Effects of oxygen administration, bicarbonate infusions, and brief hyperventilation on patients with pulmonary vascular obstructive disease.

In an attempt to clarify further the mechanisms underlying labile rise in pulmonary vascular resistance, the effects of administering high oxygen concentrations, briefvoluntary hyperventilation, and correction of acidosis were studied in 16 patients in whom congenital heart disease was associated with pulmonary vascular disease. On breathing 100 per cent oxygen thele was a significant fall in pulmonary vascular resistance from 21 8 4.6 to 12.9 3-6 units/M2 (P < 0.001), with a rise in pulmonary blood flow from 4-4 0-6 to 8-8 2-0 1/min per m2 (P < 0 025) and a fall in pulmonary artery pressure from #67.8 2.8 to 61 8 4 0 mmHg (P < 0 025). The changes occurring on sodium bicarbonate adninistra- ;tion in 6 patients did not reach levels of significance, but the size of each individual response was closely correlated with the response to oxygen administration. No significant changes occurred either on voluntary hyperventilation or, in the systemic circulation, with any intervention. However, systemic vascular resistance was positively correlated with pulmonary vascular resistance (P < 0.01). As a result of this, though age was correlated positively with both pulmonary artery mean pressure (P < 0 025) and vascular resistance (P < 0.025), it was not correlated with the ratio of pulmonary to systemic resistance. Since pulmonary vascular disease is progressive, these results cast some doubt on the validity ofresistance ratio as a measure of its severity.