DIURNAL RHYTHMS OF ORTHOSTATIC CARDIOVASCULAR RESPONSES

In 8 subjects, the reactions of heart rate and blood pressure to changes in posture on the tilt table have been tested every third hour throughout 24 hours. By computing the orthostatic index of Burkhart and Kirchhoff, a diurnal rhythm of tilt tabel tolerance has been demonstrated. There are two maxima of orthostatic lability, a minor one toward noon and a major one at about 3 o'clock in the morning. The rhythm of orthostatic lability seems to be independent from food intake. Consequences of these findings with regard to test situations in spaceflight medical operations are briefly discussed. © 1969 Springer-Verlag.