Introduction: In this study we examined the orthostatic tolerance and the baroreflex function in 9 Ethiopian high altitude dwellers (mean age 35+/-4 y). None of the subjects had history suggestive of syncope or maladaptation to hypoxia. Methods: An orthostatic stress test (HUT: 60° head-up-tilt, and progressive lower-body negative pressure) was performed at their resident altitude (3600 m). The test was stopped at the onset of presyncope and time to presyncope was taken as a measure of orthostatic tolerance. Blood pressure (Portapres) and RR interval (ECG) were recorded during the test. Cross-spectral analysis of heart period and systolic blood pressure time series was performed in the LF (. 0.1 Hz) range to estimate the coherence between heart period and systolic pressure, the mean LF central frequency, phase shift, and transfer function gain at maximal coherence. The latter was used to assess the baroreflex sensitivity (BRS). Results: The Ethiopian subjects displayed an excellent orthostatic tolerance, since only one experienced a slightly shortened time to presyncope. While supine, mean coherence in the LF band was 0.62+/-0.06, mean central frequency was 0.077+/-0.007 Hz, mean phase shift was -76.1+/-13.6 deg and mean BRS was 8.6+/-0.9 ms/mmHg. HUT did not induce significant changes in coherence (0.66+/-0.1), mean central frequency (0.08+/-0.004 Hz) and phase (-67.0+/-6.0 deg). HUT induced a significant decrease in mean BRS (5.54+/-0.94 ms/mmHg). Discussion: These results tend to indicate a lower incidence of orthostatic intolerance in comparison with age- and sex-matched sea level subjects at their resident altitude, although the outcomes of cross-spectral analysis were closer to values found in poor orthostatic tolerant see level subjects. We conclude that the cardiovascular autonomic control and the baroreflex function are not directly implied in orthostatic tolerance, in the altitude.
© Copyright 2005 International Congress Mountain & Sport. Updating study and research from laboratory to field. 11th-12th November 2005. Rovereto (TN) - Italy. Programme and book of abstracts. Veröffentlicht von Centro Interuniversitario di Ricerca in Bioingegneria e Scienze Motorie. Alle Rechte vorbehalten.