Forebrain-Specific Transgene Rescue of 11β-HSD1 Associates with Impaired Spatial Memory and Reduced Hippocampal Brain-Derived Neurotrophic Factor mRNA Levels in Aged 11β-HSD1 Deficient Mice

Mice lacking the intracellular glucocorticoid-regenerating enzyme 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) are protected from age-related spatial memory deficits. 11β-HSD1 is expressed predominantly in the brain, liver and adipose tissue. Reduced glucocorticoid levels in the brain in the absence of 11β-HSD1 may underlie the improved memory in aged 11β-HSD1 deficient mice. However, the improved glucose tolerance, insulin sensitisation and cardioprotective lipid profile associated with reduced peripheral glucocorticoid regeneration may potentially contribute to the cognitive phenotype of aged 11β-HSD1 deficient mice. In the present study, transgenic mice with forebrain-specific overexpression of 11β-HSD1 (Tg) were intercrossed with global 11β-HSD1 knockout mice (HSD1KO) to examine the influence of forebrain and peripheral 11β-HSD1 activity on spatial memory in aged mice. Transgene-mediated delivery of 11β-HSD1 to the hippocampus and cortex of aged HSD1KO mice reversed the improved spatial memory retention in the Y-maze but not spatial learning in the watermaze. Brain-derived neurotrophic factor (BDNF) mRNA levels in the hippocampus of aged HSD1KO mice were increased compared to aged wild-type mice. Rescue of forebrain 11β-HSD1 reduced BDNF mRNA in aged HSD1KO mice to levels comparable to aged wild-type mice. These findings indicate that 11β-HSD1 regenerated glucocorticoids in the forebrain and decreased levels of BDNF mRNA in the hippocampus play a role in spatial memory deficits in aged wild-type mice, although 11β-HSD1 activity in peripheral tissues may also contribute to spatial learning impairments in aged mice.

The role of brain-derived neurotrophic factor in learned fear processing: an awake rat fMRI study

Brain‐derived neurotrophic factor (BDNF) signaling is implicated in the etiology of many psychiatric disorders associated with altered emotional processing. Altered peripheral (plasma) BDNF levels have been proposed as a biomarker for neuropsychiatric disease risk in humans. However, the relationship between peripheral and central BDNF levels and emotional brain activation is unknown. We used heterozygous BDNF knockdown rats (BDNF^+/−) to examine the effects of genetic variation in the BDNF gene on peripheral and central BDNF levels and emotional brain activation as assessed by awake functional magnetic resonance imaging (fMRI). BDNF^+/− and control rats were trained to associate a flashing light (conditioned stimulus; CS) with foot‐shock, and brain activation in response to the CS was measured 24 h later in awake rats using fMRI. Central and peripheral BDNF levels were decreased in BDNF^+/− rats compared with control rats. Activation of fear circuitry (amygdala, periaqueductal gray, granular insular) was seen in control animals; however, activation of this circuitry was absent in BDNF^+/− animals. Behavioral experiments confirmed impaired conditioned fear responses in BDNF^+/− rats, despite intact innate fear responses. These data confirm a positive correlation [r = 0.86, 95% confidence interval (0.55, 0.96); P = 0.0004] between peripheral and central BDNF levels and indicate a functional relationship between BDNF levels and emotional brain activation as assessed by fMRI. The results demonstrate the use of rodent fMRI as a sensitive tool for measuring brain function in preclinical translational studies using genetically modified rats and support the use of peripheral BDNF as a biomarker of central affective processing.

Explanations for variation in cognitive ability: Behavioural ecology meets comparative cognition

Sara Shettleworth has played a defining role in the development of animal cognition and its integration into other parts of biology, especially behavioural ecology. Here we chart some of that progress in understanding the causes and importance of variation in cognitive ability and highlight how Tinbergen's levels of explanation provide a useful framework for this field. We also review how experimental design is crucial in investigating cognition and stress the need for naturalistic experiments and field studies. We focus particularly on the example of the relationship among food hoarding, spatial cognition and hippocampal structure, and review the conflicting evidence for sex differences in spatial cognition. We finish with speculation that a combination of Tinbergen and Shettleworth-style approaches would be the way to grapple with the as-yet unanswered questions of why birds mimic heterospecifics.

