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Biomedical subjects

S A Bergman

Publications and source records attributed to S A Bergman.

At least 37 records · Page 2Linked to original sources
PubMed1976

Lower body negative pressure: the second manned Skylab mission.

Results of orthostatic evaluations of the crew of Skylab 3 with lower body negative pressure (LNBP) stress tests during their 59-d mission are reported. The test protocol was identical to that used in the first manned Skylab mission and the latter Apollo flights. Except for an inflight increase (rather than a decrease) in resting heart rates, results were essentially parallel to those observed in crewmen of the shorter Skylab 2 mission. Exaggerated elevations in heart rate and decreases in pulse pressure during LBNP stress inflight and immediately postflight corresponded to lowered orthostatic tolerance. Large decrements in resting calf size inflight and in total leg volume postflight indicated significant headward fluid shifts as had already been seen in the Skylab 2 crewmen. In addition, decreases in calf circumference gave no certain indication of a plateau over the 59 d inflight. On the other hand, percentage volume increase in calf size during LBNP stress inflight was greater than those in either preflight or postflight tests. Hypotheses elaborated after the Skylab 2 mission seem to have been substantiated, but several enigmas await data from the last and longer mission for clarification.

Adult↗
PubMed1976

Pre- and postflight systolic time intervals during LBNP: the second manned Skylab mission.

After space flight of 59 d, Skylab 3 astronauts were stressed with lower body negative pressure (LBNP). During this stress procedure vectorcardiograms, pneumograms, phonocardiograms, and carotid pulse tracings were monitored and recorded onto analog tape. Accepted techniques were used to measure the intervals of systole. The postflight results were compared to multiple preflight tests and each of the three crewmen served as his own control. Immediately postflight, there were elevations in heart rate and blood pressure in response to a fixed level (-50 mm Hg) of LBNP. Total electromechanical systole, (Q-S2) I, was unchanged. Ejection time index (ETI) was depressed at rest and during stress, while pre-ejection period was elevated compared with preflight values. Systolic time intervals (STI) were within preflight limits after 1 month on earth in all crewmen. Resting STI returned sooner than did stressed STI. The magnitude and direction of STI in the postflight period were similar to those obtained from patients with moderate heart disease, although signs and symptoms were absent in the astronauts. However, the abnormality of the stressed STI persisted after both blood volume repletion and lowered afterload. These findings suggest a compromise in cardiac function, peripheral circulatory integrity, or both after exposure to long-duration space flight, and are consistent with findings reported after 3 weeks of absolute bedrest.

Adult↗
PubMed1975

Response of local vascular volumes to lower body negative pressure stress.

The present study involved an intravenous injection of radio-active iodinated serum albumin, equilibration of this isotope within the vascular space, and the continuous measurement of isotope activity over selected anatomical areas before, during and following multiple human LBNP tests. Both rate and magnitude of vascular pooling were distinctly different within each of five selected lower body anatomical areas. In the upper body, all areas except the abdomen showed depletions from their resting vascular volumes during LBNP. The presence of uniquely different pooling patterns in the lower body, the apparent stability of abdominal vascular volumes, and a possible decrease in cerebral blood volume during LBNP represent the major findings of this study.

Abdomen↗
PubMedDate not supplied

Skylab experiment M-092: results of the first manned mission.

