Prolonged nonpulsatile left heart bypass diminishes vascular contractility

We investigated possible functional changes in the vascular system accompan ying the morphological change in prolonged nonpulsatile left heart bypass ( LHB). Three adult goats underwent pulsatile LHB. Two weeks postoperatively, the pulsatile ventricular assist device was replaced with a centrifugal pu mp and nonpulsatile LHB was subsequently conducted for 4 weeks. The mean ao rtic pulse pressure was 39 and 16 mmHg during the pulsatile and nonpulsatil e LHB, respectively. Systemic vascular resistance (SVR) and plasma norepine phrine levels were measured at the end of pulsatile LHB (PUL), and at the e nd of 1st, 2nd, 3rd, and 4th week of nonpulsatile LHB (NP1w, NP2w, NP3w, NP 4w, respectively). At each point, 50 mu g/kg nitroglycerin and 1 mu g/kg no repinephrine were injected and the minimal and maximal values of SVR after injection were calculated as parameters reflecting the vascular tonus and c ontractility The SVR and plasma nor epinephrine level did not significantly change during the entire course (SVR: 1106, 895 982, 920, and 938 dyne.sec .cm(-5); norepinephrine level: 03, 0.2, 0.1, 0.2 and 0.1 ng/ml; at PUL, NP1 w, NP2w, NP3w, and NP4w, respectively). The minimal value of SVR after nitr oglycerin injection remained unchanged, indicating that vascular tonus was stable during the entire course (618, 687, 623, 560, 653 dyne.sec.cm(-5), r espectively). In contrast, the maximal Value of SVR after norepinephrine in jection at NP3w and NP4w (1695 and 1759 yne.sec.cm(-5)) became significantl y reduced compared to that at PUL (2346 dyne.sec.cm(-5)). These results ind icated that prolonged nonpulsatile left heart bypass did not affect the vas cular tonus, but significantly diminished the vascular contractility.