Postural shock in pregnancy

Signs and symptoms of shock may be produced in some patients in late pregnancy by putting them in the dorsal recumbent posture. Change from this position will relieve the condition. The features of the supine hypotensive syndrome can be duplicated by applying pressure to the abdomen with the patient in a lateral position. The postural variations of venous pressure, blood pressure, and pulse appear to be due to obstruction of venous return from the lower portion of the body caused by the large uterus of late pregnancy compressing the vena cava. When shock is observed in a woman in late pregnancy, she should be turned to a lateral position before more active measures of treatment are begun.     

Pathogenesis of Lethal Shock After Intravenous Staphylococcal Enterotoxin B in Monkeys

The pathogenesis of shock in the rhesus monkey given intravenous staphylococcal enterotoxin B (SEB) is not understood. Several cardiovascular changes produced by a highly purified preparation of SEB were studied after administration of doses ranging from 50 to 1,000 mug/kg. Irreversible arterial hypotension was found consistently at the higher doses. Arterial blood pressure and cardiac output declined substantially as shock developed. Total peripheral vascular resistance did not rise at any time, but showed a significant fall during the late stages of shock. Portal and central venous pressures remained essentially unchanged. Venous O(2) content and pO(2) declined gradually throughout the period of toxemia, but arterial O(2) content remained constant until just prior to death, when a slight fall was noted in some monkeys. These changes were consistent with a pooling of blood in the peripheral vascular beds and seemed to resemble cardiovascular responses reported to occur in monkeys during shock due to bacterial endotoxin. Epinephrine, administered in the late stages of shock, caused arterial pressure to increase almost immediately and cardiac output to return to normal about 1 min later. Although life could occasionally be prolonged for several hours by continuous or intermittent epinephrine infusions, this therapy never succeeded in reversing the lethal effects of high doses of SEB.     

Pulmonary hemodynamics and lung water content during splanchnic ischemic shock

Pulmonary hemodynamics and lung water content were evaluated in open-chest dogs during splanchnic arterial occlusion (SAO) shock. Mean pulmonary arterial pressure [Ppa = 13.0 +/- 0.6 (SE) mmHg] and pulmonary venous pressure (4.1 +/- 0.2 mmHg) were measured by direct cannulation and the capillary pressure (Ppc = 9.0 +/- 0.6 mmHg) estimated by the double-occlusion technique. SAO shock did not produce a significant change in Ppa or Ppc despite a 90% decrease in cardiac output. An 18-fold increase in pulmonary vascular resistance occurred, and most of this increase (70%) was on the venous side of the circulation. No differences in lung water content between shocked and sham-operated dogs were observed. The effect of SAO shock was further evaluated in the isolated canine left lower lobe (LLL) perfused at constant flow and outflow pressure. The addition of venous blood from shock dogs to the LLL perfusion circuit caused a transient (10-15 min) increase in LLL arterial pressure (51%) that could be reversed rapidly with papaverine. In this preparation, shock blood produced either a predominantly arterioconstriction or a predominantly venoconstriction. These results indicate that both arterial and venous vasoactive agents are released during SAO shock. The consistently observed venoconstriction in the intact shocked lung suggests that other factors, in addition to circulating vasoactive agents, contribute to the pulmonary hemodynamic response of the open-chest shocked dog.     

MANAGEMENT OF VARICOSE VEINS DURING PREGNANCY

The incidence of recurrences after radical venous operations done during pregnancy or where pregnancy has occurred subsequently is much higher than it is in cases in which pregnancy is not a factor. These discouraging results are due to increased venous pressure, obstruction to the venous drainage of the lower extremities and hormonal factors. The management of varicose veins during pregnancy should be by conservative means consisting of proper elastic support, elevation of the extremities at night and during rest periods in the day, avoiding static dependency of the legs, and control of body weight. In event of venous stasis and severe symptoms of varicosis that cannot be controlled by conservative measures, limited surgical intervention is indicated. This should consist of high ligation and division of the involved venous trunk and the immediate tributaries. Radical extirpation of varicose veins should be reserved until further pregnancy is not contemplated.     