Blood pressure at 30-sec intervals, heart rate, and percentage increase in leg volume continuously were recorded during a 25-min protocol in the M092 Inflight Lower Body Negative Pressure (LBNP) experiment carried out in the first manned Skylab mission. These data were collected during six tests on each crewman over a 5-month preflight period. The protocol consisted of a 5-min resting control period, 1 min at -8, 1 min at -16, 3 min at -30, 5 min at -40, and 5 min at -50 mm Hg LBNP. A 5-min recovery period followed. Inflight tests were performed at approximately 3-day intervals through the 28-day mission. Individual variations in cardiovascular responses to LBNP during the preflight period continued to be demonstrated in the inflight tests. Measurements of the calf indicated that a large volume of fluid was shifted out of the legs early in the flight and that a slower decrease in leg volume, presumably due to loss of muscle tissue, continued throughout the flight. Resting heart rates tended to be low early in the flight and to increase slightly as the flight progressed. Resting blood pressure varied but usually was characterized by slightly elevated systolic blood pressure, lower diastolic pressure, and higher pulse pressures than during preflight examinations. During LBNP inflight a much greater increase in leg volume occurred than in preflight tests. Large increases occurred even at the smallest levels of negative pressure, suggesting that the veins of the legs were relatively empty at the beginning of the LBNP. The greater volume of blood pooled in the legs was associated with greater increases of heart rate and diastolic pressure and larger falls of systolic and pulse pressure than seen in preflight tests. The LBNP protocol represented a greater stress inflight, and on three occasions it was necessary to stop the test early because of impending syncopal reactions. LBNP responses inflight appeared to predict the degree of postflight orthostatic intolerance. Postflight responses to LBNP during the first 48 hours were characterized by marked elevations of heart rate and instability of blood pressure. In addition, systolic and diastolic pressures were typically elevated considerably both at rest and also during stress. The time required for cardiovascular responses to return to preflight levels was much slower than in the case of Apollo crewmen.

Adaptation, Physiological↗
PubMedDate not supplied

GABAmimetics diminish antinociception of meperidine under conditions which enhance other opioid mu-agonists.

This study investigated the effects of pretreatment with muscimol (GABA-agonist) or diazepam (indirect GABAmimetic) on i.v. meperidine, fentanyl, alphaprodine and morphine, using rabbit tooth pulp and mouse hot plate assays. A previous study reported that the ED50 values for fentanyl in rabbits were significantly lowered by 0.25 mg/kg of muscimol (13.8 to 1.8 micrograms/kg) and by 1.5 mg/kg of diazepam (13.1 to 1.1 micrograms/kg). ED50 values for meperidine in rabbits in this study were increased by muscimol (1.2 to 3.2 mg/kg) and diazepam (1.5 to 3.1 mg/kg). ED50 values for fentanyl in mice were significantly lowered by 0.25 mg/kg of muscimol (23.0 to 8.9 micrograms/kg) and 1.0 mg/kg of diazepam (23.3 to 12.8 micrograms/kg). ED50 values for meperidine in mice were significantly increased by muscimol (2.1 to 5.0 mg/kg) and diazepam (2.0 to 4.8 mg/kg). ED50 values for alphaprodine and morphine were significantly lowered by muscimol and diazepam in mice. A higher dose of muscimol (1.0 mg/kg) had no effect on the ED50 values of meperidine in mice. The antinociception of a submaximal dose of meperidine in rabbits was significantly reduced by a 10 min pretreatment with i.v. diazepam (1.5 mg/kg) at 15, 20, 30 and 45 min after i.v. meperidine. The antinociception of a submaximal dose of fentanyl in rabbits was significantly increased by a 10 min pretreatment with i.v. diazepam (1.5 mg/kg) at 5, 10, 15 and 20 min after i.v. fentanyl. Pretreatment with 0.1 mg/kg of scopolamine enhanced the antinociceptive effect of a submaximal dose of fentanyl in both animal models. Diazepam reduced the antinociception produced by the combination scopolamine-fentanyl to that of fentanyl-vehicle control in both animal models. Pretreatment with 0.1 mg/kg of scopolamine did not change the magnitude of antinociception of a submaximal dose of meperidine in rabbits. Since meperidine possesses inherent anticholinergic activity, it is suggested that this anticholinergic activity may be involved in the reduction effects by muscimol and diazepam.

Alphaprodine↗
PubMedDate not supplied

Opioid analgesics.

Explore the source record for details and available documents.

Analgesics, Opioid↗
PubMedDate not supplied

Relief of dental surgery pain: a controlled 12-hour comparison of etodolac, aspirin, and placebo.

