ABSTRACT
Pregnancy is accompanied by increases i n b l o o d and plasma volumes, b l o o d f low and cardiac output, whi le total peripheral resistance and arterial b l o o d pressure decrease (Gant et al, 1980). These changes are thought to be due i n part to uteroplacental c i rcula t ion acting as a l ow resistance shunt (Ferris , 1983). A n o t h e r characteristic o f the cardiovascular adaptations dur ing pregnancy is decreased responsiveness to some vasoconstrictors ( A b d u l - K a r i m and Assa l i , 1961; Ferr is et al, 1983; Dav idge and M c L a u p h l i n , 1992), wh ich may result f rom changes i n number and function o f adrenoceptors (Smiley and Finster , 1996), i n baroreflex con t ro l o f the sympathetic outf low because o f an increased level o f some metabolites (Heesh and Rohger , 1995), and i n pre-and pos t junc t iona l nerve endings (Ravel ic and Burns tock, 1996).