Uterine vein prostaglandin levels in late pregnant dogs.

We studied the uterine venous plasma concentrations of prostaglandins E2, F2 alpha, 15 keto 13,14 dihydro E2 and 15 keto 13,14 dihydro F2 alpha in late pregnant dogs in order to evaluate the rates of production and metabolism of prostaglandin E2 and F2 alpha in pregnancy in vivo. We used a very specific and sensitive gas chromatography-mass spectrometry assay to measure these prostaglandins. The uterine venous concentrations of prostaglandin E2 and 15 keto 13,14 dihydro E2 were 1.35 +/- .27 ng/ml and 1.89 +/- .37 ng/ml, respectively; however, we could not find any prostaglandin F2 alpha and very little of its plasma metabolite in uterine venous plasma. Since uterine microsomes can generate prostaglandin F2 alpha and E2 from endoperoxides, prostaglandin F2 alpha production in vivo must be regulated through an enzymatic step after endoperoxide formation. Prostaglandin E2 is produced by pregnant canine uterus in quantities high enough to have a biological effect in late pregnancy; however, prostaglandin F2 alpha does not appear to play a role at this stage of pregnancy.     

Atrial natriuretic factor in pregnancy and pregnancy-induced hypertension.

In normal pregnancy, cross-sectional clinical data do not consistently show plasma ANF concentration differences between early pregnancy and the nonpregnant state. Sequential data in the baboon (but not in rat) show a significant decrease in plasma ANF concentration and in cardiac filling pressures in early pregnancy. The latter data support the view that pregnancy is an underfill state secondary to a primary vasodilatation. Cross-sectional and longitudinal studies in normal pregnancy in humans show that plasma ANF levels tend rise to values that are, in the third trimester, higher than in the nonpregnant state. However, late postpartum sequential data (1.5-3 months) in humans do now show a significant drop in plasma ANF concentrations, suggesting that plasma ANF is not actually increased in normal pregnancy. In the baboon (but not in the rat) there is a steady rise in plasma ANF levels to values that are significantly higher in third trimester than before pregnancy. These data suggest that in human pregnancy, in contrast with the baboon, the plasma volume expansion induced by normal pregnancy is not sensed as such by the atria probably because of an isopressive adaptation of plasma volume to an enlarged vascular bed. However, acute decrease or increase of venous return induced by low sodium diet, changing position or infusion of isotonic saline are sensed as such by the atria in normal pregnancy as in the nonpregnant state.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of positive end-expiratory pressure ventilation on cerebral venous pressure with head elevation in dogs.

Mechanical ventilation with positive end-expiratory pressure (PEEP) may prevent venous air embolism in the sitting position because cerebral venous pressure (Pcev) could be increased by the PEEP-induced increase in right atrial pressure (Pra). Whereas it is clear that there is a linear transmission of the PEEP-induced increase in Pra to Pcev while the dog is in the prone position, the mechanism of the transmission with the dog in the head-elevated position is unclear. We tested the hypothesis that a Starling resistor-type mechanism exists in the jugular veins when the head is elevated. In one group of dogs, increasing PEEP linearly increased Pcev with the dog in the prone position (head at heart level, slope = 0.851) but did not increase Pcev when the head was elevated. In another group of dogs, an external chest binder was used to produce a larger PEEP-induced increase in Pra. Further increasing Pra increased Pcev only after Pra exceeded a pressure of 19 mmHg (break pressure). This sharp inflection in the upstream (Pcev)-downstream (Pra) relationship suggests that this may be caused by a Starling resistor-type mechanism. We conclude that jugular venous collapse serves as a significant resistance in the transmission of Pra to Pcev in the head-elevated position.     

Temporal relationship between changes in oxytocin and prostaglandin F levels in response to vaginal distension in the pregnant and puerperal ewe.

