Effect of oxygen and of carbon dioxide tension on the incidence of apnea in fetal lambs

Fetal breathing movements (FBM) in unanesthetized lambs in utero were correlated with measurements of arterial blood gases. One hundred and eighty-seven observations, consisting of the incidence of FBM during the hour preceding and the hour after the blood gas determinations, were made on 125 separate days in 30 fetuses of 117 to 146 days' gestational age. Fifty-eight percent of the observations with fetal apnea (FBM 0 to 9% in 2 hours) showed hypoxia (PaO2 less than or equal to 16 torr), whereas only 4% of the observations with FBM greater than 10% were associated with hypoxia. Sevety-eight percent of the hypoxic and normocarbic (PaCO2 42 to 53 torr) observations demonstrated apnea. However, only 44% of hypoxic plus hypercarbic (PaCO2 57 to 63 torr) fetuses were apneic, and with an elevated PaCO2, apnea tended to develop at a lower level of PaO2. We conclude that FBM may persist in the presence of hypercarbia with hypoxia.     

Ovine hourly fetal urine production: relation to fetal electrocortical activity

OBJECTIVE: Ultrasound studies of hourly urine production rate in human fetuses have suggested that a fall in urine production occurs in state 2F (fetal quiet sleep) secondary to a state-dependent decrease in renal blood flow. We sought to ascertain the relationship between fetal hourly urine production rate and behavioral state in the near-term ovine fetus, a model in which urine production and fetal brain activity can be directly measured. METHODS: Six ewes with singleton pregnancies were prepared with vascular and amniotic fluid catheters. Fetuses were prepared with hindlimb vascular catheters, a bladder catheter, and biparietal ECoG electrodes. After at least 5 days of recovery (ga 130 +/- 2 days; term = 145-150 days), each animal was monitored for a 6-h period. Urine production was measured by draining the bladder catheter through a drop counter and fetal ECoG was continuously recorded (sampling rate of 50 Hz). ECoG activity was analyzed using power spectral analysis and periods of active and quiet sleep identified using both signal amplitude and corresponding 85% spectral edge frequency. RESULTS: Basal fetal arterial pH (7.36 +/- 0.01), pO2 (22.0 +/- 1.2 mmHg) and pCO2 (47.0 +/- 1.6 mmHg) and plasma (295 +/- 2 mOsm/kg) and urine (179 +/- 3 mOsm/kg) osmolalities were within normal ranges. Active and quiet sleep comprised 50 +/- 2 and 43 +/- 1% time, respectively. There was no difference in hourly urine production rate in active sleep (21.4 +/- 9.7 ml/h) and quiet sleep (18.8 +/- 7.7 ml/h). CONCLUSIONS: 1) Hourly fetal urine production rate is independent of ECoG activity state in the near-term ovine fetus. 2) Assuming only minor species differences, ultrasound measurement of human fetal hourly urine production rate can be performed without concern for fetal neurobehavioral state changes.     

Ovine fetal breathing and swallowing activity in response to plasma glucose changes.

Fetal swallowing activity generally occurs simultaneously with fetal breathing movements (FBM) in sheep. The present study investigated the FBM and swallowing responses to altered fetal plasma glucose. Fetal lambs were chronically prepared with laryngeal, esophageal and diaphragm electromyogram (EMG) wires, an esophageal flow probe and vascular catheters. Beginning at 138 +/- 1 day, FBM and swallowing were monitored during control periods and in response to intravenous glucose infusions (14 mg/kg/min for 120 min) to fetuses of fed and fasted ewes. Glucose infusions to fetuses of fed ewes resulted in significant increases in fetal plasma glucose (21.2 +/- 0.7 to 40.5 +/- 1.9 mg/dl) and time breathing (46.2 +/- 6.3 to 60.0 +/- 9.5 min/2 h). In response to maternal fasting, fetal glucose levels (13.4 +/- 1.0 mg/dl) and time breathing (23.0 +/- 7.2 min/2 h) decreased significantly. Glucose infusion to fetuses of fasted ewes resulted in significant increases in time breathing (50.3 +/- 13.4 min/2 h) and diaphragmatic EMG activity (1,295 +/- 654 to 3,012 +/- 1,182 spikes/2 h). There was no change from basal levels of fetal EMG swallows (83.2 +/- 4.3 swallows/2 h) or esophageal flow (40.8 +/- 7.9 ml/2 h) in response to maternal fasting or fetal glucose infusions.     

