OBJECTIVE The present investigation compared and contrasted steady and pulsatile pulmonary hemodynamics at rest and during exercise in patients with primary pulmonary hypertension and normal control subjects. BACKGROUND A complete description of the relation between pressure and flow in the pulmonary circulation includes both steady and pulsatile hemodynamic behavior. Patients with primary pulmonary hypertension provide a unique opportunity to study the effects of primary alterations in pulmonary vasculature on pulmonary artery vascular hydraulic load. METHODS Catheter tip pressure and velocity recordings from the main pulmonary artery in 8 patients with primary pulmonary hypertension and 10 control subjects were used to derive the pulmonary artery input impedance spectrum and the extent of pulse wave reflection at rest and during exercise. RESULTS As expected, in patients with primary pulmonary hypertension, mean pulmonary artery pressure (50 +/- 10 mm Hg) and pulmonary vascular resistance (880 +/- 446 dynes.s.cm-5) were markedly elevated at rest and remained so during exercise (mean pressure 71 +/- 15 mm Hg, mean resistance 750 +/- 530 dynes.s.cm-5). Pulmonary artery characteristic impedance was elevated at rest and did not change with exercise (rest 55 +/- 25 dynes.s.cm-5; exercise 66 +/- 33 dynes.s.cm-5). Measures of arterial wave reflection indicated that the extent of wave reflection in the pulmonary bed in those with primary pulmonary hypertension is large at rest (reflection coefficient 0.89 +/- 0.09) and that the composite reflected wave arrived during the midportion of right ventricular ejection. Although the extent of wave reflection decreased with exercise (reflection coefficient 0.81 +/- 0.10, p < 0.05), the magnitude and timing of these reflections remained adverse. Furthermore, in patients with primary pulmonary hypertension, the stroke volume response to exercise was strongly related to rest levels of pulmonary artery diastolic pressure, pulmonary vascular resistance and the reflection factor, whereas no such relation was found in the control subjects. CONCLUSIONS In addition to the expected abnormalities in steady measures of pulmonary artery hemodynamics at rest in patients with primary pulmonary hypertension, rest and exercise measures of oscillatory behavior (characteristic impedance and pulse wave reflection) are perturbed. Measures of steady and pulsatile behavior, particularly wave reflection, appear to have an important role in the exercise response of these patients.