Excessive ventilatory response during exercise in patients with non-hypoxic pulmonary hypertension

The slope of the regression line between carbon dioxide output (VCO2) and minute ventilation (VE) (SLOPE) is useful for evaluating ventilation-perfusion inequality during exercise. A cardiopulmonary exercise test was carried out in 8 pulmonary hypertension (PH) patients without hypoxemia (group PH), 38 male patients with old myocardial infarction (group OMI), and 20 healthy men (group Ctrl). The average SLOPE for each group was 36.3+/-3.3, 28.7+/-0.9 and 25.6+/-0.5, respectively. There were significant differences among them. Group OMI was divided into 3 groups: OMI class 0: peak oxygen consumption (VO2) > or =21 ml x kg(-1) min(-1); OMI class I: 14 ml x kg(-1) x min(-1) < or =peak VO2<21 ml x kg(-1) min(-1); OMI class II: peak VO2< 14ml x kg(-1) x min(-1). There were no significant differences in peak VO2 between the groups PH and OMI class I, but the SLOPE in the group PH was greater than the SLOPE in OMI class I (p=0.0019). Compared with OMI class II, group PH had a greater peak VO2 (p=0.0215), although their SLOPE was equivalent to that of OMI class II. These results suggest that PH patients have severe ventilation-perfusion inequality despite good exercise capacity. When performing a cardiopulmonary exercise test on PH patients, it is necessary to observe not only VO2 or VCO2, but also VCO2/VE, in order to prevent aggravation of the ventilation-perfusion inequality, which leads to exercise-induced hypoxemia.