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Biomedical subjects

G Plourde

Publications and source records attributed to G Plourde.

At least 37 records · Page 2Linked to original sources
PubMed1996

The effects of propofol on the 40-Hz auditory steady-state response and on the electroencephalogram in humans.

The auditory steady-state response (ASSR) is a nearly sinusoidal electrical response of the brain to auditory stimuli delivered at fast rates. The amplitude of the response is largest for stimulus rates near 40/s, hence the label 40-Hz ASSR. We have studied the effects of propofol (1.5 mg/kg) on the 40-Hz ASSR in 14 patients. The spectral edge frequency (SEF) and median frequency (MDF) of the electroencephalogram were recorded for comparison. The study was limited to 6 min after the injection of propofol. Recordings were obtained every minute. Consciousness, defined as responsiveness to verbal command, was assessed in all patients within 1 min. Nine patients, regained consciousness before the end of the study. Propofol caused disappearance of the 40-Hz ASSR for 2 min. Th 40-Hz ASSR reappeared afterward, reaching, at the end of the study period, an amplitude of about 65% of baseline. Recovery of the 40-Hz ASSR occurred whether or not consciousness was regained during the study, but the amplitude tended to be larger in patients who had regained consciousness compared with patients still unconscious during the same recording. The SEF was reduced by 24% within 2 min and recovered more quickly than the 40-Hz ASSR, reaching 91% of baseline within 4 min. The SEF tended to be higher in patients who had regained consciousness. The MDF was reduced by 27% within 2 min, and exceeded baseline values by 25% during recovery. The MDF was not higher in patients who had regained consciousness. We conclude that propofol transiently abolishes the 40-Hz ASSR. Recovery of the 40-Hz ASSR occurs whether or not consciousness is regained, but the 40-Hz ASSR tends to be larger after the return of consciousness. An association between higher amplitude 40-Hz ASSR and the return of consciousness could not be conclusively established, perhaps because of low signal-to-noise ratio in three patients. The 40-Hz ASSR did not offer any clear advantage over the SEF in predicting the return of consciousness.

Adult↗
PubMed1994

Sedation with midazolam during regional anaesthesia: is there a role for flumazenil?

The aim of this study was to reassess the efficacy of flumazenil for reversal of sedation with midazolam. Twenty-four ASA I or II patients undergoing elective surgery under epidural anaesthesia participated. Following epidural block, midazolam was administered to keep the patient sleepy but still responsive to verbal commands. At the end of surgery the patients were randomly allocated to receive, in a double-blind manner, either flumazenil (0.1 mg.ml-1) or placebo. The study drug (maximum dose: 10 ml) was titrated until the patient became fully awake. Sedation was assessed with the Modified Steward Coma Scale (MSCS), the Trieger test (TT) and Critical Flicker Frequency (CFF). The assessments were done before anaesthesia (baseline), at the end of surgery immediately before administration of study drug, and serially afterwards, at 10, 30, 60, 90, 120, 150 and 180 min. Analyses of variance for repeated measures and pooled t tests were used. The duration of surgery was (mean +/- SD) 0.72 +/- 0.25 hr in the flumazenil group and 0.74 +/- 0.28 hr in the placebo group. The total dose of midazolam was 7.2 +/- 2.2 mg for the flumazenil group and 8.9 +/- 2.7 mg for the placebo group. The volume of study drug administered was 5.5 ml +/- 1.9, equivalent to 0.55 mg, for the flumazenil group and 6.7 +/- 2.2 ml for the placebo group. Critical Flicker Frequency is the only measure which revealed a difference (P < 0.005) between the flumazenil and placebo groups and this occurred only at the ten-minute assessment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

The severity of visual hemineglect follows a bimodal frequency distribution.

The purpose of this study was to determine whether the severity of visual hemineglect follows a unimodal or bimodal frequency distribution. Seventy-seven consecutive patients with a unilateral cerebral infarct (36 left- and 41 right-hemisphere lesions) were evaluated. The severity of neglect was measured as the number of omissions on a line cancellation task. The frequency distribution of the number of lines omitted was bimodal following right lesions. One group of patients showed no or only mild neglect, whereas other patients showed severe neglect. Very few patients showed neglect of intermediate severity. The frequency distribution following left lesions was unimodal. Most patients exhibited no or only mild neglect. These results suggest that, following right lesions, the dichotomy regarding the severity of neglect is real and cannot be explained by observers' tendency to categorize.

Aged↗
PubMed1993

The P3a wave of the auditory event-related potential reveals registration of pitch change during sufentanil anesthesia for cardiac surgery.

