Effect of Sildenafil on VO2max in Collegiate Runners Acclimatized to Moderate Altitude

Introduction: There are many factors that contribute to reduced performance at altitude. Some of the physiological responses to hypoxia include a decreased stroke volume, decreased blood oxygen saturation, and an increase in both systemic and pulmonary vasoconstriction. Sildenafil, a potent vasodilator, inhibits phosphodiesterase type 5 which promotes vasodilation via the augmentation of intracellular cGMP. Methods: Eight well-trained men (18.5 ± 0.53 yrs), acclimatized to 2348m, were asked to complete three graded exercise tests: A familiarization test, one after taking 50mg orally-ingested sildenafil (SIL) and one with a placebo (PLA). Subjects began the test on the treadmill at a speed of 8mph and a grade of 0%. Speed remained the same and grade was increased 1% each minute until volitional fatigue was reached. Performance was determined by measuring heart rate (HR), blood pressure (BP), time to exhaustion (TTE), blood oxygen saturation (SpO₂), rating of perceived exertion (RPE), and maximal oxygen consumption (VO₂max). HR and VO₂max were continually monitored, while RPE was measured every minute and SpO₂ data was collected every two minutes. BP was measured at rest, at maximal effort (immediately following volitional fatigue), and five minutes post completion. SPSS version 25.0 was used to run a paired-samples t-test for each independent variable and for both groups (PLA vs SIL). Results: TTE significantly increased in the SIL group compared to PLA (631.25 ± 52.07 vs. 584.63 ± 51.58, p<.001) as well as average SpO₂ (87.5 ± 2.05% vs. 92.6 ± 1.53%, p<.002). VO₂max decreased in the SIL group compared to PLA (62.38 ± 3.51 vs. 63.43 ± 3.52) though not significantly (p>0.05). Systolic BP at maximal effort decreased in the SIL group compared to PLA (156.88 ± 3.48 vs. 134.38 ± 11.48, p<.001). Conclusions: Athletes training or competing at altitude may see an increase in performance with sildenafil. This research is preliminary and further research should include a larger subject pool, a shorter timeframe for data collection, and additional performance measures such as a live race/competition.