Gender does not affect fetal heart rate variation

There is a widespread but erroneous view among the lay public that there is a difference in the baseline fetal heart rate between male and female fetuses. It has been suggested that this perception might reflect an actual difference in fetal heart rate variability. Therefore, we studied the fetal heart rate variation in 79 white European women using the Sonicaid System 8002 computer. Fourty-four of the fetuses were male and 35 were female. There was no significant gender difference in any measured aspect of fetal heart rate variation.     

The effect of carotid sinus denervation on fetal heart rate variation in normoxia, hypoxia and post-hypoxia in fetal sheep

Objective To investigate whether carotid sinus nerve reflexes are linked to the increase in heart rate variation in acute (one hour) hypoxia in late gestation fetal sheep
Design Comparison of short term variation between intact and carotid sinus denervated fetuses in normoxia, hypoxia and post-hypoxia.
Subjects Sixteen chronically catheterised pregnant sheep in late gestation.
Results There was no significant difference in short term variation between intact and denervated fetuses in normoxia. In intact fetuses short term variation increased significantly in hypoxia. In denervated fetuses it tended to increase in hypoxia, but this was not statistically significant. During the post-hypoxia period, short term variation increased significantly in denervated fetuses, although at this time it was decreasing in intact fetuses. When the decrease in pH was small intact fetuses showed a significantly greater increase in short term variation than denervated fetuses in hypoxia. In contrast, short term variation increased similarly in both groups when the pH decrease was greater (> 0.03 in early hypoxia and > 0.05 in late hypoxia).
Conclusions Carotid sinus nerve reflexes have an important influence on heart rate variation in hypoxia and post-hypoxia. It appears that other mechanisms (e.g. a rise in circulating catecholamines) are linked to an increase in heart rate variation when mild acidemia occurs in hypoxia.     

Presence of a single fetal major anomaly in a twin pregnancy does not increase the preterm rate

OBJECTIVE: To evaluate whether the presence of one major anomaly in a twin pregnancy would affect the perinatal outcome of the unaffected co-twin. MATERIALS AND METHODS: From 1992 May to July 2003, a total of 1400 twin pregnancies were included in the present study and there were 35 pairs of twins with one major anomaly. Major anomaly was defined as the anomaly that had a significant impact on neonatal morbidity and mortality. The perinatal outcomes of the affected and unaffected co-twins, the gestational age of diagnosis of the anomaly and the gestational age of delivery were the parameters for evaluation. RESULT: The incidence of a twin with one major anomaly was 2.5%. Nineteen of 35 (54.3%) affected twins and five of the 35 (14.3%) unaffected co-twins suffered a perinatal death. In the five cases of unaffected co-twins suffering a perinatal death, four were intrauterine fetal deaths and one was a neonatal death. Three of the perinatal deaths of the unaffected co-twins could be attributed to twin-to-twin transfusion syndrome. The gestational age at delivery, the perinatal mortality rate, and the incidence of low 5 min Apgar scores of the unaffected co-twins were not different from those in twin pregnancies without a major anomaly. CONCLUSION: The perinatal outcomes of the unaffected co-twin were not affected by the fact that its counterpart had one major anomaly, nor were these twin pregnancies at increased risk of preterm labour.     

Fetal heart rate variability changes during brief repeated umbilical cord occlusion in near term fetal sheep.

OBJECTIVE: To determine whether changes in fetal heart rate variation during repeated umbilical cord occlusions reflect evolving cardiovascular compromise in near term fetal sheep. DESIGN: Fetal heart rate variation, fetal mean arterial pressure, electroencephalogram (EEG) and acid-base status were measured during one minute umbilical cord occlusions, repeated either every five minutes (1:5 group) or every 2.5 minutes (1:2.5 group) for four hours or until mean arterial pressure fell below 20 mmHg for two successive occlusions. SAMPLE: Fourteen chronically instrumented fetal sheep, mean gestation 126.3 (2.6) days. RESULTS: Cord occlusion caused variable decelerations with initial sustained hypertension. In the 1:5 occlusion group mean arterial pressure remained elevated throughout, with little change in acid-base status (pH = 7.34 (0.07), base deficit = 1.3 (3.9) after 4 hours) and no significant change in fetal heart rate variation. In contrast, in the 1:2.5 group from the third occlusion there was progressive hypotension during occlusions, severe progressive metabolic acidaemia (pH 6.92 (0.1), base deficit 17.0 mmol/L (4.7) after the last occlusion) and marked EEG suppression (P < 0.01). Fetal heart rate variation increased with the onset of occlusions (P < 0.05) and then progressively fell with continued occlusions. During the last 30 minutes of occlusions, fetal heart rate variation was severely suppressed in four, but increased in two fetuses, while all six fetuses developed overshoot-instability of fetal heart rate and mean arterial pressure following each occlusion. CONCLUSIONS: Acute progressive asphyxia was typically associated with an immediate, transient increase in fetal heart rate variation. Subsequently variation became suppressed in only two-thirds of fetuses during terminal acidaemia and hypotension. Fetal heart rate overshoot-instability may be a useful marker of fetal decompensation following variable decelerations.     

