Wearable hemodynamic sensor

• US 10,285,599 B2
• Filed: 01/07/2016
• Issued: 05/14/2019
• Est. Priority Date: 01/08/2015
• Status: Active Grant

• Current Assignee: CNSystems Medizintechnik AG
• Original Assignee: CNSystems Medizintechnik AG
• Inventors: Fortin, Jurgen
• Primary Examiner(s): Jang, Christian
• Application Number:
  US14/989,973
• Publication Number:
  US 20160198955A1
• Time in Patent Office: 1,223 Days
• CPC Class Codes: A61B 2560/0261 using hydrostatic pressure
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/02108 from analysis of pulse wave characteristics
• CPC Class Codes: A61B 5/02225 using the oscillometric method
• CPC Class Codes: A61B 5/02233 Occluders specially adapted therefor tourniquets A61B17/132
• CPC Class Codes: A61B 5/02241 of small dimensions, e.g. adapted to fingers
• CPC Class Codes: A61B 5/02255 the pressure being controlled by plethysmographic signals, e.g. derived from optical sensors
• CPC Class Codes: A61B 5/02422 within occluders
• CPC Class Codes: A61B 5/02438 with portable devices, e.g. worn by the patient
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: A61B 5/1117 Fall detection
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence

Abstract

A wearable device and the accompanying method for the determination of continuous pulsatile BP are described. The absolute values can be obtained in the initial phase and how a transfer function can transform the BP-signal obtain at the finger or wrist to correct BP-values corresponding to the brachial artery and at heart level. The wearable device contains an orthostatic level-correcting element, which can measure the vertical distance between heart level and finger/wrist level, where the actual measurement takes places. The wearable device may be in the form of a ring, a watch, or a bracelet. Further, the wearable device has elements for wirelessly transmitting signals to host devices such as a smart phone, tablet or other computers.

Claims

1. A method for the continuous non-invasive measurement of hemodynamic parameters within a wearable device comprising:

measuring a photoplethysmographic signal disposed on a body part containing an artery using a photoplethysmographic system having;

at least one light source; and

at least one light detector generating the photoplethysmographic signal;

wherein the contact pressure of the photoplethysmographic system can be varied by an actuator;

wherein the movement of the actuator and the contact pressure is controlled by a control system using at least a part of the photoplethysmographic signal;

wherein the true pulsatile BP-signal and further calculated hemodynamic parameters are derived from the contact pressure and the photoplethysmographic signal;

wherein the hemodynamic parameters are further derived from a transfer function; and

wherein at least one of different modes of operation A to C is implemented;

a mode A for continuous measurement of hemodynamic parameters, wherein the contact pressure is adjusted by the control system and the actuator according to mean arterial pressure multiplied by a constant factor, and wherein the transfer function is applied to the photoplethysmographic signal and the contact pressure;

a mode B for the initialization of the continuous measurement of hemodynamic parameters,

wherein the contact pressure is adjusted by the control system and the actuator to different pressure levels,

wherein the amplitude of the photoplethysmographic signal is determined,

wherein mean blood pressure is determined at the contact pressure, where coevally the highest amplitude of the photoplethysmographic signal is measured, and

wherein the mean blood pressure multiplied by a constant factor is used as the starting point for the measurement modus; and

an idle mode C wherein the contact pressure is adjusted to a constant pressure around 30-40 mmHg,

wherein the system waits for user interaction in order to bring the system in initialization and further into the measuring mode,

wherein the photoplethysmographic signal is measured for obtaining heart rate, and

wherein the system can be further brought in initialization and thereafter into the measuring mode if heart rate increases over or decreases under a predefined threshold.

2. The method of claim 1 wherein contact pressure is measured by a pressure sensor.

3. The method of claim 1 wherein the hemodynamic parameters are corrected to heart level using an orthostatic level-correcting element.

4. The method of claim 3 wherein the orthostatic level-correcting element comprises a fluid filled hose between the photoplethysmographic system and heart level;

wherein the hose is filled with a fluid having a density similar to that of blood;

wherein the hose is closed on one end with a freely floating membrane;

wherein the hose is closed on the other end with a pressure sensor; and

wherein the pressure obtained from this heart level pressure sensor is used for heart level correction.

5. The method of claim 3 wherein the orthostatic level-correcting element comprises an accelerometer or motion sensor;

wherein the accelerometer or motion sensor is placed next to the photoplethysmographic system;

wherein the movement in the same direction as gravity is used for calculating orthostatic distance between heart level and the location of the photoplethysmographic system; and

wherein the correcting procedure can be zeroed by simultaneously placing the wearable device on heart level.

6. The method according to claim 1 wherein the transfer function is a general transfer function valid for humans.

7. The method according to claim 1 wherein the transfer function is personalized by using the individual systolic and diastolic blood pressure of a patient.

8. The method of claim 1 wherein systolic and diastolic blood pressure is estimated using the distribution of the amplitude of the photoplethysmographic signal versus the applied contact pressure;

and

wherein systolic and diastolic blood pressure is used for the calibration of the transfer function.

9. The method according to claim 1 wherein the accelerator detects falls of the patient and initiates or re-initiates the initialization mode.

10. The method according to claim 1 wherein some of the hemodynamic parameters are calculated by using biomedical algorithms applied to the photoplethysmographic signal, the contact pressure and the transfer function.