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Biomedical subjects

C W Hess

Publications and source records attributed to C W Hess.

At least 37 records · Page 2Linked to original sources
PubMed1999

High prevalence of glaucoma in patients with sleep apnea syndrome.

OBJECTIVE: To determine the prevalence of glaucoma in sleep apnea syndrome (SAS), an entity characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of cardiovascular and neurologic sequelae. DESIGN: Cross-sectional study. PARTICIPANTS: A total of 114 white patients consecutively referred for polysomnographic evaluation of suspected SAS. INTERVENTION: Complete ophthalmologic examination, including computerized perimetry and simultaneous stereoscopic optic disc photographs. MAIN OUTCOME MEASURES: Spearman rank correlations between the respiratory disturbance index during night sleep (RDI), a value used to diagnose and grade SAS, and visual acuity, intraocular pressure (IOP), visual field indices, presence or absence of glaucomatous optic disc changes, and diagnosis of glaucoma. Each correlation was controlled for age and body mass index. To compare proportions of patients harboring glaucoma, the binomial test was used. RESULTS: Sixty-nine (60.5%) of the 114 patients had an RDI > or =10, which indicates SAS. Three patients had primary open-angle glaucoma, and two had normal-tension glaucoma. All patients with glaucoma had SAS. The observed prevalence of glaucoma in patients with SAS (5 of 69, 7.2%) was significantly higher than expected in a white population (2%) (P = 0.01). The RDI correlated positively with IOP (P = 0.025), visual field loss variance (P = 0.03), glaucomatous optic disc changes (P = 0.001), and diagnosis of glaucoma (P = 0.01). CONCLUSIONS: Patients with SAS constitute a high-risk population for glaucoma and should therefore be screened for glaucoma.

Adult↗
PubMed1999

Eyelid, conjunctival, and corneal findings in sleep apnea syndrome.

OBJECTIVE: To determine the prevalence of eyelid, conjunctival, and corneal findings in patients with sleep apnea syndrome (SAS). DESIGN: Case series. PARTICIPANTS: Seventy-two white patients referred for evaluation of suspected SAS. INTERVENTION: Complete examination of eyelids, conjunctiva, and cornea, including videokeratography. MAIN OUTCOME MEASURES: Spearman rank correlations were determined between the respiratory disturbance index (RDI) during night sleep, a value used to diagnose and grade SAS, and tear film break-up time, eyelid distraction distance, presence or absence of ocular irritation symptoms, blepharoptosis, floppy eyelids, lacrimal gland prolapse, keratoconus, and endothelial dystrophy. Each correlation was controlled for age and body mass index. RESULTS: According to the RDI, 44 (61 %) of the 72 patients had SAS. The RDI correlated positively with the eyelid distraction distance (P = 0.05), presence or absence of floppy eyelids (P = 0.01), and lacrimal gland prolapse (P = 0.01), and correlated negatively with tear film break-up time (P = 0.02). None of our patients with floppy eyelids had corneal abnormalities. One patient with SAS had bilateral keratoconus; another had bilateral Fuch endothelial dystrophy. CONCLUSIONS: Sleep apnea syndrome was significantly associated with reduced tear film break-up time, floppy eyelids, and lacrimal gland prolapse. However, ocular irritation symptoms and corneal involvement were rare among patients with SAS. These findings do not confirm previous studies that reported a high prevalence of corneal involvement in floppy eyelid syndrome.

Adult↗
PubMed1999

A clinical study of motor evoked potentials using a triple stimulation technique.