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.     

Vibro-acoustic stimulation does not alter the duration of high and low fetal heart rate variability episodes.

To study the effect of vibro-acoustic stimulation on high and low fetal heart rate (FHR) variability episodes. Prospective control study, in 21 high risk pregnancies between 32 to 39 weeks gestation. FHR pattern was recorded with cardiotocograph (CTG). After 5 min low FHR variability a vibro-acoustic stimulator was activated in contact with or above the maternal abdomen (sham) on a random basis on two consecutive days, and CTG was continued to obtain a complete high and low FHR variability cycle. Complete high and low FHR variability cycles were obtained in 12 patients with mean recording time of 129.5 minutes (range 69-185 min). The mean baseline FHR increased by 32.5 +/- 9.4 bpm after contact vibro-acoustic stimulation, but remained unchanged after sham stimulation. Mean duration of high FHR variability was 56.6 +/- 32.9 min and 47.3 +/- 23.7 min, respectively, and mean duration of the consecutive low FHR variability episode was similar after contact and sham stimulation. The complete cycles were 71.1 +/- 34.7 min and 66.2 +/- 21.2 min, respectively. Vibro-acoustic stimulation induced an abrupt change from low to high FHR variability, but the complete cycle of high and low FHR variability was not altered, when compared with the corresponding cycle following sham stimulation on the same fetus.     

Increased fetal heart rate variability with acute hypoxia in chronically instrumented sheep

Fetal heart rate (FHR) and oxygen consumption were determined in 45 studies in 20 chronically instrumented, normoxic sheep. FHR variability was measured by a template device to determine amplitude range, and oscillatory frequency was manually counted over 5-min periods. During 26 min of isocapnic hypoxia, fetal O₂ consumption decreased 39% and FHR decreased 18%, and FHR variability increased, the changes being maintained over the treatment period. It is suggested that the maintenance of FHR variability during this profound hypoxia denotes adequate cardiorespiratory compensatory mechanisms during the short period; prolongation of the hypoxia would probably result in fetal cerebral or myocardial decompensation, and disappearance of FHR variability. The increased variability may be due to increased α-adrenergic activity.     

Mimicking low amniotic pressure by chronic pharyngeal drainage does not impair lung development in fetal sheep.

OBJECTIVE: The etiology of oligohydramnios-related pulmonary hypoplasia is not understood but is known to involve chronic lung liquid loss. We tested the hypothesis that low amniotic pressure in oligohydramnios disturbs the normal tracheal-amniotic pressure gradient to increase lung liquid loss and impair lung development. STUDY DESIGN: Chronic pharyngeal catheterization with drainage to the exterior was used in 15 fetal sheep to mimic reduced amniotic pressure at the upper airway in the presence of normal amniotic fluid volume. RESULTS: Pharyngeal pressures relative to amniotic pressures were negative in all drained fetuses (mean +/- SE -3.0 +/- 0.6 mm Hg), in contrast to positive pressures in controls (0.7 +/- 0.1 mm Hg). There was no significant difference in lung weight or deoxyribonucleic acid relative to body weight, or in lung morphometry, between 10 fetuses drained for 10 to 21 days and their control cotwins. CONCLUSION: Mimicking low amniotic pressure in the upper airway by chronic fetal pharyngeal drainage does not impair lung development in fetal sheep.     

