Rapid adaptation of vagal baroreflexes in humans

We evaluated the time course of carotid baroreflex adaptation to arterial pressure elevations induced by phenylephrine infusion (1 microgram/kg per min) in 13 normotensive volunteers. Vagally-mediated carotid baroreceptor-cardiac reflex responses were assessed serially with a staircase pressure/suction sequence delivered to a neck chamber. Carotid baroreflex stimulus-response relations shifted up the response (R-R interval) axis and to the right on the stimulus (pressure) axis (determined as the carotid distending pressure at saturation) within 90-120 s (time between measurements) during the first 10 min. The shifts in position of the reflex relation were sustained throughout the infusion. The position of operational point pressure, relative to carotid distending pressure at saturation, was unchanged throughout the infusion period. These data suggest that human carotid baroreceptor reflex relations change within minutes to retain beat-to-beat pressure regulation as the prevailing pressure increases.

Acidosis induced by hypercapnia exaggerates ischemic brain damage

Although preischemic hyperglycemia is known to aggravate damage due to transient ischemia, it is a matter of controversy whether or not this is a result of the exaggerated acidosis. It has recently been reported that although tissue acidosis of a comparable severity could be induced in normoglycemic dogs by an excessive rise in arterial CO2 tension, short-term functional recovery was improved, rather than compromised. In the present experiments we induced excessive hypercapnia (PaCO2, approximately 300 mm Hg) in normoglycemic rats before inducing forebrain ischemia of 10-min duration. This reduced the brain extracellular pH to values normally encountered in hyperglycemic rats subjected to ischemia. The events induced by hypercapnia clearly enhanced ischemic brain damage, as assessed histologically after 7 days of recovery. We hypothesize that the decisive event was an exaggerated decrease in extra- and intracellular pH and that the results thus demonstrate an adverse effect of acidosis. However, since postischemic seizures did not occur in the hypercapnic ischemic rats, the results also demonstrate that changes in intra-extracellular pH and bicarbonate concentrations modulated ischemic damage in an unexpected way.

Postoperative effects of fentanyl, ketorolac, and piroxicam as analgesics for outpatient laparoscopic procedures

OBJECTIVE

To compare postoperative analgesia and side effects of intramuscular ketorolac, intravenous fentanyl, and oral piroxicam on healthy women undergoing laparoscopic surgery.

METHODS

The study was a randomized double-blind clinical trial of three analgesic drugs. An initial 100-micrograms dose of fentanyl was given at induction, with 25-micrograms boluses after 45 and 90 minutes of operating time. Piroxicam, 40 mg, and ketorolac, 60 mg, were administered 90 and 30 minutes before induction, respectively.

RESULTS

Eighty-four subjects were included in the analysis. Ketorolac patients (N = 29) spent significantly less time in the recovery room (median 96 minutes) than those receiving fentanyl (N = 27) (median 121 minutes; P < .01) or piroxicam (N = 28) (median 124 minutes; P < .01) or a verbal descriptive scale, more fentanyl patients (38%) experienced moderate pain at discharge than ketorolac (11%; P < .05) or piroxicam (4%; P < .01) patients. The incidence of measured side effects did not differ significantly between groups.

CONCLUSIONS

Intramuscular ketorolac was associated with shorter recovery room stays while providing analgesia equal to intravenous fentanyl or the oral nonsteroidal antiinflammatory drug piroxicam.

Potassium-induced changes in excitability in the hippocampal CA1 region of immature and adult rats

