Actigraphic Monitoring of Heart Rate and Movement as an Index of Daily Body Energy Expenditure in Health and Disease

Abstract

The studies in this thesis were prompted by the rapidly emerging field of actigraphy which can provide nonintrusive measurements of physical activity over prolonged periods in free-living conditions. These features offer a unique opportunity to investigate daily activities and how such activities can be impaired by clinical disorders. A series of investigations were carried out to evaluate the accuracy of actigraphic based estimates of body energy expenditure made with an Actiheart system at rest and during exercise in healthy individuals (Studies 1 and 2 described in Chapters 2 and 3). A subsequent study (Study 3 described in Chapter 4) examined Actiheart based measurements of daily body energy expenditure in obstructive sleep apnoea (OSA) patients, how body energy expenditure varied throughout the day in these patients, and whether daily body energy expenditure and the daily body energy expenditure profile changed after commencement of nightly treatment with continuous positive airway pressure (CPAP). A central hypothesis in the OSA study (Study 3 described in Chapter 4) was that reversal of excessive daytime sleepiness by CPAP would result in increased daily activities and increased body energy expenditure. As shown in Study 2, the Actiheart system provided accurate estimates of body energy expenditure in healthy men under resting conditions and during mild and moderate levels of 3 types of exercise (arm ergometry, bicycle ergometry and treadmill walking) performed at matched workloads. This study is the first to demonstrate that the accuracy of Actiheart based BEE estimates at matched mechanical workloads remains high over a range of different modes of exercises which involved different body movements utilising different muscle groups. As predicted, the heart rate response to arm exercise was higher than during bicycle and treadmill exercise at matched workloads. However, this did not impair the Actiheart's ability to provide accurate estimates of body energy expenditure.