Cardiovascular effects of fever in the ewe and fetal lamb.

Ewes carrying fetuses with permanently implanted cannulas developed fevers following intravenous injections of bacterial pyrogen (1 microng). During the rising phase of the fever, maternal heart rate increased, but no consistent changes in mean arterial blood pressure (MABP), arterial pH, PO2, or PCO2 were observed during the course of the fever. Fetal temperature, which was initially 0.3 to 0.8 degrees C. higher than maternal temperature rose in parallel with the ewe's temperature. During the maternal fever, fetal MABP, pH, PO2, and PCO2 remained unchanged, but on several occasions the fetal heart rate developed irregularities that persisted after the fever had subsided. These observations suggest that maternal fever does not appear to have adverse effects on fetal oxygenation but has a variable effect on cardiovascular function.     

Insulin-induced hypoglycemia in pregnant diabetics. Maternal and fetal cardiovascular reactions

Insulin (0.1 IU/kg bw) was injected intravenously in 9 pregnant diabetics in the last trimester of pregnancy. Maternal levels of blood glucose, estriol, human placental lactogen, blood pressure and pulse rate were measured and fetal heart rate (FHR) recorded. During hypoglycemia maternal blood pressure remained unchanged but maternal pulse rate tended to increase. Plasma levels of estriol and HPL remained unchanged. In 6 of the 9 patients there was a decrease in FHR variability during the hypoglycemic period. FHR variability increased after normalization of maternal blood glucose levels. The decrease in FHR variability could be a direct effect of glucopenia on the fetal heart.     

Effects of ethanol on the circulation and acid-base balance of pregnant sheep

Nine infusions of 15 cc/kg/120 min of 9.5% ethanol were administered to 4 chronically catheterized ewes, at 109-135 days' gestation. Stabilization periods ranged from 6 to 28 days postoperatively. Maternal and fetal concentrations of ethanol were almost identical (r = 0.9925), with peak levels of 122 +/- 20 mg/100 ml (mean +/- 1 SE) and 121 +/- 19 mg/100 ml, respectively, at the end of infusion. Maternal pH decreased from 7.50 +/- 0.02 to 7.44 +/- 0.02 (P less than 0.005) at 120 minutes. Maternal glycemia increased from 76 +/- 14 mg/100 ml to 162 +/- 23 mg/100 ml (P less than 0.005) at 120 minutes. Maternal heart rate, blood pressure, PO2, O2 content, PCO2, and bicarbonate remained unchanged. Fetal PO2 increased during and following infusion from 18.9 +/- 0.9 mmHg to 22.0 +/- 1.0 mmHg (P less than 0.005) at 180 minutes. Fetal blood pressure increased from 51.3 +/- 3.1 mmHg to 53.7 +/- 3.3 mmHg (P less than 0.01) at 30 minutes. Fetal pH, PCO2, glucose, and lactate levels remained unchanged. The authors conclude that ethanol crosses the sheep placenta readily, causes maternal acidosis and hyperglycemia, and increases fetal PO2, blood pressure, and heart rate without any effects on fetal acid-base status.     

Influence of maternal hyperoxia or hypercarbia on the hemodynamics of the placenta and fetal brain

Pregnant rabbits were subjected to inhalation of different gases, and the changes in placental blood flow (PBF), fetal heart rate (HR), and fetal cerebral blood flow (CBF) associated with the changes in maternal blood gas levels were studied. The results are given below. In maternal hyperoxia, maternal blood pressure (BP) was not much influenced and PBF remained unchanged or was slightly decreased when the PCO2 level was not varied or when it was lowered. In contrast, not only maternal BP but also PBF was increased when the PCO2 level was elevated. In the absence of a conspicuous increase in PCO2, neither fetal HR nor CBF varied, regardless of PBF. Both maternal BP and PBF were increased in mild to moderate maternal hypoxia (PO2 greater than 40 mmHg) and decreased in severe hypoxia (PO2 less than 30 mmHg). The decreasing trend of fetal HR or CBF was strengthened as maternal hypoxia was intensified. An obvious decrease in either parameter was observed in severe maternal hypoxia (PO2 less than 30 mmHg). Fetal HR and CBF were well maintained. in hypoxic dams with increased PBF as compared with those with unchanged or decreased PBF. The higher the PCO2 level or the lower the pH value, the more was fetal bradycardia that was apt to occur, even in a mildly hypoxic state.     

Effects of ritodrine hydrochloride on uterine activity and the cardiovascular system in toxemic patients.

