Changes in venous flow and intra tracheal flow in fetal breathing movements

Using pulsed Doppler ultrasound combined with a real-time B-mode image, changes in the central venous blood flow and tracheal fluid flow were recognized during fetal breathing movements. The blood flow in the umbilical vein was increased with fetal inspiration in which the abdominal wall of fetus moved inward, and decreased with expiration in which the abdominal wall moved outward. Velocity in the fetal vena cava revealed a complex blood flow, in accordance with both fetal cardiac motions and breathing movements. The tracheal flow velocity during fetal breathing was measured at a maximum of 40 cm s-1 and the flow volume was estimated at a maximum of 6 ml breath-1 in the matured fetus.     

Cerebral blood flow during open-chest cardiac massage with occlusion of the descending aorta in dogs

Cerebral blood flow (CBF) and carotid blood flow (CAF) during open-chest cardiac massage with and without occlusion of the descending aorta was examined in 10 dogs to assess whether they were augmented by occlusion. In control measurements with a normally beating heart, CBF with and without occlusion of the descending aorta were 17.8 +/- 2.3 and 13.8 +/- 2.2 ml/min (+/- S.E.M.), which were not significantly different. Cerebral blood flow during open-chest cardiac massage were 6.1 +/- 1.0 with occlusion and 5.7 +/- 1.0 ml/min without occlusion of the descending aorta, which were also not significantly different. By contrast, CAF increased significantly with occlusion of the descending aorta both during control measurement, with mean increases of 61.1% and 92.2% during open-chest cardiac massage (P = 0.05). While occlusion generally failed to augment CBF; in two dogs resuscitation was successful by manual cardiac massage. With the restoration of cardiac activity it increased immediately to twice that of control blood flow, and then gradually returned to the control level. Based on these observations, it is the author's opinion that every effort should be directed toward the restoration of cardiac activity as quickly as possible during circulatory arrest, and to increase CBF which is essential for neurological recovery.     

Quantitative blood flow in the fetal descending aorta and in the umbilical vein in normal pregnancies. Longitudinal and cross-sectional studies

Quantitative blood flow in the fetal descending thoracic aorta and in the umbilical vein was measured both in a longitudinal study where each of 13 fetuses was examined three times and in a cross-sectional study where 45 fetuses were examined once only in the last trimester of normal pregnancy. The waveform of the velocity curves from fetal descending aorta was examined and the Pulsatility Index, the A/B ratio and the least diastolic velocity were calculated. The longitudinal study showed that all these parameters and the fraction of the flow in the fetal descending aorta, which was distributed to the placental circulation, were constant during the last trimester. The problems of longitudinal inference from cross-sectional studies are discussed. For all 58 fetuses the flow in the descending thoracic aorta was 234 ml/min/kg and in the umbilical vein 127 ml/min/kg. The Pulsatility Index was 1.83, the A/B ratio 4.75, the least diastolic velocity 9.9 cm/s. The fraction of blood flow in the descending aorta distributed to the placental circulation was 55%.     

Antenatal fetal blood flow in the descending aorta and in the umbilical vein and their ratio in normal pregnancy

One hundred and sixty sequential measurements of umbilical vein blood flow (UVBF) and descending aorta blood flow (DABF) in normal fetuses were performed in utero by the duplex real-time ultrasound and pulsed Doppler technique. Throughout pregnancy from 26 to 41 weeks the blood flow velocity of the umbilical vein (UV) and the descending aorta (DA) remained relatively constant, while the diameter of UV and DA, UVBF and DABF increased with advancing gestational age. Moreover, the UVBF-to-DABF ratio was nearly constant, with a mean value of 64% from 26 weeks onwards. The DABF-to-abdominal area (DABF-to-AA) ratio was constant throughout pregnancy, with a mean value of 7.0 ml/min/cm2. We call these two constants the umbilical-aortic index and descending-aortic index. These relationships may be of help in the diagnosis of intrauterine growth retardation and other fetal disorders.     

Fetal cardiac arrhythmias and their effect on volume blood flow in descending aorta of human fetus

Using a two-dimensional linear array real-time and pulsed Doppler ultrasound system, volume blood flow measurements were made in 86 normal pregnancies, seven cases of fetal bradycardia, and seven cases of fetal tachycardia at the lower thoracic level of the fetal descending aorta. During fetal cardiac arrhythmias, volume blood flow was maintained within the normal range until the heart rates reached around 50 bpm and 230 bpm, after which the volume blood flow diminished. The changes observed suggest that the Frank-Starling mechanism is functional in the fetal myocardium and demonstrate the stability of the fetal circulation.     

