Elna Robinson

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.

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.

Hypertension and sleep apnea in black South Africans a case control study

Despite relatively consistent findings that patients with hypertension have higher than anticipated prevalences of sleep apnea/hypopnea (SAH), inadequately controlled factors such as age and obesity have been implicated as possibly accounting for these findings. All-night polysomnograms were performed on 20 hypertensive black South Africans, a group with increased risk for this disease. They were matched with a control group of black subjects in respect of age, gender, body mass index (BMI), neck circumference and scores on a sleep questionnaire. While the groups failed to differ significantly in terms of demographic variables, nor in regard to 8/9 anthropometric measures, the hypertensive group had a significantly higher apnea/hypopnea index (AHI) (P = .01), longer duration of AH (P = .01) and lower mean minimum arterial oxygen saturation levels (P = .005). Of the anthropometric measures, only age and neck circumference were found to be cofactors for AHI and were accounted for in the analysis. Five of the hypertensive patients and two of the controls had an AHI > 10, giving a prevalence odds ratio of 3 (95% confidence interval: 0.66-14.50). The present study appears to be the first in black African subjects and with prevalence findings largely comparable to those obtained in other ethnic groups. There was a trend for more severe SAH to occur in this subgroup of five hypertensives (AHI = 14-30) than in controls (maximum AHI = 12). While data are lacking to link antihypertensive medication to SAH in humans, further study is necessary before discarding this factor.

Posterior tibial and sural nerve somatosensory evoked potentials in dystrophia myotonica

Somatosensory evoked potentials (SEPs) were recorded in a group of 18 patients with dystrophia myotonica and in 28 control subjects after stimulating the right and left posterior tibial (SEP-PT) and sural (SEP-S) nerves at the ankles. Recording electrodes were placed in the popliteal fossae, overlying the L3 spinal vertebrae, and at the appropriate scalp sites. In all control subjects and dystrophia myotonica subjects SEP-PT latencies were shorter than equivalent SEP-S latencies, probably reflecting conduction along group I muscle afferents and along slower conducting cutaneous afferents, respectively. Intergroup comparisons revealed prolonged absolute and interpeak latencies in the dystrophia myotonica group, showing both peripheral and central somatosensory pathway involvement. Individual abnormal latencies which exceeded the control group mean plus 3 standard deviations were found in 66% of the dystrophia myotonica group, mainly due to prolonged peripheral conduction times. Results pointed to the concomitant involvement of both the posterior tibial and sural nerve somatosensory pathways in dystrophia myotonica.

Burst Patterns Occurring during Drowsiness in Clinical EEGs

ABSTRACT.There is an extensive range of EEG patterns associated with drowsiness. The occurrence of burst patterns with a sharp configuration or containing sharp transients was evaluated in 700 consecutive clinical EEGs of adults and children. All recordings included 16 channels of EEG and two channels of eye movements. Recordings included mostly bipolar but also referential montages. Patterns were classified by consensus and regarded as normal variants or of uncertain significance. The main reasons for referral were epilepsy or psychiatric disorders. One or more of 16 different patterns were found in 39% of all subjects. Vertex sharp waves were the most common (n = 178) and were initially asymmetrical in 17 cases. Hypnagogic paroxysmal spike-wave bursts were seen in 21/165 children. Sharp transients were also prominent in generalized sharp bursts (n = 21), frontocentral sharp bursts (n = 3), temporal or vertex sharp waves with alpha (n = 6), and beta bursts (n = 11). Some drowsiness patterns containing sp...

Effects of Two Anticholinergic Drugs on Electroretinograms and Visual Evoked Potentials in Healthy Human Subjects

A battery of electroretinograms (ERGs) and visual evoked potentials (VEPs) were recorded from 12 normal, male volunteers after the intravenous administration of either biperiden 2.5 mg, atropine 1.5 mg or placebo, at weekly intervals. Self-reports indicated that both drugs caused significantly reduced levels of alertness compared to placebo, but more so with biperiden than atropine. Biperiden was not, however, associated with significant changes to ERGs, while atropine caused a few isolated, significant increases to implicit times. There were no significant treatment effects on pattern ERGs or VEPs. The flash VEP latencies and amplitudes recorded after the anticholinergics did not differ from placebo. These preliminary findings suggest that these anticholinergics do not have marked effects on either ERGs or VEPs.