Wearable hemodynamic sensor
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.
1. A wearable device for measuring hemodynamic parameters comprising:
a photoplethysmographic system having:
one or more light sources;
one or more light detectors that generate the photoplethysmographic signal;
a mounting element for attaching the photoplethysmographic system to a body part containing an artery having an actuator;
a control system for controlling the actuator and the contact pressure of the photoplethysmographic system; and
an accelerator or motion sensor placed next to the photoplethysmographic system used for heart level correction;
wherein the hemodynamic parameters are further derived from a transfer function;
wherein the control system is configured to implement at least one of different modes of operations A to C:
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 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; and
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 wearable device of claim 1 wherein the contact pressure is measured by a pressure sensor.
3. The wearable device of claim 1 further comprising a transmitter for sending the resulting hemodynamic parameters to a host device that is connected to the Internet.
4. The wearable device of claim 1 wherein at least two or more light sources or wavelengths are used;
wherein the least one light detector generates two or more photoplethysmographic signals corresponding to the at least two or more light sources or wavelengths; and
further comprising means for calculating oxygen saturation by using the at least two different photoplethysmographic signals.
5. The wearable device of claim 1 wherein the elements of the device are placed into a ring, wherein the circumference of the ring can be altered by the actuator.
6. The wearable device of claim 1 wherein the elements of the device are placed in a bracelet or watch, wherein the actuator changes the contact pressure of the bracelet or watch at the wrist, where the radial artery can be palpated.