Pulse pressure assessment in the human fetal descending aorta.

Pulsatile vessel diameter recordings were obtained at two different levels of the fetal descending aorta in ten third-trimester human fetuses using an echo-tracking system. A derivation of the Moens-Korteweg equation was used to estimate the pulse pressure amplitude in this vessel. The positive phase of the first derivative of the diameter curves was cross correlated to assess the propagation time of the pulse wave. It is postulated that this method minimises the measuring errors resulting from diameter pulse wave changes during propagation along the longitudinal axis of the descending aorta. It was estimated from repeated measurements that approximately 13 recordings of 5.2 s each are required to assess the mean pulse pressure amplitude for an individual fetus with an estimated random error of 10%.     

Human fetal foramen ovale flow velocity waveforms relative to fetal breathing movements in normal term pregnancies.

The relationship between foramen ovale flow velocity waveforms and high-amplitude fetal breathing movements was studied in ten normal term pregnancies using Doppler ultrasonography. Peak systolic and averaged flow velocities demonstrated a statistically significant increase during fetal breathing activity, suggesting a raised pressure gradient between the right and left atria. This could be explained by a temporal reduction in pulmonary venous return to the left atrium during the inspiratory phase of the fetal breathing cycle. The breathing-related increase in foramen ovale flow velocity suggests that fetal breathing activity facilitates the distribution of well-oxygenated blood to the aorta and cerebral circulation.     

Reverse flow in the human fetal descending aorta as a sign of severe fetal asphyxia preceding intrauterine death

Flow velocity waveforms (FVW) in the descending part of the human fetal aorta were monitored in 35 cases of severe intrauterine growth retardation (IUGR) showing pathological intrauterine circulation (end-diastolic block). In 5 of the 35 fetuses, reversed aortic flow was observable during diastole and the simultaneously recorded CTG findings were pathological. All 5 fetuses having this circulatory sign died in utero within the next day. Controls were 260 healthy fetuses with normal growth curves; no end-diastolic block or reverse flow was found in this group. Diastolic reverse flow in the fetal descending aorta appears to reflect severely altered circulation preceding imminent fetal death.     

Changes in inferior vena cava blood flow velocity and diameter during breathing movements in the human fetus.

Breathing movements in the human fetus cause distinct changes in Doppler flow velocity measurements at arterial, venous and cardiac levels. In adults, breathing movements result in a momentary inspiratory collapse of the inferior vena cava vessel wall. The study objective was to quantify the inferior vena cava flow velocity modulation during fetal breathing movements and to evaluate possible inferior vena cava vessel diameter changes in normal third-trimester pregnancies.We studied 57 women after oral administration of dextrose (50 g). In 40 fetuses (n = 19, 27-32 weeks and n = 21, 36-39 weeks), fetal inferior vena cava waveforms were obtained during apnea and fetal breathing activity. In 30 fetuses (27-39 weeks) inferior vena cava vessel diameter changes were studied using the M-mode during apnea and breathing movements. Peak and time-averaged velocities of inferior vena cava flow velocity waveforms showed a gestational age-independent increase of 60-160% during breathing activity. A temporary inferior vena cava vessel wall collapse (range, 50-83%) was recorded, which was significantly different from vessel diameter changes during apnea (range, 11-19%). The marked increase of inferior vena cava flow velocities is due to a raised thoraco-abdominal pressure gradient, which may cause a reduction in vessel size and additional volume flow into the right atrium. The significance of the caval index for recognition of elevated right atrial pressure in abnormal human fetal development needs further investigation.     

Time domain measurement of blood flow in the human fetal aorta during normal pregnancy.

OBJECTIVE: To evaluate blood-volume flow-rate measurement in the fetal descending thoracic aorta using a non-invasive, non-Doppler, ultrasound technique. METHODS: This was a cross-sectional, observational study. Volume flow measurements were obtained from the descending thoracic aorta in 59 human fetuses between 20 and 40 weeks' gestation. These were uncomplicated pregnancies that resulted in the live births of appropriately grown infants. The measurements were obtained using a time domain processing technique: color velocity imaging quantification (CVI-Q). RESULTS: The blood-volume flow rate increased consistently from the second trimester until term. The mean values ranged between 100 mL/min at 20 weeks' gestation and approximately 350 mL/min at term. The normalized (weight-adjusted) volume flow rates decreased with increasing gestation, from a maximum of 626 mL/min/kg at 23 weeks to a minimum of 45.6 mL/min/kg at 37 weeks. CONCLUSIONS: The regular measurement of blood-volume flow in the descending fetal thoracic aorta is feasible using CVI-Q. Although there is a considerable learning curve, with adequate training there are potential clinical applications for this non-Doppler technique. However, limitations exist with the currently available technology for clinical use in fetal vascular studies.     

