Theoretical and practical considerations in the application of whole body plethysmography to sleep research

The sleep-wake state has a profound influence on many, perhaps most, aspects of normal physiology and is strongly implicated in the mediation (or remediation) of impaired health and performance. Many sleep disorders stem from abnormal respiratory anatomy or sleep-induced changes in respiratory control, underscoring the need for research into the effects of the sleep-wake state on respiratory control processes. Whole body plethysmography is being increasingly used to study respiration in freely behaving animals, and is especially well suited to studies of sleeping animals and human subjects. The method is simple in principle, but care is required in its application to ensure reliable results, and there are circumstances in which it is an inappropriate technique. This review describes the main advantages, pitfalls, and limitations inherent in the use of whole body plethysmography for non-invasive measurement of lung ventilation and metabolic rate in sleeping animals. Sources of potential error, and ways of avoiding such errors, are discussed, with reference to studies involving animal models of sleep-related breathing disorders.