A method to evaluate a heart rate and/or a respiratory rate of a subject wearing a monitoring device comprising at least one accelerometer, at least one gyroscope, at least one photoplethysmograph, and a processor comprising a microprocessor and a controller, wherein said method comprises the following steps:
- estimating, by the processor, a level of activity of the subject according to signals acquired by the at least one accelerometer and the at least one gyroscope;
- comparing, by the processor, said level of activity to a predefined threshold;
- and either:
- if the photoplethysmograph is in a deactivated state, activating, by the processor, the photoplethysmograph, or activating, by the processor, the photoplethysmograph and maintaining, by the processor, the photoplethysmography in an activated state when the level of activity is above the predefined threshold and calculating, by the processor, the heart rate and/or the respiratory rate using the photoplethysmographic signal;
- or
- if the photoplethysmograph is in an activated state, deactivating, by the processor, the photoplethysmograph, or deactivating, by the processor, the photoplethysmograph and maintaining, by the processor, the photoplethysmograph in a deactivated state when the level of activity is below the predefined threshold and implementing, by the processor, a method to monitor physiological signals by processing signals acquired with at least one accelerometer and one gyroscope for the evaluation of a heart rate and/or a respiratory rate of a subject wearing a monitoring device comprising said accelerometer, said gyroscope, and the processor, said method comprising the following steps:
- receiving, by the processor, the signals acquired by the accelerometer and the gyroscope with a predefined sampling frequency at n sampling times in a given time window, so as to obtain a pair of n successive samples of the signals acquired by the accelerometer and the gyroscope in the given time window;
- for each pair of the n successive samples of the signals acquired by the accelerometer and the gyroscope in the given time window, combining, by the processor, the n successive samples of the signals of the accelerometer and the gyroscope, by the processor using a quaternion representation so as to output an orientation vector for each n sampling time, the processor using the quaternion representation providing computational simplicity and increased power efficiency, wherein the orientation vectors for all n sampling times in the given time window collectively define an orientation signal;
- applying, by the processor, at least one filter to the orientation signal so as to obtain a filtered signal for the given time window;
- calculating, by the processor, an average breath cycle and/or an average time interval separating two consecutive heart beats, the processor using an algorithm for modeling an average signal, said algorithm iteratively determining said average breath cycle and/or said average time interval separating two consecutive heart beats by computing an average signal between the filtered signal obtained for the given time window and an average signal obtained in a preceding iteration for a preceding time window;
- estimating, by the processor, a heart rate and a respiratory rate from the average breath cycle and the average time interval separating two consecutive heart beats calculated;
- and
- transmitting, by the processor, data to a companion device or a server operating system, said data selected from the group consisting of:
- the pair of n successive samples of signals, the average breath cycle and/or the average time interval separating two consecutive heart beats calculated, the heart rate and/or the respiratory rate estimated, and combinations thereof,
- wherein the deactivating, by the processor, of the photoplethysmograph when the level of activity reduces energy consumption of the monitoring device.