ACUTE HYPOXIA STUDY (EARLIER STUDY)
The effects of sildenafil 100 mg and placebo on the pulmonary vascular response to an acute hypoxic challenge were compared in 10 male volunteers aged 18 to 27 years in a randomized, double blind study. The volunteers attended the catheterization laboratory at the National Center of Cardiology in Bishkek (760 meters above sea level), Kyrgyz Republic, on 2 occasions, 1 week apart. All gave written, informed consent and were judged to be healthy on the basis of medical examination and routine hematology and biochemistry. The study was approved by the local hospital ethics committee in Bishkek and followed international guidelines for medical research on human subjects. On each occasion, a Swan-Ganz thermodilution catheter (Baxter Healthcare Ltd) was sited in the pulmonary artery via a jugular vein. Baseline measurements were made after 30 minutes rest, and then sildenafil or placebo (lactose) was given orally in a gelatin capsule with 100 mL of water. One hour later, the volunteers breathed via a mouthpiece connected to a Douglas bag containing 11% O2. Measurements of PAP, systemic blood pressure, and heart rate were repeated after 30 minutes of hypoxia. Blood samples were taken in 1% 0.5 mmol/L EDTA on ice just before and at the end of 30 minutes of hypoxia and stored for cGMP analysis. Arterial oxygen saturation was measured by pulse oximeter (PROPAQ 102, Protocol Systems Inc).
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