E-28 Free Communication/Poster - Environmental Heat Stress: JUNE 3, 2011 7:30 AM - 12:30 PM: ROOM: Hall B
Orthostatic hypotension (OH) occurs among soldiers, athletes and laborers, and may lead to unwanted syncope or basic training casualties. Elevated temperatures may increase an individual's susceptibility to OH, whereas the effect of sleep loss (SL) remains inconclusive.
PURPOSE: (1) To evaluate the effects of exercise heat acclimation (HA) and SL on OH, and (2) to determine the best measurements to assess OH in clinical and field settings.
METHODS: Eleven males (mean ± SD; age, 20 ± 1 y; mass, 81.7 ± 12.2 kg) were studied using a repeated measures research design. Before and after 90 min of HA, and after 28 h of SL, subjects performed a lie-to-stand OH test in which blood pressure (BP), heart rate (HR) and six OH signs and symptoms via visual analog scales were obtained.
RESULTS: The incidence and intensity of OH, assessed via changes in post-exercise systolic BP, significantly decreased during HA (P = 0.004) from Day 5 (23 ± 18 mmHg) to Day 8 (7 ± 18 mmHg), while SL on Day 10 (9 ± 12 mmHg) and Day 11 (7 ± 17 mmHg) showed no effect (p > 0.05) on OH. As OH responses decreased (Day 8 vs. Day 2) acute HR increases diminished (103 ± 14 beats·min-1, 113 ± 15 beats·min-1; P = 0.042). Three post-exercise OH signs and symptoms (lightheadedness, dizziness, nausea) significantly decreased from Day 2 to Day 8 (P = 0.049, 0.045, 0.027, respectively), while no changes were observed after SL (p > 0.05).
CONCLUSIONS: During 10 days of HA, BP control improved and cardiovascular strain was reduced, along with OH signs and symptoms; mild SL had no effect on OH. Acute HR changes may be explained by the decrease in cardiac output and increase in stroke volume paradigm. In a clinical setting, systolic BP Δ may indicate the threshold at which OH signs and symptoms may arise. Additionally, in the absence of a sphygmomanometer, HR taken immediately upon standing and determining ratings of lightheadedness, dizziness and nausea may be used as alternative field expedient techniques.