Biomedical subjects
Publications and source records attributed to C B Martin.
Morning and evening simultaneous fetal and maternal plasma samples were analyzed for thyroid-stimulating hormone. An a.m.-p.m. variation in fetal concentrations was identified, whereas the majority of the maternal values (28 of 32) were below the sensitivity of the assay. The importance of this cyclic fetal activity is discussed.
The preejection period (PEP) of the fetal cardiac cycle was studied in the chronically instrumented fetal lamb. A specially constructed device permitted the occlusion of either both umbilical veins, or of both umbilical arteries, or of the total umbilical cord. A prolongation of the PEP together with an increase in blood pressure was a consistent finding during any type of cord occlusion. In poorly oxygenated fetal lambs a two-step increase in the duration of the PEP was observed during the occlusion. It was accompanied by a simultaneous two-step increase in fetal arterial blood pressure. A correlation was found between the steady-state fetal pO2 before the occlusion and the increase in fetal arterial diastolic blood pressure during the blockade of the umbilical circulation. During occlusion the main determining factors of the PEP prolongation appear to be the increase in afterload and the decrease in preload of the fetal heart. The second step in the prolongation of the PEP during the occlusions in poorly oxygenated fetal lambs is attributed to a chemoreceptor-induced reflex, resulting in a redistribution of cardiac output in the fetal lamb.
The preejection period (PEP) of the fetal cardiac cycle was studied in the chronically instrumented fetal lamb. An inflatable cuff occluder was positioned around the maternal common internal iliac artery, the pregnant ewe's main uterine blood-supplying vessel. Occlusion of the maternal common internal iliac artery produced a fall in pO2 and pH and a rise in pCO2. Fetal arterial blood pressure increased and PEP shortened, especially in the longer lasting occlusions. Fetal heart rate exhibited a bradycardia also during this type of occlusion. The fetal lamb's cardiovascular adjustments to biochemical changes caused by occlusion of the maternal uterine blood supply appear to be determined during the initial phase of occlusion by a chemoreceptor reflex-induced peripheral vasoconstriction mediated by the adrenergic nervous system. The condition is comparable to the one observed during the second part of the umbilical cord occlusions. The interaction between a supersensitive fetal myocardium and the adrenal release of catecholamines may play a dominant role during the second part of occlusion in the longer lasting experiments. Increase in peripheral resistance in the course of redistribution of blood flow during hypoxemia induces a prolongation of the PEP in the early phase of occlusion; overriding of this effect by an increase in myocardial contractility due to rising levels of adrenal catecholamines abbreviates the PEP in the later part of the longer lasting occlusions.
Eye movements of the human fetus were detected in utero by means of real-time B-scan and M-mode ultrasonography. In 14 low-risk fetuses studied between 32 weeks menstrual age and term either rapid or slow eye movements or a mixture of both types were detected in 60 +/- 10% (mean +/- SD) of 558 2 min scoring epochs. A comparison of direct echoscopic detection of eye movements in a 3-day-old neonate confirmed that the movements observed in the orbital region with the real-time scanner corresponded well with eye movements seen directly. Thus eye movements can be added to the list of phenomena which can be observed noninvasively for the study of human fetal behaviour.
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Simultaneous use of real-time ultrasonographic scanning and cardiotocography has demonstrated that the human fetus exhibits well-developed behavioral states from about 36 week's menstrual age onward. Four states have been identified that are very similar to states that have been described in neonates of equivalent age. Prior to 36 weeks, cycles are present in the state variables individually: however, these cycles are not synchronized. The implications of the alternation of behavioral states in the fetus for antepartum assessment of fetal condition are discussed.
Cardiac output (CO) and organ flows were measured in five nonpregnant and 14 pregnant unstressed guinea pigs between the thirty-ninth and sixty-fifth postconceptional day by means of radionuclide-labeled microspheres. Blood pressure, heart rate, and cardiac output in nonpregnant animals were 60 torr, 234 bpm, and 248 ml/min, respectively. These parameters did not change significantly during pregnancy. The uterine fraction of cardiac output increased to approximately 18% at term and there was an equivalent decrease in the CO fractions to the carcass and skin. Blood flow per gram of wet weight increased during pregnancy by approximately 140% and 70% for the thyroid and gastrointestinal tract, respectively, but did not change significantly for the heart, brain, kidneys, and adrenals. In pregnant animals near term the weight of the heart, kidneys, intestines, and lungs was approximately 25% lower than that observed in nonpregnant guinea pigs.