The effects of ritodrine hydrochloride were evaluated in 25 toxemic patients in active labor utilizing continuous electronic monitoring of fetal and maternal cardiovascular systems and uterine activity. Fetal scalp blood and free flowing maternal antecubital venous blood was obtained for pH, Po2, Pco2, base deficit and blood glucose determinations prior to and immediately following the study period. The initial ritodrine dose was 50 mug/min for 15 minutes. The dose was increased by 50 mug/min each 15 minutes until there was a clinically apparent reduction in uterine activity. Once this was accomplished, the infusion was maintained for 30 minutes. There was a consistent increase in the maternal heart rate (MHR) and a significant rise in fetal heart rate (FHR) late in the infusion and in the postinfusion period. There was a widening of the maternal pulse pressure mainly due to a reduction in diastolic pressure with little change in the mean blood pressure. Maternal and fetal pH decreased and base deficit increased during the study although the PO2 and PCO2 remained unchanged. Maternal and fetal blood glucose rose significantly following ritodrine infusion.     

Effect of propranolol infusion on the umbilical and uterine circulations of pregnant sheep.

Propranolol was infused intravenously for 60 minutes to five ewes (4 mug per kilogram per minute) or five fetal sheep (10 mug per kilogram per minute). The umbilical blood flow was significantly decreased by 18 per cent from control at 60 minutes with either maternal or fetal propranolol infusion. Uterine blood flow and maternal and fetal mean arterial pressure did not significantly change. Maternal and fetal heart rates decreased 18 and 9 per cent from control, respectively, during maternal propranolol infusion. With propranolol to the fetus, fetal heart rate decreased 15 per cent and maternal heart rate did not change. During all infusion, maternal and fetal arterial pH, PCO2 and PO2 remained within normal physiologic limits.     

Acute effects of maternal smoking on human fetal heart function

M-mode echocardiography was used to evaluate fetal heart function following maternal smoking in 21 healthy smoking pregnant women between 24 and 39 weeks of uneventful gestation. Prior to smoking one cigarette (nicotine content 1.7 mg), a fetal M-mode echocardiographic examination was performed and repeated 5 and 10 min after maternal smoking. Maternal heart rate and systolic blood pressure increased 8.7% and 15.0%, respectively, immediately after smoking, while diastolic blood pressure remained unchanged. Fetal heart rate increased 4.3% and left ventricular diastolic and systolic diameters decreased 4.5% and 15.0%, respectively. No changes in right ventricular dimensions, ventricular ejection times, ventricular wall thickness or septal thickness were observed. Fractional shortening, mean velocity of fractional shortening, stroke volume and cardiac output of the left ventricle also remained unchanged subsequent to smoking. Thus, maternal smoking of one cigarette seems to elicit only a transitory acceleration in fetal heart rate without concomitant significant changes in fetal heart function.     

Umbilical cord pH, PCO2, and bicarbonate following uncomplicated term vaginal deliveries

Normal values for umbilical arterial and venous pH, PCO2, PO2, and bicarbonate must be known before these parameters can be used for assistance in clinical decisions. We evaluated the cord blood from 146 infants born after uncomplicated labor and vaginal deliveries at 37 to 42 weeks' gestation. All infants had a normal baseline fetal heart rate and normal beat-to-beat variability for at least 10 minutes preceding expulsion. The cord blood of infants born to women with pregnancy complications such as diabetes mellitus, preeclampsia, twins, meconium-stained amniotic fluid, or fetal growth retardation was not included. Mean umbilical arterial values +/- 1 SD for the parameters studied were: pH, 7.28 +/- 0.05; PCO2, 49.2 +/- 8.4 mm Hg; PO2, 18.0 +/- 6.2 mm Hg; bicarbonate, 22.3 +/- 2.5 mEq/L. Umbilical venous values were: pH, 7.35 +/- 0.05; PCO2, 38.2 +/- 5.6 mm Hg; PO2, 29.2 +/- 5.9 mm Hg; bicarbonate, 20.4 +/- 4.1 mEq/L.     