Orthodromic and spontaneous population spike activity was measured in vitro in the CA1 region of rat hippocampal slices to determine maturational differences in excitability and susceptibility to K(+)-induced seizures. Several indices of excitability in the CA1 region changed in a non-monotonic fashion during maturation, in response to step-wise increases in bath [K+]. Slices from rats 18-22 days old, showed a greater probability of both spontaneous epileptiform activity and episodes of seizure-like activity followed by spreading depression, and more prolonged durations of evoked seizure-like events. Elevation of [K+] in the bathing medium increased these indices in a similar manner in older rats but not to the same degree as in 18- to 22-day-old rats. However, the threshold level of bath [K+] resulting in evoked bursts of population spikes was lower in adult and 28- to 32-day-old rats than in 18- to 22-day-old rats, suggesting that excitability is not uniformly greater at any given age. In 10- to 15-day-old rats, elevation of bath [K+] either produced persistent blockade of population responses, or increased the amplitude of the initial population spike, without producing bursts. Basal levels of [K+] in the interstitium of the slices corresponded to the various levels of [K+] placed in the bathing medium and there were no differences among age groups. Therefore, differences in basal [K+]o cannot account for the maturational changes in excitability and seizure activity. The period from 18-22 days of age in the rat is a useful focal point for investigating mechanisms underlying maturational changes in propensity to develop seizures.

Renal sympathetic responses to conflicting baroreceptor inputs: rapid ventricular pacing in dogs

1. Ventricular tachycardia generates complex changes in baroreceptor input to the central nervous system: arterial baroreceptors are unloaded while cardiopulmonary receptors are stimulated. In humans with heart diseases, muscle sympathetic nerve activity increases during ventricular tachycardia. This suggests that arterial baroreceptor-mediated sympathoexcitation overrides cardiopulmonary receptor-mediated sympathoinhibition. However, the relative roles of each reflex are difficult to determine in humans. 2. We measured efferent renal sympathetic neural responses to simulated ventricular tachycardia, to determine what pathophysiological mechanisms are invoked when inputs from different baroreceptive areas change in opposite directions. In alpha-chloralose anaesthetized, mechanically ventilated dogs, we recorded the electrocardiogram, mean left atrial and arterial pressures and multifibre efferent renal sympathetic nerve activity (RSNA) during 1 min of right ventricular pacing at 214 beats min-1. Pacing was repeated after either sinoaortic or vagal cardiopulmonary denervation and again after both sinoaortic and cardiopulmonary denervation. 3. With all afferent baroreceptor pathways intact, right ventricular pacing elicited transient sympathoinhibition (delta RSNA, -19 +/- 10%, mean +/- S.E.M.). After sinoaortic denervation (cardiopulmonary receptors intact), right ventricular pacing elicited abrupt and sustained sympathoinhibition (delta RSNA, -53 +/- 8%, P < 0.05 vs. intact). After vagal cardiopulmonary denervation (sinoaortic receptors intact), right ventricular pacing elicited abrupt and sustained sympathoexcitation (delta RSNA, + 56 +/- 19%, P < 0.05 vs. intact). After both sinoaortic and vagal cardiopulmonary denervation, right ventricular pacing elicited a gradual increase in sympathetic outflow (delta RSNA, + 16 +/- 6%, P < 0.05 vs. intact). 4. We conclude that interactions between vagal cardiopulmonary and arterial baroreflexes determine renal sympathetic outflow during simulated ventricular tachycardia. In healthy anaesthetized dogs, the balance of the two opposing reflexes is weighted towards vagal cardiopulmonary-mediated sympathoinhibition.

Detection of amphetamine and methamphetamine in urine by gas chromatography/Fourier transform infrared (GC/FTIR) spectroscopy

New methods for identification of amphetamines have been employed using gas chromatography/Fourier transform infrared spectroscopy (GC/FTIR). These methods have provided identification of the drug and its metabolites, with detection at the low picogram levels or less than 10 ng/mL. Developments in cryogenic sample deposition for GC/FTIR spectroscopy have increased the sensitivity of GC/FTIR to levels that match or surpass that of gas chromatography/mass spectrometry (GC/MS). This advancement in technology has allowed the highly selective ability of infrared spectroscopy to be used for identification and quantitation in studies where the analytes are in low concentrations. The limits of detection (LOD), quantitation (LOQ), and linearity (LOL), and precision have been determined in this study, and these instrumental parameters have been compared with those of established techniques.