Fetal breathing and generalized fetal movements in normal antenatal patients.

Fetal breathing movements (FBM) and generalized fetal movements (GFM) were recorded for 30 minutes using a real time B-scan instrument in 46 women with uncomplicated pregnancies. FBM occurred for 10.9+/-0.9 (SE) per cent of the recording time. The time occupied by FBM was not significantly related to smoking, meal times or plasma glucose concentrations. FBM were absent during the observation period in 15 per cent of patients and present for less than 10 per cent of the time in 33 per cent of patients.     

Cardiovascular and metabolic responses to intermittent umbilical cord occlusion in the preterm ovine fetus

OBJECTIVE: To determine the cardiovascular and metabolic responses to umbilical cord occlusion in the preterm ovine fetus and the impact of repetitive intermittent insults over a 4-day period. METHODS: Repetitive umbilical cord occlusions (experimental group, n = 7; control group, n = 7) were performed daily (112-115 days' gestation, term = 147 days). Mean arterial pressure (MAP), fetal heart rate (FHR), and FHR variation were monitored, and arterial blood was sampled at predetermined intervals. RESULTS: During umbilical cord occlusions, arterial oxygen pressure (PaO2) (approximately 17 mmHg) and glucose (approximately 0.3) millimoles per liter (mmol/L) fell and arterial carbon dioxide pressure (approximately 8 mmHg) rose (P < .01) to a similar extent on days 1 and 4. Umbilical cord occlusion produced a rise in lactate over the course of successive umbilical cord occlusions each day, the magnitude of which tended to be reduced by day 4 (0.3 +/- 0.1 versus 0.6 +/- 0.1 mmol/L). Control hour FHR and MAP were unaltered over the 4 days, but the delta (delta) FHR to delta PaO2 ratio during umbilical cord occlusions was less on day 4 than on day 1 (6.0 +/- 0.4 versus 10.9 +/- 1.5 beats per minute/mmHg; P < .01). During occlusion hours, high FHR variation episodes, as a measure of fetal activity, were reduced (14.6 +/- 1.5 versus 4.2 +/- 1.3 min/h; P < .01), whereas the reduction in short-term (7.4 +/- 0.7 to 5.8 +/- 0.6 milliseconds; P < .05) and long-term (34.9 +/- 2.7 to 30.0 +/- 0.6 milliseconds; P < .05) FHR variation reached significance only on day 4. CONCLUSION: The increase in lactate and reduced high-FHR variation episodes over successive umbilical cord occlusions may affect fetal growth and development. Furthermore, repeated umbilical cord occlusions over several days alter the preterm FHR response to subsequent stresses, suggesting an altered chemoreflex response.     

Effects of acute hypoxemia on fetal movement in the fetal lamb

Chronically instrumented pregnant models were established using 5 Dorset-Rambouillet pregnant ewes with gestational age between 120 and 138 days. Observation of fetal movements were started on the 3rd postoperative day or later when recovery from the surgery to the physiological condition was confirmed by maternal and fetal biophysical parameters. Fetal movements were observed using real-time ultrasound equipment with linear-array transducer placed on the maternal abdomen. Observation encompassed the control period which lasted one hour followed by an experimental period of fetal hypoxemia created by decreasing maternal FIO2. Observation was also continued during the recovery period when the mother was re-exposed to room air. Maternal and fetal samples were periodically obtained during these periods. Frequency of fetal movements was studied in 10 minute periods under the control and hypoxemic conditions. All fetuses exhibited movements during the control period, ranging 1-42 movements/10 minutes, the mean incidence being 16.9 movements/10 minutes. During fetal hypoxemia (average PaO2 decrease: 8.6 mmHg), fetal movements were significantly reduced to 5.5 movements/10 minutes with complete cessation in some cases. In 4 animals which exhibited complete cessation of both fetal movement (FM) and fetal breathing movement (FBM), FBM disappeared before FM, and reappearance of FM was following by FBM during recovery from hypoxemia.     

