LETTER TO THE EDITOR
Reply
B.K.S. Sastry, MD, DM* and
Calambur Narasimhan, DM
* Department of Cardiology, CARE Hospital, Exhibition Road, Nampally, Hyderabad, India 500 001 (Email: bkssastry{at}hotmail.com).
We appreciate the interest of Drs. Oudiz and Wasserman in our study (1). Our primary objective was to compare sildenafil with placebo in improving the exercise capacity in patients with primary pulmonary hypertension. From this study, we did not mean to conclude that sildenafil is superior to other pulmonary vasodilators like bosentan; beraprost, iloprost, and others.
Improvement in exercise capacity can be measured by different means including 6-min walk distance, submaximal exercise time, and maximum oxygen uptake during exercise (VO2 max). These tests measure different physiological parameters. In a group of patients treated by the same intervention, different tests may demonstrate different degrees of improvement depending upon the method chosen. Even different exercise protocols may give different results. As was pointed out, nearly 40% improvement in exercise time using the Naughton protocol need not result in similar degree of improvement in 6-min walk distance. Interestingly, however, apart from our initial study, other investigators also have reported a similar degree of improvement (ranging from 30% to 50%) in 6-min walk distance with sildenafil in pulmonary hypertension patients (2–5). It is possible that the exercise on treadmill test using the Naughton protocol may give similar results to the 6-min walk test, unlike the kind of exercise protocol used by Oga et al. (6) in their studies.
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References
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1. Sastry BK, Narashimhan C, Reddy NK, Raju BS. Clinical efficacy of sildenafil in primary pulmonary hypertension: a randomized, placebo-controlled, double-blind, crossover study J Am Coll Cardiol 2004;43:1149-1153.[Abstract/Free Full Text]
2. Kothari SS, Duggal B. Chronic oral sildenafil therapy in severe pulmonary artery hypertension Indian Heart J 2002;54:404-409.[Medline]
3. Bharani A, Mathew V, Sahu A, Lunia B. The efficacy and tolerability of sildenafil in patients with moderate-to-severe pulmonary hypertension Indian Heart J 2003;55:55-59.[Medline]
4. Michelakis ED, Tymchak W, Noga M, et al. Long-term treatment with oral sildenafil is safe and improves functional capacity and hemodynamics in patients with pulmonary arterial hypertension Circulation 2003;108:2066-2069.[Abstract/Free Full Text]
5. Mikhail GW, Prasad SK, Li W, et al. Clinical and haemodynamic effects of sildenafil in pulmonary hypertension: acute and mid-term effects Eur Heart J 2004;25:431-436.[Abstract/Free Full Text]
6. Oga T, Nishimura K, Tsukino M, Hajiro T, Ikeda A, Izumi T. The effects of oxitropium bromide on exercise performance in patients with stable chronic obstructive pulmonary diseaseA comparison of three different exercise tests. Am J Respir Crit Care Med 2000;161:1897-1901.[Abstract/Free Full Text]
Related Article
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Clinical efficacy of sildenafil in primary pulmonary hypertension
- Ronald J. Oudiz and Karlman Wasserman
J. Am. Coll. Cardiol. 2004 44: 2256.
[Full Text]
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