Placental growth during pregnancy was studied serially by ultrasonographic measurement of placental area in 50 primigravid women. Placental area at a menstrual age of 150 days was compared to infant birth weight. Small placental area at a menstrual age of 150 days was significantly related to low infant birth weight (< tenth percentile of birth weight for gestational age). A "warning limit" of placental area at midpregnancy was calculated. If placental area was equal to or smaller than this limit of 187 sq cm, six of nine patients (67%) compared to four of 41 subjects with larger placentas (p < 0.01) were delivered of a small-for-gestational age baby. Ultrasonographic placental area measurement in midpregnancy thus appears to be of prognostic value in identifying pregnancies at high risk for the subsequent occurrence of fetal growth.
Differences in blood pressure between the supine and left lateral positions were studied in pregnant subjects under standardized conditions with an automated ultrasound device. Cross-sectional studies were performed in 125 nulliparous pregnant women after the twenty-eighth week of amenorrhea and in 42 nonpregnant controls. Arterial blood pressure in the left lateral position was lower than in the supine position. This difference was due largely to differences in hydrostatic pressure. Large errors in measurement and regression to the mean contributed to wide spread in measured values. Neither hypertension nor pregnancy alone gave an enhanced postural difference in blood pressure. Hypertension in pregnancy was associated with a significantly larger positional change in diastolic blood pressure (D) than in systolic blood pressure (S). This study pleads for a standardized procedure for the measurement of blood pressure in gravidas in the supine position, for the detection of peripheral vasoconstriction in the supine position, and to compare clinical blood pressure studies in different institutions.
The VET of the fetal cardiac cycle, measured as the interval between the semilunar valve opening and closing signals of the ultrasound Doppler cardiogram, was studied in chronically catheterized fetal rhesus monkeys. VET varied inversely with FHR between approximately 150 and 250 bpm. Below 150 bpm, however, there was no further prolongation of VET. VET was not related to gestational age. VET, corrected for heart rate, was shortened in the presence of combined hypoxemia and acidosis, but not when either hypoxemia or acidemia was present alone. Corrected VET was shortened by epinephrine, but was not consistently altered by atropine. VET was not affected by changes in the concentration of glucose in fetal blood.
To examine diurnal changes in maternal and fetal steroids in chronically catheterized pregnant rhesus monkeys, we have measured cortisol (F), progesterone (P4), estone, and estradiol in maternal blood and F, P4, and dehydroepiandrosterone sulphate (DHAS) in simultaneous samples of fetal blood taken in the morning (0700--1000 h) and in the evening (1700--2100 h). In the mother, the concentrations of F, estradiol, and estrone were higher in the morning than in the evening. In contrast, progesterone was higher in evening than in morning samples. In fetal blood, there was no significant morning-evening difference for F; however, the concentrations of P4 and DHAS were higher in the evening than in the morning samples. In three individual monkeys, the concentrations of P4 and DHAS in serial samples of fetal blood were correlated. We conclude 1) that there are marked diurnal changes in the concentration of several steroids in samples of maternal and fetal blood and 2) that the concentration of F in maternal blood shows the opposite pattern to that of possible fetal adrenal steroids in fetal blood.
The incidence and character of fetal breathing movements (FBMs) were determined by analysis of continuous tracheal pressure recordings in a 48 hour period preceeding fetal death in utero in 7 chronic pregnant monkey preparations (Macaca mulatta). All fetuses were judged normal by blood gas tensions, pH, and fetal heart rate within 48 hours of death. In the normal fetus breathing movements were periodic and a circadian distribution in the incidence of FBMs was observed. Four distinct patterns of FBMs were observed in the normal fetuses. In five fetuses death occurred in the intrapartum period; all five fetuses were breathing at the onset of labor. A progressive fall in the incidence of FBMs was observed in labor coincident with the development of fetal acidemia. In the remaining two fetuses death occurred before labor. Apnea and gasping were observed in all fetuses before death. The duration of apnea and gasping appeared dependent upon the nature of the lethal insult.
Simultaneous recordings of the fetal electrocardiogram and ultrasound Doppler-cardiogram were used for the determination of the pre-ejection period (PEP) of the fetal cardiac cycles. All 50 fetuses selected for the present study experienced uneventful perinatal lives despite maternal antepartum complications which required hospitalization. A significant positive correlation between the PEP and gestational age of the fetuses was again demonstrated. The PEP of the fetus measured within one week prior to delivery was also found to be significantly correlated with the newborn body weights at birth. Statistical analysis demonstrates that fetal body weight was more closely related to the physiologic lengthening of the PEP.
