Introduction: Orthostatic hypotension (OH) occurs among several populations; elevated temperatures increase an individual's susceptibility, whereas the effect of sleep loss (SL) remains inconclusive. The purpose was: 1) to evaluate the effects of 10 d of heat acclimation (HA) and 28 h of SL on OH; and 2) to determine the best measurements to assess OH in clinical and field settings.
Methods: There were 11 men (mean +/- SD; age, 20 +/- 1 yr; mass, 81.7 +/- 12.2 kg) who underwent a repeated measures research design. Before and after 90 min of HA, with the 11th day performed in conjunction with SL, subjects performed a lie-to-stand test where blood pressure (BP), heart rate (HR), and OH signs and symptoms were obtained.
Results: OH incidence and intensity, assessed via acute changes in post-exercise systolic BP (SBP), significantly decreased during HA from Day 2 (15 +/- 12 mmHg) to Day 8 (8 +/- 8 mmHg), while SL showed no effect. As OH responses decreased, concomitant HR increases diminished from Day 2 (113 +/- 15 bpm) to Day 8 (103 +/- 14 bpm). Post-exercise lightheadedness, dizziness, and nausea significantly decreased from Day 2 to Day 8, while no changes were associated with SL.
Conclusions: During HA, BP control improved and cardiovascular strain was reduced, along with OH signs and symptoms; mild SL had no measurable effect. Acute HR changes may be explained by decreased cardiac output and increased stroke volume. In clinical settings, SBP delta may indicate the threshold at which OH signs and symptoms arise. In the absence of a sphygmomanometer, HR taken upon standing, or ratings of lightheadedness and dizziness may be used as alternative field expedient techniques.