To investigate the r?le of oxytocin in the increase in utero-ovarian venous prostaglandin F (PGF) level caused by vaginal distension, jugular venous oxytocin and utero-ovarian venous PGF were measured simultaneously in one sheep in late pregnancy and in one sheep shortly before parturition. Vaginal distension raised oxytocin and PGF levels in both animals and oxytocin levels increased before those of PGF. These findings support the suggestion that the elevated PGF levels resulting from vaginal distension are caused by the reflex secretion of oxytocin.     

Influence of pregnancy on mean systemic filling pressure and the cardiac function curve in guinea pigs.

To assess the degree of circulatory fullness and to evaluate the influence of peripheral and cardiac factors in the regulation of cardiac output during pregnancy, the following studies were conducted using pentobarbital-anesthetized, open-chest nonpregnant and late term pregnant guinea pigs. Mean circulatory filling pressure was taken as the equilibrium pressure when the pulmonary artery was constricted. Total vascular compliance was assessed by +/- 5-mL changes in blood volume performed while this constriction was maintained. A separate group of guinea pigs was prepared with a pulmonary artery electromagnetic flow probe and right atrial catheter. Rapid infusion of saline was used to increase right atrial pressure while the cardiac output was determined. Pregnancy was characterized by the following changes relative to nonpregnant controls: 51Cr-labelled RBC blood volume increased from 55 +/- 3 to 67 +/- 3 mL/kg; mean circulatory filling pressure increased from 7.1 +/- 0.2 to 8.0 +/- 0.5 mmHg (1 mmHg = 133.322 Pa); right atrial pressure decreased from 3.4 +/- 0.2 to 2.1 +/- 0.3 mmHg; and cardiac output increased from 71.8 +/- 3.9 to 96.8 +/- 3.3 mL.min-1.kg-1. Total vascular compliance was not changed (2.1 +/- 0.1 mL.kg-1.mmHg-1) and most of the expanded blood volume was accommodated as unstressed volume. The cardiac function curve was shifted upwards in pregnant animals. The resistance to venous return, as determined from the slope of the venous return curves, was not changed. These data suggest that the circulation of the pregnant guinea pig is slightly overfilled.(ABSTRACT TRUNCATED AT 250 WORDS)     

Arterial pressure in humans during weightlessness induced by parabolic flights.

Results from our laboratory have indicated that, compared with those of the 1-G supine (Sup) position, left atrial diameter (LAD) and transmural central venous pressure increase in humans during weightlessness (0 G) induced by parabolic flights (R. Videbaek and P. Norsk. J. Appl. Physiol. 83: 1862-1866, 1997). Therefore, because cardiopulmonary low-pressure receptors are stimulated during 0 G, the hypothesis was tested that mean arterial pressure (MAP) in humans decreases during 0 G to values below those of the 1-G Sup condition. When the subjects were Sup, 0 G induced a decrease in MAP from 93 +/- 4 to 88 +/- 4 mmHg (P < 0.001), and LAD increased from 30 +/- 1 to 33 +/- 1 mm (P < 0.001). In the seated position, MAP also decreased from 93 +/- 6 to 87 +/- 5 mmHg (P < 0.01) and LAD increased from 28 +/- 1 to 32 +/- 1 mm (P < 0.001). During 1-G conditions with subjects in the horizontal left lateral position, LAD increased compared with that of Sup (P < 0.001) with no further effects of 0 G. In conclusion, MAP decreases during short-term weightlessness to below that of 1-G Sup simultaneously with an increase in LAD. Therefore, distension of the heart and associated central vessels during 0 G might induce the hypotensive effects through peripheral vasodilatation. Furthermore, the left lateral position in humans could constitute a simulation model of weightlessness.     

Periodic limb movements in sleep during pregnancy: a common but benign disorder?