Amplitudes of motor evoked potentials (MEPs) are usually much smaller than those of motor responses to maximal peripheral nerve stimulation, and show marked variation between normal subjects and from one stimulus to another. Consequently, amplitude measurements have low sensitivity to detect central motor conduction failures due to the broad range of normal values. Since these characteristics are mostly due to varying desynchronization of the descending action potentials, causing different degrees of phase cancellation, we applied the recently developed triple stimulation technique (TST) to study corticospinal conduction to 489 abductor digiti minimi muscles of 271 unselected patients referred for possible corticospinal dysfunction. The TST allows resynchronization of the MEP, and thereby a quantification of the proportion of motor units activated by the transcranial stimulus. TST results were compared with those of conventional MEPs. In 212 of 489 sides, abnormal TST responses suggested conduction failure of various degrees. By contrast, conventional MEPs detected conduction failures in only 77 of 489 sides. The TST was therefore 2.75 times more sensitive than conventional MEPs in disclosing corticospinal conduction failures. When the results of the TST and conventional MEPs were combined, 225 sides were abnormal: 145 sides showed central conduction failure, 13 sides central conduction slowing and 67 sides both conduction failure and slowing. It is concluded that the TST is a valuable addition to the study of MEPs, since it improves detection and gives quantitative information on central conduction failure, an abnormality which appears to be much more frequent than conduction slowing. This new technique will be useful in following the natural course and the benefit of treatments in disorders affecting central motor conduction.

Adult↗
PubMed1999

Task-dependent effects on motor-evoked potentials and on the following silent period.

The silent period (SP) after transcranial stimulation is used as a diagnostic tool in various central nervous system disorders although no standardized experimental setup has been established. The aim of this study was to demonstrate the influence of an isotonic compared to an isometric experimental condition. The SP after transcranial magnetic brain stimulation in the biceps brachii and brachioradialis muscle was up to 130% longer when elicited during a maintain-position (isotonic) task as compared to a maintain-force task (isometric) when stimulus intensities of 5% to 25% above threshold were used. The mean SP duration in these muscles was positively correlated to the mean contraction time in both tasks. However, no such relationship was observed for the trials within the individual subjects. We speculate that the invariably longer SP of the maintain-position task was due to the different "motor set" which predictively determined the muscle behavior after the stimulus. In the maintain-position trials, the stimulus-induced long-lasting flexion movement is counteracted by a motor set aiming to relax the elbow flexors immediately after the stimulus. In the maintain-force task the contraction twitch is short and a force drop below the preset level must be prevented by a motor set aiming to contract the elbow flexors immediately after the stimulus. The latter may increase the synaptic input to the motoneuron pool and facilitate the reoccurrence of the electromyogram terminating the SP. At high-stimulus intensities the SP duration increased in both tasks, and the task-dependent differences disappeared. Therefore, when using the SP duration for diagnostic purposes, isometric conditions and high-stimulus intensities should be used.

Adult↗
PubMed1998

[X-chromosomal bulbospinal muscular atrophy (Kennedy syndrome)].

Two brothers with slowly progressive weakness and congenital nystagmus are presented. DNA analysis confirmed X-linked recessive bulbospinal muscular atrophy (XBSMA, Kennedy's disease) by demonstration of increased size of a CAG-triplet repeat on the androgen receptor gene on the X-chromosome. XBSMA is characterized by almost symmetrical muscular atrophy, weakness and fasciculations predominantly of bulbar, facial and proximal muscles of the extremities, with onset in the third to fifth decade. Tendon reflexes are depressed and pyramidal signs are absent. Sensory symptoms are clinically rare, but sensory nerve action potentials are frequently abnormal. Additional symptoms are important for differential diagnosis, and include postural tremor, gynecomastia, diabetes mellitus, testicular atrophy and impotence. Differentiation of this hereditary disorder from treatable conditions such as multifocal motor neuropathy or amyotrophic lateral sclerosis is essential. Though life expectancy is normal, patients become disabled in the course of the disease and need supportive care. Periodic testing for diabetes is recommended, and genetic counseling should be provided for patients and their relatives.

Adult↗
PubMed1998

Task-dependent facilitation of motor evoked potentials during dynamic and steady muscle contractions.