Retrograde aortic isthmus net blood flow and human fetal cardiac function in placental insufficiency.

OBJECTIVE: Retrograde aortic isthmus (AoI) net blood flow has been associated with diminished oxygen delivery to cerebral circulation. This study was designed to characterize the cardiac function in human fetuses with retrograde AoI net blood flow in pregnancies complicated by placental insufficiency. METHODS: The control group comprised 43 fetuses in uncomplicated pregnancies. Study groups consisted of fetuses with placental insufficiency, and either antegrade (Group 1; n = 18) or retrograde (Group 2; n = 11) AoI net blood flow. Volume blood flows (Q) of left (LVCO) and right (RVCO) ventricles, ductus arteriosus (Q(DA)), pulmonary arterial bed (Q(P)) and foramen ovale (Q(FO)) were calculated and their proportions (%) of combined cardiac output (CCO) were determined. Ventricular ejection forces were calculated. Blood velocity waveforms of the mitral (MV) and tricuspid (TV) valves were obtained. The proportion of left ventricular isovolumetric relaxation time (IRT%) of the cardiac cycle, and index of myocardial performance (IMP) were calculated. RESULTS: In Group 1, Q(DA)% was increased (P < 0.05) and Q(P)% decreased (P < 0.05) compared with the control group, and Q(FO)% was greater (P < 0.01) compared with the control group and Group 2. In Group 2, the distribution of CCO did not differ from that of the control group. Ventricular ejection forces were similar among the groups. In Group 2, the MV early filling/atrial contraction time-velocity integral ratio was greater (P < 0.05) compared with those of the control group and Group 1. In Groups 1 and 2, IRT% and IMP were increased (P < 0.001) compared with the control group. CONCLUSIONS: In placental insufficiency, fetuses with antegrade AoI net blood flow show a shift in RVCO from the pulmonary to the systemic circulation, and Q(FO) makes up the majority of LVCO. Fetuses with retrograde AoI net blood flow fail to demonstrate these changes, suggesting a relative drop in the oxygen content of the blood entering the left ventricle.     

Enrollment in clinical trials: institutional factors affecting enrollment in the cardiac arrhythmia suppression trial (CAST).

Recruitment and Enrollment Assessment in Clinical Trials (REACT), an NHLBI-sponsored substudy of the Cardiac Arrhythmia Suppression Trial (CAST), was conducted to assess factors associated with enrollment in clinical trials. We report on the relationships of institutional factors at CAST sites to patient enrollment. The proportion of CAST-eligible patients enrolling at each CAST site during the REACT study period was defined as the number of subjects enrolled divided by the sum of (1) the number enrolled plus (2) the number of eligibles who refused plus (3) the number of eligibles whose physicians refused to permit CAST personnel to attempt to enroll them. A questionnaire that included 78 questions regarding factors hypothesized to be associated with enrollment was completed between August 1988 and February 1990 by the nurse coordinators at all 112 CAST sites in the United States and Canada. Sixteen items were unanalyzable, and 37 of the remaining 62 were grouped into seven scales. The remaining items were analyzed individually. Enrollment proportions varied widely across the 112 CAST sites (mean 32.7% SD 22.6). Five variables or scales were included in the final multiple regression model (multiple R2 = .39). The most important of these was the proportion of eligible patients at a site cared for by medical staff other than private attending physicians (multiple R2 for this variable alone, .26). This proportion tended to be high in teaching hospitals. Other variables in this model that were associated with higher enrollment proportions included the number of days per week a nurse coordinator was present at the site, the number of nurse coordinator full-time equivalents at the site, fewer other clinical trials for which the nurse coordinator was responsible, and fewer perceived obstacles to enrollment. These findings indicate that enrollment was more successful at hospitals with higher proportions of eligible subjects cared for by fellows, housestaff, and service attending physicians and at institutions with the committed presence of a nurse-coordinator.     

Predicting the severity of fetal anemia using time-domain measurement of volume flow in the fetal aorta.

