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Biomedical subjects

C R Brinkman

Publications and source records attributed to C R Brinkman.

At least 19 recordsLinked to original sources
PubMed1990

A comparison of the morbidity of midforceps and cesarean delivery.

Neonatal and maternal outcome in 358 midforceps and 486 cesarean deliveries was compared by retrospective analysis. Neonatal outcome was evaluated on the basis of Apgar score, cord blood gas values, admission to the neonatal intensive care unit, and birth trauma. Maternal outcome was based on intraoperative and postoperative complications, blood loss, and hospital stay. There was no increase in significant short-term neonatal morbidity in the midforceps group, while maternal morbidity was higher in the cesarean delivery group. It is concluded that, in selected cases, midforceps delivery is safe for the neonate and mother.

Apgar Score↗
PubMed1989

Changes in peripheral venous tone before the onset of hypertension in women with gestational hypertension.

Forearm venous tone was measured throughout pregnancy in 68 nulliparous women thought to be at high risk of the development of gestational hypertension. Normotensive pregnancy was associated with a progressive venodilatation. Gestational hypertension subsequently developed in 12 women. Before the onset of hypertension, these 12 women showed a greater degree of venodilatation, compared with women who remained normotensive throughout their pregnancies (p less than 0.001). As the hypertension became manifest, the women became relatively venoconstricted (p less than 0.001). Simple, noninvasive measurements of forearm venous tone provide important information about the pathophysiology of gestational hypertension and may be useful in the detection of women who are at increased risk.

Adult↗
PubMed1987

Antihypertensive drugs in pregnancy.

This article considers the pathophysiology, diagnosis, and etiologies of hypertensive conditions, and considers specific agents for treating this condition. It also reviews the side effects of these agents and their efficacy, and details their use in the hypertensive pregnant patient.

Antihypertensive Agents↗
PubMed1986

Experimental hypertension in pregnant sheep. III. Central hemodynamic alterations in the one-kidney model.

Experimental renal hypertension, with use of the one-kidney, one-clip model, was produced in nine pregnant ewes who were then studied during the last one third of gestation. The animals were chronically instrumented for the recording of arterial pressure, heart rate, and cardiac output; blood volume was determined weekly. The studies were carried out in four phases; a control period of 2 weeks, a surgery period of 1 week, a constriction or hypertensive period, and a postpartum period of 2 weeks. We detected no significant changes in heart rate or cardiac output during any phase of the study. The arterial pressure significantly increased during the constriction and postpartum phases (p less than 0.05). Blood volume remained relatively stable during the three pregnancy phases but significantly decreased in the postpartum phase (p less than 0.05). Systemic vascular resistance followed a pattern similar to that of the arterial pressure.

Animals↗
PubMed1986

Heat flux and oxygen consumption of the pregnant uterus.

Heat flux (conductive and convective heat) and oxygen consumption of the pregnant uterus and its content were measured simultaneously in the same group of pregnant ewes during the acute postoperative period, during a chronic resting period, and during alpha- and beta-adrenergic-receptor stimulation with norepinephrine and ritodrine. Results indicated four conclusions. First, an excellent correlation existed between heat flux and oxygen consumption in the acute and chronic resting condition as well as during increasing uteroplacental vascular resistance and decreasing blood flow produced by norepinephrine infusion; the correlation was not as good during ritodrine infusion. Second, during rest, about 85% of heat generated by the pregnant uterus is eliminated through the uteroplacental circulation while the remaining heat diffuses through the myometrium. Third, during decreasing uteroplacental blood flow and elevated resistance, the pregnant uterus is able to maintain a normal thermostasis by widening the temperature difference in the blood entering and leaving the uterus and by increasing the myometrial heat exchange; oxygen consumption also is maintained at normal level through increase in oxygen extraction. Fourth, with the exception of uteroplacental circulation, the circulatory, metabolic, and thermal conditions of the pregnant ewe are not different after 5 hours from 5 to 7 days after the surgical procedure.

Animals↗
PubMed1984

Circulatory and renal effects of beta-adrenergic-receptor stimulation in pregnant sheep.

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.

Animals↗
PubMed1983

The contribution of the beta-adrenergic system to the cardiovascular response to hypovolemia.

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.

Animals↗
PubMed1982

Mixing problems in using indicators for measuring regional blood flow.

A basic requirement for using indicators for measuring blood flow is adequate mixing of the indicator with blood prior to sampling the site. This requirement has been met by depositing the indicator in the heart and sampling from an artery. Recently, authors have injected microspheres into veins and sampled from venous sites. The present studies were designed to investigate the mixing problems in sheep and rabbits by means of Cardio-Green and labeled microspheres. The indicators were injected at different points in the circulatory system, and blood was sampled at different levels of the venous and arterial systems. Results show the following. (a) When an indicator of small molecular size (Cardio-Green) is allowed to pass through the heart chambers, adequate mixing is achieved, yielding accurate and reproducible results. (b) When any indicator (Cardio-Green or microspheres) is injected into veins, and sampling is done at any point in the venous system, mixing is inadequate, yielding flow results which are inconsistent and erratic. (c) For an indicator or large molecular size (microspheres), injecting into the left side of the heart and sampling from arterial sites yield accurate and reproducible results regardless of whether blood is sampled continuously or intermittently.

