EP-4734836-A1 - SYSTEM FOR USE IN HEMODYNAMIC PARAMETER MEASUREMENT

EP4734836A1EP 4734836 A1EP4734836 A1EP 4734836A1EP-4734836-A1

Abstract

A system for use in non-invasive hemodynamic parameter measurement which comprises a cuff having a pressure actuator and a tissue pressure sensor, where the tissue pressure sensor comprises a fluid pad hydraulically connected to a fluid pressure transducer unit. Provided is a height monitoring means for tracking a change in a height of the transducer unit relative to the cuff and the cuff relative to a heart level of the patient, wherein the heart level is indicated by proxy using a height reference unit mounted to the patient's torso. Changes in these relative heights are used to compute a correction parameter for the tissue pressure signal. In some embodiments, changes in height of each of the cuff, transducer unit and height reference unit may be independently tracked. In some embodiments, this is done by motion tracking of each unit and aggregating net motion to determine position change.

Inventors

SCHMITT, LARS
MUEHLSTEFF, JENS
MENA BENITO, Maria, Estrella
WIJSHOFF, Ralph, Wilhelm, Christianus, Gemma, Rosa
HILGERS, Achim, Rudolf
PELSSERS, EDUARD, GERARD, MARIE
DAVIDOIU, Valentina-Geta

Assignees

Koninklijke Philips N.V.

Dates

Publication Date: 20260506
Application Date: 20240621

Claims (15)

1. A system (30) for use in blood pressure measurement comprising: a cuff (52) for wrapping around a body part of a user, and wherein the cuff includes an actuator for use in applying a variable pressure to the body part by the cuff, a tissue pressure sensor arranged for sensing a pressure between a surface of the body part and the cuff, wherein the tissue pressure sensor comprises: a fluid-containing pad (53) arranged so as to be in pressure-coupled relationship with the tissue of the body part when the cuff is wrapped around the body part, wherein changes in said pressure between a surface of the body part and the cuff are coupled to changes of fluid pressure in the pad; and a pressure transducer unit (54) fluidically coupled via a fluid line to the fluid pad and comprising readout electronics for transducing pressure exerted on the pad to an output tissue pressure signal (P(t)); a height reference unit (56) for attachment at a reference location on the body of the user; a height sensing sub-system (60) adapted to sense and monitor changes in: a first relative height (Hl), between the cuff and pressure transducer unit, and a second relative height (H2) between the cuff and the reference unit; and a controller (32) adapted to compute a correction parameter (• (t)) for the tissue pressure signal (P(t)) based on changes in the first and second relative heights using a pre-determined function.
2. The system of claim 1, wherein the height reference unit (56) is body-mountable.
3. The system of claim 1 or 2, wherein the height sensing sub-system is adapted to independently detect changes in height of each of the reference unit, the cuff and the pressure transducer unit, and to determine the changes in the first and second relative heights based thereon.
4. The system of any of claims 1-3, wherein the height sensing sub-system is adapted to compute at each of a series of sampling points, t, spanning a monitoring period: a net change (• Hl(t)) in the first relative height since a start of the monitoring period; and a net change (• H2(t)) in the second relative height since a start of the monitoring period.
5. The system of claim 3 or 4, wherein the height sensing sub-system comprises a first motion sensor integrated in the cuff, a second motion sensor integrated in the pressure transducer unit and a third motion sensor integrated in the height reference unit, wherein the height sensing sub-system is adapted to monitor the changes in the first and second relative heights based on monitoring motion of each of the cuff, pressure transducer unit and height reference unit in the height direction.
6. The system of claim 5, wherein the controller is adapted to compute a net change in height, at time t of a monitoring period, of each of the cuff, pressure transducer unit and height reference unit based on aggregating a respective motion in the height direction of each of the cuff, pressure transducer unit and height reference unit between a start of the monitoring period and time t.
7. The system of claim 5 or 6, wherein each of the first, second and third motion sensors comprises a respective inertial measurement unit adapted to output a 3D acceleration signal, and wherein the controller is adapted to monitor motion in a height direction for each of the cuff, pressure transducer unit and height reference unit based on a component of the 3D acceleration signal of each respective inertial measurement unit in a direction of gravity.
8. The system of claim 7, wherein the controller is adapted to compute a net change in height, at time t of a monitoring period, of each of the cuff, pressure transducer unit and height reference unit based on double integration with respect to time of the component of the respective acceleration signal in the direction of gravity for each of the first, second and third inertial measurement unit.
9. The system of any of claims 1-8, wherein the controller is adapted to periodically compare a net change in the first relative height to a first threshold and the net change in the second relative height to a second threshold and control a user interface to generate user feedback responsive to exceeding the threshold.
10. The system of any of claims 1-9, wherein the controller is adapted to compute a correction of the tissue pressure signal based on the function: P_c (t) = P_O(t) + • (t) where • (t) = • • Hl(t) + • • H2(t) where P_c (t) is the corrected tissue pressure measurement, P_0 (t) is the original tissue pressure measurement, • (t) is the correction parameter, • is a constant proportional to a density of the fluid contained in the pad, • Hl(t) is the net change in the first relative height at time t, • is a constant proportional to the density of blood, and • H2(t) is the net change in the second relative height at time t.
11. The system of claim 10, wherein • = 0.69 mmHg / cm height difference, and wherein • = 0.78 mmHg / cm height difference.
12. The system of any of claims 1-11, wherein the pressure transducer unit, cuff and/ or reference unit comprises an inertial measurement unit adapted to output an acceleration signal; wherein the controller is further adapted to detect motion events of the pressure transducer unit, cuff and/or reference unit using the acceleration signal output from the inertial measurement unit; wherein the controller is adapted to generate user feedback through control of a user interface responsive to the detection.
13. The system of claim 12, wherein the controller is further adapted to determine a severity of each detected motion event based on a feature of the acceleration signal corresponding to the event; wherein the controller is adapted to classify a measurement quality of a blood pressure measurement obtained over a time period which coincided with the motion event, wherein the quality classification is determined based on a pre-determined mapping between motion event severity and measurement quality.
14. The system of any of claims 1-13, wherein the height sensing subsystem includes a fluid line connected between the height reference unit and the pressure transducer unit and wherein the change in the relative height between the reference unit and the pressure transducer unit is computed based on a change in a pressure differential between the reference unit and the pressure transducer unit.
15. The system of any of claims 1-14, wherein the system comprises a base unit, wherein the base unit houses the controller, wherein the base unit comprises a user interface including a display device, wherein the base unit includes a hemodynamic measurement module for computing one or more hemodynamic measurements based on the tissue pressure signal.