Naloxone does not prevent vasovagal syncope during simulated orthostasis in humans

The mechanism of vasovagal syncope during orthostasis in humans is unknown. Opioid receptors have been implicated in the vasovagal-like responses to hemorrhagic hypotension in conscious animals. We sought to determine if opioid receptor blockade with naloxone (mu receptor antagonist) would prevent or delay the onset of vasovagal syncope in humans. Three protocols were performed in which heart rate, arterial pressure, sympathetic nerve activity, thoracic impedance and forearm vascular resistance were measured during stepwise steady-state increments of lower body negative pressure (LBNP) in nine healthy volunteers. In protocol 1, duplicate trials of LBNP to syncope or -60 mmHg were performed with a 30-45 minute rest period separating the trials. No significant differences in any physiologic responses or cumulative stress tolerance were found. In protocol 2, graded LBNP was repeated after administration of saline or naloxone (0.1 mg/kg) in six subjects in which vasovagal syncope occurred prior to -60 mmHg LBNP. The peak increase of sympathetic nerve activity during LBNP was augmented after naloxone (P = 0.02), but the occurrence of vasovagal syncope was not prevented nor was the cumulative stress tolerated affected (P = 0.42). The heart rate and arterial pressure responses to LBNP were not affected by naloxone. Similarly, in protocol 3, naloxone given just prior to the onset of pre-syncopal symptoms did not alter the physiologic response or the occurrence of vasovagal syncope. These data show that naloxone does not prevent or delay the onset of vasovagal syncope in humans which suggests that mu opioid receptors do not mediate the vasovagal response.

An intoxication involving BRON and verapamil

A case is presented in which the body of a 19-year-old white male was found in his family's quarters by his mother. An autopsy failed to determine the cause of death, and specimens were sent out for toxicologic analysis. No ethanol or volatile substances were detected in the blood, urine, or vitreous fluid. Comprehensive drug testing of the urine identified chlorpheniramine, dihydrocodeine, methylephedrine, salicylate, and verapamil. The first three drugs listed appear together in an over-the-counter cold medication in Japan, under the trade name BRON. Blood quantitations (in mg/L) were as follows: chlorpheniramine, 2.6; dihydrocodeine, 4.7; methylephedrine, 5.6; salicylate, 150; and verapamil, 6.0. The cause of death was multiple drug intoxication, and the manner of death was suicide.

Abnormalities of baroreflex control in heart failure

This brief review summarizes abnormalities of arterial and cardiopulmonary baroreflex control of heart rate and sympathetic nerve activity. The potential role of these abnormalities in the development of the neurohumoral excitatory state associated with heart failure is discussed. Major emphasis is placed on the identification of important issues still to be investigated in this area. The potential importance of altered cardiovascular reflexes in the context of the interaction of the patient with heart failure and environmental stresses is discussed. The use of the canine rapid ventricular pacing model of biventricular failure in the investigation of abnormalities of baroreflexes in heart failure is emphasized. Insights obtained from this model should be extended to human investigations.

Computer simulation of selection in a hypothetical crop species

A computer simulation model demonstrating the effect of directional selection upon a simplified quantitative genetic character, is presented. Complementary homozygous parents were crossed to generate a fully heterozygous F1 population. Phenotypic truncation selection was effected upon the F2 and subsequent generations, and genotypic and phenotypic response to selection, as well as the change in population heterozygosity, was monitored to generation F9. The model simulates selection for alternative breeding regimes, modes of allelic interaction, selection pressure, population size and levels of environmental variation. Three alternative methods for the simulation of the environmental component of phenotypic variance are incorporated, and mechanisms and relative merits of the rival methods are discussed. Data generated by the model conformed closely to theoretical expectation, lending support to the use of the model as a platform for development of more comprehensive simulation models. Potential improvements to the model are discussed.

A multiple drug intoxication involving cyclobenzaprine and ibuprofen

A 19-year-old black man presented to the emergency room with superficial cuts on the anterior wrists, lethargy, tachycardia, and metabolic acidosis. Multiple containers of medication were found at the scene. Dysrhythmias developed and the patient died 7 h after admission. No anatomic cause of death was identifiable at autopsy. Toxicologic analysis identified the following drugs in the blood (mg/L): cyclobenzaprine (0.3), phenylpropanolamine (2.5), chlorpheniramine (0.2), lidocaine (6.6), phenytoin (19), and ibuprofen (130). Lidocaine and phenytoin had been administered therapeutically. The major symptoms displayed by the patient were tachycardia and metabolic acidosis, symptoms consistent with cyclobenzaprine and ibuprofen intoxication, respectively. Therefore, the medical examiner ruled that the cause of death was multiple drug intoxication and that the manner of death was suicide.