Effect of maternal exercise with graded treadmill on fetal heart rate]

The effect of maternal exercise on the fetal and maternal heart rate was studied in 10 normal pregnant women in their third trimester. They participated in 15 minute graded treadmill exercise. Fetal heart rate (FHR), uterine contraction, maternal blood pressure, electrocardiogram, and oxygen consumption were monitored, before, during, and after exercise. FHR could be monitored in 7 women. Maternal maximal heart rate ranged from 143 to 168 bpm which approximated 61% to 84% training intensity. FHR showed a significant rise in 4 women during exercise. Of four cases which showed more than 70% training intensity, 3 demonstrated fetal tachycardia over 160 bpm and one demonstrated fetal bradycardia under 120 bpm. The baseline fetal heart rate remained from 120 bpm to 160 bpm in cases under 70% training intensity. There was no pathological deceleration and the variability was preserved in all cases. It is suggested that maternal exercise intensity should be less than 70% of the patient's maximal capacity, which approximates maternal heart rate of about 150 bpm.     

Fetal heart rate and uterine contraction during automobile driving

OBJECTIVE: The purpose of this study was to clarify the influence of automobile driving in the third trimester of pregnancy on fetal heart rate and uterine contraction. METHODS: Twenty-nine pregnant women with singleton pregnancies after 28 weeks of gestation were monitored using a portable cardiotocogram during driving, and the results obtained before and after driving were compared. RESULTS: Baseline fetal heart rate and its variability, as well as periodic fetal heart rate patterns, showed no abnormal patterns during car driving. Automobile driving in late pregnancy was not a reinforcement factor for uterine activity. Maternal systolic and diastolic blood pressure and heart rate showed no specific characteristic or adverse change during driving. CONCLUSION: The results of this study suggest that automobile driving in the third trimester of pregnancy has no adverse influences on either pregnant women or fetuses.     

Redistribution of power spectrum of heart rate variability during acute umbilical artery embolism and hypoxemia in late-gestation fetal sheep

OBJECTS: Fetal heart rate variability (HRV) is subject to a number of factors, including fetal distress. The aim of this study was to investigate the power spectral distribution of fetal heart rate variability during acute hypoxemia following umbilical artery embolism and to test the hypothesis that the relative proportion of frequency domains in total power of HRV, reflects the changes in HRV during hypoxemia more closely than the absolute values. METHODS: Acute hypoxemia was induced in seven catheterized late-gestation fetal sheep by repeated injections of microspheres to cause umbilical artery embolism. The very-low, low-, middle- and high-frequency domains (0-0.025, 0.025-0.125, 0.125-0.20, and 0.20-0.50 cycles/beat, respectively) were determined by power spectral analysis. RESULTS: Umbilical artery embolism induced marked fetal hypoxemia, hypercapnia and acidosis, accompanied by an increase in heart rate and a decrease in arterial blood pressure. These changes were associated with the increase in power over the entire frequency range and in the relative power in the low-frequency range (P<0.01), and with decrease in the relative power in the high-frequency range (P<0.05). Correlations were found between the relative power in the low- and high-frequency ranges and PO2 and between the relative power in these ranges and mean arterial blood pressure (P<0.05), but not PCO2 or pH. CONCLUSIONS: The present study indicates that acute hypoxemia induced by umbilical artery embolism leads to the redistribution of power spectral density of fetal HRV and that the relative proportion of individual frequency domains may reflect the changes in HRV during acute hypoxemia more closely than the absolute power values.     

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia

The effect of beta-adrenergic stimulation on fetal cardiovascular function during hypoxemia was studied in six lamb fetuses with gestational ages of 119 to 140 days. In chronic preparations, we determined fetal heart rate, umbilical blood flow (by electromagnetic flowmeter), PO2, PCO2, and pH and calculated fetal cardiac output and organ blood flows (using 15 mu nuclide-labeled microspheres). Observations were made during control periods and periods of hypoxemia, beta-adrenergic blockade by propranolol, and hypoxemia superimposed upon the beta-adrenergic blockade. Beta blockade effected a decrease in fetal heart rate both at rest and with hypoxemic stress. Propranolol produced a fall in cardiac output with hypoxemia, but the meaning of this in regard to beta-adrenergic effects is unclear. Beta blockade did not alter fetal arterial pressure or general blood flow distribution. However, we observed a decrease in umbilical blood flow in response to propranolol under both normoxic and hypoxemic conditions.     

External vibratory acoustic stimulation near term: fetal heart rate and heart rate variability responses

Twenty-five pregnant women between 36 and 40 weeks' gestational age were studied to examine effects of a 5-second external vibratory acoustic stimulus on the fetal heart rate and fetal heart rate variability. There was an immediate significant increase in the basal heart rate, which persisted for 1 hour after the stimulus, compared to that of the control subjects. There was also a significant increase in the total time during which accelerations occurred for the first 20 minutes after the stimulus. There were no changes in computer-derived indices of fetal heart rate variability. Maternal blood pressure and heart rate were not altered following vibratory acoustic stimulus. We hypothesize that external vibratory acoustic stimulus causes a change from a state of sleep to a state of wakefulness in near term healthy fetuses.     

