Hypovolemia explains the reduced stroke volume at altitude. Issue 5 (2nd October 2013)

• Record Type: Journal Article
• Authors: Siebenmann, Christoph; Hug, Mike; Keiser, Stefanie; Müller, Andrea; van Lieshout, Johannes; Rasmussen, Peter; Lundby, Carsten
• Is Part Of: Physiological reports. Volume 1:Issue 5(2013:Oct.)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2013-10-02
• Subjects: Acclimatization -- blood -- Frank–Starling -- heart -- hypoxia; Physiology -- Periodicals; 571
• DOI: 10.1002/phy2.94
• Languages: English
• ISSNs: 2051-817X

Abstract

Abstract: During acute altitude exposure tachycardia increases cardiac output (Q) thus preserving systemic O2 delivery. Within days of acclimatization, however, Q normalizes following an unexplained reduction in stroke volume (SV). To investigate whether the altitude‐mediated reduction in plasma volume (PV) and hence central blood volume (CBV) is the underlying mechanism we increased/decreased CBV by means of passive whole body head‐down (HDT) and head‐up (HUT) tilting in seven lowlanders at sea level (SL) and after 25/26 days of residence at 3454 m. Prior to the experiment on day 26, PV was normalized by infusions of a PV expander. Cardiovascular responses to whole body tilting were monitored by pulse contour analysis. After 25/26 days at 3454 m PV and blood volume decreased by 9 ± 4% and 6 ± 2%, respectively ( P < 0.001 for both). SV was reduced compared to SL for each HUT angle ( P < 0.0005). However, the expected increase in SV from HUT to HDT persisted and ended in the same plateau as at SL, albeit this was shifted 18 ± 20° toward HDT ( P = 0.019). PV expansion restored SV to SL during HUT and to an ~8% higher level during HDT ( P = 0.003). The parallel increase in SV from HUT to HDT at altitude and SL to a similar plateau demonstrates an unchanged dependence of SV on CBV, indicating that the reduced SV during HUT was related to an attenuated CBV for a given tilt angle. Restoration of SV by PV expansion rules out a significant contribution of other mechanisms, supporting that resting SV at altitude becomes reduced due to a hypovolemia. Abstract : e00094 Abstract : We tested the hypothesis that stroke volume at altitude is reduced due to hypovolemia. In seven lowlanders exposed to 3454 m for 4 weeks we manipulated central blood volume by whole body tilting and by plasma volume expansion. Stroke volume at altitude was reduced during head‐up tilt but normalized by head‐down tilt or plasma volume expansion, indicating that hypovolemia explains the reduced stroke volume at altitude.