Behavioral profiles of inbred strains on novel olfactory, spatial and emotional tests for reference memory in mice

Studying the behavior of genetic background strains provides important information for the design and interpretation of cognitive phenotypes in mutant mice. Our experiments examined the performance of three commonly used strains (C57BL/6J, 129S6, DBA/2J) on three behavioral tests for learning and memory that measure very different forms of memory, and for which there is a lack of data on strain differences. In the social transmission of food preference test (STFP) all three strains demonstrated intact memory for an odor-cued food that had been sampled on the breath of a cagemate 24 hours previously. While C57BL/6J and 129S6 mice showed good trace fear conditioning, DBA/2J mice showed a profound deficit on trace fear conditioning. In the Barnes maze test for spatial memory, the 129S6 strain showed poor probe trial performance, relative to C57BL/6J mice. Comparison of strains for open field exploratory activity and anxiety-like behavior suggests that poor Barnes maze performance reflects low exploratory behavior, rather than a true spatial memory deficit, in 129S6 mice. This interpretation is supported by good Morris water maze performance in 129S6 mice. These data support the use of a C57BL/6J background for studying memory deficits in mutant mice using any of these tasks, and the use of a 129S6 background in all but the Barnes maze. A DBA/2J background may be particularly useful for investigating the genetic basis of emotional memory using fear conditioning.

Fetal cerebral and peripheral circulatory responses to hypoxia after nitric oxide synthase inhibition

The increase in cerebral blood flow (CBF) during hypoxia in fetal sheep at 0.6 gestation is less than the increase at 0.9 gestation when normalized for differences in baseline CBF and oxygen consumption. Nitric oxide (NO) synthase (NOS) catalytic activity increases threefold during this period of development. We tested the hypothesis that administration of the NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME) decreases the CBF response to systemic hypoxia selectively at 0.9 gestation. We also tested whether any peripheral vasoconstriction during hypoxia is potentiated by L-NAME at 0.9 gestation. Administration of L-NAME increased arterial blood pressure and decreased microsphere-determined CBF during normoxia in fetal sheep at both 0.6 and 0.9 gestation. With subsequent reduction of arterial oxygen content by approximately 50%, the percent increase in forebrain CBF in a control group (57 +/- 11%; +/- SE) and L-NAME-treated group (51 +/- 6%) was similar at 0.6 gestation. Likewise, at 0.9 gestation, the increase in CBF was similar in control (90 +/- 25%) and L-NAME (80 +/- 28%) groups. At 0.9 gestation, L-NAME treatment attenuated the increase in coronary blood flow and increased gastrointestinal vascular resistance during hypoxia. We conclude that NO exerts a basal vasodilatory influence in brain as early as 0.6 gestation in fetal sheep but is not an important mechanism for hypoxic vasodilation in brain at either 0.6 or 0.9 gestation. Thus the developmental increase in NOS catalytic capacity does not appear to be responsible for developmental increases in the CBF response to hypoxia during this period. In contrast, NO modulates the vascular response to hypoxia in heart and gastrointestinal tract.

Blood-brain barrier permeability during dopamine-induced hypertension in fetal sheep

Dopamine is often used as a pressor agent in sick newborn infants, but an increase in arterial blood pressure could disrupt the blood-brain barrier (BBB), especially in the preterm newborn. Using time-dated pregnant sheep, we tested the hypothesis that dopamine-induced hypertension increases fetal BBB permeability and cerebral water content. Barrier permeability was assessed in nine brain regions, including cerebral cortex, caudate, thalamus, brain stem, cerebellum, and spinal cord, by intravenous injection of the small tracer molecule [(14)C]aminoisobutyric acid at 10 min after the start of dopamine or saline infusion. We studied 23 chronically catheterized fetal sheep at 0.6 (93 days, n = 10) and 0.9 (132 days, n = 13) gestation. Intravenous infusion of dopamine increased mean arterial pressure from 38 +/- 3 to 53 +/- 5 mmHg in 93-day fetuses and from 55 +/- 5 to 77 +/- 8 mmHg in 132-day fetuses without a decrease in arterial O(2) content. These 40% increases in arterial pressure are close to the maximum hypertension reported for physiological stresses at these ages in fetal sheep. No significant increases in the brain transfer coefficient of aminoisobutyric acid were detected in any brain region in dopamine-treated fetuses compared with saline controls at 0.6 or 0.9 gestation. There was also no significant increase in cortical water content with dopamine infusion at either age. We conclude that a 40% increase in mean arterial pressure during dopamine infusion in normoxic fetal sheep does not produce substantial BBB disruption or cerebral edema even as early as 0.6 gestation.

