William M. Barron

Plasma catecholamine responses to physiologic stimuli in normal human pregnancy

The dynamic response of the sympathoadrenal system was evaluated during and after pregnancy in 13 healthy women with a protocol that compared cardiovascular parameters and plasma catecholamine levels during the basal state, after postural maneuvers, and following isometric exercise. Plasma epinephrine and norepinephrine levels were similar during and after gestation when the women rested on their sides, but heart rate was greater in pregnancy. Ten minutes of supine recumbency produced minimal changes, but attenuation of the anticipated increases in heart rate and plasma norepinephrine levels during standing and isometric exercise were observed during pregnancy. In contrast, alterations in plasma epinephrine appeared unaffected by gestation. Plasma renin activity and aldosterone levels were, as expected, greater during pregnancy; however, increments in response to upright posture were similar in pregnant and postpartum women. To the extent that circulating catecholamines may be considered indices of sympathoadrenal function, these data suggest that normal pregnancy alters cardiovascular and sympathetic nervous system responses to physiologic stimuli.

Indirect blood pressure measurement in pregnancy: Korotkoff phase 4 versus phase 5.

Controversy exists regarding which Korotkoff phase should be used to estimate diastolic blood pressure during pregnancy, some authorities recommending phase 5 (disappearance of sounds) and others suggesting phase 4 (muffling). Available data indicate that Korotkoff phase 5 more closely approximates true intraarterial diastolic pressure in pregnant women. Nonetheless, it has been suggested that phase 5 is unmeasurable in a significant number of gravid women, making this end point less desirable. However, studies examining this issue indicate that Korotkoff phase 5 is determinable in more than 90% of gravid women and that the incidence of an indeterminable phase 4 is at least as great as that for phase 5. Moreover, there appears to be greater observer variability in the measurement of phase 4 compared with phase 5. We conclude that available evidence supports recommendations for the use of Korotkoff phase 5 as the preferred end point to estimate diastolic blood pressure during pregnancy. In those few patients having very low or indeterminate phase 5 determinations, both phase 4 and phase 5 should be recorded and the former used to guide patient management. An alternative strategy is to record both phases in all gravid women beginning at the first prenatal visit so that baseline phase 4 values are available in the event that phase 5 becomes indeterminate.

Osmotic and Volume Control of Vasopressin Release in Pregnancy

This article, a review of factors controlling vasopressin (AVP) release in pregnancy, extends our contribution to a symposium in this journal published in 1987 (vol X, pp 270-275). Body tonicity decreases (approximately 10 mOsm/kg) very early in pregnancy due to decrements in the osmotic thresholds for AVP release and thirst. In addition, the metabolic clearance rate (MCR) of AVP markedly increases between gestational week 10 and midpregnancy, and is paralleled by the appearance and increase of circulating cystine aminopeptidase (vasopressinase), while the MCR of 1-deamino-8-D-AVP (DDAVP), an analogue resistant to inactivation by the enzyme, changes little in pregnancy. These increases (MCR of AVP and plasma vasopressinase) may explain certain syndromes of transient diabetes insipidus (DI) that complicate gestation. Finally, mechanisms responsible for the altered osmoregulation in pregnancy are obscure, but chorionic gonadotropin may be involved in the changes during human gestation.

Water Homeostasis and Vasopressin Release During Rodent and Human Gestation

Body tonicity decreases during both human and rodent gestation, manifested by a decrease in Posm of approximately 10 mosm/kg. In humans, the decrease in the osmotic threshold for thirst may precede decrements in the arginine vasopressin (AVP) secretory threshold by several weeks, whereas the metabolic clearance rate of AVP appears markedly increased in the third trimester. The cause of these osmoregulatory changes are unclear, since through 1986 we have been unable to implicate placental extracts, estrogens, progesterone, prolactin, angiotensin II, and certain endorphins in the decreased Posm observed during rat pregnancy. Changes also occur in volume-AVP secretory relationships in pregnancy. For instance, the volume-sensing AVP release mechanisms are altered during gestation in Sprague-Dawley rats in such a way that the increased intravascular volume is recognized as normal.

Interobserver Variability in the Measurement of Diastolic Blood Pressure in Pregnancy

Objective: The objective of this study was to evaluate and compare the magnitude of interobserver variability present when measuring Korotkoff phase 4 versus phase 5 in pregnant women.Methods: Three observers with different backgrounds simultaneously measured both phase 4 and phase 5 on 98 gravidas. Data were used to estimate detectability rates, perform an analysis of variance to assess interobserver variability, examine the distribution of interobserver differences, and evaluate the magnitude of the difference between the two diastolic end points.Main Outcome Measures: Detectability rates of phase 4 and phase 5 diastolic pressure and measures of interobserver variability in diastolic readings.Results: Detectability rates were observer dependent, ranging from 81% to 96% for phase 4 and from 79% to 85% for phase 5. Analysis of variance demonstrated similar degrees of interobserver variability for both end points. Likewise, for any two observers measuring either end point, there was a similar number of mea...