Description

SYSTEM FOR USE IN HEMODYNAMIC PARAMETER MEASUREMENT FIELD OF THE INVENTION The present invention relates to the field of non-invasive hemodynamic parameter measurement. BACKGROUND OF THE INVENTION The most common method for non-invasive blood pressure (NIBP) measurement is the use of an oscillometric blood pressure measurement cuff. The cuff comprises an inflatable bladder. The cuff wraps around the upper arm of a patient and is controlled to progress through an inflation and deflation cycle during which a pressure inside the bladder is sampled and a single set of values for systolic arterial pressure, mean arterial pressure and diastolic arterial pressure (and pulse pressure) are derived through processing of the pressure signal. A variant approach to non-invasive blood pressure measurement has previously been proposed. This also uses a cuff which wraps around the body part of the patient. A cross-sectional illustration is shown in Fig. 1. The cuff 2 is shown wrapped around the arm 10 of a patient, and the brachial artery 8. The cuff 2 includes a pressure actuator 14, which optionally may be an inflatable bladder, as in the traditional NIBP cuff. In variance with the traditional NIBP cuff, the variant cuff also includes a separate tissue pressure sensor 4 arranged to measure a pressure between the body part 10 and the cuff. The tissue pressure sensor in some examples comprises a fluid-filled sensor pad, wherein a pressure in the pad varies as a function of pressure exerted on the pad. The pad may be fluidically coupled to a pressure transducer for read-out of a tissue pressure signal. When blood pulses in the artery 8, this results in a pressure wave 6 which can be detected by the tissue pressure sensor 4. The tissue pressure sensor 4 can be connected to the pressure transducer via a fluid-filled tube/line. The pressure transducer converts the pressure in the fluid into an electrical signal. Also in variance with the traditional NIBP cuff, the variant cuff includes a hard shell 12 which extends around the body part and is disposed (radially) between the actuator 14 and the body part 10. The pulse waves in the brachial artery 8 cause a change in the arm volume which causes a compression of the liquid in the sensor pad 4. The sensor pad is fluidly connected via a flexible tube filled with fluid to the pressure transducer which measures the pressure signal. The pressure sensor pad 4 is enclosed by a hard shell 12 to enable a sufficient signal from the pressure sensor. In similarity with a standard NIBP cuff, the pressure actuator 14 may comprise a bladder which is inflatable with an air pump, to compress the arm tissue, so that the brachial artery 8 can be closed. Due to the inclusion of the separate tissue pressure sensor 4 with hard shell 12 backing, this cuff can obtain a real time pulse signal for the patient, and, from this, multiple different hemodynamic parameters can be obtained, including stroke volume and cardiac output. The shell structure 12 has an annular form, and, in the most common design, is formed from a single piece of material which is curled round to span a complete (closed) loop. Fig. 2 schematically shows an example shell structure 12 according to the state of the art. Fig. 2 (left) shows a cross-section across a plane normal to a longitudinal axis of the shell and parallel with tangential and radial axes of the shell. Fig. 2 (right) shows a cross-section across a plane parallel with a longitudinal axis of the shell. The shell structure is for extending around the body part 10 and is for arrangement between the tissue pressure sensor and the pressure actuator during operation, the shell structure being discontinuous circumferentially so as to having at least one pair of tangentially overlapping edge surfaces 13a, 13b which are tangentially slidable relative to one another during operation. In order to obtain accurate blood pressure measurements using conventional non-invasive inflatable blood pressure (NIBP) cuffs, it is important that the cuff is vertically aligned with the patient’s heart level. Patient motion and/or changes in patient posture have an impact on blood pressure measurements and consequently, on the reliability of the information obtained. This requirement is also true for the shell-backed cuff described above. An additional requirement for the shell-backed cuff arises from the fluid-based tissue pressure sensor. As mentioned above, this comprises a fluid-filled pad coupled hydraulically to a pressure transducer unit via a fluid line. The fluid line for example is a fluid conduit in the form of a flexible hose or tube. In order to obtain accurate tissue pressure measurements with the tissue pressure sensor, the pressure transducer unit needs to be arranged level with the phlebostatic axis (PA) of the patient as well as the cuff being level with the phlebostatic axis. If the cuff or transducer unit is placed above the PA, erroneously low readings are obtained, whereas i