M. Tchirikov

Blood flow through the ductus venosus in singleton and multifetal pregnancies and in fetuses with intrauterine growth retardation

OBJECTIVE It is known from animal experiments that blood flow through the ductus venosus changes with fetal strain. Therefore the ratio of umbilical vein to ductus venosus flow rate in human intrauterine growth retardation and multifetal pregnancies was investigated and compared with that in control subjects. STUDY DESIGN Blood flow rates in the umbilical vein and in the ductus venosus, as well as peak velocity, minimum velocity, mean velocity, and pulsatility index (maximum velocity envelope curve) in the ductus venosus, were measured in women with normal pregnancies (n = 55), intrauterine growth retardation (n = 20), and multifetal pregnancies (10 women with 20 fetuses) with color Doppler ultrasonography. RESULTS Average ductus venosus blood flow rates (mean +/- SD), normalized for estimated fetal body weight, were 60 +/- 30, 69 +/- 35, and 77 +/- 28 (ml x min(-1) x kg(-1)) in control subjects, intrauterine growth retardation, and multifetal pregnancies, respectively. Umbilical vein blood flow rates amounted to 140 +/- 59, 111 +/- 54, and 141 +/- 47 (ml x min(-1) x kg(-1)). Both absolute flow rates increased with gestational age, whereas normalized flow rates decreased. The percentage of umbilical blood flow passing through the ductus venosus in the control group was 43% + 9%. It was significantly increased in both intrauterine growth retardation (62% +/- 8%) and in multifetal pregnancies (55% +/- 12%). Peak velocity, minimum velocity, mean velocity, and pulsatility index in the ductus venosus were not significantly different between groups. CONCLUSION The increased ratio of ductus venosus blood flow to umbilical vein blood flow may indicate fetal strain.

Ductus venosus shunting in the fetal venous circulation: regulatory mechanisms, diagnostic methods and medical importance

The fetal liver is located at the crossroads of the umbilical venous circulation. Anatomically, the ductus venosus (DV) and the intrahepatic branches of the portal vein are arranged in parallel. The actual DV shunting rate, i.e. the percentage of umbilical blood flow entering the DV measured by Doppler velocimetry, seems to be lower than that estimated using radioactively‐labeled microspheres. In human fetuses the DV shunting rate is about 20–30%. Increases in the DV shunting rate are a general adaptational mechanism to fetal distress. Hypoxia results in a significant increase in the DV shunting rate, most probably in order to ensure an adequate supply of oxygen and glucose to vitally important organs such as the brain and heart. The mechanism of blood flow redistribution between the fetal liver and the DV is still a matter of debate. The isthmic portion of the DV contains less smooth muscle tissue than the intrahepatic branches of the portal vein, which in vitro react more forcefully in response to catecholamines than the DV.

Laser coagulation of placental anastomoses with a 30° fetoscope in severe mid-trimester twin–twin transfusion syndrome with anterior placenta

To assess outcome after fetoscopic laser coagulation (FLC) of placental vascular anastomoses with the 30° fetoscope in mid‐trimester severe twin‐to‐twin transfusion syndrome (TTTS) with completely anterior placenta compared with the regular 0° fetoscope in TTTS with other placental locations.

Differential effects of catecholamines on vascular rings from ductus venosus and intrahepatic veins of fetal sheep