Influence of cigarette smoking on human autonomic function

BACKGROUND

Although cigarette smoking is known to lead to widespread augmentation of sympathetic nervous system activity, little is known about the effects of smoking on directly measured human sympathetic activity and its reflex control.

METHODS AND RESULTS

We studied the acute effects of smoking two research-grade cigarettes on muscle sympathetic nerve activity and on arterial baroreflex-mediated changes of sympathetic and vagal neural cardiovascular outflows in eight healthy habitual smokers. Measurements were made during frequency-controlled breathing, graded Valsalva maneuvers, and carotid baroreceptor stimulation with ramped sequences of neck pressure and suction. Smoking provoked the following changes: Arterial pressure increased significantly, and RR intervals, RR interval spectral power at the respiratory frequency, and muscle sympathetic nerve activity decreased. Plasma nicotine levels increased significantly, but plasma epinephrine, norepinephrine, and neuropeptide Y levels did not change. Peak sympathetic nerve activity during and systolic pressure overshoots after Valsalva straining increased significantly in proportion to increases of plasma nicotine levels. The average carotid baroreceptor-cardiac reflex relation shifted rightward and downward on arterial pressure and RR interval axes; average gain, operational point, and response range did not change.

CONCLUSIONS

In habitual smokers, smoking acutely reduces baseline levels of vagal-cardiac nerve activity and completely resets vagally mediated arterial baroreceptor-cardiac reflex responses. Smoking also reduces muscle sympathetic nerve activity but augments increases of sympathetic activity triggered by brief arterial pressure reductions. This pattern of autonomic changes is likely to influence smokers' responses to acute arterial pressure reductions importantly.

Free radicals and brain damage due to transient middle cerebral artery occlusion: the effect of dimethylthiourea

The objective of this study was to assess whether dimethylthiourea (DMTU), an established free radical scavenger, ameliorates ischaemic damage due to 2-3 h of transient middle cerebral artery (MCA) occlusion, induced by an intraluminal filament. A major point addressed was whether DMTU given before MCA occlusion only delayed the "maturation" of the damage, or if it had a lasting effect on infarct size. The end point was morphological, and either encompassed triphenyltetrazolium chloride (TTC) staining of tissue slices after 24 h or 48 h of recovery, or histopathological assessment of infarct size after 7 days of recovery. In a preliminary series of experiments, rats were subjected to 3 h of MCA occlusion, and infarct volume was assessed by TTC staining after 24 h of recovery. DMTU in a dose of 750 mg/kg reduced infarct volume by more than 50%. However, due to a high mortality rate, that protocol was not subsequently pursued. When the ischaemia duration was reduced to 2 h and the DMTU dose to 400 mg/kg, a similar amelioration of the tissue damage was observed. However, since DMTU reduced a spontaneous rise in body temperature to 39.0-39.5 degrees C, DMTU-treated animals in the main series of experiments with 24 and 48 h of recovery were treated so that they had the same temperature rise as the saline controls. Under such constant temperature conditions, the effect of DMTU at 24 h of recovery was borderline (P = 0.052) and at 48 h it was nil. The lack of a lasting effect of DMTU was supported by the findings on evaluation of infarct area after 7 days of recovery. The results raise the important question whether DMTU, and perhaps other free radical scavengers, delay rather than ameliorate the ischaemic lesion developing after transient MCA occlusion.