Intensive care utilization during hospital admission for delivery: prevalence, risk factors, and outcomes in a statewide population

BACKGROUND

During childbirth, the maternal need for intensive care unit (ICU) services is not well-defined. This information could influence the decision whether to incorporate ICU services into the labor and delivery suite.

METHODS

This study reports (1) ICU use and mortality rates in a statewide population of obstetric patients during their hospital admission for childbirth, and (2) the risk factors associated with ICU admission and mortality. A case-control design using patient records from a state-maintained anonymous database for the years 1984-1997 was used. Outcome variables included ICU use and mortality rates.

RESULTS

Of the 822,591 hospital admissions for delivery of neonates during the study period, there were 1,023 ICU admissions (0.12%) and 34 ICU deaths (3.3%). Age, race, hospital type, volume of deliveries, and source of admission independently and in combination were associated with ICU admission (P < 0.05). The most common risk factors associated with ICU admission included cesarean section, preeclampsia or eclampsia, and postpartum hemorrhage (P < 0.001). Black race, high hospital volume of deliveries, and longer duration of ICU stay were associated with ICU mortality (P < 0.05). The most common risk factors associated with ICU mortality included pulmonary complications, shock, cerebrovascular event, and drug dependence (P < 0.05).

CONCLUSIONS

This study shows that ICU use and mortality rate during hospital admission for delivery of a neonate is low. These results may influence the location of perinatal ICU services in the hospital setting.

Efficacy of the cushing response in maintaining cerebral blood flow in premature and near-term fetal sheep

Fetal head compression during labor may increase intracranial pressure (ICP) and decrease cerebral perfusion pressure (CPP). An increase in mean arterial pressure (MAP) associated with the Cushing response normally acts to mitigate an ischemic insult when the increase in ICP approaches MAP. However, the premature fetus may be limited in its ability to increase MAP. We compared the efficacy of the pressor response in sustaining CPP, cerebral blood flow (CBF), and cerebral O2 consumption (CMRO2) in chronically catheterized fetal sheep at 0.6 gestation (92 d; n = 7) and 0.9 gestation (133 d; n = 7). When fetal ICP was increased to baseline MAP (41 +/- 3 mm Hg; +/-SEM) in 92-d fetuses, MAP increased by 7 +/- 2 mm Hg and remained stable during 30 min of constant ICP elevation; CBF decreased by 72% and CMRO2 decreased by 46%. In 133-d fetuses, MAP increased from 53 +/- 2 to 65 +/- 4 mm Hg at 3 min of elevated ICP; CBF decreased by 62% and CMRO2 decreased 30%. However, MAP continued to increase after 3 min and reached a stable level of 75 +/- 3 mmHg at 30 min in 133-d fetuses. The additional increase in MAP restored CBF and CMRO2 to baseline values. Plasma epinephrine and vasopressin concentrations increased between 6 and 33 min of elevated ICP to levels, exceeding those in 92-d fetuses. We conclude that the arterial pressure response to intracranial hypertension is present at 0.6 gestation but is less well developed than at 0.9 gestation in fetal sheep, possibly due to immaturity of the sympathoadrenal and vasopressin systems. Consequently, CBF and CMRO2 are not as well defended at mid-gestation against elevated ICP as might occur during difficult labor.

A randomized, double-blind, dose-response comparison of epidural fentanyl versus sufentanil analgesia after cesarean section