Task-dependent differences in the facilitation of motor evoked potentials (MEPs) following cortex stimulation were studied in a proximal (deltoid) and a distal muscle (abductor digiti minimi; ADM) in 23 healthy subjects during both dynamic and steady contractions of the target muscle under isometric and under nonisometric conditions. In the deltoid, MEP amplitudes were significantly greater if stimulation was performed during dynamic contractions than during steady contractions, despite equal background electromyographic levels just prior to the stimulus. The same task-specific extra facilitation of deltoid MEP amplitudes was also found with magnetic stimulation of the brain stem instead of the cortex in 3 subjects. In the ADM, no such task-dependent extra facilitation of MEPs during dynamic contractions was found. It is concluded that in the deltoid, during dynamic contractions, a greater proportion of the spinal motoneurons is close to depolarization threshold (greater "subliminal fringe") whereas the number of firing motoneurons is similar to that during steady contraction. The lack of task-dependent extra facilitation of MEPs in the ADM is explained by the predominant recruitment principle for force gradation in small hand muscles, which is in contrast to the predominant frequency principle used in proximal muscles.

Adult↗
PubMed1998

Recording of electrical brain activity in a magnetic resonance environment: distorting effects of the static magnetic field.

The technical limitations of electroencephalography (EEG) and flashed visually-evoked potentials (VEP) recordings in the static magnetic field of the MR system were systematically studied. A main artifact occurring in the magnetic field was found to be correlated with the heart cycle and had amplitudes in the range of EEG and VEP signals. For VEP recordings, a substantial reduction of this effect was achieved by subtraction of the averaged artifact from the averaged composed signal (VEP and artifact) resulting in the VEP signal alone. However, for continuous EEG recordings, there is no such solution, since the observed effect is not sufficiently constant in amplitude, and the standard deviation of the amplitude of the effect is often larger than the EEG amplitude.

Artifacts↗
PubMed1998

Optic neuropathy associated with sleep apnea syndrome.

OBJECTIVE: The study aimed to determine ocular abnormalities in sleep apnea syndrome (SAS), an entity characterized by repetitive upper airway obstructions during sleep, inducing hypoxia and sleep disruption with the risk of cardiovascular and neurologic sequelae. DESIGN: The study design was a case series. PARTICIPANTS: Nine patients referred for evaluation of suspected SAS participated. INTERVENTION: Complete ophthalmologic examination, including computerized perimetry, was performed. MAIN OUTCOME MEASURES: Correlations between the respiratory disturbance index (RDI) during night sleep, a value used to diagnose and to grade SAS, and visual field indices using the Spearman rank correlation coefficient (r(s)) were measured. RESULTS: One patient was excluded from the statistical analysis because of optic nerve drusen with constricted visual fields, another because of tilted discs with corresponding temporal visual field defects. All three patients with severe SAS and one patient with moderate SAS had relative nasal arcuate visual field defects; two patients with severe SAS also had paracentral relative defects. One patient with normal polysomnographic result and two patients with mild or moderate SAS had normal visual fields. The RDI correlated positively with the mean visual field defect (r(s) = 0.81, P < 0.05) and with the visual field loss variance (r(s) = 0.78, P < 0.05). The clinical ophthalmologic examination results were normal in all seven patients. In two of the three patients with severe SAS treated with continuous positive airway pressure (CPAP), visual field defects remained stable over 18 months. The patient with optic nerve drusen also had severe SAS and was, therefore, treated with CPAP. His constricted visual fields improved dramatically after treatment. CONCLUSIONS: Visual fields of patients with SAS showed defects consistent with an optic neuropathy. The CPAP therapy seems to stabilize or even reverse visual field defects.

Adult↗
PubMed1998

Dependence of the transcranially induced silent period on the 'instruction set' and the individual reaction time.

