RESULTS	All sildenafil doses reduced the mean pulmonary-artery pressure ( P = 0.04 , P = 0.01 , and P < 0.001 , respectively ) , improved the WHO functional class ( P = 0.003 , P < 0.001 , and P < 0.001 , respectively ) , and were associated with side effects such as flushing , dyspepsia , and diarrhea .\