Effect of sex difference and pregnancy on the normal reactive hyperemia curve

The 10-min reactive hyperemia reaction was studied in a group of normal males, 10 normal females, 10 females in each trimester of pregnancy, and 10 females 6 wk postpartum. Sex difference had a marked effect on the hyperemic reaction, in that 5 and 15 s after release of circulatory arrest, the mean forearm blood flow in normal males was significantly reduced below that of normal females. During pregnancy there was a shift in the reaction of the pregnant female toward that in the normal male. In the 1st trimester of pregnancy, 5 s after circulatory arrest the mean forearm blood flow was diminished below that of the normal female; in the 2nd and 3rd trimesters at 5 s, the reaction was significantly diminished below that of the normal female. At 6wk postpartum, the reaction was essentially the same as in the nonpregnant female. Although these changes may be explained by a hormonal difference, they portray that there may be a marked difference in vascular reactivity due to sex difference only.