ACUTE EFFECT OF PERCUTANEOUS TRANSVENOUS MITRAL COMMISSUROTOMY ON VENTILATORY AND HEMODYNAMIC-RESPONSES TO EXERCISE - PATHOPHYSIOLOGICAL BASIS FOR EARLY SYMPTOMATIC IMPROVEMENT

Background. Improvement of exertional dyspnea occurs immediately after percutaneous transvenous mitral commissurotomy (PTMC), but the pathop hysiological basis for this early symptomatic improvement has not been elucidated. Methods and Results. Exercise hemodynamic measurement and exercise ventilatory measurement with arterial blood gas analysis wer e performed in 21 patients aged 50.4+/-9.5 years (mean+/-SD) with symp tomatic mitral stenosis before and a few days after PTMC. Exercise ven tilatory measurement were also performed in 14 normal control subjects aged 48.9+/-4.9 years. After PTMC, mitral valve area increased (from 1.0+/-0.3 to 1.7+/-03 cm2, p<.001), mean mitral gradient (from 12.2+/- 5.2 to 5.2+/-2.2 mm Hg, P<.001), and mean left atrial pressure (from 1 8.7+/-6.1 to 12.1+/-4.0 mm Hg, P<.001) decreased. All patients experie nced significant symptomatic improvement soon after PTMC. Comparison o f hemodynamic parameters at the same ergometer work rate showed a sign ificant decrease in pulmonary artery systolic pressure (from 77+/-18 t o 67+/-14 mm Hg, P<.001) and diastolic pressure (from 36+/-10 to 28+/- 7 mm Hg, P<.001) and a significant increase in cardiac output (from 6. 4+/-1.4 to 8.1+/-1.9 L/min, P<.001). Despite the improvement in exerci se hemodynamics and symptoms, exercise capacity determined by peak oxy gen uptake (from 18.0+/-2.9 to 18.6+/-3.1 mL . kg-1 . min-1) and anaer obic threshold (from 11.7+/-2.4 to 12.0+/-2.4 mL . kg-1 . min-1) remai ned unchanged. Excessive exercise ventilation, as assessed by the slop e of the regression line between expired minute ventilation and carbon dioxide output, decreased significantly from 37.2+/-6.7 to 33.9+/-5.8 (P<.001), but remained significantly higher than that in the normal s ubjects (27.9+/-3.6, P<.01). The ratio of total dead space to tidal vo lume and total dead space per breath during exercise decreased signifi cantly after PTMC (P<.05). The change in excessive exercise ventilatio n after PTMC was correlated with the change in dead space to tidal vol ume ratio (r=.59). Conclusions. Significant relief of exertional dyspn ea immediately after PTMC is not accompanied by an improvement in exer cise capacity. A decrease in excessive exercise ventilation due to a d ecrease in physiological dead space resulting from hemodynamic improve ment partly contributes to the early relief of symptoms after PTMC. Ho wever, lung compliance, which was not measured in the present study, m ay have changed after PTMC. This change may also contribute to the sym ptomatic improvement.