Search

There is currently no standard means of detecting amniotic fluid contamination in fetal blood obtained by percutaneous umbilical blood sampling. The ferning test is proposed for this purpose. An in vitro model, using centrifuged serial dilutions of neonatal cord blood and amniotic fluid, showed that ferning of the supernatant occurs in proportion to the degree of contamination. A system for grading ferning was devised, and tested in a blind trial. For the detection of amniotic fluid contamination of 10% or more, the method showed a sensitivity of 98% and a specificity of 81%. The method may be useful in percutaneous umbilical blood sampling, and in the diagnosis of spontaneous rupture of membranes with vaginal bleeding.

The effects of acute hypoxia on the resting arterial pressure as well as on heart rate and its beat-to-beat variability were studied in chronically instrumented, unanesthetized newborn lambs at 2 to 8 weeks of neonatal life. Lung ventilation with a gas mixture containing 10% oxygen and 3% carbon dioxide decreased arterial blood PO2 by about 50% in all animals regardless of age without significantly altering blood pH and PCO2. This degree of hypoxia produced a mild pressor response, accompanied by a significant tachycardia; the pattern of these changes, however, differed somewhat according to neonatal growth. The impact of hypoxia on beat-to-beat variability of the neonatal heart rate also varied with age. When the lambs were 2 to 3 weeks old, both the long- and short-term variabilities decreased progressively during hypoxia and the decrement reached a maximum at 10 minutes of oxygen deprivation. As the lambs became older, however, there was some initial and transient increase in the long- and short-term variabilities in the early period of hypoxia but thereafter the changes were inconsistent. The significance of these observations is discussed in terms of our knowledge of the pathophysiologic alterations in the cardiovascular system produced by acute hypoxia.

The effects of beta-adrenergic-receptor stimulation with ritodrine on systemic and pulmonary hemodynamics and on renal handling of water and electrolytes were studied in unanesthetized, chronically instrumented pregnant sheep. Each animal was studied during control, ritodrine, and recovery periods, each lasting 60 minutes, with the use of three different modes of hydration. beta-receptor stimulation produced a significant increase in heart rate and cardiac output and a decrease in systemic vascular resistance. Pulmonary arterial and wedge pressures tended to increase. These circulatory effects were similar for the three types of hydration and they persisted after cessation of infusion. In terms of its renal effects, beta-receptor stimulation elicited a profound decrease in urine flow and in the excretions of sodium and potassium, irrespective of the mode of hydration. The antidiuresis and antinatriuresis were accompanied by no changes in plasma osmolality and sodium concentration, whereas plasma potassium levels decreased. All of these effects persisted for 60 minutes after the cessation of infusion. In the water-loaded experiments, the antidiuresis seemed to be related to increased antidiuretic hormone secretion; in the saline-loaded experiments, however, both the antidiuresis and antinatriuresis appeared to be related to increased renal reabsorption. The changes in renal hemodynamics seemed to have an insignificant role. The amount of fluid retained in the body was greater when ritodrine was infused with saline solution than with dextrose solution. These cardiovascular and renal studies suggest that a circulatory overload may be the major factor in the pathogenesis of pulmonary edema observed during beta-adrenergic-receptor stimulation.

It has been suggested that sodium nitroprusside, a potent vasodilator, be used in the management of an acute hypertensive crisis during pregnancy. The present study was designed to evaluate the hemodynamic effects of this agent in the same group of chronically instrumented, unanesthetized pregnant sheep during two experimental periods: (a) normotension with intact kidneys, and (b) one-kidney hypertension. The results demonstrate that (1) nitroprusside is a potent vasodilator which lowers mean arterial pressure; (2) nitroprusside-induced tachycardia was greater in the hypertensive animal; (3) uterine blood flow decreased with the development of hypertension; (4) the hypertensive-induced reduction in uterine blood flow was increased by the infusion of nitroprusside.

