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.