Upper arm cuff blood pressure measurement method

Description

[0001] The invention relates to a blood pressure measuring method and a blood pressure measuring device suitable for the method.

[0002] Measuring blood pressure on the upper arm using a cuff filled with compressed air is a fundamentally simple and widely used procedure that provides important information about an individual's health. However, many factors are known to influence the accuracy and significance of this measurement, such as age, gender, pain, changes in heart rhythm, arm shape, or an inappropriate cuff size. For the latter factor, one study found that, with the same cuff, a 5 cm longer arm circumference can lead to a 2-5 mmHg higher measured systole and a 1-3 mmHg higher measured diastole (Fonseca-Reeyes S, de Alba-Garcia JG, Parra-Carillo JZ, Paczka-Zapata JA; Effect of standard cuff on blood pressure readings in patients with obese arms; Blood Press Monit 2003; 8:101-106).

[0003] Methods for measuring blood pressure with determination of the upper arm circumference are known from JP-2009297161-A, JP-2010068922-A, US-2005 / 245832-A1 and from STERGIOU GS ET AL: "Can an electronic device with a single cuff be accurate in a wide range of arm size? Validation of the Visomat Comfort 20 / 40 device for home blood pressure monitoring", JOURNAL OF HUMAN HYPERTENSION, Vol. 22, No. 11, July 2008, ISSN: 0950-9240, DOI: 10.1038 / JHH.2008.70.

[0004] It is therefore an object of the invention to propose a method which measures blood pressure using simple standard cuffs or using a single cuff and thereby achieves better measurement accuracy for different upper arm circumferences.

[0005] To solve the problem, claim 1 proposes a blood pressure measurement method on an upper arm, the method comprising the following steps: Providing a blood pressure monitor with a cuff; placing the cuff around a patient's upper arm; inflating the cuff and during inflation: determining the inflation behavior of the cuff by recording at least the integral of the electrical pumping power at a predetermined rate of increase of the internal cuff pressure; determining an upper arm circumference of the patient from the inflation behavior of the cuff, wherein the inflation behavior of the cuff is stored as information and the stored information is compared with information of the same type previously stored by this blood pressure monitor and this cuff, if available, and is assigned to a person from a group of people in the case of identity or predetermined similarity.

[0006] It has been surprisingly shown that the inflation behavior of a blood pressure cuff generally changes predictably with the circumference of the upper arm. The automatic circumference detection associated with the determination of the inflation behavior advantageously allows for the selection of suitable calibration parameters using suitable, conventional software. This allows the blood pressure measurements to be adjusted to the actual upper arm circumference, for example, using conventional algorithms or a simple correction factor, thereby improving the results, particularly for upper arms with large circumferences. It is understood that the correction factor can also be suitable for improving measurement accuracy for small upper arm circumferences.

[0007] Depending on the upper arm circumference, the blood pressure calculation algorithm is adjusted for the calculation of systole and diastole. The calculated values ​​can be displayed or output in a subsequent process step.

[0008] Among the above-mentioned parameters defining inflation behavior, the pressure increase per unit of time, i.e., the rate of pressure change during the inflation process, has proven particularly suitable. The pressure change rate, i.e., the pressure increase in mmHg / s, is almost completely linear with respect to the upper arm circumference, particularly in a range between 40 mmHg and 100 mmHg. For example, in the aforementioned pressure range, for a specific cuff with known inflation behavior, an upper arm circumference of 23 cm can be assumed for a pressure increase of 32 mmHg / s, and an upper arm circumference of 41 cm for a pressure increase of 11 mmHg / s.

[0009] In a further aspect of the invention, the pressure change during inflation can also be recorded for a predetermined period of time. Thus, a first cuff pressure can be recorded after 5 seconds and a second cuff pressure after 7 seconds. Alternatively, a first cuff pressure can be recorded after 9 seconds and a second cuff pressure after 11 seconds.