Animals↗
PubMed1982

Circulatory effects of chemical sympathectomy in fetal, neonatal, and adult sheep.

Circulatory effects of chemical sympathectomy with 6-hydroxydopamine (6-HD), including changes in vascular sensitivity to neurotransmitters, were investigated in chronically instrumented unanesthetized fetal, neonatal, and adult sheep. In all animals acute response to 6-HD consisted of hypertension and tachycardia, which lasted 2-3 h. Chronic phase of sympathetic ablation then followed during which arterial pressure and heart rate of sympathectomized fetus and neonate returned to and remained at levels observed in intact animals, whereas adult sheep were slightly hypotensive throughout this period. In all animals supersensitivity of peripheral circulation to norepinephrine occurred, but only the fetus exhibited supersensitivity to acetylcholine and isoproterenol. Our conclusions are as follows: 1) acute phase of chemical sympathectomy in fetal, neonatal, and adult sheep simulates strong adrenergic stimulation; 2) absence of significant alteration in arterial pressure of fetus and neonate during the chronic phase of sympathectomy suggests a minor role for the adrenergic system in the maintenance of resting tone of peripheral circulation; and 3) on the basis of present and previous data, we postulate that the supersensitivity of fetal circulation to acetylcholine and isoproterenol may be secondary to changes occurring in pulmonary vascular bed.

Acetylcholine↗
PubMed1982

Diabetes mellitus.

Diabetes mellitus is classified into two major categories: type I, which is insulin dependent, and type II, which is not. Insulin resistance in type II diabetes may be related to impaired receptor binding in some forms of the disorder. In the past, diabetes in pregnant women resulted in high rates of maternal and infant mortality. During the past 10 years, however, better management of maternal diabetes has led to a significant sharp reduction in maternal and fetal morbidity and mortality. The long-term outcome of insulin-dependent diabetes remains gloomy, probably because adequate control of the disease has rarely been achieved. Recently, more stringent efforts have been made to achieve tighter control. Frequent monitoring of blood glucose levels at home and use of constant infusion insulin pumps may help to achieve this end until successful islet transplantation is feasible.

Animals↗
PubMed1982

Lecithin:sphingomyelin ratio in pregnancies complicated by insulin-dependent diabetes mellitus.

One hundred forty-one samples of amniotic fluid in 105 pregnancies from 95 insulin-dependent diabetics were analyzed for the lecithin:sphingomyelin (L:S) ratio. Fetal pulmonary maturity seemed to progress at a normal rate. The mean L:S ratio was not significantly different in diabetic and nondiabetic patients at various stages of gestation. Only 3 cases of respiratory distress syndrome (RDS) were observed in 77 infants with an L:S ratio of 2.0 or more delivered of diabetic mothers within 72 hours of amniocentesis. This 3.9% incidence of RDS in infants of diabetic mothers with L:S ratios of more than 2.0 was not significantly higher than the 1.5% incidence in the nondiabetic mothers. It is concluded that by using the method of Gluck, an L:S ratio of 2.0 or greater at 36 weeks' gestation or later is a reliable indicator of fetal lung maturity in insulin-dependent diabetic pregnancies, and abdominal delivery after 36 weeks' gestation does not increase the risk of RDS in a diabetic pregnancy with an L:S ratio at 2.0 or more.

Amniocentesis↗
PubMed1982

The effect of general and epidural anesthesia upon neonatal Apgar scores in repeat cesarean section.

One-hundred and ninety-five elective cesarean deliveries were studied to determine the effects of general and epidural anesthesia upon the neonatal condition, as reflected by the one and five minute Apgar scores. Ninety were performed under general anesthesia, 0.5 per cent halothane, 50 per cent nitrous oxide and 50 per cent oxygen; 105 used the epidural technique, 3 per cent chloroprocaine plus 0.75 per cent bupivacaine. All patients were tilted to the left during operation. No statistically significant difference was found between the two groups in terms of mean Apgar scores at one and five minutes, p less than 0.1. Neither was a significant difference noted in terms of depressed infants, Apgar score less than 7, at one or five minutes, p greater than 0.1. More significantly, no correlation was noted between the duration of anesthesia and the Apgar scores in either group, p greater than 0.1. Specifically, no significant increase was found in depressed infants in the prolonged, greater than or equal to 15 minutes, incision to delivery group, p greater than 0.05. These data seem to suggest that the use of general anesthesia, in the technique described, yields infants with Apgar scores as good as those of infants delivered under regional block anesthesia and that prolonged duration of general anesthesia is not associated with a depression of the Apgar scores.