Effects of chronic hyperglycemia on electrocortical activity states in unanesthetized fetal lambs

Electrocortical activity (ECoG), tracheal pressure and nuchal muscle activity were recorded in utero in 8 chronically hyperglycemic and 10 control unanesthetized fetal lambs to investigate the effects of chronic hyperglycemia on fetal electrocortical activity states. The chronically hyperglycemic state, induced by alloxan administered to the ewes, existed for at least 40 days prior to the experiments. The mean duration of episodes of high voltage (HV) ECoG was significantly increased in the hyperglycemic group (mean +/- SD: 21.8 +/- 9.2 min) compared with the control group (14.8 +/- 3.3 min), but the incidence of low voltage (LV) ECoG was not different between the groups. ECoG power spectra were not different between the groups. During LV ECoG, the proportions of time with neck movements were significantly less in the hyperglycemic than in the control group. No difference in percentages of time with long neck muscle activity was seen during the HV state in both groups. The incidence of breathing movements was equal in both groups, during HV as well as LV ECoG. No differences in breathing interval were observed.     

Effect of hypoxia on the auditory system of goat fetuses during extrauterine incubation

AIM: To investigate the effect of hypoxia on the auditory system in fetuses, we attempted to analyze the auditory brainstem response, the middle latency response, and changes of several physiological parameters of goat fetuses during extrauterine incubation. METHODS: We conducted extrauterine incubation of five goat fetuses at around 127days of gestation (term = 148 days). Their physiological parameters, such as fetal heart rate, mean blood pressure, flow rate of carotid artery, as well as the auditory brainstem response and middle latency response, were recorded prior to and during hypoxia, and the two sets of data were compared with each other. RESULTS: In all five cases, the fetal heart rate decreased from 178 +/- 12.2 b.p.m. to 144 +/- 15.2 b.p.m. during hypoxia, while mean blood pressure and flow rate of carotid artery increased from 37.3 +/- 3.7 mmHg to 43.2 +/- 5.1 mmHg, and from 38.5 +/- 5.5mL/min to 47.0 +/- 5.1 mL/min, respectively. The latency of the auditory brainstem response's wave V and of the middle latency response's Pa wave elongated from 5.24 +/- 0.24 ms to 5.69 +/- 0.20 ms, and from 19.2 +/- 1.6 ms to 20.9 +/- 1.4 ms, respectively. CONCLUSIONS: Although fetal compensatory reactions, such as increases in mean blood pressure and flow rate of carotid artery during hypoxia were recognized, elongation of latency, and decrement of amplitude were observed in the auditory brainstem response and middle latency response. These results suggest that hypoxia itself influences the auditory system of the fetus.     

Fetal responses to maternal infusions of angiotensin II

It is unclear whether the fetus is affected by maternal infusions of angiotensin II; therefore we studied maternal and fetal responses (n = 9) to angiotensin II (1.15, 2.29, 11.5 micrograms/min) infused 5 minutes into the vena cava of chronically instrumented sheep (129 to 137 days of gestation) while monitoring PO2, PCO2, pH, heart rate, uterine blood flow, and arterial and umbilical venous pressures. Pregnant sheep demonstrated expected dose-related increases in mean arterial pressure and decreases in uterine blood flow (p less than 0.05). Increases in fetal mean arterial pressure also correlated with the maternal dose of angiotensin II (r = 0.77, p less than 0.001). Fetal heart rate appeared to increase with 2.29 micrograms/min; however, bradycardia was observed with 11.5 micrograms/min (p less than 0.05) and was associated with decreased PaO2, 19.0 +/- 1.0 to 14.3 +/- 1.4 mm Hg (p less than 0.05), increased PaO2 (p less than 0.05), and decreased umbilical venous PO2, 31.4 +/- 2.3 to 27.0 +/- 1.9 mm Hg. The decreases in PO2 correlated with decreases in uterine blood flow (r = 0.60, p less than 0.002, and r = 0.75, p less than 0.005, respectively). Nevertheless, changes in fetal mean arterial pressure also occurred in the absence of altered fetal oxygenation; thus decreased uterine blood flow and fetal oxygenation alone cannot explain the fetal cardiovascular responses. It is suggested that angiotensin II or an active metabolite may cross the ovine placenta.     

