Sildenafil improves cardiac output and exercise performance during acute hypoxia, but not normoxia

Abstract

Sildenafil causes pulmonary vasodilation, thus potentially reducing impairments of hypoxia-induced pulmonary hypertension on exercise performance at altitude. The purpose of this study was to determine the effects of sildenafil during normoxic and hypoxic exercise. We hypothesized that 1) sildenafil would have no significant effects on normoxic exercise, and 2) sildenafil would improve cardiac output, arterial oxygen saturation (SaO2), and performance during hypoxic exercise. Ten trained men performed one practice and three experimental trials at sea level (SL) and simulated high altitude (HA) of 3,874 m. Each cycling test consisted of a set-work-rate portion (55% work capacity: 1 h SL, 30 min HA) followed immediately by a time trial (10 km SL, 6 km HA). Double-blinded capsules (placebo, 50, or 100 mg) were taken 1 h before exercise in a randomly counterbalanced order. For HA, subjects also began breathing hypoxic gas (12.8% oxygen) 1 h before exercise. At SL, sildenafil had no effects on any cardiovascular or performance measures. At HA, sildenafil increased stroke volume (measured by impedance cardiography), cardiac output, and SaO2 during set-work-rate exercise. Sildenafil lowered 6-km time-trial time by 15% (P<0.05). SaO2 was also higher during the time trial (P<0.05) in response to sildenafil, despite higher work rates. Post hoc analyses revealed two subject groups, sildenafil responders and nonresponders, who improved time-trial performance by 39% (P<0.05) and 1.0%, respectively. No dose-response effects were observed. During cycling exercise in acute hypoxia, sildenafil can greatly improve cardiovascular function, SaO2, and performance for certain individuals.

Stroke work progressively increased until maximal exercise in long distance runners, but plateaued at submaximal exercise in sprinters

“…Charloux et al 25) showed that cardiac output measured by this impedance method was as accurate as that obtained with the Fick method during exercise in patients with sleep apnea syndrome and chronic obstructive pulmonary disease. Also, the stroke volume values obtained by the Physioflow were reproducible, and the coefficient of variation was 1.8% in our previous findings and 3.6% in other reports 37) . Furthermore, the superior aspect of the Physioflow is that it calculates stroke volume independently from baseline impedance values 25,37) , and that sweating and dehydration cannot affect stroke volume 37) .…”

Can sildenafil improve physical performance at altitude? Current scientific evidence

“…However, data are not categorical, both at rest and during exercise. The arterial blood pressure (systolic, diastolic and mean) 1,18,29,31,32 and systolic volume 18,31,32 were almost not affected. Lung function parameters (ventilation, tidal volume, respiratory rate and respiratory exchange ratio) were unaffected by the drug 14,15,18,30 .…”

“…Lung function parameters (ventilation, tidal volume, respiratory rate and respiratory exchange ratio) were unaffected by the drug 14,15,18,30 . Finally, the exercise values such as W peak 1,14,15,18,29,31,32 or VO 2max 14,29 are not conclusive at all to affirm that sildenafil significantly improves performance during exposure to acute hypoxia, regardless its normobaric or hypobaric nature.…”

“…14---16 VO 2max tends to diminish in direct proportion to the decrease in CaO 2 , which occurs as hypoxia increases. 17,18 Exercise exacerbates CaO 2 reduction due to the lower uptake of O 2 during gas exchanging in the lungs, 1,19 which may increase the risk of pulmonary edema, 11,20 especially in people predisposed to suffer this complications associated to rapid ascent. 21 Considering that the increase in PAP could be an important factor limiting performance during exercise in hypoxia, 22 sildenafil has been proposed as a potential ergogenic aid for physical activity in hypoxic conditions due to its possible benefits for athletic performance, and has been widely used.…”

“…Hsu et al 18 reported data on 10 trained men, cyclists and triathletes, who performed a peak work capacity test (W peak ) at SL followed by four exercise tests (1 practice, 3 experimental). The same procedure was used during hypoxic gas breathing (12.8% oxygen; equivalent to 3874 m) to simulate HA.…”