Relationship between Oxygen Uptake and Oxygen Delivery in Patients with Pulmonary Hypertension

Dependency of oxygen consumption (VO2) on oxygen delivery (DO2) in patients with adult respiratory distress syndrome and with congestive heart failure has been reported previously. We evaluated this relationship in 11 patients with pulmonary hypertension, 8 with primary pulmonary hypertension (PPH), and 3 with pulmonary hypertension secondary to chronic obstructive lung disease (SPH) at baseline and during treatment with vasodilating calcium channel antagonists. The mean baseline DO2 and VO2 were 11.0 +/- 4.2 and 3.9 +/- 1.1 ml/min/kg, respectively. After increasing cardiac output via vasodilators, we obtained an average of 3 additional data points per patient. We found a significant relationship between changes in VO2 and changes in DO2 (delta VO2 = -0.19 +/- 0.27 x delta DO2; r = 0.88, n = 37). In 4 patients, VO2 was determined both by respired gas analysis and by calculation from thermodilution cardiac output and measured arteriovenous oxygen gradient; results by the 2 methods were virtually identical. There was no significant relationship between cardiac output and mixed venous oxygen content or mixed venous oxygen tension (r = 0.20 and 0.47, respectively). Mean baseline oxygen extraction ratio was 36.7 +/- 6.4% and did not increase significantly after vasodilator therapy. We conclude that in patients with pulmonary hypertension, changes in oxygen consumption appear to be dependent on changes in oxygen delivery. This may represent evidence of tissue hypoxemia, which is otherwise not apparent. This dependency may support the use of vasodilators in these patients.