THE EFFECTS OF OXYGEN AND DOPAMINE ON RENAL AND AORTIC BLOOD-FLOW IN CHRONIC OBSTRUCTIVE PULMONARY-DISEASE WITH HYPOXEMIA AND HYPERCAPNIA

Renal blood flow is reduced in patients with chronic respiratory failu re caused by chronic obstructive pulmonary disease (COPD), and changes in renal hemodynamics are likely to be important in the pathogenesis of the edematous state of cor pulmonale. We therefore examined the hyp othesis that this renal vasoconstriction is reversible by comparing th e effects of oxygen therapy and the renal vasodilator dopamine on rena l hemodynamics in both hypoxemic patients with COPD and those who were also hypercapnic. We assessed renal hemodynamics noninvasively with c olor-flow Doppler ultrasound. In order to validate the technique we re corded renal hemodynamics in a group of healthy volunteers before and during a dopamine infusion, and in a subgroup we simultaneously measur ed effective renal plasma flow (ERPF) with para-aminohippurate clearan ce. In the healthy volunteers there was a 22.5% rise in time-adjusted mean arterial velocity (Tamx) measured by Doppler compared with a 22% rise in ERPF with dopamine. This rise was significant (p < 0.05). In h ypoxemic, normocapnic subjects Tamx rose by 25% with oxygen (p < 0.005 ), 20% with dopamine (p < 0.005), and 24% with both therapies. There w as no significant change in aortic flow whether the subjects received air, oxygen, or dopamine (p = 0.77). In the hypercapnic patients there was no significant change in aortic or renal velocities while receivi ng oxygen or dopamine (p = 0.85 and 0.86). We conclude that color-flow Doppler velocity measurements can accurately detect changes in renal blood flow. Oxygen and dopamine are equipotent renal vasodilators in h ypoxic COPD, but the effect is not additive. Renal hemodynamics did no t improve with oxygen or dopamine with hypercapnia, suggesting that th ere is a difference in renovascular control between normocapnic and hy percapnic patients with COPD.