OBJECTIVES: To assess the value of fetal aortic time-domain measurement of volume flow (using color velocity imaging quantification (CVI-Q)) in predicting the severity of fetal anemia. METHODS: This was a prospective observational study, in which 24 pregnant women with suspected fetal anemia due to rising anti-red blood cell antibody titers underwent cordocentesis. The fetal aortic time-domain volume flow was measured before fetal blood sampling for fetal hemoglobin investigation. We examined the correlation between increased fetal aortic time-domain volume flow (>2 SD for gestational age) and fetal anemia (hemoglobin level <2 SD for gestational age). RESULTS: Seventeen fetuses had anemia, and seven had normal hemoglobin. There was a strong correlation between the increase in fetal aortic time-domain volume flow and the drop in hemoglobin value (r = 0.81; P < 0.01). The sensitivity of this technique to predict fetal anemia was 81.3% and the specificity was 71.4%. The mean increase over time in aortic CVI-Q in anemic fetuses was 323.2 mL/min (95% CI, 200.1 to 446.4) compared with 86.9 mL/min (95% CI, -17.7 to 191.5) in the non-anemic group (P = 0.004). CONCLUSION: Fetal aortic time-domain measurement of volume flow is significantly increased in cases of fetal anemia due to red-cell alloimmunization. These findings can be used to improve the sensitivity, specificity and positive predictive value of the non-invasive techniques used to predict fetal anemia, and may help in the selection of pregnancies that require cordocentesis and transfusion.     

Regional blood flow distribution in dog during induced hypotension and low cardiac output. Spontaneous breathing versus artificial ventilation.

Respiratory muscle blood flow and organ blood flow was studied in two groups of dogs with radioactively labeled microspheres to assess the influence of the working respiratory muscles on the regional distribution of blood flow when arterial pressure and cardiac output were lowered by pericardial tamponade. In one group (n = 6), the dogs were paralyzed and mechanically ventilated (Mv), while in the other (n = 6), they were left to breathe spontaneously (Sb). Cardiac output fell to 30% of control values during tamponade in both groups and was maintained constant. None of the dogs was hypoxic. Ventilation in the Sb group peaked after 50 min of hypotension, but remained unchanged in the Mv group. Duplicate measurements of blood flow were made during a control period and after 50 min of tamponade (corresponding to the peak ventilation in Sb). Blood flow to the respiratory muscles increased significantly (P less than 0.001) during tamponade in Sb (diaphragmatic flow increased to 361% of control values), while it decreased in Mv. Although the arterial blood pressure and cardiac output were comparable in the two groups, blood flow distribution during tamponade was different. In Sb, the respiratory muscles received 21% of the cardiac output, compared with only 3% in the Mv group. Thus, by muscle paralysis and Mv, a large fraction of the cardiac output used by the working respiratory muscles can be made available for perfusion of other organs during low cardiac output state: blood flows to the liver, brain, and quadriceps muscles were significantly higher during tamponade in the Mv group compared with the Sb group. Similarly, blood lactate at all times after the induction of low cardiac output and hypotension was significantly lower in the Mv animals (P less than 0.005).     

Blood flow in the left anterior descending coronary artery in children with ventricular septal defect.

High-frequency echocardiography offers a noninvasive approach for imaging left anterior descending coronary artery (LAD) blood flow from a transthoracic window. The purpose of this study was to assess the effects of left ventricular (LV) volume overload on LAD flow in pediatric patients with ventricular septal defect (VSD). The study subjects consisted of 38 children with VSD and 15 healthy children. LV mass, LAD diameter, and LAD flow were measured by using transthoracic echocardiography, then LAD diameter and LV mass were indexed for body surface area. Pulmonary to systemic flow ratios (Qp/Qs) were obtained by cardiac catheterization. The Qp/Qs ratios ranged from 1.2 to 3.1 (mean 2.1 +/- 0.5). The mean LAD flow velocities, flow velocity integrals, and flow volumes were significantly higher in the patients than in the control subjects. LAD flow velocity and flow volume showed significant positive correlations with Qp/Qs, LV mass, and LV end-diastolic volume. Stepwise regression analysis revealed that Qp/Qs was the most important determinant of both LAD flow velocity (r(2) = 0.45, P < .0001) and LAD flow volume (r(2) = 0.44, P < .0001). The ratios of LAD flow volume to LV mass did not differ between the 2 groups. In 8 patients who underwent surgical treatment, LAD flow velocity, flow velocity integral, and flow volume decreased significantly after surgery. The current results suggest that patients with VSD have a higher resting coronary blood flow, and that LAD flow pattern is dependent on LV volume overload and changes after surgery.     