[0010] In a further aspect of the invention, the pressure change during inflation is recorded in a predefined pressure range, in particular in a pressure range between 40 mmHg and 100 mmHg. In practice, for example, a first time can be recorded after reaching the lower of the two aforementioned internal pressures, and the second time after reaching the other, higher internal pressure. The gradient or pressure change per unit of time, usually per second, is the quotient of the absolute value of the pressure difference, in this case 60 mmHg, and the absolute value of the time difference.

[0011] The invention proposes determining the upper arm circumference based on the cuff's inflation rate. In a further development, the determined upper arm circumference can be displayed on the blood pressure monitor's screen.

[0012] This allows the patient or another person to easily read the upper arm circumference and use it, for example, to check blood pressure measurements. For example, an upper arm circumference that is a few centimeters higher than previous readings may indicate that the cuff is not sitting properly on the upper arm and thus help correct an inaccurate measurement.

[0013] The invention further provides that the inflation behavior of the cuff is stored as information, and that the stored information is compared with previously stored information of the same type, if available, by this blood pressure monitor and this cuff. If the information is identical or predefined similar, the stored information is assigned to a person from a group of people. The information about the inflation behavior can be information from the following group: upper arm circumference, pressure increase in a specific time interval, pressure change during inflation, cuff internal pressure after a predefined inflation time, inflation time required to reach a predefined cuff internal pressure, and the integral of the electrical pump power at a predefined rate of increase of the cuff internal pressure.

[0014] Storing and comparing this information allows for improved assignment of blood pressure measurements to a person.

[0015] The data can be stored either on the blood pressure monitor itself or via a conventional internet interface on an external server.

[0016] A further aspect of the invention is a machine-readable medium, for example in the form of a memory card with a program code stored thereon, which, when executed by means of a machine, carries out the blood pressure measuring method according to the invention or according to at least one of the above-mentioned aspects or further developments or developments of the invention.

[0017] A further aspect relates to a blood pressure monitor suitable for carrying out the blood pressure measurement method, including all of the variants described above or further aspects.

[0018] In particular, the blood pressure monitor may have an internet interface by means of which the inflation behavior recorded by the blood pressure measurement method is stored as information on a server.

[0019] The invention can be used both for blood pressure monitors that measure blood pressure during the pressure drop in the cuff and for those that measure blood pressure during inflation. In the latter case, the inflation rate can be kept constant by means of a suitable software control algorithm. A typical value can be selected, for example, between 2 mmHg / s and 15 mmHg / s, preferably between 2 mmHg / s and 10 mmHg / s, and even more preferably 5 mmHg / s. In particular, the pressure increase rate can be constant and selected to be independent of the upper arm circumference. In this case, the applied pump power can be used to determine the circumference. The pump power can be defined, for example, as an integral over the pulse-width-modulated signal at a constant signal amplitude.

[0020] The invention will be described in more detail using an exemplary embodiment. Fig. 1a diagram showing the gradient of blood pressure in a range of 40 mmHg to 100 mmHg for different arm circumferences and Fig. 2 a diagram with four pressure curves over time for different upper arm circumferences.

[0021] In Fig. 1 The graph shows the increase in blood pressure in a range from 40 mmHg to 100 mmHg for different arm circumferences. Each plotted point indicates a gradient value, i.e. the quotient of pressure difference and unit of time. For this purpose, 14 blood pressure measurements were taken beforehand, with each measurement being taken at a different known arm circumference. The arm circumferences in centimeters 23; 23.5; 24; 25; 27; 28; 30; 31; 32; 33; 38; 40; 41 were used to record the respective rate of increase (mmHg / s). The graph clearly shows that, especially for larger arm circumferences, there is an almost completely linear relationship between the rate of increase and the respective arm circumference.

[0022] In Figure 2The pressure curves for arm circumferences of 23, 28, 32, and 40 cm are shown in various shades of gray. A smaller slope of the curves shown can be seen with a larger arm circumference. Remarkably, the 32 cm curve reaches the 100 mmHg mark later than the 40 cm curve, i.e., the upper limit of the pressure range considered in this example and used to determine the pressure increase rate. Nevertheless, by considering the increase rate, i.e., the slope of the curve, an almost completely linear correlation to the corresponding upper arm circumference is possible.

