Cerebral blood flow during hemorrhagic hypotension in the unanesthetized goat

Changes in cerebral blood flow (CBF), arterial blood pressure (AP), and cardiac output (CO) were studied during stepwise blood losses in 12 unanesthetized goats. Bleeding was followed by a drop in CBF, AP and CO in a nearly parallel fashion. Control values (means +/- SE) for CBF, AP, and CO were 117 +/- 5.6 ml/min per 100 g, 105 +/- 3.1 mmHg, and 2,825 +/- 124 ml/min, respectively; and after bleeding, 66 +/- 3.9 ml/min per 100 g, 57 mmHg, and 1, 383 ml/min. Arterial blood samples obtained before bleeding, during the hypotensive state, and after reinfusion did not show any significant differences in pH, PCO2, and PO2 values. In phentolamine-treated animals, bleeding produced a drop in AP and CO similar to that observed in the nontreated animals; however, the decrease in CBF was less marked. These findings show that CBF follows pari passu the fall in AP, and they indicate that the alpha-adrenergic receptors of the cerebral vessels are involved in the cerebral blood flow changes in hemorrhage.