BACKGROUND: The N1 and P3 waves of the auditory event-related potential provide information on consciousness and cortical function. The N1 wave is reduced during states of low vigilance. The P3 wave occurs only for stimuli that somehow capture the subject's attention. There are two types of P3:P3a and P3b. The P3a predominates frontally and probably occurs when the subject simply notices the stimulus. The P3b predominates parietally and indicates conscious awareness of the evoking stimulus. The N1 and P3 were recorded in 12 patients during cardiac surgery under sufentanil anesthesia to search for unintentional awareness. The study was limited to the period before cardiopulmonary bypass. METHODS: After premedication with diazepam, morphine, and scopolamine, sufentanil was used for induction (mean dose, 7.9 micrograms/kg) and maintenance (4 micrograms/kg) of anesthesia. No other anesthetics were administered. Recordings were obtained before induction, during induction after loss of consciousness, after tracheal intubation before incision, and before cardiopulmonary bypass. RESULTS: The N1 was attenuated significantly by sufentanil but was not abolished. The P3b occurred only during preinduction. There was no P3 during induction. There was a P3a during postintubation and precardiopulmonary bypass. CONCLUSIONS: The attenuation of N1 from induction onward reflects a decrease in the level of arousal caused by sufentanil. A P3a during postintubation and precardiopulmonary bypass indicates that pitch discrimination at the cortical level occurs but does not prove that conscious awareness has occurred. Whether or not the P3a reflects the regaining of consciousness is not known.

Acoustic Stimulation↗
PubMed1993

Effect of endurance training on beta-adrenergic system in three different skeletal muscles.

The beta-adrenergic receptor density (Bmax) and adenylate cyclase (AC) activity in the soleus muscle and deep red and white superficial portions of the vastus lateralis muscle were evaluated in a group of rats submitted to a progressive 10-wk treadmill running program (n = 19) and compared with a group of rats kept sedentary (n = 17) during the same period of time.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1992

Measuring recovery from general anaesthesia using critical flicker frequency: a comparison of two methods.

Critical flicker frequency (CFF) is the frequency at which a flickering light appears steady. It is a sensitive measure for assessing recovery from anaesthesia. The CFF is almost always determined with the method of limits by which the flickering frequency is progressively decreased (or increased) until the patient reports a change from fusion to flicker (or flicker to fusion). This method has two disadvantages: it is influenced by the response bias (i.e., the subjective criterion used by the subject to decide that flicker is present or absent) and by the response delay (i.e., the interval between the perceptual change and the response). To avoid these problems, the method of forced choice is recommended. For each trial, the subject observes the light during two short successive periods. The light flickers during only one period, according to chance. The patient must indicate the period during which flickers occur. If uncertain, the patient has to make a guess. The aim of this study was to compare the two methods for assessing recovery from general anaesthesia. Two induction agents were used to obtain different recovery profiles. Twenty patients undergoing uncomplicated surgery lasting less than two hours were tested. They received either thiopentone or midazolam for induction, according to a randomized design. Vecuronium was used to facilitate tracheal intubation and anaesthesia was maintained with fentanyl, isoflurane and nitrous oxide. The CFF was measured before induction and at 60, 120 and 180 minutes after arrival in the recovery room. The person measuring CFF was unaware of the induction agent used.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Physical training increases beta-adrenoceptor density and adenylate cyclase activity in high-oxidative skeletal muscle of diabetic rats.

The effects of physical training on beta-adrenergic-receptor density (Bmax) and adenylate cyclase (AC) activity in soleus muscles (type I) and the deep red portion (type IIa) and superficial white portion (type IIb) of vastus lateralis muscles in diabetic rats were investigated. Rats were rendered diabetic with streptozotocin ([STZ] 45 mg/kg intravenously [IV]) and were either kept sedentary ([SD] n = 12) or submitted to a progressive 10-week treadmill running program ([TD] n = 13). A group of normal sedentary rats served as controls ([SC] n = 13). Plasma glucose levels were increased in SD rats in comparison with SC rats (21.3 +/- 1.4 mmol/L v 7.7 +/- 0.2; mean +/- SE, P < .001), but levels were partially reversed to normal by training (10.7 +/- 1.7; P < .01 v SD). The gastrocnemius nicotinamide adenine dinucleotide (NAD)-isocitrate dehydrogenase (ICDH) activity was significantly increased in TD rats in comparison to SC or SD rats (P < .001). The Bmax and antagonist affinity (Kd) determined with 125iodocyanopindolol (ICYP) were not affected by diabetes in any of the three types of muscle. In type I muscle, TD rats showed a significant 67% increase in Bmax compared with that of SD rats (TD 26.7 +/- 2.0 v SD 16.0 +/- 1.0; P < .001). In type IIa muscle, Bmax was significantly higher by 68% in TD rats as compared with SD rats (TD 16.5 +/- 1.7 v SD 9.8 +/- 0.9 fmol/mg protein; P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗
PubMed1991

Validation of the polyethylene glycol precipitation technique for the characterization of rat ventricular beta-adrenoceptors.

