New Methods for the Non-Invasive Assessment
of Sympathetic Activity During Sleep

Summary Autonomous nervous functions do change with normal sleep and do show characteristic changes with sleep disorders. This is why the investigation of autonomous nervous function during sleep plays an important role. Two different and new methods will be introduced here. The pulse transit time (PTT) determines the time delay between ECG and the resulting peripheral pulse wave. PTT is reverse proportional to arterial blood pressure and changes in amplitude of the PTT signal do correlate well with intra-thoracic pressure changes. The peripheral arterial tonometry (PAT) determines the peripheral arterial vascular tone using a plethysmographic method. The peripheral arterial tone is modulated by sympathetic and parasympathetic activity, by peripheral blood pressure, and by the peripheral resistance of the vessels. Both signals are non-invasive methods to assess changes of autonomous nervous function. With the help of both signals in addition to cortical arousal it is possible to detect sub-cortical arousal. This effect and the high correlation with oesophageal pressure and blood pressure changes result in characteristic changes in PTT and PAT for obstructive sleep apnoea. The changes are so characteristic that they can be used diagnostically. In summary, PTT and PAT do show different aspects of the autonomous nervous function and cannot be substituted by each other. Both give important additional information to characterise arousal during sleep and sleep disorders. The clinical and cardiovascular consequences of sub-cortical arousal need prospective long-term follow-up studies.