Regulation of transplacental water transfer: the role of fetoplacental venous tone

We used the in vitro dually perfused human placental lobule to test the hypothesis that known vasoconstrictors of the fetal placental circulation, angiotensin II and the thromboxane mimetic U46619 could induce fetomaternal water transfer. Secondly, we used a combination of vasoconstrictor and mechanically induced increases in fetal placental circulatory pressure to examine the role of the venous system in this context. Fetal-side administration of angiotensin II (A-II) and U46619 (n=6 and n=9, for A-II and U46619, respectively) induced dose dependent, recoverable elevations in fetal inflow hydrostatic pressure (HP; A-II: maximum contractility=83 mmHg, EC50=22.0 nM; U46619: maximum contractility was not achieved, but exceeded the A-II effect) and loss of perfusate from the fetal side (A-II: EC50=70.2 nM, maximum fetal-side solvent loss=1906 microl/min; U46619: maximum fetal-side solvent loss was not achieved, but exceeded the A-II effect). Fetal-side solvent loss, for both agonists, was correlated linearly with fetomaternal inflow HP (FMIHP) in a biphasic manner (between 0 and 30 mmHg the slopes (+/-S.E.) were 6.4+/-2.2 and 17.1+/-5.8 microl/(min mmHg) for A-II and U46619, respectively; between 30 and 70 mmHg the slopes (+/-S.E.) were 35.6+/-6.5 and 43.7+/-15.9 microl/(min mmHg) for A-II and U46619, respectively). Increasing fetal-side lumenal pressure (n=3) by raising the fetal outflow catheter caused a loss of perfusate from the fetal side which was reduced in the presence of U46619 (fetal solvent loss per unit increase in fetal-side inflow HP: slopes were 1.198+/-0.123 and 0.783+/-0.085 microl/(min mmHg mmHg), respectively). Notwithstanding the possibility of fetoplacental arterial constriction, we conclude that vasoconstrictive agonists in the fetoplacental circulation affect venous resistance, causing fetomaternal fluid loss. These observations could be relevant to the oligohydramnios associated with intrauterine growth restriction, a condition associated with increased resistance in the umbilical circulation.     

Effects of narcotic drugs on fetal behavioral activity: acute methadone exposure

The effects of acute methadone exposure on fetal behavioral activity were investigated in 10 unanesthetized fetal lamb preparations. Fetal behavioral activity was interpreted indirectly from the electrocorticogram (ECoG), electromyogram, electrooculogram, blood pressure, heart rate (FHR), and breathing movements (FBMs) of the fetus. Methadone infusion to the mother (5 micrograms/kg/min) resulted in a suppression of all synchronized ECoG activity, and an increase in FBM, FHR, eye movements, nuchal tone, and body movements. Similar effects were observed when 10% of the dose was given directly to the fetus. These results demonstrate that methadone acts directly om the fetus to suppress both quiet sleep and rapid eye movement sleep and results in a "hyperactive" state that has previously been shown to be associated with a 20% increase in fetal oxygen consumption.     