[0023] For the measurements described above, a standard cuff was used. The cuff is designed as an air-filled balloon with dimensions on the order of 30 cm x 10 cm x 1 cm, which is wrapped around the upper arm with a non-stretchable material. After inflation or automatic inflation, the outer wall of the cuff becomes rigid, and the cuff's compliance is due solely to the air it contains. During an oscillometric sweep, the cuff is inflated to a pressure that is usually well above the systolic pressure, e.g., 150 mmHg to 200 mmHg, and then gradually reduced at a deflation rate of, e.g., 3 mmHg / second. Small oscillations in the cuff pressure occur as the artery fills and empties with blood and manifest as systolic and diastolic pressure in the artery.When the systolic and diastolic pressure are displayed on the blood pressure monitor, the blood pressure values ​​have already been corrected to take the upper arm circumference into account.

[0024] In one aspect of the invention, a blood pressure measuring device is thus proposed which, depending on the speed of the pressure increase in the cuff measured by the pressure sensor, makes an estimate of the circumference of the applied body part, usually the upper arm or a wrist, and advantageously achieves a higher accuracy than through a fixed calibration by selecting various calibration functions or calibration programs known per se.

[0025] It is understood that the calibration can also be selected for ranges that each cover several upper arm circumferences, for example a first calibration for a first range for upper arm circumferences under 25 cm, a second calibration for a second range for upper arm circumferences from 25 to 28 cm and a third calibration for a third range for upper arm circumferences over 28 cm.

[0026] Remarkably, measuring upper arm circumference is also suitable for personalizing blood pressure measurements. This is especially true when additional individual factors, such as the recorded blood pressure values ​​themselves, are taken into account.

[0027] In the example of the four pressure curves shown in Figure 2, for example, each pressure curve could be assigned to an individual. For a family of four using the method according to the invention, even error-free personal assignment would be possible without considering additional individual factors, since the arm circumferences, due to the larger distance between them, lead to significant changes in the respective pressure increase rate, here 32 mmHg / s (child 1, 5 years old) or 25 mmHg / s (child 2, 12 years old), or 20 mmHg / s (mother), or 12 mmHg / s (grandmother).

Claims

1. Blood pressure measuring method on an upper arm, the method comprising the following steps: - providing a blood pressure measuring device having a cuff; - fitting the cuff around an upper arm of a patient; - inflating the cuff and during inflation; - determining the inflation behaviour of the cuff on the basis of the detection of at least the integral of the electrical pumping power at a predetermined cuff internal pressure increase rate; - determining an upper arm circumference of the patient from the inflation behaviour of the cuff, wherein the inflation behaviour of the cuff is stored as information and the stored information is compared with information of the same type, which is previously stored by this blood pressure measuring device and this cuff, if present, and is allocated to a person from a group of persons in the case of identity or predetermined similarity.

2. Blood pressure measuring method according to claim 1, wherein the pressure change during inflation is detected for a predetermined period of time or for a predefined pressure range.

3. Blood pressure measuring method according to one of the above claims, wherein the pressure change during inflation is detected in a predefined pressure range, in particular in a pressure range between 40 mmHg and 100 mmHg.

4. Blood pressure measuring method according to one of the above claims, wherein the blood pressure measuring device comprises a display, and wherein the determined circumference of the upper arm is displayed on the display.

5. Blood pressure measuring method according to one of the above claims, wherein the information about the inflation behaviour is information from the following group: Upper arm circumference, pressure increase in a certain time interval, pressure change during inflation, cuff internal pressure after a predetermined inflation time, inflation time that is required to reach a predetermined cuff internal pressure; integral of the electrical pumping power at a predetermined cuff internal pressure increase rate.

6. Machine-readable medium having a program code that is stored thereon, which, when executed by means of a machine, implements the blood pressure measuring method according to claims 1 to 5.

7. Blood pressure measuring device, suitable for implementing the blood pressure measuring method according to claims 1 to 5.

8. Blood pressure measuring device according to claim 7, wherein the blood pressure measuring device comprises an internet interface, by means of which the inflation behaviour that is detected by means of the blood pressure measuring method is stored as information on a server.