OBJECTIVES AND METHODS: We looked for influences of the experimental condition on the silent period (SP) from transcranial motor cortex stimulation and analyzed how the instruction given to the subject, as well as the individual reaction time, might affect the duration of the SP in the biceps brachii muscle. RESULTS: The duration of the SP was found to critically depend on the subject's voluntary reaction of the target muscle immediately after the stimulus. With low stimulus intensity and low background force, the duration of the silent period was significantly longer in 10 of 13 subjects (P = 0.002) when they were instructed to relax quickly after the stimulus rather than to maintain the the force at a constant level. A significant shortening of the SP (P = 0.02) was observed when the subjects were instructed to perform a rapid contraction of the target muscle in reaction to the cortical stimulus. With low stimulus intensity and high background force, the same influence of the instruction set was found in 6 of 13 subjects. When the subjects were left without precise instruction, the SP duration was unpredictable. In 10 subjects, the SP corresponded to that obtained with the instruction to maintain the force at a constant level. However, in 3 subjects it was prolonged to the value observed in the 'relax' instruction. With greater stimulus intensities, the effect of the instruction set on the SP duration was generally smaller. A significant prolongation was nevertheless found at low background forces with rapid relaxation (P < 0.001), and a significant shortening was found at high background forces with rapid contraction (P < 0.001) after the stimulus. The SP duration observed with 20% of maximal voluntary contraction (MVC) significantly correlated with the individual reaction time. No such correlation was found for the SP obtained with 80% MVC. The SP was slightly longer at 20% MVC, as compared to 80% MVC within each instruction group. This effect was significant (P < 0.05) at low stimulus intensities. CONCLUSIONS: Therefore, when assessing the SP duration for diagnostic purposes, not only the stimulus intensity but also the background force and the voluntary reaction must be standardized. Furthermore, great stimulus intensities and high background forces should be used to minimise the effects of instruction set and individual reaction time.

Adult↗
PubMed1998

Developmental background and outcome in patients with nonepileptic versus epileptic seizures: a controlled study.

PURPOSE: This study was designed to evaluate the relevance of developmental emotional stress factors, which are considered to influence emotional functioning, as contributing factors in the development of psychogenic symptoms. METHODS: Ten patients with nonepileptic seizures (non-ESs) (frequently referred to as psychogenic seizures), in whom diagnosis had been confirmed by a placebo-infusion test (PT), and 10 control patients with complex partial seizures (ESs) were evaluated with regard to developmental background by using structured in-depth interviews performed by a single interviewer blinded to the diagnosis. In addition, outcome assessment in the non-ES group after PT was done. RESULTS: There were no significant differences between groups in developmental psychosocial stress or in any single developmental stress factor. Six months after PT, the outcome was favorable in patients with non-ES: six were seizure free, and two had a considerable reduction in frequency of seizures. CONCLUSIONS: Our research indicates the following: (a) a high incidence of developmental stress factors and functional disturbances may be found in patients with non-ESs and ESs; (b) assessment of developmental emotional stress and functional disturbances as a basis for validating the diagnosis of non-ES should be treated with caution; (c) use of PT followed by supportive information about the nonepileptic origin of the attacks may have a positive therapeutic effect or help to introduce psychotherapeutic treatment.

Adult↗
PubMed1998

Functional organisation of saccades and antisaccades in the frontal lobe in humans: a study with echo planar functional magnetic resonance imaging.

The cortical activation pattern of saccades and antisaccades (versus rest) in the frontal lobe was analysed using an echo planar imaging (EPI) technique in 10 healthy subjects. Statistical analysis of activity in the dorsolateral prefrontal cortex disclosed a significantly greater activation during antisaccades in this region than during saccades. On the other hand, activity in the frontal eye fields was not statistically different in both tasks. These results confirm the important role of the dorsolateral prefrontal cortex for the correct performance of antisaccades obtained by studies in humans with isolated lesions of the dorsolateral prefrontal cortex.

Adult↗
PubMed1997

[Sleep disorders and dementia].

