ALTERED OXYGEN METABOLIC CONDITIONS ASSOCIATED WITH INCREASED NOREPINEPHRINE LEVELS IN A NONPULSATILE SYSTEMIC CIRCULATION

Change in oxygen metabolic conditions accompanying the conversion of s ystemic flow from pulsatile to nonpulsatile (from P-mode to N-mode) wa s investigated in association with blood norepinephrine levels. Total left heart bypass was instituted through a left thoracotomy under gene ral anesthesia in 10 adult goats. Pulsatile and nonpulsatile pumps wer e incorporated in the circuit in parallel, and the flow character was rapidly converted from the P-mode to the N-mode. Norepinephrine levels increased significantly after the conversion, from 222 +/- 54 pg/ml t o 285 +/- 65 pg/ml. While oxygen delivery (DO2) was kept constant, the oxygen extraction ratio significantly decreased, from 21 +/- 3% to 16 +/- 3%, and venous oxygen saturation (SvO(2)) significantly increased , from 77 +/- 6% to 84 +/- 6% after depulsation. The serum lactate lev el was significantly higher in the N-mode than the P-mode (P-mode: 35 +/- 2 mg/dl, N-mode: 45 +/- 5 mg/dl). Strong positive and negative cor relations of norepinephrine levels were observed with oxygen extractio n ratio and SvO(2), respectively, whereas norepinephrine levels did no t correlate with DO2. Regression lines in these correlations unveiled higher oxygen uptake in the P-mode than the N-mode at the same norepin ephrine level. These results indicate that, in the setting of an acute animal experiment, oxygen uptake is less efficient with the absence o f pulsatility, and the higher norepinephrine concentration functioned to tune the oxygen metabolism in the initial stage of nonpulsatile sys temic circulation.