• José Antônio Baddini Martinez, Fábio Senra Rocha, Elizabet Sobrani, Fabíola Paula Lovreto Galhardo, and João Terra Filho.
• Departamento de Medicina Interna, Faculdade de Medicina de Ribeirão Preto, São Paulo, Brazil. jabmarti@fmrp.usp.br
• Sao Paulo Med J. 2002 Sep 2; 120 (5): 141145141-5.

ContextDyspnea remains a therapeutic challenge, especially in chronic respiratory conditions. Recent studies have shown that the induction of unpleasant dyspnea sensations activates areas in the insular cortex.ObjectiveThis study was designed to investigate the potential effects of ondansetron, a potent anti-serotonin agent, on induced dyspnea sensation.Type Of StudyA randomized double blind study.SettingPulmonary Function Laboratory of Hospital das Clínicas de Ribeirão Preto.ParticipantsTen healthy male volunteers (mean age +/- standard error = 23.1 +/- 0.41 years) without respiratory diseases and showing normal spirometric tests.InterventionsUncomfortable breathing was induced in the volunteers on two different days, via the use of inspiratory resistors (loads of 0, 7, 14 and 21 cm H2O/l/sec) and breathholding, two hours after taking 8 mg of ondansetron (Ond) or placebo (Plac).Main MeasurementsRespiratory discomfort during breathing under loading was evaluated on a 100-mm visual analog scale. The maximum length of time of voluntary apnea was measured in seconds.ResultsThe mean maximum voluntary apnea time did not differ between the ondansetron and placebo days (Plac = 96 +/- 6.6 sec vs. Ond = 100 +/- 7.9 sec). Ondansetron did not influence the dyspnea sensation induced by different inspiratory loads (0 cm H2O/l/sec: Ond = 1.4 mm +/- 0.44 vs. Plac = 2.1 +/- 0.85 mm; 7 cm H2O/l/sec: Ond = 16.6 +/- 2.74 mm vs. Plac = 13.7 +/- 2.06 mm; 14 cm H2O/l/sec; Ond = 30.5 +/- 4.50 mm vs. Plac = 27.1 +/- 3.44 mm; 21 cm H2O/l/sec: Ond = 50.3 +/- 6.72 mm vs. Plac = 49.4 +/- 6.72 mm). Ondansetron led to significant decreases in tidal volume under basal conditions and when breathing under the highest inspiratory loading (0 cm H2O/l/sec: Ond = 0.83 +/- 0.26 l vs. Plac = 1.0 +/- 0.28 l; 21 cm H2O/l/sec: Ond = 0.86 +/- 0.23 l vs. Plac = 1.1 +/- 0.22 l)ConclusionThe present results suggest that 5-HT3 receptors do not play an important role in the mediation of dyspnea sensations.

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