Peter Bartel

Attention and working memory in resident anaesthetists after night duty: group and individual effects

Aims: To investigate the effects of a single period of night duty on measures of attention and working memory in a group of residents (registrars) in anaesthesiology. Emphasis was placed on individual deficits using a reference point of the equivalent effect of a blood alcohol concentration (BAC) >0.05% determined by other researchers. Methods: There were 33 subjects aged 26–42 years. Night duty was performed on a weekly basis. Baseline assessments were conducted at either 08 15 or 08 55 preceding night duty and repeated 24–25 hours later, just after the completion of duty. Questionnaires included items regarding duration of sleep and the Stanford Sleepiness Scale. A battery of four reaction time (RT) tasks of increasing difficulty, lasting approximately 35 minutes, was administered on a personal computer. These ranged from simple RT to progressively more complex RT tasks incorporating working memory. A significant change was regarded as >15% deterioration in respect of speed or accuracy. Results: The mean duration of sleep preceding night duty was 7.04 hours and 1.66 hours during the period of night duty. Intergroup comparisons revealed significant prolongation in mean response speed in the first three tests. Mean accuracy was significantly reduced only in respect of the two more complex tests. A >15% deterioration in response speed occurred in up to 30% of subjects on a single task, rising to 52% (17/33) overall. Deterioration occurred in a patchy distribution in most subjects, involving no more than one or two of the four tasks. As regards accuracy, the prevalence of deterioration increased with task complexity. Conclusions: Results are in general agreement with previous group analyses. A new dimension was added by the analysis of a broad spectrum of individual response to sleep deprivation. The effects of sleep loss in residents cannot be overlooked, even in a relatively benign work schedule.

The effects of levodopa and haloperidol on flash and pattern ERGs and VEPs in normal humans

We investigated the effects of single doses of the dopamine agonist levodopa and the dopamine antagonist haloperidol on pattern and flash electroretinograms (ERGs) and visual evoked potentials (VEPs) in normal subjects. A placebo and two treatment regimens were administered in a randomized double-masked design. No significant intertreatment differences in the pattern ERGs and VEPs were noted. Although not statistically significant, a clearly discernible tendency was found for increased flash ERG b-wave amplitudes after levodopa administration compared with placebo. In comparison with placebo and levodopa, haloperidol was associated with significantly prolonged flash ERG b-wave implicit times, including each oscillatory potential, which also showed increased duration, particularly in the O1–O3 interpeak implicit time. The failure of pattern ERGs and VEPs to show changes after haloperidol may have been related to the timing of the recordings, which took place during the presumed phase of rising blood levels and before the flash ERG and VEP recordings. Our findings further demonstrated the reliability of the flash ERG in revealing changes in dopaminergic status in the visual system and suggest that steady-state (flicker) ERGs, cone ERGs, and oscillatory potentials have particular use in this regard.

Once versus twice daily amikacin in neonates: Prospective study on toxicity

Objective: To compare the potentially toxic effects in fullterm neonates of amikacin administered once daily, versus amikacin administered twice daily.

Effects of clobazam and clonazepam on saccadic eye movements and other parameters of psychomotor performance.

SummaryThe effects of two benzodiazepine anti-convulsants clobazam (20 mg) and clonazepam (2 mg) in a variety of psychomotor performance tests were compared in a placebo controlled double-blind acute oral dose study in ten healthy volunteers. Assessments included critical flicker fusion (CFF) threshold, the Sternberg memory scanning and choice reaction time (CRT), peak saccadic velocity (PSV) and visual analogue scales, all previously shown to be sensitive to the effects of benzodiazepines.Clobazam did not significantly impair saccadic eye movements, CFF threshold, Sternberg memory scanning and CRT compared to placebo. Clonazepam significantly lowered PSV, reduced the CFF threshold, slowed the Sternberg CRT and decreased an alertness factor in the visual analogue scales compared to placebo. Clonazepam significantly increased memory scanning time compared to clobazam. Clobazam was remarkably free of cognitive and psychomotor side-effects.

Short-latency somatosensory evoked potentials in dystrophia myotonica.

Somatosensory evoked potentials (SEPs) were recorded in a group of 21 patients with dystrophia myotonica and in a group of controls. Those with dystrophia myotonica had longer absolute peak latencies due to slower peripheral conduction. SEP abnormalities revealed peripheral and/or central conduction delays in 33% of the dystrophia myotonica subjects. There was no apparent relationship between the clinical severity of the disease and SEP abnormality.

The effects of alprazolam, quazepam and diazepam on saccadic eye movements, parameters of psychomotor function and the EEG

Summary— The effects of a single oral dose of alprazolam (1 mg), quazepam (15 mg) and diazepam (10 mg) on the peak saccadic velocity (PSV) of saccadic eye movements (SEM), the Sternberg memory scanning and choice reaction time (SMS‐CRT), critical flicker fusion frequency (CFFF), spectral analysis of the EEG and a mood scale were assessed in 9 healthy volunteers in a double‐blind, placebo‐controlled crossover study. Alprazolam revealed greater sedative effects than diazepam in the above‐mentioned tests. Quazepam had the least sedative effect of the 3 drugs tested, showed a time lag at the onset of its effects and a more prolonged effect on psychomotor impairment than reported previously.