Pregnant women have a two- to threefold increased prevalence of restless legs syndrome (RLS) compared to the general population, and the majority of RLS patients also experience periodic limb movements in sleep (PLMS). PLMS have been associated with sleep disturbance as well as autonomic heart rate and blood pressure responses; however, the prevalence, cause and significance of PLMS during pregnancy remain unknown. This study evaluated the presence of PLMS in late pregnancy and its relationship to hypertensive disorders of pregnancy. Ninety-one women in the third trimester of pregnancy underwent overnight polysomnography. An RLS questionnaire and the Multivariate Apnea Risk Index were administered and venous blood was sampled within 2 weeks of the sleep study. After exclusions due to obstructive sleep apnoea and signal loss, PLMS data were available for 73 women, 36 hypertensive women and 37 BMI- and gestation-matched controls. PLMS were found to be very common during pregnancy; 45% of women had a PLMS index > 5 and 25% had a PLMS index > 15. The number of PLMS per hour did not differ by hypertensive status. Sleep quality was mostly unaffected by PLMS, as was change in blood pressure overnight. While RLS was reported by 18.3% of the sample, this did not reliably predict the presence of PLMS. Despite iron deficiency being common in this population, it was not associated with PLMS. This novel study investigating the frequency and impact of PLMS during pregnancy revealed that PLMS are very common in the third trimester; however, this disorder appears to be benign in terms of objective sleep quality and relationship with pregnancy-related hypertension.

     

Essential hypertension and pregnancy.

Approximately 1% of pregnancies are complicated by essential hypertension. During pregnancy the blood pressure often stabilizes or improves. In patients with sustained hypertension, prospective controlled studies have demonstrated enhanced fetal survival when the blood pressure was controlled with antihypertensive medication. Such medication must be chosen carefully to avoid fetal and mateerial toxicity, and diuretics and salt restriction during pregnancy should be avoided. Among patients with essential hypertension the problem accelerates late in pregnancy in 2% to 11%; the acceleration may be predicted by determination of maternal mean arterial pressures and intravascular volumes early in pregnancy. The treatment of accelerated hypertension is identical to that of severe pre-eclampsia. Fetal loss is considerable but can be lessened by careful fetal and maternal monitoring and early controlled delivery. The risks of pregnancy in most patients with essential hypertension are small, and essential hypertension is not a uniform contraindication to pregnancy.     

Peripheral plasma progesterone and utero-ovarian prostaglandin F concentrations in the cow around parturition

The concentration of prostaglandin F in utero-ovarian venous plasma and progesterone in jugular venous plasma were determined by radioimmunoassay in 3 cows over the last 2–3 weeks of gestation. Utero-ovarian prostaglandin F concentrations did not show any consistent pattern in two of three cows until 48–72 h before term when the levels rose sharply from 1 ng/ml to a maximum 4–9 ng/ml during labour. The concentration of progesterone in jugular venous plasma tended to fall gradually over the last 20 days of gestation with a further fall occurring 48-36 h before delivery.In two other cows at around 240 days of gestation the concentration of plasma progesterone in ovarian venous plasma was 50 to 150 times the concentration of progesterone in uterine or jugular venous plasma. It is concluded from these results that the ovaries are the major source of progesterone in cows during late pregnancy. The findings also suggest that prostaglandin F may be the luteolytic factor responsible for the sharp decline in plasma progesterone concentrations over the last 48-36 h preceding parturition.     

Interference of the PAF-acether antagonist BN 52021 with endotoxin-induced hypotension in the guinea-pig