Ductus venosus (DV) sparing means the maintenance of blood flow through the DV following reduction of liver venous blood supply during fetal hypoxia. The present study compared the reactions of the isthmic portion of the DV and intrahepatic veins (IHVs) to catecholamines in vitro. Vessel rings of 1 mm width and 3 mm diameter were obtained from 17 fetal sheep (88–136 days gestational age, median 120 days). The immunohistochemical examination of the DV and IHV was performed in eight cases using an antibody against α‐smooth muscle actin and an antibody against α‐adrenergic receptors. Five vessel rings of the DV in early gestation (median 95 days) did not respond to KCl‐induced depolarisation. Force development in response to KCl of both vessel types increased with gestational age (P < 0.05). The IHV required 4.1 ± 0.8 min (mean ±s.e.m.) and the DV 14.5 ± 4.0 min to reach the maximum tension in response to KCl, which was 5.0 ± 4.0 mN in the IHV and 2.2 ± 1.9 mN in the DV (n= 12, P < 0.05). The maximum forces developed in response to noradrenaline (norepinephrine; 42 μm, n= 9) and adrenaline (epinephrine; 100 μm, n= 12) were about sixfold higher in the IHV rings than in the DV rings (P < 0.05). The EC50 values of the DV and the IHV rings to noradrenaline were 5.9 ± 1.3 μm and 5.0 ± 1.3 μm, respectively (P= 0.03). The EC50 values of the adrenaline responses were 2.5 ± 0.5 μm for the DV and 2.2 ± 0.7 μm for the IHV (not significant). The α‐adrenergic receptors were present in the well‐structured media of IHVs, but were less distinctive in the wall of the DV. DV sparing can be attributed to an increased resistance of IHVs to catecholamines compared with the DV. The different responses can be explained by different anatomical and functional properties of the two vessel types.

Unloading of baroreceptors by carotid occlusion does not increase heart rate in fetal sheep

UNLABELLED Unloading of baroreceptors by carotid occlusion does not increase heart rate in fetal sheep; OBJECTIVES To test the hypothesis that in fetal sheep reduction of carotid sinus pressure by carotid occlusion increases heart rate. STUDY DESIGN Fetal sheep (gestational age 121-132 days) were chronically instrumented with bilateral carotid occluders, catheters and electrodes (ECG) to measure systemic arterial and carotid sinus (CSP) blood pressures, and fetal heart rate. RESULTS Bilateral carotid occlusion (BCO) increased mean arterial blood pressure from 46+/-7 mmHg to 53+/-8 mmHg (mean+/-S.D.) while CSP decreased from 44+/-7 mmHg to 17+/-7 mmHg. Fetal heart rate fell during occlusion significantly from 186+/-34 bpm to 159+/-26 bpm (n=20 animals). Infusion of phenylephrine (8.5-20 microg min(-1)kg(-1)) or methoxamine (60-200 microg min(-1)kg(-1)) increased mean blood pressure from 44+/-6 to 61+/-9 mmHg, and fetal heart rate decreased from 186+/-30 to 132+/-31 bpm (n=12). BCO increased systemic arterial pressure further to 70+/-11 mmHg whereas carotid sinus pressure was reduced to 31+/-13 mmHg. However, average heart rate did not increase significantly (136+/-28 bpm). CONCLUSION We conclude that in contrast to adult animals, in fetal sheep carotid occlusion with subsequent unloading of baroreceptors does not increase heart rate even when the baroreflex had been activated by arterial hypertension. It seems likely that stimulation of carotid chemoreceptors prevents the expected baroreceptor mediated heart-rate response.

Ductus venosus shunting in marmoset and baboon fetuses

The increased shunting of blood through the ductus venosus (DV) during stress situations is an important mechanism that ensures fetal survival. Although primate fetuses may serve to study the function of this important venous shunt, the rate of DV shunting has not been determined in non‐human primates under normal conditions.

Contraction kinetics of isolated human myometrium during menstrual cycle and pregnancy

Objective To investigate the interaction between actin and myosin in the myometrium by studying the contraction kinetics of isolated samples of human myometrium.

OC117: Laser coagulation of placental anastomoses in severe mid-trimester twin–twin transfusion syndrome and anterior placenta with a 30° fetoscope

