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RESEARCH

Circadian and Sleep Physiology

Circadian rhythms are biological rhythms that fluctuate across the 24 hour day and repeat every 24 hours. In humans the biological clock is located in the brain, and coordinates the activities of nearly all our behavioural and physiological processes, including endocrine, thermoregulatory, immune, cardiovascular, respiratory, gastrointestinal, renal, neurobehavioural and sleep-wake activities. Circadian disruption results from misalignment in the timing of circadian rhythms in relation to either the environment or to each other, as experienced by shiftworkers and travellers suffering from jet lag.

The effects of circadian disruption and sleep loss in patients suffering from medical disorders, such as asthma and sleep apnea, have not been widely studied and remain poorly understood. There is also little known about the relative contributions of the circadian and sleep systems on understanding of disease severity and pathways, as well as optimal treatment regimes for these disorders. Our current research work is focussed in the following areas:

• understanding the interaction of sleep disturbance due to sleep apnea and asthma with further challenges to the sleep system by chronic sleep restriction and how the effects may differ in healthy, well sleeping individuals.
• understanding the interaction of sleep disturbance due to sleep apnea and asthma with circadian disruption due to simulated jet lag, and how the effects may differ in healthy, well sleeping individuals.
• understanding the profile and time course of neurobehavioural changes induced by acute periods of total sleep deprivation in individuals with sleep apnea and healthy, well sleeping individuals

Measures in these studies include assessment of neurocognitive function using a range of computerised performance tests and subjective assessments, sleep physiology, waking EEG, respiratory symptoms and body temperature.