Development of a device for monitoring heart rate during Positive Airway Pressure therapy

Author: Mark Gardner

Gardner, Mark, 2019 Development of a device for monitoring heart rate during Positive Airway Pressure therapy, Flinders University, College of Science and Engineering

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Obstructive Sleep Apnoea (OSA) is a condition where during sleep a person’s upper airway becomes obstructed, limiting breathing and reducing the quality of sleep. OSA is commonly treated using Positive Airway Pressure (PAP) therapy, in which a positive pressure is applied to the person’s upper airway via a mask. People with OSA are at a higher than normal risk of developing heart problems. It is thought that by monitoring a person’s Heart Rate (HR) and Heart Rate Variability (HRV) long-term, it may be possible to identify if a person’s heart health is declining before a serious cardiac event occurs.

Adding HR monitoring to PAP therapy offers a good opportunity for long-term continuous cardiac monitoring as, when used correctly, the PAP therapy is used for several hours every night. This thesis details the development of a device that is able to measure the HR and HRV of people with OSA during PAP therapy.

A PAP mask was modified to be able to measure HR; it was modified such that it can measure Electrocardiography (ECG), Photoplethysmography (PPG) and Ballistocardiography (BCG) signals from the wearer, from which HR values were extracted. The ECG signals were measured using Stainless Steel electrodes which were held in place against the wearer’s face and neck by the straps of the PAP mask. The PPG signal was measured using a reflectance pulse oximeter that was located on the wearer’s forehead. The BCG signal was measured from a solid-state gyroscope which was attached to the PAP mask.

Signals from the modified mask were recorded from a group of 19 healthy participants who wore the mask whilst lying on a bed, experiencing PAP therapy. A beat-to-beat interval (BBI) correction algorithm was developed for improving the accuracy of the HR and HRV analysis from the measured signals. The analysis of the recorded ECG and PPG signals showed that HR and HRV values could be accurately measured from the healthy participants, however not consistently. Data fusion methods were developed for combining the HR and HRV information from the ECG and PPG signals, which were able to further increase the consistency of the HR and HRV analysis without a significant decrease in the accuracy.

For the BCG signal, the instantaneous HR analysis was only accurate when the participants were lying on their back, as when they were lying on their side there was a decrease in the BCG signal quality. Two data fusion methods were developed to combine the HR information from the 3 axes of the gyroscope to improve the accuracy and consistency of the HR measurements.

These results show that is possible to accurately monitor the HR and HRV of the Cardiomask wearer. With further development, this technology could be used to monitor the HR and HRV of OSA patients during PAP therapy.

Keywords: Heart Rate, Heart Rate Variability, ECG, PPG, BCG, Sleep apnoea, Positive Airway Therapy

Subject: Engineering thesis

Thesis type: Doctor of Philosophy
Completed: 2019
School: College of Science and Engineering
Supervisor: Professor Karen Reynolds