Effects Of Ischemic Conditioning And Altitude On Brachial Artery Flow Mediated Dilation

Purpose of Study: Flow mediated dilation (FMD) of the brachial artery is used to assess endothelial function. Attenuated FMD correlates with adverse cardiovascular events. Many factors affect flow-mediated vascular reactivity including plasma nitric oxide (NO) levels. Ischemic conditioning of the extremity (ICE) has cardio-protective effects and one of the mechanisms may be via NO. NO is also important in the physiologic responses to high altitude (HA) exposure but the effect of HA on FMD is unknown. The purpose of this study was to evaluate the effects of ICE and HA on FMD. Methods Used: FMD was measured in 13 healthy runners at baseline, after daily ICE or sham-ICE at sea level (SL) and 60 minutes after completing a 12.8km competitive run to the summit of White Mountain, CA at 4342m. Each subject completed the course twice (with ICE and with sham-ICE) separated by 6 weeks in a randomized cross-over design. ICE was administered using blood pressure (BP) cuffs around the thigh inflated to 200mmHg for 5 minutes, deflated for 5 minutes and repeated for 4 cycles. The cuffs were inflated to 40mmHg for sham-ICE. This was done daily for 5 days at SL before ascent. Duplex ultrasonography with a linear array transducer was used to measure brachial artery diameter before and after 5 min of brachial artery occlusion. The effects of HA and ICE on FMD were evaluated using repeated-measures ANOVA. Summary of Results: Complete data were obtained in 12 subjects. At SL, FMD was 15.5% +/- 7.0% (mean +/- SD) without ICE and 9.8% +/- 6.1% with ICE. At HA, FMD was 11.5% +/- 9.5% without ICE and 6.0% +/- 5.1% with ICE. Compared to SL without ICE, FMD was attenuated by 36.5% with ICE at SL, 60.7% with ICE at HA and 25.5% without ICE at HA. Both ICE and HA blunted the FMD response (p