High altitude native populations have adapted to the environmental stress of chronic hypoxia over generations, often demonstrating superior hypoxia tolerance. Up to a third of Andean high altitude natives, however, lose their ability to cope with chronic hypoxia and develop maladaptation syndrome chronic mountain sickness (CMS), which is associated with an increased risk of cardiovascular disease. Autonomic dysfunction has been implicated in the development and progression of many cardiovascular diseases; therefore we investigated whether autonomic function is impaired in CMS sufferers. We assessed baroreflex function in 7 Andean natives with CMS (CMS+; Hb 19.3g/dL) and 7 Andean natives without CMS (CMS-; 22.6g/dL) at their resident altitude (Cerro de Pasco, Peru; 4383m). R-R interval (RRI; Electrocardiogram), beat-by-beat arterial blood pressure (BP; photoplethysmography) and muscle sympathetic nerve activity (MSNA; microneurography) were recorded at rest and during pharmacologically induced changes in arterial blood pressure (modified Oxford method). The responsiveness (i.e gain) of the vascular-sympathetic baroreflex was determined from the slope of the linear relationship between diastolic blood pressure and MSNA burst probability, and the responsiveness of the cardiovagal baroreflex was determined from the slope of the linear relationship between RRI and systolic blood pressure. Values are presented as means (± SD) and were compared using unpaired T-tests. Resting mean arterial pressure was similar in CMS+ (83 ± 7mmHg) and CMS- (86 ± 10mmHg; P = 0.58). Resting RRI was higher in CMS+ (936 ± 156msec) compared with CMS – subjects (817 ± 50; P = 0.07). Vascular-sympathetic baroreflex gain was similar in both CMS + (-2.7 ± 1.1 %/mmHg) and CMS – subjects (-2.5 ± 1.0%/mmHg; P = 0.72). Cardiovagal baroreflex gain, however, was greater in CMS+ subjects (17.2 ± 6.8msec/mmHg) versus their CMS- counterparts (8.8 ± 2.6msec/mmHg; P = 0.009). Our data show that the responsiveness of the vascular-sympathetic baroreflex is preserved in CMS sufferers and the responsiveness of the cardiovagal baroreflex is in fact enhanced, compared to CMS- subjects. In conclusion, maladaptation to chronic hypoxia in CMS does not impair baroreflex control of blood pressure.
Extreme Environmental Physiology (University of Portsmouth, UK) (2019) Proc Physiol Soc 44, C15
Oral Communications: Baroreflex function in Andean high altitude natives with and without chronic mountain sickness
L. L. Simpson1, V. L. Meah2, A. Steele2, S. A. Busch1, S. Oliver1, J. S. Lawley3, M. Tymko4, G. Vizcardo-Galindo5, R. J. Figueroa-Mujíca5, F. Villafuerte5, P. N. Ainslie4, C. D. Steinback2, M. Stembridge6, J. P. Moore1
1. School of Sport, Health and Exercise Sciences, Bangor University, Walsall, United Kingdom. 2. Neurovascular Health Laboratory, Faculty of Kinesiology, Sport, and Recreation, University of Alberta, Edmonton, Alberta, Canada. 3. Department of Sport Science, Division of Physiology, University of Innsbruck, Innsbruck, Austria. 4. Centre for Heart, Lung, and Vascular Health, University of British Columbia Okanagan, Kelowna, British Columbia, Canada. 5. Laboratorio de Fisiología Comparada, Departamento de Ciencias Biológicas y Fisiológicas, Facultad de Ciencias y Filosofía, Universidad Peruana Cayetano Heredia, Lima, Peru. 6. Cardiff School of Sport and Health Sciences, Cardiff Metropolitan University, Cardiff, United Kingdom.
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