The use of polyethylene glycol (PEG) to separate [125I]cyanopindolol bound to rat ventricular membranes from free ligand in the characterization of beta-adrenoceptors was compared with the more frequently utilized filtration technique through GF/F glass-fiber filters. The results obtained in tissue from 14 rats demonstrated the following: (i) no significant difference between the two methods for the density of beta-adrenoceptors in ventricular tissue (PEG: 30.9 +/- 1.5 vs GF/F: 28.6 +/- 2.0 fmol/mg of protein); (ii) no significant difference for the dissociation constant (PEG: 70.7 +/- 5.3 vs GF/F: 57.7 +/- 7.7 pM); (iii) similar values for the Hill coefficient (PEG: 0.996 +/- 0.004 vs GF/F: 0.988 +/- .016); (iv) a significant difference for the relationship of bound/free vs bound, expressed as r2 (PEG: 0.82 +/- 0.03 vs GF/F: 0.74 +/- 0.03 P less than 0.05). The apparently greater accuracy of the PEG method over the filtration technique is probably explained by a lower degree of nonspecific binding observed with this method than with the filtration technique. In conclusion, the PEG precipitation method is an interesting and accurate alternative to the more standard filtration technique in ventricular beta-adrenoceptor characterization.

Animals↗
PubMed1991

Effect of physical training on ventricular beta-adrenergic receptor adenylate cyclase system of diabetic rats.

This study was designed to assess the effect of physical training on the ventricular beta-adrenergic receptor adenylate cyclase system of diabetic rats. Mild diabetes mellitus was induced by an intravenous (IV) injection of streptozotocin (45 mg/kg). Rats were randomized into a group submitted to a progressive 10-week running program on a treadmill, while another group was kept sedentary. A group of sedentary nondiabetic rats was used as normal controls. Results showed a similar reduction in the density of beta-adrenergic receptors in sedentary diabetic (P less than .05) and trained diabetic rats (P less than .01) compared with controls, without any significant alteration in the dissociation constant. The basal and the sodium fluoride-stimulated maximal adenylate cyclase activities were similar in the three groups. However, the maximal response of adenylate cyclase to isoproterenol was significantly reduced in the two diabetic groups compared with controls (P less than .01). The decrease in adenylate cyclase response to isoproterenol observed in the diabetic groups appeared to be associated with a reduction in the total number of beta-adrenergic receptors and more specifically in those existing in the high-affinity state. On the other hand, the hyperglycemia and hyperglucagonemia present in sedentary diabetic rats was improved by training. These data suggest that the beneficial effects observed in response to training in experimental diabetes are not associated with changes in beta-adrenergic receptor adenylate cyclase system on membranes from ventricular tissue.

Adenylyl Cyclases↗
PubMed1991

The long-latency auditory evoked potential as a measure of the level of consciousness during sufentanil anesthesia.

The long-latency auditory evoked potential was recorded during opioid anesthesia to evaluate its usefulness for assessing the level of consciousness. Eight patients undergoing coronary artery surgery under high-dose sufentanil anesthesia following a lorazepam premedication were tested. Four waves were studied: the N1, P2, P3, and the slow wave (SW). The amplitude of N1 and that of the SW were reduced by sufentanil, but the differences did not reach significance. The amplitude and latency of P2 and the latency of the SW were significantly reduced. The P3, which is possibly a specific indicator for consciousness, was present before induction and absent during anesthesia. There was no conscious recall for intraoperative events. Preservation of the N1, P2, and SW, which are abolished by nonopioid general anesthetics, suggests that auditory processing proceeds further during anesthesia with sufentanil. However, no electrophysiologic evidence of consciousness was found during sufentanil anesthesia.

Adult↗
PubMed1991

The auditory steady state response during sufentanil anaesthesia.

The auditory steady state response (ASSR) is a sinusoidal evoked potential elicited by rapidly repeated auditory stimuli. The ASSR was recorded in eight patients during high-dose sufentanil anaesthesia for cardiac surgery in order to assess its usefulness as a measure of the level of consciousness. The electroencephalogram (EEG) was recorded for comparison. The ASSR was present before induction in all patients. It was attenuated severely or possibly abolished with loss of consciousness, and reappeared at low amplitude 5-10 min later and remained attenuated until the end of surgery. The amplitude increased with early signs of awakening in the Intensive Care Unit. With few exceptions, changes in the simultaneously recorded EEG were similar to those of the ASSR. The ASSR deserves further evaluation as a tool for monitoring level of consciousness during high-dose opioid anaesthesia.

Adult↗
PubMed1991

Beta-adrenoceptor adenylate cyclase system adaptation to physical training in rat ventricular tissue.

