Biomedical subjects

B Nuwayhid

Publications and source records attributed to B Nuwayhid.

At least 19 recordsLinked to original sources

PubMed2000

Maternal deaths in an urban perinatal network, 1992-1998.

OBJECTIVE: The object of this study was to use an in-depth peer-review process to determine the maternal mortality ratio at a single urban perinatal center and to identify factors associated with fatal outcomes to elucidate opportunities for preventive measures to reduce the maternal mortality ratio. STUDY DESIGN: Between 1992 and 1998 all maternal deaths occurring within our perinatal network were identified. A peer-review committee was established to review all available data for each death to determine the underlying cause of death, whether it was related to pregnancy, and whether the death was potentially preventable. RESULTS: There were 131,500 births and 42 maternal deaths, for a maternal mortality ratio of 31.9 maternal deaths per 100,000 live births. The adjusted pregnancy-related maternal mortality ratio was 22.8 maternal deaths per 100,000 live births, with 37% of those deaths (11/30) deemed potentially preventable and a provider factor cited in >80% of these. Pulmonary embolus and cardiac disease together accounted for 40% of the pregnancy-related deaths. CONCLUSION: Local maternal mortality ratios identified through a peer-review process indicate that the magnitude of the problem is much greater than is recognized through national death certificate data. The high proportion of potentially preventable maternal deaths indicates the need for improvement in both patient and provider education if we are to reduce the maternal mortality ratio to 3.3 maternal deaths per 100,000 live births, the stated national health goal of Healthy People 2000.

Female↗

PubMed1995

Maternal asthma and idiopathic preterm labor.

Previous studies suggest that women with asthma are at increased risk of preterm birth. Moreover, drugs (especially beta-agonists) used to treat asthma are also used to treat preterm labor. The authors carried out a case-control study of 555 women from three hospital centers with idiopathic preterm labor (< 37 weeks), including two overlapping (i.e., non-mutually exclusive) subsamples: cases with early idiopathic preterm labor (< 34 weeks) and cases with idiopathic recurrent preterm labor (< 37 weeks plus a previous history of preterm delivery or second-trimester miscarriage). Controls were matched to cases according to race and smoking history prior to and during pregnancy. All subjects responded in person to questions about atopic, respiratory, obstetric, and sociodemographic histories. Subjects in the early and recurrent preterm labor subsamples were also asked to undergo spirometric testing with methacholine challenge 6-12 weeks after delivery. Cases were significantly more likely to report histories of asthma symptoms and physician-diagnosed asthma (matched odds ratios of 2-3) than controls, particularly those cases with recurrent preterm labor. No significant associations were observed, however, with methacholine responsiveness. These results could not be explained by residual confounding by smoking or other variables, nor by selective recall of asthma symptoms and histories by cases. Women with asthma are at increased risk of idiopathic preterm labor. The fact that no such association was seen with methacholine responsiveness suggests that nonatopic, noncholinergic mechanisms may link bronchial and uterine smooth muscle lability.

Adult↗

PubMed1995

Control of atrial natriuretic factor by right and left atrial distension in pregnant sheep.

Previous studies of the atrial stretch-atrial natriuretic factor (ANF) relationship during pregnancy have employed volume expansion and measured only right atrial pressure (RAP). Consequently, we studied nonpregnant (n = 7) and 115- to 125-day pregnant (n = 7) sheep and assessed the ANF response to changes of RAP and left atrial pressure (LAP) induced by graded balloon inflation. Ewes prepared with vascular catheters and atrial balloons were studied after recovery from preparatory surgical procedures. The basal levels of mean arterial pressure (MAP, 83 +/- 3 mmHg), RAP (2.1 +/- 0.7 mmHg), LAP (4.7 +/- 0.9 mmHg), and heart rate (HR, 102 +/- 6 beats/min) were similar in nonpregnant and pregnant sheep. Pregnancy also resulted in elevation of ANF concentration from 25 +/- 6 to 57 +/- 4 fmol/ml. With right atrial distension, the RAP-ANF relationships were similar in both nonpregnant and pregnant sheep, with a 10-mmHg increase in RAP increasing ANF by an average of 95 +/- 9 fmol/ml. In nonpregnant sheep, the LAP-ANF relationship was more responsive than RAP-ANF because a 10-mmHg increase in LAP resulted in a 193 +/- 10 fmol/ml increase in ANF. Moreover, during pregnancy, the LAP-ANF relationship was significantly more sensitive because a 10-mmHg increase in LAP resulted in a 433 +/- 15 fmol/ml elevation of ANF. These data demonstrate that plasma ANF levels are more responsive to distension of the left atria than to the right. More importantly, the ANF response to left, but not right, atrial distension is enhanced by pregnancy.

Analysis of Variance↗

PubMed1994

Perinatal research and its support. Corporate contributions at McGill University.