Because of the potential role of PAF-acether in the pathogenesis of endotoxin shock, we examined the preventive and curative effects of BN 52021, a new PAF-acether antagonist in guinea-pig challenged with S. Typhimurium endotoxin. A biphasic reduction of mean arterial pressure was elicited by i.v. endotoxin (300 micrograms/kg) in control animals, with a rapid drop of blood pressure (maximal decrease within 10 min), partial recovery at 20 min and a second gradual decrease after 30 min. Treatment with BN 52021 injected 15 min prior to endotoxin reduced the initial rapid drop of blood pressure from 38.5 +/- 5 mmHg in vehicle-treated controls (n = 15) to 17 +/- 3 mmHg (p less than 0.01) in animals treated with 1 mg/kg BN 52021(n = 10) and to 9.5 +/- 8 mmHg (p less than 0.01) in guinea-pigs treated with 6 mg/kg BN 52021 (n = 5). The early hypotensive phase was associated with severe thrombocytopenia-leukopenia; only the thrombocytopenia was reduced by BN 52021. The prolonged secondary phase of hypotension was reduced by BN 52021 pretreatment whereas a small increase of hematocrit persisted. The two phases of the arterial pressure profile during endotoxic shock were not observed in animals previously made thrombopenic by rabbit and anti-platelet serum and only the late hypotensive phase persisted. This late hypotension induced by endotoxin in thrombopenic animals was suppressed by BN 52021 pretreatment suggesting that BN 52021 may act via a platelet-independent mechanism. The intravenous injection of BN 52021 during the prolonged secondary phase of shock was followed by an immediate increase of the depressed blood pressure. This increase of blood pressure was dose-dependent, maximum at 6 mg/kg BN 52021, and observed in normal and thrombopenic animals. The interference of BN 52021 with endotoxin shock may be related to its PAF-acether antagonist properties and suggests that PAF-acether is an important participant in endotoxic shock.     

妊娠中晚期胎儿轻度侧脑室增宽的超声诊断

目的:研究妊娠中晚期轻度侧脑室增宽胎儿的超声表现以及妊娠结局情况。方法:回顾性分析我院产前诊断的60例轻度侧脑室增宽的胎儿的声像图资料,均经引产或产后随访证实。结果:60例胎儿中,孤立性者42例,合并其它畸形的轻度侧脑室增宽者18例(1例NTD高风险,2例21-三体高风险)。30例单侧,30例双侧,脑室宽度为10.5~14.5 mm,平均宽度13.1 mm。22例终止妊娠,32例(包括2例双胎之一)产前超声侧脑室随访变为正常宽度,4例产后随访正常,2例产后超声和MRI证实为脑积水。结论:超声是诊断胎儿轻度侧脑室增宽的重要影像学手段,对指导妊娠结局有重要意义。     

Uterine vein prostaglandin levels in late pregnant dogs

We studied the uterine venous plasma concentrations of prostaglandins E₂, F_2α, 15 keto 13,14 dihydro E₂ and 15 keto 13,14 dihydro F_2α in late pregnant dogs in order to evaluate the rates of production and metabolism of prostaglandin E₂ and F_2α in pregnancy $\text{in vivo}$. We used a very specific and sensitive gas chromatography-mass spectrometry assay to measure these prostaglandins. The uterine venous concentrations of prostaglandin E₂ and 15 keto 13,14 dihydro E₂ were 1.35±.27 ng/ml and 1.89±.37 ng/ml, respectively; however, we could not find any prostaglandin F_2α and very little of its plasma metabolite in uterine venous plasma. Since uterine microsomes can generate prostaglandin F_2α and E₂ from endoperoxides, prostaglandin F_2α production $\text{in vivo}$ must be regulated through an enzymatic step after endoperoxide formation. Prostaglandin E₂ is produced by pregnant canine uterus in quantities high enough to have a biological effect in late pregnancy; however, prostaglandin F_2α does not appear to play a role at this stage of pregnancy.     

Haematological, blood gas and acid-base effects of central histamine-induced reversal of critical haemorrhagic hypotension in rats.