Single doses of the study drugs were evaluated for 12 hours by 201 out-patients reporting moderate or severe pain following oral surgery. The results of this double-blind study indicated that 50, 100, and 200 mg of etodolac as well as 650 mg of aspirin were significantly more effective than placebo. A dose-response relationship was found for the three doses of etodolac, which was significant for summed pain relief scores for up to 8 hours. In terms of total analgesic effect, etodolac 200 mg was significantly superior to placebo for 8 hours, while aspirin and the two lower doses of etodolac were similarly effective in the range of 3-6 hours postdrug. All doses showed a favorable onset of analgesia (½-1 hour). Etodolac 200 mg resulted in a duration of action which was approximately twice as long as aspirin's and also produced a peak pain relief which was significantly greater than the lower doses of etodolac and aspirin. All study medications were well tolerated with no reports of significant adverse side effects. No dose-related effects were observed with etodolac

Acetates↗
PubMedDate not supplied

The benzodiazepine receptor.

The benzodiazepines are among the most widely used drugs in the world. When first introduced, little was known about their mechanism of action. However, in the last 20 years, our understanding of the chemistry and function of the central nervous system (CNS) has increased substantially. This knowledge has shed some light on the mechanism of action of the benzodiazepines and other centrally acting drugs. It is well established that the benzodiazepines act by combining with specific receptors in the central nervous system. These receptors are anatomically in close association with gamma amino butyric acid (GABA) receptors and appear to reside on the neuronal membrane in the same supramolecular protein complex. GABA is the major inhibitory neurotransmitter of the CNS. The benzodiazepines act by increasing the affinity of the GABA receptor for its ligand, thereby augmenting the inhibitory effect of a given concentration of GABA. Two hypotheses of benzodiazepine ligand-receptor interactions in this supramolecular protein complex have been proposed: (1) multiple receptor subtypes analogous to the opioid receptors; (2) single receptor with multiple conformations. The multiple receptor hypothesis suggests that each pharmacologic effect of the benzodiazepines (i.e., anxiolysis) is mediated by interaction with a specific receptor subtype. On the other hand, the alternative hypothesis suggests that only one receptor exists which has a dynamic conformation. Experimental evidence in support of each hypothesis is presented and critically evaluated.

Benzodiazepines↗
PubMedDate not supplied

Diazepam enhances fentanyl and diminishes meperidine antinociception.

A rabbit tooth pulp antinociceptive model was used to investigate the effect of prior administration of diazepam or muscimol on the potency and duration of fentanyl and meperidine Potency experiments compared ED(50) values in all-or-none dose-response assays between both muscimol (0.25 mg/kg) and saline, and diazepam (1.5 mg/kg) and propylene glycol vehicle. An all-or-none effect was defined as doubling of voltage threshold to elicit a lick/chew evoked response. Duration experiments compared time (minutes) to 50% maximum possible effect (MPE) of an ED(90) dose of fentanyl (0.04 mg/kg) and to 50% and 20% MPE of an ED(98) dose of meperidine (17 mg/kg) 10 minutes after pretreatment with diazepam (1.5 mg/kg). Prior (10 minutes) injection of diazepam (1.5 mg/kg) increased the ED(50) value for meperidine (3.06 mg/kg) compared with its control (1.48 mg/kg), indicating a decrease in antinociceptive potency. The same dose of diazepam decreased the ED(50) value for fentanyl (1.1 μg/kg) compared with its control (13.1 μg/kg), indicating an increase in antinociceptive potency. Muscimol also had a similar effect on fentanyl (ED(50), 1.8 μg/kg) compared with saline control (ED(50), 13.8 μg/kg). Diazepam, vehicle, and muscimol by themselves had no effect on voltage thresholds to elicit a lick/chew response. Time to 50% MPE for diazepam-fentanyl was 38 minutes vs. 25 minutes for vehicle-fetanyl; time to 20% MPE for diazepam-meperidine was 38 minutes vs. 54 minutes for vehicle-meperidine (maximum percentage of MPE produced by diazepam-meperidine was 40% compared with 100% MPE for vehicle-meperidine). Percentages of MPE for diazepam-meperidine were significantly lower than those for vehicle-meperidine at all time intervals, whereas percentages of MPE for diazepam-fentanyl were significantly greater than those for vehicle-fentanyl over time.

Animals↗