A clinically relevant sleep-wake disturbance is found in up to half the patients with dementia, and the sundowning agitation is a common cause of institutionalisation of demented geriatric patients. The circadian rhythm of demented patients is levelled off with increased daytime sleep and disrupted night sleep. Particularly in vascular dementia, Korsakow syndrome, Parkinson's disease, and depression the alteration of sleep architecture may be pronounced, whereas in Alzheimer's disease prominent hypersomnolence or insomnia is typically only found in later stages of the diseases. Greatly increased daytime sleepiness or striking insomnia at the very beginning of suspected dementia should thus prompt the search for other, possibly treatable causes of dementia. Neuropathological and neurophysiological studies support the hypothesis of a deteriorated hypothalamic suprachiasmatic nucleus (harbouring the biological clock) as a cause for the deranged circadian sleep-wake system in dementia. Management of sundowning behaviour includes restriction of daytime sleep, exposure to bright lights, and social interaction schedules during the day. The benzodiazepines and analogues usually not being sufficiently effectual, low doses of mild neuroleptics are often needed. Whether recent reports on efficacy of melatonin in elderly insomniacs also apply to demented patients is yet uncertain. The careful search and treatment of possible extracerebral physiologic factors causing reversible hypersomnia or insomnia is an important requisite. Polysomnographic studies are needed to recognise treatable sleep disturbance which could deteriorate or mimic dementia and sundowning. Particularly, a sleep-apnea-hypopnea syndrome must be searched for at the beginning of a suspected dementia, when successful treatment is still possible. Sleep studies should also identify periodic leg movements of sleep with restless legs and/or increased daytime sleepiness, and hyperkinetic parasomnias such as REM sleep behaviour disorder which may complicate or imitate sundowning.

Aged↗
PubMed1997

[Ocular myositis].

We report a young woman presenting with "painful diplopia" caused by inflammation of external eye muscles affecting both eyes sequentially. Orbital MRI disclosed swelling, signal hyperintensity and enhancement of isolated eye muscles. Corticosteroid treatment led to a complete remission within a few days. The compiled data of a literature review enclosing 52 sufficiently documented patients diagnosed as orbital myositis is reported with respect to clinical features, laboratory findings, associated disease, value of imaging procedures (CT,MRI). Therapeutic aspects and differential diagnosis are reviewed.

Adult↗
PubMed1997

Patterns of muscle activity in legs in sleep apnea patients before and during nCPAP therapy.

Nocturnal muscle activity in legs (MAL) was studied in 19 patients with sleep apnea syndrome before and during nCPAP. We distinguished periodic (P-MAL) and nonperiodic (N-MAL) as well as apnea-associated and independent MALs. N-MALs were strongly associated with apneas and disappeared during nasal continuous positive airway pressure (nCPAP). P-MALs showed a rather long intermovement interval (IMI) of about 54 s when associated with respiratory disturbances and a shorter one of about 38 s when occurring independently. In 5 patients with predominantly independent P-MALs and a short IMI before and during nCPAP an incidental coexistence of sleep apnea with periodic leg movements in sleep syndrome (PLMS) was postulated. Five patients with an equal number of apnea-associated and independent MALs before nCPAP had a long IMI which shortened under nCPAP, while the majority of MALs become independent. This could indicate a facilitating or an unmasking effect of nCPAP on PLMS. Four patients with predominantly apnea-associated MALs with a long IMI before nCPAP showed an unchanged MAL pattern under nCPAP, despite the disappearance of apneas. Since some arousals persisted in these patients, insufficient nCPAP pressure with an upper airway resistance syndrome was suspected. We conclude that when P-MALs persist under nCPAP therapy a long IMI may indicate an upper airway resistance syndrome, whereas a short IMI may indicate a coexisting or even induced PLMS.

Adult↗
PubMed1997

Human cortical plasticity: functional recovery with mirror movements.

Cortical plasticity of the human brain permits functional recovery after brain injury even in the absence of neuronal recovery. We report the combined evaluation, including electrophysiology and functional magnetic resonance imaging, of the pattern of cortical and cerebellar reorganization, in a patient with mirror movements as a sequel of perinatal unilateral brain injury. Recovery resulted in motor control by the healthy hemisphere using direct ipsilateral corticospinal projections and the contralateral cerebellum.

Adolescent↗