This study was designed to determine and compare the dose-response characteristics, speed of onset, and relative potency of single-dose epidural fentanyl (F) and sufentanil (S) for postoperative pain relief. Eighty women undergoing cesarean section (C/S) with epidural 2% lidocaine with epinephrine (1:200,000) were randomly assigned to receive double-blind epidural administration of F (25, 50, 100, or 200 microg) or S (5, 10, 20, or 30 microg) (n = 10 per group) upon complaint of pain postoperatively. Visual analog scales (VAS, 0-100 mm) were used to assess pain and sedation at baseline; at 3, 6, 9, 12, 15, 20, 25, 30, 45, and 60 min; and every 30 min until further analgesia was requested. The study was terminated at 30 min if satisfactory analgesia was not achieved. Side effects were recorded. A dose-response was demonstrated for both opioids. F 25 microg and S 5 microg were ineffective, with significantly fewer women achieving VAS scores <10 mm (P < 0.05 compared with F 100 or 200 microg and S 20 or 30 microg). F 100 and 200 microg and S 20 and 30 microg all achieved VAS scores <10 mm in all women with no differences in time to 50% reduction in VAS (mean 11-16 min) and no differences in duration of analgesia (mean 117-138 min). The 50% and 95% effective dose values for each opioid to achieve a VAS score <10 mm were F 33 microg and 92 microg and S 6.7 microg and 17.5 microg. There were no differences among groups in sedation scores or side effects. Our data suggest that the relative analgesic potency of epidural S:F is approximately 5 and that there are no differences between the opioids in the onset, duration, and effectiveness of analgesia when equianalgesic doses are administered postoperatively after lidocaine anesthesia for C/S.

Developmental and regional differences in nitric oxide synthase activity and blood flow in the sheep brain

Nitric oxide synthase (NOS) participates in the regulation of cerebral blood flow and neurotransmitter release and as a second messenger of glutamatergic and cholinergic systems. Developmental differences in NOS activity have been described in the rat, but not in a species with longer gestation and a larger, lobulated brain at birth. We assayed NOS activity by conversion of [14C]L-arginine to [14C]L-citrulline in 50-mg tissue samples from eight brain regions in sheep at 70, 92, 110, and 135 days gestation (term = 145 days); newborns (< 7 days); and adults to test the hypothesis that NOS activity in the brain is developmentally regulated from midgestation through adulthood and matures along the neuroaxis in parallel with the known development of cerebral blood flow and neuronal activity. Three patterns of maturation of NOS activity were evident: increasing to or exceeding adult levels before 70 days gestation in the thalamus, cerebellum, and medulla; increasing to adult levels between 70 and 92 days in the hippocampus; and increasing to adult levels after 92 days in the cortex and caudate. Additionally, there were regional differences in cortical NOS activity: at 70 and 92 days of gestation, frontal cortex NOS activity was greater than parietal or occipital activity, and at 135 days gestation and in the newborn and adult, cortical and caudate activity exceeded that in most of the more caudal regions. The up to fourfold increase in regional cortical NOS activity between 92 and 135 days gestation was associated with twofold increases in cerebral blood flow and oxygen consumption during this period. Inhibition of NOS activity with administration of 60 mg/kg of NG-nitro-L-arginine methylester (L-NAME) resulted in 27% and 25% reductions in cerebral blood flow at 93 and 133 days gestation. While the associated increases in NOS activity with increases in CBF and CMRO2 do not appear causative, at various points in gestation the development of NOS activity may participate in the development of mature patterns of cerebral blood flow regulation in parallel with development of synaptic and electrical activity.

Bacteremia due to Stenotrophomonas (Xanthomonas) maltophilia: a prospective, multicenter study of 91 episodes

We identified 91 cases of bacteremia due to Stenotrophomonas (Xanthomonas) maltophilia in a prospective, multicenter observational study. The patients were highly compromised; the majority had an underlying malignancy, had received immunosuppressive therapy, and had indwelling venous catheters. Although 94% of patients received an antimicrobial agent to which the blood isolate was susceptible, the mortality among these patients 14 days after the onset of bacteremia was 21%. Mortality was significantly correlated with the presence of a hematologic malignancy or neutropenia or transplantation, immunosuppressive therapy, and a severity-of-illness score of > 4. S. maltophilia infection is associated with substantial morbidity and mortality among highly compromised patients. The organism is typically resistant to expanded spectrum beta-lactam agents and aminoglycoside antibiotics. Trimethoprim-sulfamethoxazole should be administered if the isolate is susceptible to this combination; addition of another agent to which the isolate is susceptible should be considered in treating patients who are neutropenic, immunocompromised, or critically ill.

Anesthesia in obstetrics

Some of the topics which have generated particular interest in obstetric anesthesia recently include the effects of epidural anesthesia on the progress of labor, the efficacy of volume preloading prior to spinal anesthesia for cesarean section, and the use of intraspinal opioids and of alpha-2 adrenergic agonists for labor analgesia.

