a predetermined target value.

6. 5. The portable system of claim 4, wherein during the initial stage, the rotational speed of the fan is controlled by the microprocessor to produce a pressure signal whose peak-to-peak amplitude increases exponentially until a predetermined target value is reached.

7. 7. The portable system of claim 4, 5 or 6, wherein during the steady-state measurement phase, the rotational speed of the fan is controlled by a closed-loop control system to produce a pressure signal whose peak-to-peak amplitude is kept constant and equal to a value determined based on one or more of the individual's pressure, flow, impedance, resistance and reactance values ​​measured during the initial measurement phase.

8. A method for operating a portable system according to any one of claims 1 to 7, comprising: generating a pressure stimulus that generates a pressure fluctuation; measuring the pressure and flow values ​​produced by the stimulus and by the individual's spontaneous breathing activity; receiving the data measured by the detection system from the microprocessor; calculating a measure of the mechanical impedance of the individual's respiratory system based on the values ​​measured by the detection system; A method comprising:

9. A computer program which, when executed by a microprocessor, performs the method of claim 8.

10. 1. A kit for measuring the mechanical impedance of an individual's respiratory system during spontaneous breathing, comprising: A system according to any one of claims 1 to 7; 1. A test and calibration apparatus comprising a hollow conduit having two generally frusto-conical opposing ends with a smaller cross section converging inward, said two frusto-conical ends joined together by a generally cylindrical central portion, said test apparatus having a known, predetermined impedance value. A kit comprising:

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