The influence of oxygen administration to the mother during labor on the fetal transcutaneously measured carbon-dioxide partial pressure

The aim of this study was to plot the course of the transcutaneously measured PCO2 (tcPCO2) in the fetus during oxygenation of the mother. In our examination 35 parturients with a suspicious or pathologic CTG were given pure oxygen for 10 minutes at a flow speed of 10 l/min. The fetal tcPCO2 was measured with a TCM 3 measuring device from Radiometer. The measuring temperature was 41 degrees C. The fetal tcPCO2 was 67.2 +/- 3.9 mmHg before the O2 application, during the O2 application it was 67.3 +/- 14.1 mmHg and for the period after the O2 application we found an average measurement of 66.7 +/- 13.9 mmHg. Further we investigated whether, depending on the original levels of the fetal tcPCO2 an O2 application to the mother had a measurable effect on the fetal tcPCO2 levels. The average levels of the tcPCO2 in the fetuses with pathological original levels of greater than or equal to 60 mmHg or with normal levels of less than 60 mmHg did not show any significant differences before, during or after the O2 application. Our own results and reports given in the literature about an increase in the fetal O2 partial pressure during maternal oxygenation lead to the conclusion that in cases with fetal hypoxia, the O2 application to the mother--in addition to other measures for intrauterine reanimation or speedy termination of labor--could be of advantage.     

Increased urinary flow without development of polyhydramnios in response to prolonged hypoxia in the ovine fetus

OBJECTIVE: In the ovine fetus subjected to 24 hours of hypoxia, urinary flow is normal within a few hours from the onset of hypoxia and there is a maintained inhibition of swallowing. We hypothesized that 4 days of fetal hypoxia would lead to polyhydramnios. STUDY DESIGN: Five late-gestation fetal sheep were subjected to hypoxia for 4 days and 7 other late-gestation fetal sheep served as time control animals. Fetal hypoxia was produced on postsurgical days 5 through 9 by continuous intratracheal nitrogen insufflation to the ewe. On days 3, 5, 7, and 9 after surgery, amniotic fluid volume, fetal urinary flow rate, and the compositions of maternal and fetal blood, amniotic fluid, and fetal urine were measured. A 3-factor analysis of variance was used for statistical analysis. RESULTS: During the period of experimental hypoxia the mean (+/-SE) fetal PaO(2) was 16.0 +/- 0.6 mm Hg, versus 21.2 +/- 0.7 mm Hg in control sheep (P <.001). Fetal hypoxia was associated with increased urinary flow on days 7 and 9, averaging 1410 +/- 310 and 2101 +/- 345 mL/d, respectively, versus 585 +/- 92 and 699 +/- 78 mL/d, respectively, in control animals (P <.001). Amniotic fluid volume was unchanged with time and averaged 960 +/- 159 mL in hypoxic fetuses on postsurgical days 7 through 9 and 851 +/- 130 mL in control animals (P =.60). Fetal blood lactate increased in the hypoxic animals, averaging 3.4 +/- 2.1 mmol/L versus 1.6 +/- 0.3 mmol/L in control animals (P =.02). Fetal urinary excretions of sodium, potassium, chloride, and lactate increased significantly during hypoxia, by 170% to 400%. CONCLUSION: Four days of nitrogen-induced hypoxia in the ovine fetus resulted in excess fetal urinary flow approximating 1000 mL/d greater than normal without the development of polyhydramnios. Because amniotic fluid volume did not change and hypoxia is a known inhibitor of fetal swallowing, we speculate that intramembranous absorption of amniotic water, electrolytes, and lactate increased.     

The influence of beta-adrenergic activity on fetal heart rate and the umbilical circulation during hypoxia in fetal sheep

To determine the importance of beta-adrenergic activity during hypoxia in the fetus, 13 studies were carried out on seven chronically instrumented sheep at nine tenths of gestation. Hypoxia was induced by having the mother breathe gas mixtures that resulted in a reduction of maternal arterial oxygen tension to 32 mm Hg. Hypoxia resulted in a decrease in fetal heart rate (165 +/- 17 to 140 +/- 28 bpm) and fetal oxygen consumption (5.9 +/- 1.3 to 3.0 +/- 1.5 ml/min/kg) and increases in fetal arterial and umbilical venous pressures. There was no change in umbilical blood flow (209 +/- 58 ml/min/kg). Propranolol, 1.1 ml/kg, was rapidly infused into a fetal vein to achieve complete beta-adrenergic blockade. Umbilical vascular resistance increased significantly, fetal heart rate decreased to 112 +/- 22 bpm, and umbilical blood flow decreased to 165 +/- 73 ml/min/kg. There was no further decrease in fetal oxygen consumption. These decreases are approximately twice those seen after propranolol without hypoxia. These findings suggest that during hypoxia there is an increase in beta-adrenergic activity, which tends to maintain fetal heart rate and umbilical blood flow. This activity counteracts the increase in vagal activity with hypoxia, which decreases heart rate.     