Changes in heart rate variability under propofol anesthesia: a possible explanation for propofol-induced bradycardia

We propose to study the bradycardia associated with propofol anesthesia. Ten women undergoing laparoscopy for benign disease were studied using ambulatory electrocardiogram monitoring. Anesthesia was induced with an intravenous bolus of propofol and maintained with an infusion. After ventilation using positive pressure via a mask for 5 min, relaxants (succinylcholine or vecuronium) and opioids (alfentanil or fentanyl) were administered and the trachea was intubated. Approximately 15 min later, the laparoscopic trocar was placed and carbon dioxide insufflated. Heart rate variability spectra using a fast Fourier transformation technique were determined from the recordings in four separate time periods (preinduction, postinduction, postintubation, and posttrocar placement). Total, high-frequency, and low-frequency power in each time period was determined. Induction of anesthesia with propofol was associated with a significant reduction in total, low-frequency, and high-frequency power. Maintenance of anesthesia with propofol alone resulted in further reductions in total and low-frequency, but not high-frequency, power. Placement of the laparoscopic trocar and insufflation of carbon dioxide resulted in a decrease in heart rate and an increase in high-frequency power. We conclude that high-frequency variability reflects parasympathetic tone. Propofol anesthesia reduces parasympathetic tone to a lesser degree than sympathetic tone. This autonomic milieu predisposes the patient to developing bradycardia in response to parasympathetic stimuli.

Effect of rapid intravenous crystalloid infusion on uteroplacental blood flow and placental implantation-site oxygen delivery in the pregnant ewe

OBJECTIVE

Our purpose in this study was to investigate the effects of rapid intravenous crystalloid infusion on placental implantation-site blood flow and oxygen delivery in the near-term pregnant ewe.

STUDY DESIGN

Maternal left ventricular, femoral arterial and venous, and bilateral fetal hind limb arterial catheters were placed in nine near-term ewes 5 days before the start of the study. Maternal and fetal arterial blood gas values, maternal hemodynamic measurements, and maternal organ blood flows (microsphere technique) were obtained before and after the intravenous infusion of 2.0 to 2.5 L of normal saline solution. Myometrial and placental implantation-site vascular resistances and oxygen delivery were calculated. The t test for paired comparisons was used for statistical analysis, with p < or = 0.05 considered significant.

RESULTS

Significant postinfusion increases in maternal mean arterial pressure, placental implantation-site blood flow, and skin, skeletal muscle, and renal blood flows were recorded. In the six animals that demonstrated a fall in hemoglobin concentration, a significant increase in placental implantation-site oxygen delivery and a significant decrease in placental implantation-site vascular resistance were also seen. No significant changes were seen in myometrial blood flow or myometrial vascular resistance.

CONCLUSION

Rapid intravenous crystalloid infusion selectively increases placental implantation-site blood flow in the near-term pregnant ewe and may improve oxygen delivery to the fetus, especially if hemodilution occurs.

Validation of arterial oxygen saturation measurements in utero using pulse oximetry

The noninvasive measurement of fetal arterial oxygen saturation using pulse oximetry could be of potential use in assessing fetal well-being in utero during labor. In this study, the accuracy and technical feasibility of reflectance pulse oximetry in utero was evaluated in acutely instrumented fetal sheep using a specially designed sensor. Following recalibration of the analysis algorithms, fetal arterial saturation could be measured by pulse oximetry in utero. Arterial oxygenation measurements obtained using pulse oximetry correlated well with simultaneous in vitro measurements over the range of 6 to 81%. We conclude that in utero pulse oximetry is technically feasible, appears useful and accurate, and merits further evaluation.

Anesthesia and analgesia for labor

Epidural analgesia remains the mainstay for providing pain relief during labor. The search continues to find the ideal combination of analgesic agents and administration techniques that will provide excellent pain relief for the mother yet minimize side effects to the mother and fetus. This article reviews recent studies of epidural analgesia, including the increased use of epidural opioids, patient-controlled epidural analgesia, and the complications of epidural analgesia (including effects on gastric emptying, maternal temperature control, and hemodynamic changes to the mother and fetus). Intrathecal (spinal) analgesia, especially using opioids, is also discussed.