Effect of prolonged hypoxemia on fetal heart rate accelerations and decelerations in sheep

Experiments were conducted in 10 chronically catheterized fetal sheep to determine the effect of 24 hours of hypoxemia in the absence of progressive acidemia on fetal heart rate accelerations and decelerations. Fetal hypoxemia was produced by mechanically restricting uterine blood flow with a vascular clamp placed around the maternal common internal iliac artery. Fetal arterial oxygen tension decreased from 22.3 +/- 1.8 to 17.8 +/- 1.5 mm Hg at 2 hours and remained low for the 24-hour experimental period. Fetal pH decreased from 7.34 +/- 0.01 to 7.20 +/- 0.05 at 2 hours and returned to normal values by 12 hours. No significant change was observed in the number or characteristics of fetal heart rate accelerations or decelerations during the 24-hour control period. There was a significant increase in the number of accelerations from 48 +/- 4 to 63 +/- 4 per hour at 8 hours of hypoxemia followed by a return to control values by 12 hours. There was no significant change in the mean amplitude or duration of accelerations. There was a significant increase in the number of decelerations per hour with an associated increase in the mean amplitude but a decrease in the mean duration of decelerations during the first 16 hours of hypoxemia. We conclude that prolonged hypoxemia in fetal sheep leads to an initial increase in the number of both accelerations and decelerations in fetal heart rate followed by a return to normal patterns indistinguishable from those of the normoexemic fetus.     

Acute hypoxemia does not affect the umbilical artery flow velocity waveform in fetal sheep

The present study in sheep was undertaken to test whether acute fetal hypoxemia causes abnormalities in the umbilical artery velocity waveform. A 1-hour period of hypoxemia was induced in six chronically catheterized fetal sheep by reducing the inspired oxygen content of the ewe. During hypoxemia, the ratio of the systolic to diastolic velocity did not change significantly compared with controls. From this experimental evidence, we conclude that normal Doppler waveforms in the umbilical artery do not necessarily imply fetal normoxemia in sheep and that, because a direct cause-effect relationship has not been established, fetuses that have abnormal waveforms are not necessarily hypoxemic. Whether this is also true in humans remains to be shown.     

Antepartum fetal evaluation by assessment of fetal heart rate and fetal movements

Three antenatal monitoring tests--fetal movement acceleration test (FMAC-test), fetal heart rate-nonstress test (FHR-NST), and daily fetal movement recording (DFMR) were evaluated in 212 high risk pregnant women. While in 196 cases all three tests were normal, in 16 patients one to three tests showed pathological results. In the latter group, there was a significantly higher incidence of perinatal mortality, low Apgar score and growth retardation. Since false positives are known to occur in these tests, at least two should be pathological to warrant delivery in am attempt to prevent fetal death in utero. The sequence in which the pathology appears in the deteriorating fetus is as follows: the first to become non-reactive is the FMAC-test, followed by decreased fetal movements till cessation, and, finally, severe changes in the FHR-NST take place. The importance of this sequence of events is discussed.     

Preoperative hair removal with clippers does not increase infection rate in clean surgical wounds

For a one year period, hair was removed from the operative site with clippers rather than by shaving with a razor or by application of depilatories. The study involved comparison of clean (Class I) wound infection rates in 2,580 patients after clipping was instituted compared with 17,424 patients studied in seven preceding years. There was no significant change in the wound infection rate (1 per cent) when compared with the three years immediately preceding. There was no change in the identified distribution of the infecting organism. Failure to show a clear reduction in wound infection rate was probably related to the low historic base line rate. There were definite benefits achieved by avoiding cancellation of elective operations, by using operating room personnel more efficiently and by expediating the surgical schedule.     