Anesthesia, Epidural↗
PubMed1981

Autonomic control of the pelvic circulation: in vivo and in vitro studies in pregnant and nonpregnant sheep.

Pregnancy alters the autonomic control of the peripheral circulation. Present in vivo and in vitro studies were designed to investigate the mechanisms of these alterations. In the in vivo studies, pelvic and systemic circulatory responses to intra-arterial and intravenous injections of agonists were monitored in unanesthetized pregnant and nonpregnant ewes. In in vitro studies, a comparison was made of responses to transmural nerve stimulation (TNS) and to norepinephrine (NE) of different blood vessels obtained from pregnant and nonpregnant ewes. The results were the following: (1) Pelvic vascular response to all vasoactive stimuli was considerably more depressed during pregnancy than was systemic circulatory response. (2) In vitro reactivity to alpha-adrenergic stimulation with NE of different blood vessels obtained from pregnant animals was similar to that of vessels from nonpregnant animals. (3) The response to TNS of blood vessels obtained from pregnant ewes was less than that of vessels from nonpregnant ewes. The conclusions were that (a) probably largely related to dilution of a given dose of the stimulus in the greater blood volume and flow; and (b) the increased neurogenic tone of the peripheral circulation during pregnancy is most likely related to increased nerve firing rather than neural density in the vessel walls.

Acetylcholine↗
PubMed1981

Experimental renal hypertension in pregnant sheep. II. Response to a one-kidney model.

Pelvic blood flow was serially determined in 19 pregnant ewes before and after the induction of one-kidney renal hypertension. The six twin gestations and 13 singleton gestations behaved similarly for all parameters, except renal blood flow. After the renal preparatory surgical procedure, there was a 19% increase in mean arterial pressure and an 18% increase in pelvic blood flow, with pelvic vascular resistance being unchanged. After right renal artery constriction, there was a 14% further increase in mean arterial pressure, whereas pelvic blood flow increased only 3.5% and pelvic vascular resistance increased nearly 9%. Thereafter, although the arterial pressure remained elevated, the pelvic blood flow decreased and pelvic vascular resistance increased. Statistical analysis by means of a general linear model and covariance before and after renal artery constriction revealed significant changes in arterial pressures, pelvic blood flow, and pelvic vascular resistance.

Animals↗
PubMed1981

Responses of the pelvic vascular bed to intra-arterial stimulation of beta-adrenergic and cholinergic receptors in pregnant and nonpregnant sheep.

The responses of different parts of the pelvic vascular bed to beta-adrenergic and cholinergic receptor stimulation were studied in chronically instrumented, unanesthetized pregnant and nonpregnant sheep. Isoproterenol and acetylcholine were administered intra-arterially in progressively increasing bolus injections, and dose-response curves were constructed for changes in blood flows, arterial pressure, and heart rate. Response to beta-adrenergic and cholinergic stimulation was measured before and after the agents reached the central circulation. In addition, data were obtained from the same animals before and after pharmacologic cardiac denervation. Results show: (1) Stimulation of beta-adrenergic and cholinergic receptors produced active vasodilatation in extrauterine vascular beds with minor changes in uterine blood flow of the pregnant horn; (2) the changes in uterine flow observed during beta-adrenergic and cholinergic stimulation were probably secondary and related to a shift of blood from the uterus to other vascular beds that were actively dilated; (3) the response of the pregnant animal to any given dose of the autonomic agonist was strikingly smaller to that of the nonpregnant animal. A number of physiologic factors peculiar to pregnancy may contribute to this difference; among these are: (1) dilution factor related to the greater volume flow; (2) near-maximal dilatation of some blood vessels and the presence of the two resistance system of placental circulation, and (3) the effect of progesterone on the vascular smooth muscle.

Acetylcholine↗
PubMed1981

Nitroprusside-induced hemodynamic alterations in normotensive and hypertensive pregnant sheep.

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.

Animals↗
PubMed1981

Hemodynamic responses of the pelvic vascular bed to vasoactive stimuli in pregnant sheep.

The responses of the common internal iliac artery and middle uterine artery of the pregnant horn to continuous infusions of graded doses of norepinephrine, epinephrine, dopamine, isoxsuprine, angiotensin and nitroprusside were investigated in chronically instrumental pregnant ewes. Norepinephrine progressively decreased the blood flow and increased the resistance in both vessels but the changes were more marked in the middle uterine artery. Isoxsuprine and epinephrine had an insignificant effect on the common internal iliac artery blood flow, but decreased that of the middle uterine artery. Nitroprusside decrease the flow in both vessels proportionately. Angiotensin in doses less than 0.16 micrograms/kg/min increased the flow in both arteries to the same extent, but higher doses decreased both flows. It is concluded that in the chronically instrumented pregnant ewe, the responses of contiguous vascular beds to different vasoactive agents may differ depending on the nature of the stimulus.

Angiotensin II↗