VASCULAR AND CARDIAC REACTIVITY IN PULMONARY-HYPERTENSION DUE TO CHRONIC OBSTRUCTIVE LUNG-DISEASE - ASSESSMENT WITH VARIOUS OXYGEN CONCENTRATIONS

The aim of the present work was to evaluate vasoreactivity in patients with pulmonary hypertension related to chronic obstructive lung disease. This was done by comparing haemodynamic data recorded while patients were breathing room air, and hypoxic and hyperoxic mixtures. We estimated the role of vasoconstriction in determining the level of pulmonary hypertension. This study included 26 patients with moderate pulmonary hypertension mean pulmonary arterial pressure (MPAP) = 27.3 +/- 1.2 mmHg) secondary t chronic obstructive lung disease (COLD), forced expiratory volume in one second (FEV1) = 0.95 +/- 0.13 l; arterial oxygen tension (Pao2) = 8.7 +/- 0.25 kPa). After insertion of a thermodilution catheter in the pulmonary artery and a cannula in the femoral artery, mixtures containing 15, 21, 30 and 100% oxygen were randomly administered for 20 min each. As fractional inspiratory oxygen (FIo2) increased, MPAP decreased relatively less than cardiac index. Cardiac output was at its highest during room air breathing and the hypoxic mixture did not lead to a further increase. Unlike normal subjects, in whom adjustment of cardiac output is achieved by heart rate alone, haemodynamic regulation in these patients also involved stroke volume. Variations in MPAP and cardiac index were strongly correlated with arterial oxygen saturation (Sao2). The greatest variations were noted in the patients with the relationship between pulmonary artery driving pressure and cardiac index was linear and its slope steeper in patients having the highest pulmonary hypertension at steady-state. In these patients the relationship remained linear at 15% FIo2, i.e. pulmonary artery driving pressure is a linear function of cardiac output. Conversely, in less severe patients, during hypoxic conditions pulmonary pressure increased but cardiac index remained constant suggesting an enhancement of hypoxic vasoconstriction.