Vasopressin-induced bradycardia in fetal and adult sheep is not dependent on an increase in blood pressure

Other investigators have reported that intravenous infusion of synthetic arginine vasopressin into fetal lambs increases mean arterial pressure and decreases heart rate. To determine if the bradycardia produced by arginine vasopressin is a reflex response to the increase in blood pressure, we studied the effect of arginine vasopressin infusion on heart rate with and without blocking the increase in blood pressure. We performed 34 experiments in 12 chronically cannulated fetal lambs between 103 and 137 days' gestation. All animals had normal blood gas and pH values. Infusion of arginine vasopressin increased mean arterial pressure 10.1 +/- 1.1 mm Hg and decreased heart rate 50 +/- 8 bpm. Fetal heart rate decreased similarly when arginine vasopressin was infused and the hypertensive response was blocked with nitroprusside or a selective vasoconstrictor antagonist. [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid) 2-(O-methyl)tyrosine] arginine vasopressin. For comparison we also studied five adult nonpregnant ewes. Bradycardia was observed in the adults after infusion of arginine vasopressin alone and when the hypertensive response was blocked with the vasoconstrictor antagonist. We conclude that arginine vasopressin infusion causes a fall in heart rate independent of any increase in blood pressure in both the fetal lamb and the adult sheep.     

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 variability and cerebral oxygen consumption in fetal sheep during asphyxia.

This study was designed to examine the relationship between fetal heart rate variability and fetal cerebral oxygen uptake. Fetal sheep were chronically prepared with catheters and electrodes to determine cerebral blood flow (microsphere method), cerebral arteriovenous oxygen difference, and the electrocardiogram. An adjustable occluder was placed on the maternal common internal iliac artery to induce fetal asphyxia by reducing uterine blood flow. Fetal heart rate variability tended to decrease in the first 11 min of asphyxia, when cerebral oxygen consumption was approximately 53% of control. Despite stable cerebral oxygen consumption and worsening metabolic acidosis, however, fetal heart rate variability progressively returned towards normal by 36 min. There was no relationship between the depression of FHR variability and the degree of reduction of cerebral oxygen consumption. Nor was there any relationship between an alteration in regional cerebral blood flow or myocardial blood flow and the return of FHR variability with increasing duration of asphyxia. We conclude that there is an association between loss of fetal heart rate variability and reduced cerebral oxygen consumption, but the reduced variability does not persist with time at this degree of reduced cerebral metabolism in fetal sheep. This appears to be at variance with human clinical experience. Among the explanations for this may be insufficiently severe asphyxia, a species difference, removal of an inhibitor to FHR variability, or progressive use of other substrates for metabolism.     

Spectral analysis of fetal heart rate in sheep: the occurrence of respiratory sinus arrhythmia

Respiratory sinus arrhythmia is a pattern of rhythmic variation in the heart rate that occurs at the frequency of respiration and is mediated principally by the vagus nerve. Spectral analysis can decompose the variance of a series of sequential measures into constituent frequencies to measure and verify whether there is respiratory sinus arrhythmia in utero in the fetal lamb. Recordings of heart period were obtained from electrodes implanted under fetal skin in six chronic preparations. Respiratory rate and heart period were recorded immediately after delivery and daily for the next 5 days. Respiratory sinus arrhythmia was clearly demonstrated in the neonatal lambs, and the same frequency of respiratory sinus arrhythmia was observed in the fetus and in the newborn lamb (0.8 to 0.1 Hz). There was a reproducible pattern of change in respiratory sinus arrhythmia from 27 days before delivery until term, with a decline in the amplitude of respiratory sinus arrhythmia 4 to 8 days before delivery. We conclude that respiratory sinus arrhythmia was demonstrated in fetal sheep and may serve as an indicator of the integrity of the central nervous system in the fetus and the neonate.     

The slope of fetal heart rate deceleration is predictive of fetal condition during repeated umbilical cord compression in sheep

The relationship between components of fetal heart rate deceleration and fetal arterial blood gas values or plasma catecholamine concentrations was investigated by repeated complete umbilical cord compression in chronically instrumented fetal lamb. Fetal arterial pH and bicarbonate levels decreased, while plasma norepinephrine and epinephrine concentrations increased more than tenfold. The slope of the descending limb of the fetal heart rate deceleration curve decreased and correlated strongly with fetal arterial pH, bicarbonate, and logarithmic plasma norepinephrine and epinephrine concentrations. Fetal arterial pH and bicarbonate levels were significantly lower in the group with lower fetal heart rate deceleration slope, and a greater plasma catecholamine concentration in this group suggested a redistribution of blood flow to vital organs. Therefore, during repeated umbilical cord compression, the fetal acid-base and hormonal state was predicted by the fetal heart rate deceleration slope. This relationship may be applicable to human fetuses in the diagnosis of fetal distress caused by umbilical cord compression during labor.