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Abstract
Studies have shown physical inactivity increases the risks of chronic illnesses, including: cardiovascular disease, obesity, and type 2 diabetes. In a clinical environment to assess fitness there are a number of relevant measures required, including: monitoring cardiac fitness through the interpretation of oxygen uptake (VO2); cardiac function through electrocardiogram (ECG) analysis and heart rate (HR) calculation; and pulmonary fitness assessment using respiratory rate (RR) and respiratory volume (RV).
The physical activity measurement devices (PAMDs) that are currently available are limited by requiring a mask to be worn or restricted to discrete tests performed in a clinical environment. As society has become more aware of the consequences of physical inactivity, a wide range of wearable fitness trackers have been developed. While demand and use of these devices has grown they are not suitable for clinical assessment as current consumer fitness trackers only monitor HR and hence can only give a rough estimate of energy expenditure (EE). To allow for long term studies, a clinical PAMD is required which is non-invasive, unobtrusive and allows for continuous measurements.
In response to the need for a clinical PAMD we have developed new methods for VO2 and RV measurement, as well as a wearable device which can implement these methods. We performed two prospective non-randomised clinical trials to allow for clinical validation of the developed methods. Our developed method for calculating VO2 combines measurements from an ECG and a triaxial accelerometer (TA) and results show that it has a much wider applicability to daily activities than other methods which are often only effective during periods of exercise. The developed VO2 method was compared to indirect calorimetry with results showing considerable improvement when compared with existing PAMDs.
For assessing pulmonary fitness, the developed method for calculating RV uses an ECG and the physiological phenomenon of respiratory sinus arrhythmia (RSA) to calculate RV breath by breath. The results from the trial performed to validate the method show a correlation coefficient of 0.94 with inspired and expired volumes as measured by a spirometer.
This thesis provides the methods to allow clinically relevant assessment of a person’s fitness using a non-invasive, wearable device. The methods developed in this thesis also allow for individual assessment of VO2 for discrete periods, thus providing an alternative to current VO2 estimation techniques.