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Viagra Improves High Altitude Exercise Performance Up To 45% For Some

  1. robin_himself
    Sildenafil (Viagra) significantly improved the cardiovascular and exercise performance measures of trained cyclists at high altitude, mostly because the drug helped some participants improve a lot -- up to 45% -- while others showed little change. Sildenafil provided no benefit at sea level.

    Ten cyclists who took sildenafil at altitude collectively lowered the time it took to cover six kilometers by 15% compared to placebo trials at altitude. The cyclists also significantly improved 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. Sildenafil also minimized the decline of arterial oxygen saturation of the arteries when the cyclists were at simulated altitude of 12,700 feet.

    But the researchers discovered that these improvements occurred largely because some people achieve major gains with sildenafil at altitude while others improve much less or not at all. The responders improved 39% in the time trial performance at altitude compared to their performance at altitude with a placebo. Some in the responder group improved as much as 45%, according to a study in the Journal of Applied Physiology published by The American Physiological Society. Non-responders improved an insignificant 1%.

    The study, "Sildenafil improves cardiac output and exercise performance during acute hypoxia but not normoxia," by Andrew R. Hsu, Kimberly E. Barnholt, and Nicolas K. Grundmann, Veterans Affairs Palo Alto Health Care System; Joseph H. Lin and Stewart W. McCallum, Stanford University Medical Center; and Anne L. Friedlander, Veterans Affairs Palo Alto Health Care System and Stanford University appears in the June issue of the Journal of Applied Physiology.

    Drug expands the blood vessels
    Sildenafil citrate is best known as Viagra, a drug used to treat erectile dysfunction. The drug was originally developed to relieve high blood pressure. It causes blood vessels in certain tissues, such as the lungs, to relax. This improves blood flow from the heart and increases oxygen transport to working muscles. Because the high altitude atmosphere contains less oxygen, it is more difficult to get enough oxygen to support strenuous physical activity than it is at sea level.

    Sildenafil works by inhibiting phosphodiestrase-5, an enzyme which degrades cyclic guanosine monophosphate (cGMP) a cell messenger that causes the blood vessels to relax, Friedlander explained. By inhibiting the enzyme, the drug allows greater vasodilation and greater blood flow. Although the drug works in different target sites, this study focused on the lungs.

    The researchers hypothesized that the drug would allow the study's participants to improve their performance at altitude because it would reduce the constriction of vessels in the lungs that sometimes occurs at altitude. In turn, that would allow greater blood flow through the heart, better transfer of oxygen from the lungs to the blood and improved oxygen delivery to working muscles.

    The participants, all trained cyclists, performed a total of 10 cycling trials, with and without sildenafil at sea level and at simulated altitude of 3,874 meters. Neither the participants nor the researchers knew whether the trial included a placebo or one of the two sildenafil doses, 50 mg or 100 mg.

    The high altitude simulation was achieved 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, Friedlander said.

    Researchers analyzed the changes in each individual's performance under various exercise conditions and also compared the group's performance under different drug conditions.

    Responders versus non-responders
    Four of the 10 participants responded to sildenafil while the remaining six did not, Friedlander said. The responders showed the greatest drops in stroke volume, cardiac output, and cycling performance between the sea level and high altitude trials without the drug.

    "Without sildenafil, their performance went down more than others," Friedlander said. "With it, it brought them back up to the levels of the non-responders." The results suggest that the responders experienced a greater degree of constriction of the vessels in the lungs at altitude and therefore benefited more from the vessel relaxation effects of sildenafil.

    "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 bigger picture

    This study adds to the scientific knowledge of what physiological factors limit performance at altitude, including the role that cardiac output plays, Friedlander said. For instance, physiologists don't know why some people have trouble at altitude and may develop illnesses such as acute mountain sickness or high altitude pulmonary edema while others adapt quickly. Studies like this may help identify some of the underlying differences between people and lead to better treatments.

    In future studies, Friedlander wants to identify:

    * what steps individuals could take to acclimatize before they go to altitude
    * who is likely to acclimatize quickly at altitude and who may need additional help
    * how to minimize performance declines at altitude

    Friedlander and her team are working on issues that could apply to those who have to rapidly acclimatize to high altitude. For instance, when soldiers deploy to Afghanistan, they must quickly undertake physically taxing work at 12,000-14,000 feet, conditions that can severely affect performance under potentially life-threatening conditions.

    In a study Friedlander and colleagues conducted at 14,000 feet on Pike's Peak, Colorado, participants showed marked hormonal changes at altitude. These changes facilitate oxygen delivery. However, this benefit is suppressed when individuals don't eat enough and the body shifts focus to store more energy, Friedlander explained. That study appears in the June issue of the American Journal of Physiology-Endocrinology and Metabolism, also published by APS.

    Next steps

    One next step is to do a study with women, to see if they react the same way to sildenafil and altitude. The researchers also want to take a closer look at sildenafil responders to see if they can identify ahead of time who will benefit from treatment. In addition, a question still outstanding is whether non-responders would benefit from sildenafil at a higher elevation.

    www.the-aps.org

Comments

  1. robin_himself
    Studies To Date Say Erectile Dysfunction Drugs Affect Other Systems, For The Better

    Another one on viagra! This one is interesting.