The intrasession repeatability of pattern electroretinograms and the effects of digital filtering

Transient pattern electroretinograms were recorded in 12 normal young volunteers with the use of 12′ and 30′ checkerboard stimuli and 1 c/deg and 2.5 c/deg vertical gratings. The intrasession repeatability of pattern electroretinograms was determined by employing alternative statistics to the frequently used correlation coefficients. Comparisons were made with the repeatability of cone electroretinograms elicited by ganzfeld stimulation. The coefficient of repeatability was substantially lower (better) for pattern electroretinogram b-wave implicit times than for a-wave implicit times and b-wave amplitudes, the latter having high coefficients of repeatability. Cone electroretinograms had better repeatability with respect to all three parameters. Digital filtering using a bandpass of 1–40 Hz was applied to the original pattern electroretinograms recorded with a bandpass of 1–250 Hz. Although peak definition was generally enhanced, repeatability did not show marked improvement. Differences between broadband analogue-filtered pattern electroretinograms and the same responses with highfrequency noise removed by digital filtering need to be taken into account. The coefficient of repeatability statistic appears to facilitate the assessment of pattern electroretinograms and permits the comparison of the repeatability of both implicit time and amplitude parameters irrespective of absolute values. The implications of the relatively poor repeatability of pattern electroretinogram b-wave amplitudes for clinical applications need to be considered.

Short-Term Antihypertensive Medication Does Not Exacerbate Sleep-Disordered Breathing in Newly Diagnosed Hypertensive Patients

It has been speculated for some time that various antihypertensive medications may have a deleterious effect on respiration during sleep and thereby enhance the apparent association between hypertension and sleep apnea/hypopnea (SAH). However, there are few data to support this contention. The present study used a double-blind, randomized, cross-over design to contrast the effects of 6 weeks treatment with alpha-methyldopa and the combination of hydrochlorothiazide and amiloride with that of amlodipine and the combined diuretics in a group of 24 newly diagnosed patients with primary hypertension. All-night polysomnography was performed before the initiation of therapy (baseline) and at the end of the two treatment periods. Respiratory variables failed to reveal any significant differences between the treatments and baseline, or between the two different treatment regimens. The two treatment regimens achieved similar reductions in blood pressure. The prevalence of SAH was 25% before treatment, which is comparable to a prevalence of 20% in a similar group drawn from the same population but receiving various antihypertensive medications. The findings of this study are in agreement with previous reports using other classes of antihypertensive drugs that also failed to detect any tendency for increases in nocturnal respiratory disturbance indices over assessment periods of 8 weeks or shorter.

The Relationship between Vitamin B6 Metabolism, Asthma, and Theophylline Therapy

Asthma can be broadly defined as enhanced reactivity of the airways to specific and nonspecific stimuli, resulting in diffuse airways obstruction with clinical symptoms like dyspnea, cough, and a tight chest. Stimuli that may provoke asthmatic responses include environmental allergens, respiratory infection, certain drugs such as nonsteroidal anti-inflammatory drugs, and exercise.’ An important aspect of asthma treatment is the administration of bronchodilators of which theophylline is most commonly used.2 As will be reviewed in this paper, vitamin B, status and asthma have been studied by several researchers3^’; however, the effect of medication per se on vitamin B, status has not been investigated. Because it would be practically impossible to study vitamin B, status in asthmatics without the use of bronchodilators, we opted for the alternative: to study the effect of bronchodilators on vitamin B, metabolism in healthy volunteers. We therefore investigated the effect of theophylline on vitamin B, metabolism in healthy volunteers, and our results are summarized and reviewed in the second part of this paper.

Effects of single doses of diazepam, chlorpromazine, imipramine and trihexyphenidyl on visual-evoked potentials.

There is increasing evidence that the P 100 peak of the pattern-reversal visual-evoked potential (VEP-PR) is delayed by drug-induced dopamine antagonism and in Parkinsons disease. Recent studies have reported that components of the flash-VEP (VEP-F) are delayed by an anticholinergic which does not affect the VEP-PR. The present study found that a single dose of chlorpromazine increased the latencies of the VEP-PR and of the VEP-F and increased the VEP-F P2 amplitude. Trihexyphenidyl increased the VEP-PR amplitude but had only minor effects on the VEP-F. There was a tendency for imipramine to increase VEP-F latencies, especially the N3 peak, but had no effect on the VEP-PR. Both VEPs were unaffected by diazepam. These VEP findings add further support to the role of dopamine in the human visual system. Possible reasons are advanced for the failure of trihexyphenidyl to cause previously reported VEP changes associated with hyoscine hydrobromide. Several important issues need to be addressed by future research.