Three technologic projects with potentially patentable end results are slowly evolving in the Department of Obstetrics and Gynecology, McGill University and Royal Victoria Hospital. A tax shelter infusion of a significant amount of venture capital developed opportunities for all three projects over two years. The three projects--fetal heart rate tracing analysis related to fetal outcome, a distributed and intelligent data acquisition system and selected ultrasonic three dimensional imaging--were advanced considerably, and their results are expressed in outline. The effects of such infusions of business support into an environment of sparse research grant support have been extremely encouraging to the investigators, but the department, with its obligations of ongoing research, teaching and patient care, must develop the next steps with care, although one of the projects has been extended by an interested corporation.

Capital Financing↗

PubMed1993

Responses of placental arteries from normotensive and preeclamptic women to endogenous vasoactive agents.

OBJECTIVE: The hypothesis that preeclampsia may be associated with an increase in the response of the placental arteries to vasoconstrictors or a decrease in their response to vasodilators was tested. STUDY DESIGN: Concentration-response curves to various agents were determined on helical strips of fetal placental arteries from normotensive (n = 33) and preeclamptic (n = 8) women to calculate the potencies and maximal effects of the agents. RESULTS: Endothelin, prostaglandin F2 alpha, and serotonin caused concentration-dependent contractions; angiotensin II and norepinephrine produced little or no effects. The prostacyclin analog iloprost and atrial natriuretic factor, but not isoproterenol, relaxed placental arteries. Iloprost was more effective on preeclamptic than on normal arteries, but the effects of other agents on the two groups of arteries did not differ. Placental arteries exhibited spontaneous oscillations that were more marked in preeclamptic than in normal arteries and were inhibited by indomethacin. CONCLUSION: Preeclampsia is not associated with an increase in the responses of fetal placental arteries to vasoconstrictors or a decrease in their response to vasodilators. However, placental arteries from preeclamptic subjects exhibit increased oscillations.

Adult↗

PubMed1987

Beta-sympathomimetic agents: use in perinatal obstetrics.

Beta-sympathomimetic agents are used extensively in obstetrics to inhibit premature labor. Knowledge of the pharmacology, mode of action on smooth muscle, and cardiovascular and metabolic side effects of these agents is essential for the obstetrician and perinatologist. This review article draws extensively on recent animal research data to explain mechanisms of action and long-term effects of beta-sympathomimetic agents.

Animals↗

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

Circulatory responses to hypovolemia in the pregnant and nonpregnant sheep after pharmacologic sympathectomy.

Circulatory responses to progressive hypovolemia, hypotensive shock, blood reinfusion, and recovery were studied in pregnant and nonpregnant sheep with an intact or pharmacologically ablated sympathetic nervous system produced by administration of 6-hydroxydopamine. These studies also provided an opportunity to assess the contribution of the sympathetic nervous system to the maintenance of vasomotor tone in the pregnant animal at rest. The results show the following: (1) Although there were some differences in the circulatory adjustments to the initial period of blood loss between intact and "sympathectomized" animals, the overall circulatory responses to progressive hypovolemia, shock, blood reinfusion, and recovery were not significantly different in animals with intact or ablated sympathetic nervous systems whether or not they were pregnant. (2) The reasons for the similarity of cardiovascular responses to hypovolemia are the marked increase in catecholamine outputs by the adrenal medulla, which was not affected by 6-hydroxydopamine, and the supersensitivity of the systemic vascular beds of the sympathectomized animal to catecholamines. (3) The contribution of the sympathetic nervous system to the maintenance of the resting vasomotor tone is considerably enhanced during pregnancy, as demonstrated by the chronic effects of adrenergic ablation on the resting arterial pressure. (4) The circulation of the pregnant uterus possesses the ability of autoregulation during chronic changes of perfusing pressure as demonstrated by the differences in the arterial pressure and uteroplacental vascular resistance between intact and sympathectomized animals.

Adrenal Medulla↗

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↗

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

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↗

PubMed1981

Atropine and glycopyrrolate: hemodynamic effects and placental transfer in the pregnant ewe.

Atropine administration in pregnant women may cause fetal tachycardia and a decrease in beat-to-beat variability of the fetal heart rate. In the present study, placental transfer and maternal and fetal hemodynamic effects of atropine and glycopyrrolate were compared in chronically and in acutely instrumented, unanesthetized pregnant ewes. Administration of either atropine (0.05 mg/kg) or glycopyrrolate (0.025 mg/kg) increased maternal heart rate by 25% without changing maternal arterial pressure, fetal arterial pressure, fetal heart rate, or beat-to-beat variability. Maternal and fetal blood gas tensions also did not change. Placental transfer or atropine was significantly greater than that of glycopyrrolate throughout the entire experimental period. The peak fetal/maternal ratios observed 4 hours after injection were 1.0 for atropine and 0.13 for glycopyrrolate. On the basis of placental transfer data only, it is possible to postulate that the use of glycopyrrolate may be preferable to atropine. However, in view of the absence of circulatory effects in the fetal lamb after either atropine or glycopyrrolate, it was concluded that neither agent is preferable to the other insofar as fetal effects are concerned during ovine pregnancy. Whether these conclusions can be applied to human pregnancy remains to be determined.

Animals↗