    Studies To Date Say Erectile Dysfunction Drugs Affect Other Systems, Mostly For The Better

    Since the Food and Drug Administration gave Viagra (sildenafil) its approval in 1998, "erectile dysfunction" has become a household term - probably to the chagrin of many parents fielding questions from their kids watching TV. But with sildenafil and the subsequent introduction and marketing of Levitra- (vardenafil) and Cialis- (tadalafil), many men have found answers to a once-unmentionable condition.

    "As more and more patients seek therapy for sexual dysfunction, it is increasingly important for clinicians in a wide range of specialties to become proficient in the mechanisms and systemic effects of these medications," said Ernst R. Schwarz, M.D., Ph.D., a cardiologist at Cedars-Sinai Medical Center who specializes in therapies for men who suffer from erectile dysfunction (ED) and have heart problems, diabetes, high blood pressure or other related conditions.

    Schwarz and colleagues recently concluded a review of the medical literature, as well as their own research findings and clinical data, to determine what actually is known about the effects of long-term use of this class of drugs on various organ systems. Their findings appears in the June, 2006 issue of the International Journal of Impotence Research.

    Studies so far suggest the drugs, called phosphodiesterase-5 inhibitors (PDE-5i), produce mostly beneficial results, and not just for erectile dysfunction. The FDA recently approved a reformulation of sildenafil for the treatment of primary pulmonary hypertension, a disease that tends to occur in young women, causing elevated blood pressures in the lung that can lead to heart failure and early death.

    "When we look at all the different organ systems - the blood, the heart, the lungs, blood flow in the brain - there are hardly any negative side effects. In fact, just the opposite is true. There are beneficial effects for primary pulmonary hypertension, as well as for conditions such as heart failure and lack of oxygen in the heart," said Schwarz. "The only issue is that the data we have are from relatively short-term studies. Viagra has been on the market since 1998 and the other two PDE-5 inhibitors were approved by the FDA in 2003. Therefore, we do not have multi-year follow-up studies. On the other hand, the drugs have been on the market for several years now and there have been no reports of negative long-term effects."

    While there are some differences among the three medications, they have many properties in common and work by limiting the activity of the enzyme phosphodiesterase-5, which is found in tissues and vessels of the penis, blood platelets, and smooth muscle of blood vessels. For the treatment of erectile dysfunction, the drugs' constraint of the enzyme's action results in increased levels of cyclic guanosine monophosphate (cGMP) and nitric oxide (NO), biochemicals that promote smooth muscle relaxation and increased blood flow in erectile tissue.

    According to the article, PDE-5 inhibitors can be effective in treating erectile dysfunction even for many men who also have diabetes, those who are older, and those who have co-existing ischemic heart disease (reduced blood flow to the heart caused by plaque buildup in the arteries). Furthermore, say the authors, "since PDE-5 is found in smooth muscles of the systemic arteries and veins throughout the body, use of PDE-5i has been associated with various cardiovascular effects."

    "The original intention was to develop PDE-5 inhibitors as a treatment for angina, chest pain that occurs when the heart is starved for oxygen," Schwarz said. "As such, their effects on the heart appear to be all beneficial. Nitrates and other substances commonly used to improve blood flow and oxygenation to the heart muscle have a side effect that we call the 'steal phenomenon,' in which blood is taken away from underperfused (flow-restricted) areas to improve blood flow in normal areas. In contrast, PDE-5 inhibitors actually improve blood flow even in areas where there is a blockage of an artery, thereby having a protective effect on the heart muscle."

    The drugs' potential impact on visual function became a matter of controversy when a suspected link between PDE-5 inhibitors and vision loss led to lawsuits filed last year against the maker of Viagra. According to the article's authors, however, "analysis of clinical trial data in more than 13,000 men and on more than 35,000 patient-years of observation" found occurrence of the visual disorder to be similar to that of the general population. "Even though individual cases have been reported for all PDE-5i, these recently published data do not suggest an increased incidence of NAION (non-arteric anterior ischemic optic neuropathy) in men who took PDE-5i for ED," the article states.

    Among other findings:

    * Although the enzyme PDE-5 has been found in tissue and arteries of the brain, sildenafil does not appear to dilate cerebral arteries or have an effect on cerebral blood flow or blood flow velocity, an indication that there is no increased risk of stroke or hemorrhage.
    * PDE-5 exists in blood platelets, cells that play a major role in the blood clotting process, but sildenafil appears to have no direct impact on platelet function. However, the drug's effects have not been specifically evaluated in patients with bleeding disorders or in those taking drugs that reduce clotting.

    "Experimental and human studies indicate that PDE-5 inhibitors are effective and well tolerated, and there is evidence that they are not being used to their utmost potential. We suggest that these drugs may prove beneficial in treating a wide variety of disorders," said Schwarz, the article's first author and a specialist in cardiology, interventional cardiology, heart failure, and transplantation. "Some studies are underway to determine the effects of long-term use of PDE-5 inhibitors, and others are warranted, especially in patients who are considered at high risk because of chronic cardiovascular disorders."

    www.cedars-sinai.edu
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