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Publication Number
US-10285599-B2
Publication Date
2019-05-14
Expiration Date
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.
Core Innovation
The invention relates to continuous non-invasive measurement of hemodynamic parameters within a wearable device by measuring a photoplethysmographic signal on a body part containing an artery using a photoplethysmographic system having at least one light source and at least one light detector. The contact pressure of the photoplethysmographic system is varied by an actuator, and movement of the actuator and the contact pressure is controlled by a control system using at least a part of the photoplethysmographic signal.
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. Operation includes a continuous measurement mode, an initialization of the continuous measurement mode, and an idle mode in which the system waits for user interaction to bring the system into initialization and further into the measuring mode.
In the initialization mode, the contact pressure is adjusted by the control system and the actuator to different pressure levels, the amplitude of the photoplethysmographic signal is determined, and mean blood pressure is determined at the contact pressure while coevally the highest amplitude of the photoplethysmographic signal is measured. The mean blood pressure multiplied by a constant factor is used as the starting point for the measurement modus, and the system can be brought into initialization thereafter into the measuring mode if heart rate increases over or decreases under a predefined threshold.
Claims Coverage
The independent claim covers a continuous non-invasive hemodynamic measurement method in a wearable device that uses actuator-controlled contact pressure together with a photoplethysmographic signal and a transfer function to derive true pulsatile blood pressure and further calculated hemodynamic parameters. It further constrains operation to three modes with specific control and starting-point logic.
Actuator-varied photoplethysmographic contact pressure controlled by the photoplethysmographic signal
Varying the contact pressure of the photoplethysmographic system by an actuator, and controlling movement of the actuator and the contact pressure by a control system using at least a part of the photoplethysmographic signal.
Deriving true pulsatile BP and further hemodynamic parameters using contact pressure and transfer function
Deriving a true pulsatile BP-signal and further calculated hemodynamic parameters from the contact pressure and the photoplethysmographic signal, and deriving the hemodynamic parameters further from a transfer function.
Continuous measurement mode with constant-factor starting point
Implementing a continuous measurement mode, 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.
Initialization mode with amplitude determination and mean blood pressure starting point
Implementing an initialization mode for 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 mean blood pressure multiplied by a constant factor is used as the starting point for the measurement modus.
Idle mode with heart-rate threshold-triggered re-initialization
Implementing an idle mode 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.
Overall, the independent claim ties actuator-controlled contact pressure and photoplethysmographic signal measurement to a transfer-function based derivation of true pulsatile BP and further hemodynamic parameters, while defining continuous, initialization, and idle modes with triggered re-initialization.
Stated Advantages
Documented Applications
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