Respiratory function in precapillary pulmonary hypertension

Since dyspnoea on exertion is very often the first symptom of precapillary pulmonary hypertension (PPH), either from chronic thromboembolic pulmonary hypertension (CTEPH) or from idiopathic pulmonary hypertension (IPH), these patients are often first examined in a pulmonary function laboratory. We carried out a retrospective study (1987-1992) on pulmonary function in 34 patients diagnosed to have PPH by means of specific diagnostic tools, out of 5,467 patients first attending our laboratory. Nine suffered from IPH, 10 from CTEPH and 15 from Eisenmenger physiology. This last group differed from the others, since its diagnosis had been known for a long time and the stage of the disease was more advanced, when pulmonary function tests were performed in our laboratory (with a view to transplantation). Respiratory function, blood gases and arterial oxyhaemoglobin saturation (HbSaO2) during exercise (Bruce protocol), diffusing capacity of the lungs for carbon monoxide (DLCO), shunt fraction (QS%) (approximation obtained from arterial oxygen tension (PaO2) after 100% oxygen breathing) had been evaluated. In the first two groups, in contrast to other reports, we could observe no obstructive defect. Only 20% of the subjects had restrictive defects, however mild. The typical functional picture of these patients revealed normal lung volumes, normal or slightly reduced DLCO, mild hypoxaemia with hypocapnia, severe HbSaO2 drops during exercise, and pathological QS%. We conclude that every time a patient presents with breathlessness at rest or on exercise, a normal chest X-ray and respiratory function tests, pulmonary hypertension must be suspected and subject to specific and invasive tests. More severe functional impairment was observed in the PPH from the Eisenmenger disorder. This might be due to a more advanced stage of this type of hypertension at the time of our observation and/or to the different mechanisms of the diseases themselves.