Objectives: Selective laser photocoagulation of communicating vessels (SLPCV) for twin–twin transfusion syndrome (TTTS) in patients with an anterior (ANT) placenta is known to be technically more challenging than in patients with posterior (POST) placentas. We describe a new trocar-assisted (TA) technique to address this issue. Methods: Four surgical techniques were used for SLPCV in ANT placentas: standard, rigid scope; flexible scope; side-firing, twoport; and TA, whereby the anastomoses were lasered from within the trocar sheath after identification with an angled diagnostic endoscope. The protocol was approved by the Institutional Review Board and all patients signed informed consent. Results: SLPCV was performed in 269 patients from February 2003 to May 2005, of which 88 (47.6%) had ANT placentas. Only 7/88 (7.9%) patients with ANT placentas were treated with a flexible scope or a two-port technique and neither of these techniques was used after November 2003. Perinatal survival was independent of placental location (89.7% vs. 85.2%, POST vs. ANT placentas) or ANT placenta techniques. Gestational age at delivery (median 33.1 (range, 17.6–39.4) weeks), and incidence of premature rupture of membranes within 21 days of surgery, was no different between techniques in patients with ANT. However, operating time was significantly less in the TA group (P < 0.05). In 50/88 patients with ANT placentas available for analysis, only one had patent anastomoses in the TA group (2.9%), compared to none in the other techniques (P = 0.7). Conclusions: Laser treatment of TTTS patients with an ANT placenta that requires more than a simple rigid endoscope can be effectively achieved with a TA technique. TA allows orthogonalization of the angle of fire, eliminating the need for a two-port or flexible endoscope technique. TA is also useful in exposing the entire vessel wall in patients with POST placentas with a tangential angle of entry.

OC72: Cardiac output and blood flow volume in central vessels after fetoscopic coagulation of cord vessels in fetal sheep

umbilical artery. Wall motion filter was kept at less than 100 MHz. Waveforms were assessed in triplicate. Percent AEDV (%AEDV) was calculated as time of the cycle spent in AEDV divided by total cardiac cycle × 100. Follow-up Dopplers were performed 16–24 hours later. IUFD was recorded if the donor twin died any time prior to delivery. A p < 0.05 was considered statistically significant. Results: Sixteen patients with pre-operative AEDV were identified during the study period, of which 5 were associated with IUFDD. Gestational age at the time of the procedure, number of anastomoses lasered, operating time or placental location were not different between patients with or without IUFD-D. The mean pre-op %AEDV was significantly higher in patients with IUFD-D than in those without (42.7% vs. 27.1%, respectively, p = 0.029). A %AEDV > 35 was 18 times more likely to be associated with IUFD-D (95% CI 1.2–260). AEDV resolved in 8 patients after surgery, with a mean %AEDV of 26.9% vs. 37% in those in whom AEDV did not resolve. However, this difference was not statistically significant. Conclusion: A %AEDV > 35 is associated with an increased risk of IUFD of the donor twin in TTTS patients treated with SLPCV. A high %AEDV is more predictive of IUFD-D than the lack of resolution of AEDV after surgery. Assessment of %AEDV should be considered part of the pre-operative evaluation of TTTS patients.

OC73: Umbilical venous volume flow in untreated and treated twin–twin transfusion syndrome (TTTS)

umbilical artery. Wall motion filter was kept at less than 100 MHz. Waveforms were assessed in triplicate. Percent AEDV (%AEDV) was calculated as time of the cycle spent in AEDV divided by total cardiac cycle × 100. Follow-up Dopplers were performed 16–24 hours later. IUFD was recorded if the donor twin died any time prior to delivery. A p < 0.05 was considered statistically significant. Results: Sixteen patients with pre-operative AEDV were identified during the study period, of which 5 were associated with IUFDD. Gestational age at the time of the procedure, number of anastomoses lasered, operating time or placental location were not different between patients with or without IUFD-D. The mean pre-op %AEDV was significantly higher in patients with IUFD-D than in those without (42.7% vs. 27.1%, respectively, p = 0.029). A %AEDV > 35 was 18 times more likely to be associated with IUFD-D (95% CI 1.2–260). AEDV resolved in 8 patients after surgery, with a mean %AEDV of 26.9% vs. 37% in those in whom AEDV did not resolve. However, this difference was not statistically significant. Conclusion: A %AEDV > 35 is associated with an increased risk of IUFD of the donor twin in TTTS patients treated with SLPCV. A high %AEDV is more predictive of IUFD-D than the lack of resolution of AEDV after surgery. Assessment of %AEDV should be considered part of the pre-operative evaluation of TTTS patients.