Unanesthetized, chronically instrumented, nonpregnant sheep were studied in periods of progressive blood withdrawal, hypovolemic shock, blood reinfusion, and recovery. Hemodynamic responses were recorded during experiments with an intact beta-adrenergic system (saline solution), beta-adrenergic blockage (propranolol), and beta-adrenergic stimulation (isoxsuprine). With an intact beta-adrenergic system, stepwise bleeding produced a progressive decrease in arterial pressure, stroke volume, and cardiac output and an increase in systemic vascular resistance; heart rate increased initially but fell when hypovolemia became severe. All circulatory parameters returned toward control valves during blood reinfusion and recovery. In animals deprived of beta-adrenergic control, the hemodynamic response to progressive hypovolemia and blood reinfusion was not greatly different from that of control animals, despite abolition of tachycardia. During beta-adrenergic stimulation, arterial pressure and cardiac output fell more rapidly than in control and tachycardia was relatively small; cardiac output and stroke volume rebounded strikingly during reinfusion and recovery. These results support findings of others that the role of the beta-adrenergic system is minor during hypovolemia. When pharmacologically activated, it might play a significant role in the posthypovolemia compensatory mechanisms.

The contributions of the intrinsic, beta-adrenergic, and cholinergic systems to the mechanisms of beat-to-beat variability of the heart rate were investigated in chronically instrumented, unanesthetized newborn lambs from the first week to the eighth week of neonatal life. During this period of neonatal growth, the resting heart rate decreased spontaneously every week; the decrease was not related to alterations in the sympathetic and parasympathetic tones but rather to changes in the intrinsic mechanisms of heart rate control. Despite the weekly decrease in the resting heart rate of the neonatal lamb, the long and short-term beat-to-beat variabilities did not change significantly. This finding suggests an absence of a significant influence of the intrinsic mechanisms of heart rate control on the genesis of beat-to-beat variability. The results obtained with the various modes of adrenergic and cholinergic blockades and stimulation seem to indicate that the autonomic nervous system contributes significantly to the appearance of beat-to-beat variability. However, the influences of the adrenergic and cholinergic systems differ from week to week of neonatal growth and the patterns of changes are not the same for the long-term and short-term variabilities. The implication of these studies in terms of physiologic and hemodynamic significance of beat-to-beat variability in heart rate is discussed.

Placental grading with real-time ultrasound was performed on 235 patients who underwent amniocentesis for determination of the lecithin/sphingomyelin (L/S) ratio between 31 and 44 weeks' gestation. Grades I, II, and III placentas were encountered in 88, 72, and 75 patients, respectively. Forty-eight percent of Grade I, 69% of Grade II, and 92% of Grade III placentas had mature L/S ratios (L/S greater than or equal to 2.0). All of the 52 patients with a Grade III placenta who underwent repeat cesarean section at term gestation had mature L/S ratios. However, 37% of the pregnancies complicated by maternal or fetal disease, with Grade III placentas, had immature L/S ratios. The gestational age of these six patients ranged from 34 to 37 weeks. These results suggest that a Grade III placenta in normal term gestation has a good correlation with fetal pulmonary maturity as predicted by the amniotic fluid L/S ratio.

Nonpregnant and pregnant sheep at 110 to 140 days' gestation were chronically instrumented for measurement of mean arterial pressure, heart rate, cardiac output, common internal iliac artery blood flow, and middle uterine artery blood flow. Systemic and regional vascular resistances were calculated from pressure/flow data. Either isoxsuprine, 10 microgram/kg/min, or terbutaline, 0.40 microgram/kg/min, was infused continuously for a period of one hour. The above-mentioned parameters were monitored during control, infusion, and postinfusion periods. The findings show that: (a) isoxsuprine had greater effects on the mean arterial pressure, heart rate, and cardiac output than did terbutaline; (b) both agents had minimal effects on the common internal iliac artery blood flow of pregnant ewes, but isoxsuprine decreased the middle uterine artery blood flow significantly; and (c) with isoxsuprine, a marked vasodilatation occurred in the common internal iliac vascular bed of nonpregnant ewes, in contrast to the insignificant changes in the pregnant ewes. The conclusions drawn were that: (1) the more pronounced effects of isoxsuprine are most probably related to a greater beta 1 stimulation; (2) contiguous regional vascular beds respond differently to pharmacologic stimuli; and (3) the state of a given vascular bed during the resting state determines its response to vasoactive agents.