Researchers at Stanford University Medical Center believe that Viagra
improves cardiovascular and exercise performance measures of trained
cyclists at high altitude. Some of the participants had an improved
performance of up to 45%, while others found no benefit and there was no
benefit for anyone at sea level.
Ten cyclists who took sildenafil (Viagra) collectively improved their
stroke volume (the volume of blood moved out of one ventricle of the
heart per beat) and cardiac output (stroke volume times heart rate)
compared to the placebo trial. The researcher also found that the
Viagra group minimized the decline of arterial oxygen saturation of the
arteries when the cyclists were at simulated altitude of 12,700 feet.
Viagra works by relaxing the blood vessels in the lungs and other
organs. This improves blood flow from the heart and increases oxygen
transport to working muscles. This is especially important in high
altitude events, since it is more difficult to support strenuous
physical activity than it is at sea level.
Sildenafil
inhibits phosphodiestrase-5, an enzyme which degrades cyclic
guanosine monophosphate (cGMP) a cell messenger that causes the
blood vessels to relax. This allows greater vasodilation and
greater blood flow. Although the drug works in different target
sites, this study focused on the lungs.
All of the participants were “trained cyclists”, and performed a total
of 10 cycling trails. Neither the riders of the researchers knew
whether the trial included a placebo or the two sildenafil doses, 50 mg
or 100 mg, according to the report.
The altitude was simulated by changing the mix of air. The cyclists
began breathing the high altitude mix starting one hour before the
exercise session and continuing through the session. The simulation did
not include the lower air pressure that would occur at altitude, Anne L.
Friedlander said. Friedlander works for the Veterans Affairs Palo Alto
Health Care System and Stanford University.
Four of the 10
participants responded to sildenafil while the remaining six did
not, Friedlander said. These 4 responders showed the greatest drops
in stroke volume, cardiac output, and cycling performance between
the sea level and high altitude trials without the drug.
"One of the messages of the paper is that not everybody benefits,"
Friedlander said. Sildenafil could be considered as a treatment for
those who suffer most at altitude but, because of side effects that can
include severe headaches and the apparent inability to help some people,
it should not be taken as an exercise aid by everyone, she said. The
research appears in the June issue of the Journal of Applied Physiology.
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