The beta-adrenergic receptor adenylate cyclase system of ventricular tissue was evaluated in a group of rats submitted to a progressive 10-wk running program on a treadmill and compared with that in a group of rats maintained sedentary during the same period. Adequate training was confirmed by a 46% increase in the gastrocnemius isocitrate dehydrogenase activity in the trained group [1.50 +/- 0.04 vs. 1.03 +/- 0.06 (SE) pmol.g-1.min-1; P less than 0.01). Binding studies with [125I]iodocyanopindolol showed a 13% reduction in the density of beta-adrenergic receptors in trained rats (42.6 +/- 2.1 vs. 49.0 +/- 2.1 fmol/mg; P less than 0.05) without any significant modification in the dissociation constant. The amount of [125I]iodocyanopindolol bound to beta-adrenoceptors in the high-affinity state was reduced by 16.6% in trained rats (12.5 +/- 0.9 vs. 15.0 +/- 0.5 fmol/mg; P less than 0.05) without any significant changes for those in the low-affinity state, indicating a decrease in the coupling between the beta-adrenergic receptors and the guanine stimulatory binding protein. Furthermore, although the basal and sodium fluoride-stimulated adenylate cyclase activities were similar in the two groups of rats, the response of adenylate cyclase maximally stimulated by 10(-5) M isoproterenol was reduced by 16% in trained rats (29.7 +/- 1.4 vs. 35.3 +/- 1.3 pmol.mg-1.min-1; P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptation, Physiological↗
PubMed1991

Long-latency auditory evoked potentials during general anesthesia: N1 and P3 components.

The N1 and P3 auditory evoked potentials were recorded to evaluate their usefulness as measures of the level of consciousness in 14 ASA physical status I and II patients undergoing elective surgery. The anesthetic agents were thiopental, fentanyl, and isoflurane with or without nitrous oxide. Recordings were carried out before induction (preinduction) and during induction, surgical anesthesia, emergence, and recovery from anesthesia. The auditory response was evoked by 700-Hz tones that occurred occasionally and unpredictably in a train of 500-Hz tones delivered at 40 per second. The patients were asked to press a button whenever they detected a 700-Hz tone. Studies with normal subjects have repeatedly shown that detected tones (HITS) evoke N1 and P3 waves, whereas undetected tones (MISSES) evoke no recognizable waves. The responses evoked by HITS were compared with those evoked by MISSES. The amplitudes of N1 and P3 were significantly different from zero for HITS before induction and during induction and recovery but not during emergence. The amplitudes of N1 and P3 were not different from zero for MISSES during induction, surgery, and emergence. During recovery, the N1 and P3 for MISSES were small and the P3 for HITS was significantly larger than for MISSES. The results indicate that except during emergence, HITS were associated with clear N1 and P3 waves, whereas MISSES were not. The lack of either N1 or P3 for HITS during emergence perhaps occurred because the patients, although responsive, were not yet fully conscious. The N1 and P3 components of the auditory evoked potential may provide specific indicators for consciousness.

Adult↗
PubMed1991

The human auditory steady-state evoked potentials.

When auditory stimuli are presented at rates near 40/s, they evoke a steady-state middle latency response. This results from the super-position of the transient responses evoked by each of the rapidly presented stimuli. The steady-state evoked potentials are most appropriately analyzed using frequency-based techniques. The response is larger for stimuli of higher intensity and of lower tonal frequency. The amplitude of the response varies with the state of arousal of the subject. Sleep results in a decrease in the amplitude to between one third and one half of the amplitude during wakefulness. The response is even further attenuated by general anesthesia. This auditory steady-state evoked potential may therefore be helpful in monitoring the state of arousal of a patient undergoing anesthesia.

Adult↗
PubMed1990

Human auditory steady-state response during general anesthesia.

The 40-Hz auditory steady-state evoked response (ASSR) is a sinusoidal electrical response of the brain to periodically presented auditory stimuli. It was recorded during anesthesia in 10 elective surgical patients to evaluate its usefulness as a measure of the level of consciousness. The anesthetic agents used were thiopental, fentanyl, and isoflurane with or without nitrous oxide. Recordings were carried out during the period before induction and during induction, surgical anesthesia, emergence, and recovery from anesthesia. The level of consciousness was measured with an auditory stimulus detection task. The electroencephalogram (EEG) was also recorded for comparison with the ASSR. The following indices were analyzed: total EEG power, relative power in the beta, alpha, theta, and delta frequency bands, and the median and spectral edge frequency. The amplitude of the ASSR was reduced significantly at the end of the induction period and decreased below noise levels during surgical anesthesia. It increased significantly during emergence and recovery. The amplitude during recovery remained significantly smaller than the preinduction values. The changes of the ASSR paralleled those of the level of consciousness. The EEG measurements were distorted by the presence of muscle artifacts that were prominent during emergence and recovery. The amplitude of the ASSR appears to provide a more reliable indicator of the level of consciousness than the EEG.

Adult↗