Circulatory dynamics during periodic intracranial hypertension in fetal sheep

The human fetal head is periodically compressed during labor. The resulting increase in intracranial pressure (ICP) may exceed the hydrostatic increase in mean arterial pressure (MAP), thereby decreasing cerebral perfusion pressure (CPP). We determined whether the cardiovascular system of near-term fetal sheep is capable of rapidly increasing MAP during periodic increases in ICP. In 12 chronically instrumented fetuses, we produced sinusoidal oscillations in ICP with a maximum of 52 +/- 1 mmHg (baseline MAP) and a minimum of 4 +/- 1 mmHg at a 3-min periodicity by ventricular fluid infusion and withdrawal. Phasic increases in MAP and decreases in electromagnetically determined renal blood flow tracked behind ICP by 0.3-0.5 min. By the sixth cycle, tonic peripheral vasoconstriction that occurred attenuated by the reduction in CPP during subsequent ICP oscillations. By the 10th cycle, plasma catecholamines and vasopressin increased 20-fold. To more closely simulate the pattern during labor, we produced an ICP triangular pulse train with 5-min periodicity and pulse duration of 1.5 min in six other fetuses. The MAP response was nearly out of phase with this more rapid rise of ICP. Thus the phasic component of the fetal pressor response is inadequate for maintaining CPP when ICP is increased to baseline MAP in less than 0.75 min. However, when the ICP pulse duration and frequency are sufficiently high, a tonic pressor response that may be humorally mediated acts to minimize transient cerebral ischemia.

Efficacy of Cushing response during development in sheep

Mean aortic pressure (MAP) increases (Cushing response) when intracranial pressure (ICP) approaches MAP. We elevated ICP to levels equivalent to normal baseline MAP with infusion of mock cerebrospinal fluid (CSF) into the lateral cerebral ventricles and contrasted responses in near-term fetal sheep, 1-wk-old lambs, and adult sheep anesthetized with pentobarbital sodium. With CSF infusion 1-wk-old lambs and adults produced sustained increases in MAP of 16 +/- 1 and 22 +/- 2 mmHg, respectively, over a 40-min period. However, cerebral blood flow fell 66 and 57%, and cerebral O2 uptake fell 34 and 37%, respectively. In the near-term fetus, MAP increased by 11 +/- 1 mmHg and cerebral blood fell 49% at 3 min of elevated ICP. However, by 15 min MAP had increased further (+17 +/- 2 mmHg) and cerebral blood flow was nearly restored. In contrast to postnatal sheep, cerebral O2 uptake was maintained throughout in the fetus. The mechanism of increased MAP differed among groups. In adults total peripheral resistance fell significantly, whereas in the fetus and lamb it remained constant. Cardiac output increased in each group, but, because of the fall in peripheral resistance, increased cardiac output was relatively more important to the rise in MAP in adults. In addition, marked vasoconstriction occurred in intestines and skin in the fetus. The Cushing response is well-developed in near-term fetal sheep. After birth it may lose its effectiveness in providing for the basal metabolic demand of the brain.

Cerebral and peripheral circulatory responses to intracranial hypertension in fetal sheep

Fetal head compression during normal labor can increase intracranial pressure (ICP). We studied the cerebral and peripheral blood flow responses to ICP elevation in utero in chronically catheterized fetal sheep using the radiolabeled microsphere technique. ICP was elevated, stepwise, in increments of 6 +/- 1 mm Hg by infusion of artificial cerebrospinal fluid into a lateral ventricle. When ICP was raised to within 28 mm Hg of baseline mean arterial blood pressure (i.e., ICP above 22 mm Hg), arterial pressure began to increase. Above this ICP level, up to 41 mm Hg, mean cerebral perfusion pressure was maintained by equivalent increases in arterial pressure. Cerebral blood flow and O2 uptake at the highest ICP levels were not different from baseline values. Changes in peripheral organ blood flow were graded according to the level of ICP. At the highest level (ICP = 41 mm Hg), renal, gastrointestinal, and skin blood flow decreased by 68%, 69%, and 65%, respectively. Myocardial and adrenal blood flow doubled, whereas heart rate and cardiac output were unchanged. Placental blood flow increased in proportion to arterial pressure. Arterial plasma epinephrine, norepinephrine and arginine vasopressin increased by nearly two orders of magnitude. Therefore, as ICP approaches baseline mean arterial pressure, fetal lambs are capable of sustaining cerebral perfusion by initiating profound visceral vasoconstriction without curtailing placental blood flow. Since cerebral O2 uptake was maintained, there is no evidence that stimulation of the peripheral response requires pronounced cerebral ischemia. This highly developed Cushing response may be important for ensuring cerebral viability when the fetal head is compressed during parturition.