Effects of prenatal music stimulation on fetal cardiac state,newborn anthropometric measurements and vital signs of pregnant women: A randomized controlled trial

BackgroundMusic has been used for medicinal purposes throughout history due to its variety of physiological, psychological and social effects.ObjectiveTo identify the effects of prenatal music stimulation on the vital signs of pregnant women at full term, on the modification of fetal cardiac status during a fetal monitoring cardiotocograph, and on anthropometric measurements of newborns taken after birth.Material and methodA randomized controlled trial was implemented. The four hundred and nine pregnant women coming for routine prenatal care were randomized in the third trimester to receive either music (n = 204) or no music (n = 205) during a fetal monitoring cardiotocograph. All of the pregnant women were evaluated by measuring fetal cardiac status (basal fetal heart rate and fetal reactivity), vital signs before and after a fetal monitoring cardiotocograph (maternal heart rate and systolic and diastolic blood pressure), and anthropometric measurements of the newborns were taken after birth (weight, height, head circumference and chest circumference).ResultsThe strip charts showed a significantly increased basal fetal heart rate and higher fetal reactivity, with accelerations of fetal heart rate in pregnant women with music stimulation. After the fetal monitoring cardiotocograph, a statistically significant decrease in systolic blood pressure, diastolic blood pressure and heart rate in women receiving music stimulation was observed.ConclusionMusic can be used as a tool which improves the vital signs of pregnant women during the third trimester, and can influence the fetus by increasing fetal heart rate and fetal reactivity.     

Doppler flow measurement of uterine and umbilical arteries in heat stress during late pregnancy

The effect of a moderate heat stress (20 minutes 70 degrees C) on uterine and umbilical artery blood flow was studied by continuous-wave Doppler ultrasound in 17 women 36 to 37 weeks pregnant. Maternal heart rate increased on average by 26 beats/minute. Maternal arterial blood pressure did not change during the heat stress but declined slightly immediately after. The fetal heart rate increased on average by 14 beats/minute by the end of the exposure. The variability of fetal heart rate was normal in each subject during the whole experiment and only one subject had a nonreactive tracing during the heat stress, which returned to normal during the recovery period. The ratio of the systolic to diastolic velocity in the uterine artery did not change significantly. Only two subjects had a marked increase in uterine artery vascular resistance; they had concomitantly a significant fall in the arterial blood pressure. Still, there was no change in umbilical artery blood flow. The fetuses of healthy pregnant women are not compromised during or after moderate thermal stress.     

The oscillating 'vena cava syndrome' during quiet standing—an unexpected observation in late pregnancy

Summary. While studying the lung function of pregnant women at term in four different postures, we were surprised to note marked cyclic accelerations in the heart rate in two-thirds of the women when in a standing position. The mean cycle length was 105 s (range: 1–4 min) and the amplitude had a mean of 27 beats/min (range: 9–51). Blood flow velocity measurements with ultrasound Doppler over the femoral vein showed that there was an intermittent reduction of flow during quiet standing. When the venous return ceased, maternal heart rate increased, cardiac output decreased and blood pressure fell. After the venous blood flow was restored, maternal heart rate, cardiac output and blood pressure returned to normal until the cycle started again. Concomitant with these maternal heart rate changes, different patterns of fetal heart rate were observed. About 70% of the fetuses showed reduction in the long-term variability, increase in fetal heart rate or periodic accelerations. Although no woman fainted during quiet standing, the maternal circulatory changes were consistent with those seen in the classical vena cava syndrome.     

Effects of calcium entry blocker (nicardipine) tocolysis in rhesus macaques: fetal plasma concentrations and cardiorespiratory changes

Tocolytic doses of nicardipine, a dihydropyridine calcium entry blocker, were administered to chronically catheterized rhesus monkeys between days 128 and 132 of gestation. During periods of spontaneous uterine contractility, a 500 micrograms nicardipine bolus was injected intravenously, and this was followed by continuous infusion (6 micrograms/kg/min) to the mother for 1 hour. Uterine activity (amniotic fluid pressure) and maternal heart rate and blood pressure were monitored continuously. Paired maternal and fetal blood samples were drawn at frequent intervals to monitor pH, PO2, PCO2, and plasma nicardipine concentrations. Peak maternal nicardipine concentrations ranged from 175 to 865 ng/ml while peak fetal levels ranged from 7 to 35 ng/ml. Fetal heart rate and blood pressure were unaffected. However, fetuses became acidotic (pH 7.26 +/- 0.01 versus 7.33 +/- 0.01) and hypoxemic (PO2 16.0 +/- 3.2 versus 24.5 +/- 2.0 mm Hg) after maternal nicardipine treatment (p less than 0.01). Despite the fact that maternal nicardipine treatment exerted a significant tocolytic effect, the undesirable fetal side effects are of concern and deserve further investigation.     