3-D reconstruction of the cholinergic basal forebrain system in young and aged rats

The 3-dimensional (3-D) distribution of cholinergic neurons located throughout the extent of the entire basal forebrain of young (4-5 months old) and aged (24-25 months old) Fischer-344 rats was examined using choline acetyltransferase immunocytochemistry (ChAT-IR). The number and 3-D position of ChAT-IR neurons spanning the basal forebrain were determined using serial sections and analyzed using computerized image analysis. The effects of aging on ChAT-IR neuron number were analyzed as a cohesive unit with respect to the classically-defined magnocellular subregions located within the basal forebrain (i.e., the medial septum, vertical and horizontal limbs of the diagonal band, and the nucleus basalis). Significant effects of age were found on ChAT-IR neuron number but no significant age-related interactions were noted with either the A-P, M-L, or D-V axes. These results suggest that a significant but diffuse age-related loss of ChAT-IR occurs along the entire length of the basal forebrain, and that this loss is not restricted to individual magnocellular nuclei (A-P axis), the M-L axis, or the D-V axis.

Cholinesterase activity in postmortem blood as a screening test for organophosphate/chemical weapon exposure

This study was undertaken to determine whether postmortem blood cholinesterase activity could be used as a screening test for exposure to nerve agents. Whole blood cholinesterase activity at 25 degrees C was analyzed for a one week period in order to simulate the battle field collection problems of: hemolyzed blood samples, delayed recovery of the specimen, and unrefrigerated transfer to the testing facility. A total of 53 nonpreserved post-mortem whole blood specimens were analyzed in triplicate for cholinesterase activity by the delta pH method of Michel. There was a negligible loss of cholinesterase activity by the seventh day of the study. The enzyme activities of the specimens had a mean value (range) of 0.48 (0.20 to 0.74) initially and 0.45 (0.07 to 0.70) pH units after one week. Whole blood from five healthy adults remained essentially unchanged during this period, with an initial value 0.59 (0.52 to 0.67) and a final value of 0.52 (0.46 to 0.62) pH units. To compare postmortem and simulated nerve agent values, aliquots from 18 of the original 53 postmortem specimens were frozen during day one of the study, thawed on day seven and a cholinesterase inhibitor added. These specimens were then analyzed with the other specimens. All values from inhibited specimens were essentially zero (0.0 to 0.01) pH units compared to a range of 0.07 to 0.61 pH units for matched, uninhibited, day seven postmortem specimens. Fifteen actual nonpreserved specimens from the battlefield were analyzed as verification of screen performance. Their results fell within the uninhibited postmortem range above.(ABSTRACT TRUNCATED AT 250 WORDS)

Two deaths involving isoflurane abuse

Two deaths due to isoflurane abuse are reported. One case was a suicide and the other a multiple drug death including isoflurane. A simple headspace gas chromatographic method was used for isoflurane quantitation. A review of the literature did not reveal blood and tissue concentrations of isoflurane. Drug tissue distributions and a discussion of the toxicological findings are presented.

Changes in bone density with lactation

OBJECTIVE

To test the a priori hypotheses that significant bone loss occurs in lactation of greater than 5 months' duration and that bone mass returns to baseline levels when breast-feeding ceases.

DESIGN

Prospective cohort study design of 12 months' duration.

SETTING

General community setting with recruitment occurring at birthing education classes.

PARTICIPANTS

Volunteer sample of 98 healthy women of white (n = 95) and Asian (n = 3) origin, aged 20 to 40 years, and 0 to 1 parity prior to parturition, grouped according to lactation duration: 0 through 1, 2 through 5, and 6 or more months.

MAIN OUTCOME MEASURES

Bone mineral density (BMD) of the proximal femur was measured by dual-energy x-ray densitometry at 2 weeks (baseline), 2 months, 4 months, 6 months, and 12 months following parturition, and BMD of the lumbar spine was measured at baseline, 6 months, and 12 months after parturition.

RESULTS

Women with lactation duration of 6 months or longer had mean BMD losses of 5.1% and 4.8% at the lumbar spine and femoral neck, respectively, comparing baseline values with those at 6 months post partum. Women who breast-fed 0 through 1 month lost no BMD at either bone site. Bone loss in women who breast-fed 6 months or longer was not explained by differences in age, diet, body size, or physical activity. Among women who breast-fed 6 months or longer, there was evidence of return to baseline levels of the lumbar spine at 12 months after parturition. The BMD of the lumbar spine of those women who continued to breast-feed more than 9 months had increased but was still significantly lower than baseline.