Enalapril and Pregnancy-Induced Hypertension

Excerpt To the editor: Shubiger and colleagues (1) have confirmed that administering angiotensin-converting enzyme inhibitors to pregnant women can provoke renal failure in the newborn. However, wh...

Role of Adrenal Mineralocorticoid in Volume Homeostasis and Pregnancy Performance in the Rat

Because of disagreement regarding the importance of maternal adrenal mineralocorticoid in gestational volume homeostasis and reproductive performance, we studied pregnant rats consuming standard or moderately sodium-restricted diets (22 or 2.2 mEq/100 gm), each subjected on gestational day 5 to SHAM surgery (SHAM) or adrenalectomy (ADNX), the latter combined with corticosterone replacement. Some animals were instrumented with chronic vascular catheters to measure plasma volume and mean arterial pressure (MAP) responses to captopril. We found that neither absolute plasma volume nor hematocrit was significantly altered by adrenalectomy in animals on either standard or sodium-restricted diets. However, Posmol, 9-10 mosmol/kg lower in SHAM pregnant than virgin controls, was 16-22 mosmol/kg below nonpregnant levels in ADNX dams. Despite this hypotonicity, plasma vasopressin (AVP) was not suppressed, suggesting hemodynamic stimulation of AVP secretion. Basal MAP was 105 ± 3 mm Hg and 100 ± 2 mm Hg in SHAM pregn...

Idiopathic acute fatty liver of pregnancy associated with transient diabetes insipidus. Case report

Versi, E.. Brincat, M. & Cardozo, L. D. (19846) Urethral physiology and skin collagen. Proc Inf Cont Soc SIV, 500-502. Versi, E. , Cardozo, L. D., Studd, J . W. W.. Brincat, M. ~ O’Dowd. T. M. & Cooper, D. J . (1986) Internal urinary sphincter in maintcnancc of female continence. Br Med J 292. 166-167. 142-144. patients. In a study of 98 women proven t o be continent on pad testing (Vcrsi & Cardozo 1986) and vidcocystourethrography (Rates et ul. 1970), we noted that 50% of them had an incompetent bladder neck on coughing (Versi et al. 1986). Analysis of urcthral pressure profile transmission pressure ratios (Hilton & Stanton 1983) rcvealcd that women with an incompetent bladder neck remained continent by augmenting their distal transmission pressure ratios and so maintained their urethral strcss profile length (Versi et al. 1984~). This suggests that women with bladder neck funnelling (beaking) on coughing use their distal sphincter mechanisms. These mechanisms can be reinforced by voluntary contraction of the periurethral sphincter (Griffiths 1980) and also possibly the pelvic floor. Such an augmentation would require an intact neural input and so we postulate that radical surgery may interfere with this. Analysis of transmission pressure ratios in women with an incompetcnt bladder neck shows that the zone of maximum pressure transmission is more distal than in women with a competent bladder neck. In other words, the most important part of their urethra that maintains continence is morc distally located. This could explain why some women are incontinent after radical vulvectomy when the distal urethra is excised and perhaps pre-operative urethral pressure proflometry could be used to predict this (Versi et al. 19846). Eboo Versi Linda Cardozo Urodynamic Unit King’s College Hospital London SES

Effect of autonomic blockade on pressor responses to vasopressin in pregnant rats

OBJECTIVE We tested the hypothesis that gestational changes in reflex neural control of the heart and vasculature contribute to altered cardiovascular responses to vasopressin during pregnancy. STUDY DESIGN Changes in mean arterial pressure, cardiac output, total peripheral resistance, and heart rate were measured in response to constant infusion of arginine vasopressin (0.15 to 2.5 mU/kg/min) in conscious pregnant and virgin rats (n = 9) with total autonomic blockade plus restoration of baseline hemodynamics by norepinephrine infusion. RESULTS Resting cardiac output was 40% higher and total peripheral resistance 30% lower in pregnant animals (p < 0.01). Constant infusion of arginine vasopressin evoked equivalent changes in mean arterial pressure in both groups, but the respective contributions of cardiac output and total peripheral resistance to mean arterial pressure differed between groups. Cardiac output was unchanged and the increase in total peripheral resistance was significantly blunted in pregnant vs virgin rats during arginine vasopressin infusion. Control data in nonblocked revealed similar pressor responses to arginine vasopressin in gravid compared with virgin rats but no differences in the contributions of cardiac output and total peripheral resistance to the change in mean arterial pressure. CONCLUSION These findings suggest that neural modulation of arginine vasopressin-induced hypertension is altered during pregnancy and are consistent with a reduction in intrinsic vascular sensitivity to arginine vasopressin during gestation.

Renal Function and Volume Homeostasis during Pregnancy

This section focuses on the striking alterations in renal function and body fluid composition that take place during normal pregnancy. As will become clear, such alterations have a number of important implications for the physician caring for pregnant women.