Circulatory changes in the fetal aorta after maternal smoking

The acute cardiovascular responses of the human fetus to maternal smoking of one cigarette were studied in 10 healthy pregnant women. Following maternal smoking, a significant increase was found in the nicotine concentration in maternal plasma accompanied by a significant increase in the fetal heart rate. The flow velocity was recorded in the fetal descending aorta by combining real-time ultrasonography and the 2 MHz pulsed Doppler technique and the waveform of the maximum blood velocity was analysed. The duration of the acceleration part of the pulse cycle (start-to-peak time) remained unchanged during the study period. The least diastolic blood velocity increased significantly after smoking. The pulsatility index fell significantly during the first 5 min after smoking, probably as the consequence of fetal tachycardia, but was normal again at 10 min. The rising slope rose significantly within the first 10 to 20 min after the onset of smoking. The results indicate, that, following maternal smoking of one cigarette, fetal central circulation increases but peripheral resistance is unchanged.     

The effect of immersion on haemodynamic and fetal measures in uncomplicated pregnancies of nulliparous women

Objective To evaluate the effect of immersion in water on maternal haemodynamic measures and fetal heart rate patterns in healthy nulliparous women.
Design A randomised cross-over study.
Participants Twenty pregnant women were studied between 26–29 weeks and between 34–37 weeks of gestation.
Methods The women were either immersed in water for 35 minutes or rested on a bed for a similar period of time. Maternal blood pressure, thoracic electrical bioimpedance, urine and blood samples, and fetal heart rate patterns were obtained before and after immersion or bedrest.
Results Compared with bedrest and pre-immersion values, immersion resulted in a significant decrease in blood pressure, which returned to baseline values within 1.5 hour. Urine production increased for a short period after immersion, but 24 hour samples showed no difference compared with bedrest. Sodium, potassium and creatinine levels in urine remained constant. No significant changes were found for the other haemodynamic measures. There were no effects on fetal heart rate nor on its variation.
Conclusion In healthy pregnant women immersion for 35 minutes has a clear effect on blood pressure and urine production. However, these effects are short lasting.     

Effects of tocolytic treatment with ritodrine on cardiovascular autonomic regulation

Objective To study the acute effects of tocolytic treatment with intravenous ritodrine on cardiovascular autonomic regulation.
Design Validated methods to assess cardiovascular autonomic nervous function—heart rate and blood pressure variability and vagal cardiac baroreflex sensitivity—were measured before and during ritodrine infusion.
Setting Turku University Central Hospital, Turku, Finland.
Sample Twelve pregnant women admitted to hospital for threatened preterm labour.
Methods Electrocardiogram and continuous noninvasive finger blood pressure signals were recorded in each woman, resting in a supine position. Autoregressive spectrum analysis was used to quantify short term heart rate and blood pressure variability. Vagal cardiac baroreflex sensitivity was measured as the bradycardia response to an intravenous bolus injection of phenylephrine.
Main outcome measures Vagal cardiac baroreflex sensitivity and spectrum analysis indices of short term heart rate and blood pressure variability.
Results Ritodrine significantly decreased vagal cardiac baroreflex sensitivity as well as total (0.00–0.40 Hz), low frequency (0.04–0.15 Hz) and high frequency (0.15–4.40 Hz) power bands of the heart rate variability spectrum. Ritodrine significantly increased mean heart rate and the low frequency power band of the systolic blood pressure Variability spectrum.
Conclusions In pregnant women with threatened preterm labour intravenous administration of ritodrine decreases vagal cardiac baroreflex sensitivity and vagal modulation of heart rate, and increases sympathetically mediated blood pressure variability. Decreased baroreflex sensitivity and heart rate variability are known to be associated with a poor prognosis in some patient groups, so the effects of ritodrine tocolysis may be unfavourable in women with impaired circulatory homeostasis.