Fetal heart rate overshoot during repeated umbilical cord occlusion in sheep

OBJECTIVE: To assess the clinical utility of overshoot fetal heart rate (FHR) decelerations by examining their occurrence after umbilical cord occlusions of varying frequency and length in near-term fetal sheep. METHODS: Fetuses were allocated to the following three groups: 1-minute umbilical cord occlusion repeated every 5 minutes (1:5 group, n = 8) or every 2.5 minutes (1:2.5 group, n = 8) or 2-minute occlusions repeated every 5 minutes (2:5 group, n = 4). Occlusions were continued for 4 hours or until fetal mean arterial pressure decreased below 20 mmHg during two successive occlusions. RESULTS: In the 1:5 group, fetuses tolerated 4 hours of occlusion without hypotension or clinically significant acidosis and overshoot never occurred. In the 2:5 group, fetuses rapidly became hypotensive and acidotic, and occlusions were terminated at 116.3 +/- 22.9 min (mean +/- standard deviation). Overshoot was seen after every occlusion, starting with the first occlusion. In the 1:2.5 group, fetuses became progressively acidotic and hypotensive and occlusions were stopped at 183.1 +/- 42.8 min. Overshoot occurred after 91.6 +/- 42.5 minutes, at a pH of 7.17 +/- 0.06, base deficit 9.3 +/- 4.5 mmol/L. After the appearance of overshoot there was a more rapid decrease in fetal mean arterial pressure (0.25 [0.21, 0.35, 25-75th percentile] mmHg/minute versus 0.11 [0.03, 0.15] mmHg/minute before overshoot appeared, P <.01). CONCLUSION: These data suggest that overshoot is related to longer (2-minute) occlusions or to developing fetal acidosis and hypotension during 1-minute occlusions. This pattern could have clinical utility, as 1-minute contractions are typical of active labor.     

Relationship between the duration of fetal breathing movements and gestational age and the development of the central nervous system at 25-32 weeks of gestation in normal pregnancy

In 15 pregnant women with normal pregnancy at 25-32 weeks of gestation, fetal breathing movements (FBM), fetal body movements and fetal heart rate were continuously and simultaneously recorded over a total period of 180 min. The frequency of successive FBM with a duration less than 10 s (apnea period greater than 3 s) showed a significant decrease (p less than 0.01), while the frequency of successive FBM with a duration greater than or equal to 30 s showed a significant increase from 25 to 32 weeks of gestation (p less than 0.001). Strong positive correlations were also demonstrated between the frequency of FBM with a duration of greater than or equal to 30 s and the number of fetal heart rate accelerations per hour, acceleration/fetal body movement ratio, and the value of fetal heart rate long-term variability. These results suggest that the length of the duration of successive FBM represents a useful parameter for the analysis of fetal respiratory patterns, and that a prolongation of the duration of successive FBM of an individual fetus is related to the functional development of the central nervous system.     

Modification of maternal and fetal oxygenation with the use of tracheal gas infusion

A new technique is described for producing changes in fetal blood gases in the chronically instrumented pregnant sheep. Gas mixtures were infused directly into the maternal trachea. Maternal and fetal carotid arterial blood gases and pH were measured. Air infusion at 16 L X min-1 produced no change. Oxygen infusion caused significant increases in maternal PaO2 at 2 L X min-1 and in fetal PaO2 at 4 L X min-1. Nitrogen infusion significantly decreased maternal anf fetal PaO2 at 4 L X min-1. During 4 L X min-1 oxygen infusion, maternal PaO2 rose rapidly to plateau at 314 +/- 47 mm Hg at 4 minutes and fetal PaO2 rose to plateau at 28.7 +/- 2.8 mm Hg after 7 to 8 minutes. Maternal PaO2 fell to 56.4 +/- 4.3 mm Hg during nitrogen infusion (4 L X min-1) while fetal PaO2 fell to 15.9 +/- 1.8 mm Hg. Continuous infusion for 5- to 6-hour periods produced a consistent rise in maternal PaO2 during oxygen infusion and a consistent decrease during nitrogen infusion. Tracheal infusion of gases can be used to change maternal and fetal PaO2 rapidly and predictably.     