Correlations in umbilical blood flow Doppler velocities in the human fetus during breathing.

We hypothesized that changes in intrathoracic pressure during fetal breathing episodes result in quantifiable variations in umbilical arterial and venous blood flow velocities, and that these variations are related to compliance properties of each system. We further hypothesized that these variations in velocities are different in fetuses with normal and abnormal umbilical arterial Doppler velocities. Umbilical arterial and venous Doppler velocities were measured simultaneously during breathing episodes in 15 normal fetuses and 14 fetuses with elevated systolic-to-diastolic (S/D) umbilical arterial Doppler velocity ratios. Umbilical arterial end-diastolic velocity changes were less than umbilical venous velocity changes in normal fetuses, but were significantly greater in four fetuses with elevated S/D ratios (p < 0.004). Furthermore, umbilical arterial diastolic velocity minima preceded umbilical venous velocity minima by a time lag that was greater in fetuses with elevated S/D ratios (p < 0.002). These results suggest that differences in umbilical arterial and venous velocity variation during fetal breathing episodes may be related in part to vascular compliance, which may be altered in fetuses with abnormal umbilical arterial Doppler velocity.     

胎膜早破后胎儿呼吸运动变化预测宫内感染的研究

目的观察未足月胎膜早破 (PPROM)孕妇胎儿呼吸运动并分析FBM变化是否可以预测早期宫内感染。方法选择PPROM (PPROM组 )、足月胎膜早破 (TPROM组 )及正常足月孕妇 (对照组 )进行FBM检查并评分。收集羊水检测病原体。结果PPROM组及TPROM组FBM评分≤ 1者高于对照组 (P均 <0 .0 5 ) ,但其平均羊水指数小于对照组(P均 <0 .0 5 )。胎膜早破组中FBM≤ 1者及FBM =2者羊水病原体阳性率无差异。结论胎膜早破孕妇 ,无论足月或未足月 ,FBM均减少 ,与羊水量减少有关但与早期宫内感染无明显关系     

Wall shear stress and related hemodynamic parameters in the fetal descending aorta derived from color Doppler velocity profiles

This paper presents a methodology for estimating the wall shear stress in the fetal descending aorta from color Doppler velocity profiles obtained during the second half of pregnancy. The Womersley model was applied to determine the wall shear stress and related hemodynamic parameters. Our analysis indicates that the aortic diameter can be modeled as a function of the gestational age in weeks as: Diameter (mm) = 0.17.ga + 0.15 (R2 = 0.64, p < 0.001). The aortic volume flow showed a log linear gestational age-related increase that fit the model: F (mL/min) = e(0.08.ga + 3.49) (R2 = 0.61, p < 0.001). The Womersley number increased linearly with gestational age from 3.3 to 6.2 (p < 0.001) and the pressure gradient decreased linearly from 2.68 to 1.16 mPa/mm (p = 0.003) during the second half of pregnancy; the mean wall shear stress for the study group was 2.2 Pa (SD = 0.59) and was independent of gestational age. This study suggests that the size of the fetal aorta adapts to flow demands and maintains constant mean wall shear stress.     

The clinical significance of absent or reverse end-diastolic flow in the fetal aorta and umbilical artery.

The clinical utility of Doppler blood flow investigations of the fetal and fetoplacental vessels is still under debate as far as timing of the delivery is concerned. However, in cases of absent or reverse end-diastolic flow, fetal compromise is usually very severe. As a consequence, we have investigated the possibility of using this information as a guide to obstetrical management. Altogether, 32 fetuses with absent or reverse end-diastolic flow in the fetal descending aorta and/or umbilical artery were studied.Reverse flow was observed in 11 cases and absence of end-diastolic flow in 21 cases. The two groups are considered separately. No significant difference was found in the mean gestational age at delivery. However, a highly significant difference was found in the mean birth weight and perinatal mortality rate.All the cases of perinatal mortality were encountered in the group presenting with reverse flow (mortality rate, 63.6%). All the live fetuses were delivered by Cesarean section and no neonatal mortality was observed in this group. Two cases of handicap were observed, one in each group. In our experience, reverse flow indicates the necessity for immediate delivery if no other clinical contraindications are present. Absence of end-diastolic flow can be observed for longer periods without adverse outcome. Absence of end-diastolic flow always precedes the appearance of fetal distress. Therefore, we believe that, after exclusion of conditions such as fetal abnormalities or extreme prematurity, a planned delivery should be considered.