Global REACH: Andean Highlanders, Chronic Mountain Sickness and the Integrative Regulation of Resting Blood Pressure
Simpson, Lydia Louise
Meah, Victoria L.
Steele, Andrew R.
Howe, Connor A.
Busch, Stephen A.
Oliver, Samuel James
Lawley, Justin Stevan
Tymko, Michael M.
Figueroa-Mujíca, Romulo J.
Ainslie, Philip N.
Steinback, Craig D.
Moore, Jonathan P.
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High‐altitude maladaptation syndrome chronic mountain sickness (CMS) is characterised by excessive erythrocytosis and frequently accompanied by accentuated arterial hypoxaemia. Whether altered autonomic cardiovascular regulation is apparent in CMS is unclear. Therefore, we assessed integrative control of blood pressure (BP) and determined basal sympathetic vasomotor outflow and arterial baroreflex function in 8 Andean natives with CMS ([Hb] 22.6 ± 0.9 g/dL) and 7 healthy highlanders ([Hb] 19.3 ± 0.8 g/dL) at their resident altitude (Cerro de Pasco, Peru; 4383 m). R‐R interval (RRI, electrocardiogram), beat‐by‐beat BP (photoplethysmography) and muscle sympathetic nerve activity (MSNA; microneurography) were recorded at rest and during pharmacologically‐induced changes in BP (modified Oxford test). Although [Hb] and blood viscosity (7.8 ± 0.7 vs 6.6 ± 0.7cP; d = 1.7, P = 0.01) were elevated in CMS compared to healthy highlanders, cardiac output, total peripheral resistance and mean BP were similar between groups. The vascular sympathetic baroreflex MSNA set‐point (i.e. MSNA burst incidence) and reflex gain (i.e. responsiveness) were also similar between groups (MSNA set‐point; d = 0.75, P = 0.16, gain; d = 0.2, P = 0.69). In contrast, in CMS the cardiovagal baroreflex operated around a longer RRI (960 ± 159 vs 817 ± 50msec; d = 1.4, P = 0.04) with a greater reflex gain (17.2 ± 6.8 vs 8.8 ± 2.6msec·mmHg−1; d = 1.8, P = 0.01) versus healthy highlanders. Basal sympathetic vasomotor activity was also lower compared to healthy highlanders (33 ± 11 vs 45 ± 13bursts·min−1; d = 1.0, P = 0.08). In conclusion, our findings indicate adaptive differences in basal sympathetic vasomotor activity and heart rate compensate for the haemodynamic consequences of excessive erythrocyte volume and contribute to integrative blood pressure regulation in Andean highlanders with mild CMS.
Simpson, L.L., Meah, V.L., Steele, A.R., Gasho, C., Howe, C.A., Dawkins, T.G., Busch, S.A., Oliver, S.J., Moralez, G., Lawley, J.S., Tymko, M.M. et al (2020) 'Global REACH: Andean highlanders, chronic mountain sickness and the integrative regulation of resting blood pressure', Experimental Physiology. https://doi.org/10.1113/EP088473
Article published in Experimental Physiology available open access at https://doi.org/10.1113/EP088473
Cardiff Metropolitan University (Grant ID: Cardiff Metropolian (Internal))
Santander Mobility Fund; Gilchrist Educational Trust; The Physiological Society research grant scheme; Heart and Stroke Foundation of Canada ‐ Joint Alberta and New Investigator Award; Canadian Network for Research and Innovation in Machining Technology, Natural Sciences and Engineering Research Council of Canada. Grant Number: RGPIN 06637; Canada Research Chairs. Grant Number: 950‐230970
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