Diminished vasoconstrictive function caused by long-term nonpulsatile leftheart bypass

We investigated the functional changes of the systemic vascular system due to prolonged nonpulsatile left heart bypass (NPLHB). Three adult goats unde rwent pulsatile left heart bypass (PLHB). Two weeks later the PLHB was chan ged to the NPLHB, which was conducted for 4 weeks. The aortic pulse pressur e was 39 and 16 mm Hg during the PLHB and NPLHB, respectively. Systemic vas cular resistance (SVR) and the plasma norepinephrine level were measured at the end of PLHB (PUL), and in the 1st, 2nd, 3rd, and 4th weeks of NPLHB (N P1w, NP2w, NP3w, and NP4w). At each point, 1 mu g/kg norepinephrine was inj ected, and the elevation of the SVR (Delta SVR) was calculated. The SVR and the plasma norepinephrine level did not change significantly during the en tire course. However, Delta SVR decreased during NPLHB and became significa ntly lower at NP3w and NP4w than that at PUL (NP3w: 839 +/- 164, NP4w: 746 +/- 268, and PUL: 1,239 +/- 324 dyne.s.cm(-5)). These results strongly indi cated that prolonged NPLHB significantly diminished the constrictive functi on of the vascular system.