Intrapartum fetal activity

Fetal activity throughout pregnancy has been thoroughly studied. Relatively little informations regarding intrapartum fetal activity is available. Richardson et al. [8] found no fetal respiratory movements. While Boylan et al. [2] and Whittman et al. [12] reported decreased fetal breathing movements in active labor. This study was undertaken to evaluate the normal pattern of fetal activity in labor. Fetal movements (FM) and fetal breathing movements (FBM) were monitored by realtime ultrasound during active labor at term. The incidence of FM and FBM were measured in 18 fetuses. Results were correlated with simultaneous fetal heart rate (FHR) changes, postpartum cord blood pH and Apgar score. Recordings were made for one hour on every patient. The mean percentage incidence (PI) of FM was 19.5 per cent (range: 10.1-28.6 percent) and FBM was 8.5 per cent (range: 0-27 percent). All FM were associated with FHR accelerations, stronger movements were associated with higher FHR accelerations. No FHR accelerations were observed with FBM alone, unless accompanied by fetal movement. The lowest PI of total fetal activity (TFA, i.e. FM plus FBM) was 12.1 per cent. Movements decreased as labor progressed, while FBM remained unaltered. All newborns had cord venous blood pH of greater than 7.25 and Apgar scores of greater than or equal to 7, at five minutes. Our data suggest that in the normal uncompromised fetus, FM and FBM continue during labor at term. However, while FM tends to decrease as labor progresses. FBM tends to be constant throughout labor. This finding might indicate the autonomous nature of FBM.(ABSTRACT TRUNCATED AT 250 WORDS)     

Maternal hypoxemia and fetal breathing movements.

Fetal breathing movements (FBM) were observed daily using a real-time B-mode ultrasound method in a patient with sickle cell anemia in crisis. Observations were made on 2 occasions in the presence of maternal hypoxemia (PO2 less than or equal to 40 mmHg), and FBM were noted to be absent. Conversely, when maternal PO2 was 60 mmHg or greater, FBM were present 23--80% of the time. The FBM were reduced or absent within 90 minutes of maternal Demerol injection. These observations suggest that the human fetal response to hypoxemia may be similar to that observed under expermental conditions in the animal fetus.     

The effects of veno-venous extracorporeal membrane oxygenation on hypoxic fetal lambs.

OBJECTIVE: The purpose of this study was to determine the applicability of veno-venous extracorporeal membrane oxygenation (V-V ECMO) to support fetal oxygenation in utero. METHODS: An ECMO system with a centrifugal pump was applied to ten chronically instrumented fetal lambs, at 126 or 127 days of gestation. Blood was obtained through a double-lumen catheter inserted into the right atrium. After oxygenation, the blood was returned through a single-lumen catheter into either the carotid artery (veno-arterial; V-A ECMO) or the right atrium (V-V ECMO). After fetal hypoxia had been experimentally produced, V-A ECMO or V-V ECMO was instituted to maintain fetal oxygenation. We compared fetal blood gases with both routes of ECMO. RESULTS: Oxygen partial pressure (pO(2)) in the fetal cranial carotid artery decreased to 12.9 +/- 0.6 mmHg after reducing the fraction inspiratory oxygen of the mother. After instituting V-A ECMO, pO(2) was found to be 23.5 +/- 2.6 mmHg; after instituting V-V ECMO, pO(2) was found to be 20.3 +/- 1.9 mmHg. Thus, fetal acidosis increased under both procedures. Fetal heart rate and blood pressure were not altered significantly during the experiments. CONCLUSIONS: This study indicates that V-V ECMO could more effectively and less traumatically maintain oxygenation in hypoxic fetal lambs.