Absorption characteristics of human fetal hemoglobin at wavelengths used in pulse oximetry

The absorption characteristics of fetal and adult human hemoglobin samples were determined for the range of 600 to 1,050 nm. Over this range, fetal hemoglobin absorption is nearly identical to that of adult hemoglobin. Since currently available two-wavelength pulse oximeters base their calculations of arterial oxyhemoglobin saturation on absorption at the wavelengths of 660 and 920 nm, we conclude that the accuracy of two-wavelength pulse oximetry previously demonstrated in adults can be extrapolated to infants with high concentrations of fetal hemoglobin.

Accuracy of pulse oximetry during arterial oxyhemoglobin desaturation in dogs

An animal model was developed to evaluate the accuracy of pulse oximetry over a wide range of oxyhemoglobin desaturation. The fractional inspired oxygen concentration was varied from 0.03-1.0 in five anesthetized dogs. One hundred and twelve simultaneous pulse oximeter oxygen saturation measurements (SpO2) and IL 282 CO-Oximeter arterial oxygen saturation (SaO2) measurements were made. Variance of SpO2 was increased for SaO2 less than 22%. Linear regression analysis of the data for SaO2 greater than 22% produced the equation y = 0.93x + 9.8 (r2 = 0.97). The mean difference between SpO2 and SaO2 was +5.5% +/- 4.2% (SD) over the range of 22-100%. Spectral analyses of oxygenated (O2Hb) and reduced (RHb) canine and human hemoglobins were performed. The absorption spectra of canine O2Hb and RHb were nearly identical to those of human O2Hb and RHb. Therefore, 1) SpO2 measurements in dogs at SaO2 greater than 22% are relatively accurate, and 2) hemoglobin absorption characteristics support the contention that such canine pulse oximeter studies can be extrapolated to humans.

Monitoring the resuscitation of preterm infants in the delivery room using pulse oximetry

The first few minutes after birth are a critical time of adaptation of the newborn infant to extrauterine life. The adequacy of that adaptation has been evaluated by means of the summed Apgar score. In preterm infants, Apgar score may correlate less with adequacy of cardiopulmonary function because of developmental immaturity. Measurement of arterial oxygen saturation by means of pulse oximetry offers a physiologic, real time method of monitoring the progress of cardiopulmonary adaptation by which the clinician can evaluate the need for and success of resuscitative efforts. Four preterm infants are reported in whom pulse oximetry was useful in assessing the changes in oxygen saturation during resuscitation.

Organ blood flow during high-frequency ventilation at low and high airway pressure in dogs

Using the radiolabeled microsphere technique, the authors studied hemodynamic variables and regional blood flow to multiple peripheral organs during conventional positive-pressure ventilation (CV) and high-frequency ventilation (HFV) at low and high mean airway pressure (Paw). Twenty supine anesthetized, paralyzed dogs were ventilated using CV (14-16 breaths/min) and HFV (rate = 10 Hz) in random order. In the first group (low Paw, n = 10), Paw was maintained at 3 cmH2O during CV and HFV. In the second group (high Paw, n = 10), Paw was increased to 13 cmH2O during CV and HFV. Pulmonary capillary wedge pressure and right atrial pressure remained constant during low and high Paw trials. No differences in heart rate, systemic arterial pressure, intracranial pressure, or cardiac output were noted during CV and HFV within the low and high Paw groups. In addition, blood flow to multiple peripheral organs during CV and HFV remained constant within each Paw group, except for a small decrease in cerebellar blood flow during HFV at high Paw trials showed a significant decrease in hepatic arterial and outer kidney cortical flow at high Paw. Total cerebral blood flow was decreased at high Paw, as were regional flows to diencephalon, midbrain, pons, medulla, and cerebellum. However, these differences were not attributable to differences in cerebral perfusion pressure or intracranial pressure, and cerebral oxygen delivery was not different between high Paw and low Paw groups. It is concluded that under conditions of similar Paw in anesthetized dogs, HFV does not significantly alter hemodynamic patterns or regional circulation relative to CV.