CONCLUSION

Extended lactation (> or = 70% of energy intake is provided for > or = 6 months) is associated with bone loss; however, there is evidence of return to baseline BMD measurement at 12 months after parturition.

Abnormalities in the p53 gene in tumors and cell lines of human squamous-cell carcinomas of the head and neck

Abnormalities in the p53 gene were studied in a series of cell lines of human squamous-cell carcinoma of the head and neck (SCCHN) and in tumor tissues. Restriction-fragment-length polymorphism (RFLP), quantitative hybridization and immunochemical analysis of mutant p53 proteins were combined to detect and characterize 3 different phases in the p53 gene alteration: mutation (in 9/9 cases), 17p13 deletion (9/10 cases) and amplification of the non-deleted allele (9/31 cases). In SCCHN, deletion of the p53 gene was nearly always accompanied by mutation, only one cell line studied having mutation without deletion. Alterations in the p53 gene are common in SCCHN, and involve a series of genetic events which occur in sequence during tumor progression.

Effects of dimethylthiourea on selective neuronal vulnerability in forebrain ischemia in rats

BACKGROUND AND PURPOSE

Attempts have been made to characterize conditions under which oxygen free radicals contribute to ischemic brain damage. According to one hypothesis, free radicals are likely mediators of damage only when ischemia is of such long duration that infarction develops or when either preischemic hyperglycemia or hyperthermia is present. The objective of the present study was to explore whether 15 minutes of forebrain ischemia, an insult that leads to selective neuronal vulnerability but not to infarction, is accompanied by production of pathogenetically important free radicals.

METHODS

Using a histopathological end point, we studied amelioration of damage by a free radical scavenger, dimethylthiourea, administered in a dose of 750 mg/kg i.p. 60 minutes before ischemia. To study whether this insult leads to detectable protein oxidation we assessed the activity of glutamine synthetase and of carbonyl compounds in the soluble protein fraction.

RESULTS

In control animals, the transient ischemia resulted in the expected damage to vulnerable neurons in hippocampus, caudoputamen, and neocortex after 7 days of recovery. Glutamine synthetase activity in caudoputamen and hippocampus and carbonyl content in the soluble protein fraction after 90 minutes of recovery were not affected. However, dimethylthiourea significantly reduced damage to hippocampus and caudoputamen (p < 0.001) and neocortex (p < 0.005).

CONCLUSIONS

Lack of evidence of protein oxidation supports the notion that 15 minutes of forebrain ischemia results in a limited insult, confined to the neurons. Provided that unspecific effects can be excluded, the results obtained with dimethylthiourea suggest that free radicals contribute to selective neuronal necrosis.

Interpretation of low postmortem concentrations of ethanol

The interpretation of postmortem blood ethanol concentrations (BAC), especially those less than 0.05 g/dL can be complicated by postmortem ethanol formation. One method used by the toxicologist to respond to this possibility is to analyze multiple specimens for ethanol. Two useful specimens to analyze are vitreous humor and urine, because they are less susceptible to the putrefaction process. A negative vitreous humor and/or urine ethanol would suggest that the measured ethanol resulted from postmortem formation. Data were collected from the Office of the Chief Medical Examiner, State of Maryland and the Armed Forces Institute of Pathology on blood specimens with ethanol concentrations less than 0.05 g/dL to develop a reasonable threshold for interpretation in the absence of other specimens. A total of 381 cases with a BAC between 0.01 and 0.04 g/dL were studied over a 2 year period. Urine and vitreous humor specimens were tested where available. At a BAC of 0.01 g/dL, 54% of the cases were associated with a positive vitreous humor and/or urine ethanol concentration. This percentage increased to 63% when BAC equals 0.02 g/dL. Seventy-three percent and 92% of the cases had a positive alternate specimen if the BAC was 0.03 g/dL and 0.04 g/dL, respectively. In addition, 90% of the cases where both vitreous humor and urine were analyzed showed consistent results, that is both specimens were positive or negative. This suggests that in the absence of additional information, a BAC of 0.04 g/dL or higher probably resulted from ethanol consumption.