[The diurnal rhythm of chemosensitivity and its contribution to nocturnal disorders of respiratory control].

UNLABELLED: Circadian variation of chemosensitivity was examined under constant standardized metabolic and climatic conditions. Progressive hyperoxic hypercapnia tests and progressive isocapnic hypoxia tests were applied every 2 h in 10 healthy male subjects employing rebreathing (6 l spirometer). During the 24 h run they were confined to bed. They were allowed sleep at their convenience, but were woken for examination, and were given a low-protein isocaloric diet after each of the 13 tests. For assessment of psychophysiological performance, auditory reaction time, flicker fusion frequency, and self ratings of mood and activation were applied. ECG, body core temperature, nasal respiration, tcpaO2 and galvanic skin resistance were recorded continuously for 24 hrs.

RESULTS: Chemosensitivity revealed a highly significant circadian variation with respect to a shift in the CO2-response (amplitude +/- 3 mmHg), and an amplitude of +/- 12 mmHg for the O2-response. Maximal sensitivity was found at 5 p.m., the absolute minimum at 5 a.m. Body core temperature, auditory reaction time, and flicker fusion frequency paralleled these changes in chemosensitivity. The results show that there is a pronounced 24 h cycle of chemosensitivity that is independent of sleep. Since chemosensitivity, and respiratory drive keeping upper and lower airways patent, are closely related, it is concluded that the circadian variation in chemosensitivity may substantially contribute to nocturnal increase in airway resistance, and central and obstructive apneas as well.