Role of O2-hemoglobin affinity in the regulation of cerebral blood flow in fetal sheep

Cerebral blood flow (CBF) and cerebral O2 transport (CBF X arterial O2 content) in the fetal sheep are nearly twice that in the adult, despite similar rates of cerebral O2 utilization. We tested the hypothesis that the difference depends on the increased oxyhemoglobin affinity in the fetus, using P50 (PO2 at which hemoglobin is 50% saturated) as the index of oxyhemoglobin affinity. We studied 18 unanesthetized fetal sheep in utero. In six animals the P50 was raised from 16.6 +/- 1.2 (SD) mmHg to 31.7 +/- 4.7 mmHg by exchange transfusing the fetus with adult sheep red blood cells. We measured CBF (with radioactive microspheres) and the PO2, PCO2, pH, and O2 content in carotid artery and sagittal sinus blood twice at the original P50 and twice after exchange transfusion. Arterial O2 content fell significantly at the higher P50. Since the fall in O2 content was not accompanied by a corresponding rise in CBF, O2 transport fell by 45%. Cerebral O2 consumption (CMRO2) did not change and cannot be implicated in the fall of O2 transport. E (the ratio CMRO2/O2 transport) rose by 77%. Sham exchange transfusions in six fetuses showed that the exchange transfusion procedure itself was not responsible for this alteration. To determine whether the fall in O2 transport and the rise in E was reproducible over a range of arterial O2 contents, a third group of six fetuses was studied. Fetal arterial O2 content varied from 4 to 12 vol%, first at P50 = 17 +/- 1.8 mmHg and again after exchange transfusion at P50 = 29.6 +/- 3.9 mmHg.(ABSTRACT TRUNCATED AT 250 WORDS)

Fetal distress during a maternal systemic allergic reaction

Systemic allergic reactions to food ingestion rarely result in life-threatening situations. When these reactions occur during pregnancy, however, the accompanying physiologic changes may result in fetal distress. A case of repetitive late decelerations in the fetal heart rate during a maternal allergic reaction is presented. Prompt and aggressive medical management brought about total resolution of maternal and fetal compromise.

Renovascular hypertension: results of medical and surgical therapy

Results of medical and surgical treatment of renovascular hypertension were compared retrospectively in 28 patients. Renal function remained normal throughout the study in all patients. After six months of follow-up, systolic and diastolic blood pressures were significantly lower in the 15 patients treated surgically than in the 13 patients treated medically. At 12 months however, a significant difference could be demonstrated only for systolic blood pressure and at 24 and 36 months, no difference in systolic or diastolic pressure could be demonstrated between the two groups. This failure to find a significant difference between surgical and medical therapy resulted from return of hypertension among the patients in the surgical group with arteriosclerotic renovascular hypertension; 6 of 7 patients with fibromuscular dysplasia as the etiology of the renovascular hypertension were cured by surgery and none of these relapsed during follow-up. All patients with arteriosclerotic renovascular disease who were operated upon required medication for the control of their blood pressure within 12 months after operation. The findings in this retrospective study emphasize the importance of prolonged follow-up when assessing the value of different therapies in renovascular hypertension and provide evidence indicating that medical management is acceptable and appropriate, particularly for high risk patients. The results also force recognition of the need for a randomized prospective trial of medical and surgical therapy in arteriosclerotic renovascular hypertension.

Content and method in a thanatology training program for paraprofessionals

A training program of paraprofessionals was developed in a university teaching hospital. Trainees were exposed to seminars and a supervised practicum. The objectives of the experience included sensitization of persons in the natural helping network to (a) psychosocial needs of seriously ill persons and their families, (b) experience and comfort in interaction with such persons; (c) the structure of the health care delivery system, and (d) the usefulness of peer support groups.

Renovascular hypertension: comparison of medical and surgical therapy

1. Results of medical and surgical therapy were compared in 28 patients with hypertension and unilateral renovascular ischaemia. 2. Renal function remained normal in both groups throughout the study period. After 6 months of follow-up systolic and diastolic blood pressures were significantly lower in the surgically treated patients. After 12 months of follow-up there was no significant difference between the two groups in diastolic blood pressure and after 24 months of follow-up there was no significant difference between the two groups in either systolic or diastolic blood pressure. 3. Sixty per cent of surgically treated patients were cured 6 months after operation, but only 40% remained cured after 24 months of follow-up. 4. All patients cured at 6 months who subsequently required antihypertensive medication had arteriosclerotic renovascular disease.