Fetal heart rate decelerations resembling the late deceleration FHR pattern were produced in fetal sheep by periodic occlusion of the maternal common hypogastric artery for 30-60 sec. Transient fetal hypertension also occurred during the occlusions. Alpha-adrenergic blockade with phentolamine eliminated or markedly reduced the hypertensive response. FHR decelerations still occurred intermittently with some occlusions; however, their character was greatly altered. After parasympathetic blockade with atropine, the decelerations were replaced by periodic FHR accelerations during the occlusions. These accelerations were, in turn, eliminated by the beta-adrenergic blocking agent, propranolol. In the presence of combined parasympathetic, alpha- and beta-adrenergic blockade, the FHR remained essentially constant during the hypogastric artery occlusions in non-acidemic fetuses. FHR decelerations persisted after parasympathetic or total autonomic blockade when the fetuses were significantly hypoxic, as judged by depressed arterial blood pH and base excess values. Beat-to-beat variability of the baseline FHR persisted in the face of severe hypoxia and acidosis. These observations demonstrate that reflex mechanisms are involved importantly in the genesis of late deceleration FHR patterns in the acutely hypoxemic fetus, but that direct depression of myocardial rhythmicity becomes a factor as hypoxic acidosis develops.
11 fetal lambs with gestational age of 116-135 days were studied while connected to a membrane-oxygenator replacing the ventilatory function of the placenta. Progressive increase in arterial oxygen tension from 20 to 220 mm Hg resulted in progressive decrease in baseline heart rate and baseline arterial blood pressure indicating presence of chemoreceptor activity over this wide range of arterial oxygen tension. The effect of 60 sec complete umbilical cord occlusion was studied at progressively higher arterial oxygen tension and it was concluded that the chemoreceptor activity at fetal normoxic condition is very brisk and is markedly attenuated at hyperoxic levels. Although it was not possible to completely separate baroreceptor and chemoreceptor reflexes involved in cardiovascular response to umbilical cord occlusion, it is postulated that the chemoreceptor and baroreceptor reflexes are complimentary during cardiovascular responses to umbilical cord occlusion.
The amniotic fluid lecithin/sphingomyelin ratio (L/S ratio) of stumptail macaque monkeys (Macaca arctoides) was investigated by means of serial amniocenteses during the second half of pregnancy. Ten dated pregnancies were studied in 9 individual monkeys. The mean number of successful amniocenteses per pregnancy was 4. A rapid increase in the L/S ratio suggesting maturation of lung surfactant synthesis occurred as early as 130--140 days of pregnancy in some animals, and as late as 150--160 days in others. The earliest and latest times at which the L/S ratio first exceeded 2.0 were 135 and 164 days, respectively. These observations indicate that the L/S ratio of M. arctoides follows a course similar to that observed in human pregnancy, with a rise at 0.7--0.8 of term gestation. M. arctoides thus appears to be a useful model for the study of factors affecting fetal lung maturity, on the basis of the amniotic fluid L/S ratio. In particular, a rapid rise in L/S ratio before 130 days of pregnancy would be highly suggestive of accelerated maturation of pulmonary surfactant production.
The placental diffusing capacity for carbon monoxide was measured in unanaesthetized monkeys (M. Mulatta). Maternal and fetal blood was sampled from chronically placed catheters while the mother breathed 50 or 100 parts per million of CO. Diffusing was calculated from the amount of CO taken up by the fetus divided by the partial pressure difference across the placenta, it averaged 0.646 plus or minus 0.062 (SEM) ml x min(-1) x torr(-1) x kg(-1) of fetal weight. The significance of this index of respiratory gas exchange in the monkey placenta is discussed with respect to previous measurements in other species and with respect to fetal growth.
The short- and long-term effects of surgical procedures and chair restraint on total plasma cortisol were assessed in the chronic rhesus monkey preparation. Three nonpregnant and six pregnant animals were sampled daily, morning and evening. Fetal plasma specimens were obtained simultaneously from the pregnant animals. In the nonpregnant rhesus monkey, a circadian rhythm is present the day following venous catheterization and chair restraint, with individual values similar to those in trained, unanesthetized animals. In the pregnant animals, a postoperative rise in cortisol is followed by a gradual decline to a plateau and a return of circadian rhythm. No consistent daily fluctuations are seen in fetal cortisol, and although correlated with maternal cortisol, the exact relationship is uncertain. The data indicate that operation, as expected, is stressful but acclimation to the chair occurs.