Flow Mediated Vasodilation In Response To 3-Weeks Of Moderate Altitude Exposure

Abstract

The effects of moderate altitude on the cardiovascular system is an extensively researched subject, but no definitive timeline regarding the vascular acclimatization for flow mediated vasodilation (FMD) measurements is currently available in the scientific literature. It has been suggested that 3 wks might be sufficient (Frick et al., 2006). However, if this amount of time is not sufficient it will complicate data interpretation. PURPOSE: To assess the timeline of acclimatization to moderate altitude (2,130 m), specific to FMD in healthy young males. METHODS: After spending ≥ 4 weeks at lower altitude (331-1,197 m), 5 male subjects (18.6±1 yr; 71.8±8.7 kg; 1.8±0.04 m; 22.8±1.9 kg/m2) were tested within 1 wk±1 day of arrival to moderate altitude (V1) and were tested again at 2 wks (V2) and 3 wks (V3) after their initial arrival. Heart rate (HR), blood pressure (BP; systolic, SBP; diastolic, DBP), and brachial artery diameter were measured (using Brachial Analyzer) during baseline (BL) and after 5 min of forearm cuff occlusion (250 mmHg). FMD was assessed as the percent increase in diameter after the cuff occlusion. RESULTS: When comparing V1, V2, and V3, HR was no different between the visits (63±10 vs. 57±11 vs. 64±20 bpm; p=0.52 for V1 vs. V2 vs. V3, respectively). SBP was significantly higher in V1 compared to V2 and V3 (116±6 vs. 106±11 vs. 106 ±12 mmHg; both p<0.05). DBP was no different (63±9 vs. 57±9 vs. 59±6 mmHg; p=0.43). BL diameter was also not different between the visits (8.1±1.5 vs. 7.5±1.5 vs. 7.5±1.2 mm; p=0.69). FMD showed a trend toward a difference between the three visits (5.1±1.1 vs. 6.5±1.6 vs. 5.0±1.5%; p=0.07). CONCLUSION: After 3 wks of exposure to moderate altitude, it appears that FMD may continue to fluctuate. This suggests that additional measurements beyond 3 wks should be obtained to determine a better timeline for when vascular acclimatization has been achieved. This will allow better guidance for FMD measurements obtained in subjects at altitude. Supported by the State of Arizona Technology and Research Initiative Fund (TRIF)