VENTILATORY INEFFICIENCY FOR CARBON-DIOXIDE DURING EXERCISE IN PATIENTS WITH PULMONARY-HYPERTENSION

The purpose of this study was to analyse the ventilatory efficiency fo r carbon dioxide (CO2) in the assessment of exercise tolerance in pati ents with pulmonary hypertension. Two groups of patients were studied. One group consisted of 37 patients with normal pulmonary artery press ure who underwent surgical closure of a left-to-right shunt. Another g roup was composed of 10 patients with pulmonary hypertension. Both pat ient groups were compared with the mean value of an age-matched pool o f normal control subjects. Aerobic exercise performance was assessed b y determination of the ventilatory threshold. The ventilatory efficien cy for CO2 was assessed by calculating the slope of ventilation over c arbon dioxide below the ventilatory threshold. The slope of ventilatio n vs. carbon dioxide output in patients with pulmonary hypertension (4 8 +/- 12) was steeper than the slope (31.3 +/- 7.0) in patients with n ormal pulmonary artery pressure (P<0.05). Significant correlations (P< 0.05) were found between the pulmonary artery pressure and the slope o f pulmonary ventilation over carbon dioxide (r = 0.92) and also with t he physiological dead space-tidal volume ratio at maximal exercise (r = 0.55). This was associated with a severe reduction in exercise perfo rmance in patients with pulmonary hypertension, whereas in patients wi th normal pulmonary artery pressure it was only slightly below the low er limit of normal. These results demonstrate that patients with pulmo nary hypertension have an inefficient ventilatory response to metaboli cally produced CO2 during exercise, which severely limits exercise tol erance.