Figure 2. Cardiovascular changes in fetuses tolerating labour‐like hypoxaemia.

Fetal heart rate (FHR, continuous lines) and mean arterial pressure (MAP, dashed lines) in near‐term fetal sheep during 1 min complete umbilical cord occlusion (UCO) repeated every 5 min (n = 8) for 4 h (total of 49 UCOs). The top panel shows the second UCO, the middle panel shows the middle UCO and the bottom panel shows the penultimate UCO. Fetuses effectively adapted to this severity and frequency of UCO. Each occlusion was associated with a rapid deceleration and sustained hypertension, mediated by peripheral chemoreflex activation. Hypotension was never observed in these fetuses. Data are 1 s means ± SEM (shown as dotted lines). The periods of umbilical cord occlusion are shown in grey. Base deficit (BD) and lactate values are given in mmol L⁻¹. Figure modified from Bennet et al. (2005).