Downstream Vascular Resistance Research Articles

Abnormal Gut Blood Flow Velocities in Neonates at Risk of Necrotising Enterocolitis

SummaryDuplex pulsed Doppler ultrasound was used to determine blood flow velocities in the coeliac axis and superior mesenteric artery in three groups of neonates: a group at high risk of developing necrotising enterocolitis (n = 27) and two control groups, i.e., a nonasphyxiated, appropriately grown group of preterm infants (n = 18) and a group of nonasphyxiated term infants (n = 14). Subjects were studied on the first, second, and fourth days of life. The median peak systolic velocities in the superior mesenteric artery were between 20 and 51% lower in the at‐risk group than in the term control group on all 3 days of measurement (p < 0.05 – p < 0.002). The ratio of peak systolic velocity in the coeliac axis to that in superior mesenteric artery, an index of relative downstream vascular resistance in the superior mesenteric artery, was 42–65% greater in the at‐risk group compared with the other two groups on days 1 and 2 (p < 0.05 – p < 0.001) and significantly greater than the term group on day 4 (73%, p < 0.002). These data demonstrate that neonates at risk of developing necrotising enterocolitis have abnormal gut blood flow velocities. Furthermore, they provide evidence that an alteration in the splanchnic circulation may be an important factor in the final common pathway that links diverse risk factors for necrotising enterocolitis with clinical disease.

Abnormal gut blood flow velocities in neonates at risk of necrotising enterocolitis.

Duplex pulsed Doppler ultrasound was used to determine blood flow velocities in the coeliac axis and superior mesenteric artery in three groups of neonates: a group at high risk of developing necrotising enterocolitis (n = 27) and two control groups, i.e., a nonasphyxiated, appropriately grown group of preterm infants (n = 18) and a group of nonasphyxiated term infants (n = 14). Subjects were studied on the first, second, and fourth days of life. The median peak systolic velocities in the superior mesenteric artery were between 20 and 51% lower in the at-risk group than in the term control group on all 3 days of measurement (p less than 0.05-p less than 0.002). The ratio of peak systolic velocity in the coeliac axis to that in superior mesenteric artery, an index of relative downstream vascular resistance in the superior mesenteric artery, was 42-65% greater in the at-risk group compared with the other two groups on days 1 and 2 (p less than 0.05-p less than 0.001) and significantly greater than the term group on day 4 (73%, p less than 0.002). These data demonstrate that neonates at risk of developing necrotising enterocolitis have abnormal gut blood flow velocities. Furthermore, they provide evidence that an alteration in the splanchnic circulation may be an important factor in the final common pathway that links diverse risk factors for necrotising enterocolitis with clinical disease.

EFFECTS OF EXTRADURAL ANAESTHESIA ON UMBILICAL AND UTEROPLACENTAL ARTERIAL FLOW VELOCITY WAVEFORMS

Flow velocity waveforms were recorded from the umbilical artery and uteroplacental arterial circulations of 15 women undergoing elective Caesarean section under extradural anaesthesia. The systolic: diastolic ratios of the flow velocity waveform were determined before and after extradural block. Extradural block did not alter fetal or maternal heart rates; however, umbilical artery systolic:diastolic ratio decreased from a mean (SD) of 2.4 (0.42) to 2.26 (0.38) (P = 0.049). There were no significant changes in the uteroplacental systolic:diastolic ratios. These results were compared with those from a control group in which no statistically significant changes in maternal and fetal systolic:diastolic ratios or heart rates were observed. The application of a pulse correction factor to standardize the data to fixed maternal and fetal heart rates had little effect on the significance of the findings. Extradural block in normal pregnant women during late gestation was associated with a small reduction in umbilical artery systolic:diastolic ratios, suggesting a decrease in downstream fetoplacental vascular resistance.

Uteroplacental blood flow velocity-time waveforms in normal and complicated pregnancy.

A simple continuous wave Doppler ultrasound system for recording arterial flow velocity waveforms in branches of the uterine artery in the placental bed is described. Twelve normal pregnancies were studied serially from 20 weeks to delivery. The diastolic flow velocity expressed as a percentage of the systolic provides an index of downstream vascular bed resistance and perfusion. This always exceeded 50% in normal pregnancy and there was a small increase with gestational age indicative of a decreasing flow resistance. Of the 91 complicated pregnancies, studied because of potential uteroplacental insufficiency and fetal risk, 25 resulted in the birth of an infant small-for-gestational-age. In 15 the uterine artery flow velocity waveform revealed a pattern of low diastolic flow velocity. It is postulated that these represent a subgroup of growth-retarded fetuses in whom there is reduced uterine artery perfusion. Reduced uterine artery diastolic flow velocity in these patients was associated with reduced umbilical artery diastolic flow velocity on the fetal side of the placenta. In contrast the 10 small-for-gestation infants associated with normal uterine artery waveforms suggest a primary fetal cause. Twelve patients with severe hypertensive disease of pregnancy were studied. Nine were associated with reduced uterine artery diastolic flow velocity (reduced uterine artery perfusion) consistent with vasospasm in the branches of the uterine artery in the placental bed.