In a rat model of volume-controlled irreversible haemorrhagic shock, which results in a severe metabolic acidosis and the death of all control animals within 30 min., intracerebroventricular injection of histamine (100 nmol) produces a prompt and long-lasting increase in mean arterial pressure and heart rate, with a 100% survival of 2 h after treatment. Histamine action is accompanied by a decrease in haematocrit value, haemoglobin concentration, erythrocyte and platelet count, and an increase in residual blood volume at the end of the experiment (2 h). Cardiovascular effects are also associated with a long-lasting rise in respiratory rate and biphasic blood acid-base changes - initial increase of metabolic acidosis with the decrease in arterial and venous pH, bicarbonate concentration and base excess, followed by almost a complete recovery of blood gas and acid-base parameters to the pre-bleeding values, with normalisation of arterial and venous pH, Pco2 bicarbonate concentration and base excess at the end of experiment. It can be concluded that in the late phase of central histamine-induced reversal of haemorrhagic hypotension there is almost a complete restoration of blood gas and acid-base status due to circulatory and respiratory compensations, while accompanying haematological changes are the result of the haemodilution and the increase in residual blood volume.     

Standing up to the challenge of standing: a siphon does not support cerebral blood flow in humans

Model studies have been advanced to suggest both that a siphon does and does not support cerebral blood flow in an upright position. If a siphon is established with the head raised, it would mean that internal jugular pressure reflects right atrium pressure minus the hydrostatic difference from the brain. This study measured spinal fluid pressure in the upright position, the pressure and the ultrasound-determined size of the internal jugular vein in the supine and sitting positions, and the internal jugular venous pressure during seated exercise. When the head was elevated approximately 25 cm above the level of the heart, internal jugular venous pressure decreased from 9.5 (SD 2.8) to 0.2 (SD 1.0) mmHg [n = 15; values are means (SD); P < 0.01]. Similarly, central venous pressure decreased from 6.2 (SD 1.8) to 0.6 (SD 2.6) mmHg (P < 0.05). No apparent lumen was detected in any of the 31 left or right internal veins imaged at 40 degrees head-up tilt, and submaximal (n = 7) and maximal exercise (n = 4) did not significantly affect internal jugular venous pressure. While seven subjects were sitting up, spinal fluid pressure at the lumbar level was 26 (SD 4) mmHg corresponding to 0.1 (SD 4.1) mmHg at the base of the brain. These results demonstrate that both for venous outflow from the brain and for spinal fluid, the prevailing pressure approaches zero at the base of the brain when humans are upright, which negates that a siphon supports cerebral blood flow.     

Effects of Treatment on the Mortality Rate in Septicaemia

The results of treatment have been analysed in 173 patients with septicaemia during 1962–8. Between 1962 and 1965 various antibiotics were used, and shock was treated with vasopressor agents. Between 1966 and 1968 kanamycin was given initially, and shock was treated with corticosteroids and with intravenous fluid therapy monitored with a central venous pressure manometer.The mortality rate in 1966–8 fell to half that of the earlier period in patients with Gram-negative infections, and in those with shock. The reduced mortality in the latter was clearly associated with the use of a central venous manometer to control intravenous fluid therapy, though whether the reduction resulted from specific improvement in intravenous therapy or from the necessary closer observation of the patient is not clear. Staphylococcal septicaemia was common during both periods, and its mortality rate did not fall; hence methicillin together with kanamycin is now given initially in all cases.     

Is cardiac filling pressure the limiting factor in adjusting to heat stress?

The concept that a specific level of central venous pressure (CVP) limits man's adjustment to heat stress has been debated. Evidence was presented that identifies a true limit of adjustment as being more related to factors affecting evaporative cooling, such as level of hydration, release of active vasodilation substance (AVS), and sweat gland fatigue. However, it was conceded that decreases in CVP and subsequent low-pressure baroreceptor activation modify cutaneous blood flow and subsequently reduce conductance of heat from the core to the periphery. It was suggested that CVP merely reflects a downstream pressure, which must be allowed to reach a pressure lower than that observed in the peripheral venous bed during active cutaneous vasodilation, to insure adequate venous return. However, a loss of evaporative cooling has been observed during prolonged progressive dehydration of subjects in the supine position, resulting in 3 to 4 percent loss of total body weight. This loss of evaporative cooling was not apparent when euhydration was maintained. As it was unlikely that CVP was reduced in these experiments in the supine position, it was concluded that CVP was not the limiting factor in man's adjustment to heat stress.