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Biomedical subjects

K Meinzer

Publications and source records attributed to K Meinzer.

11 recordsLinked to original sources
PubMed1990

Occupational performance of a paced secondary task under conditions of sensory deprivation. I. Heart rate changes in train drivers as a result of monotony.

Twelve experienced train drivers were asked to operate the train function safety circuit (SIFA)--a paced secondary motor task which is expected to guarantee the driver's fitness for service on engines of the German Federal Railway--under laboratory conditions of extreme monotony. In spite of massive decreases in vigilance as shown by theta-activity in the EEG, all subjects were able to operate the device without major errors. A prerequisite for adequate performance is an EEG-defined arousal reaction, which is synchronized with the SIFA cycles. For 7 subjects the time-related cross-correlation coefficients between SIFA operation, alpha-activity (indicative of alertness), theta-activity (indicative of reduced vigilance), and heart rate were calculated. The central-nervous arousal found in the EEG corresponded to distinct increases in heart rate. The moments of SIFA operation after phases of light sleep correlated significantly and positively with increases in heart rate. These increases constituted a physiological overcompensation as far as the physical readiness was concerned which reached its peak after the task had been performed satisfactorily, constituting additional and superfluous occupational stress. The results of this study indicate clearly that monotony stress is not a result of occupational monotony itself, but the result of the physiological effort which is required in order to regain a level of alterness which allows adequate performance under monotonous conditions.

Electroencephalography↗
PubMed1990

Occupational performance of a paced secondary task under conditions of sensory deprivation. II. The influence of professional training.

Twelve truck drivers operated the train function safety circuit (SIFA), a paced secondary task used as a job monitor on German railways engines, under laboratory conditions of extreme monotony, in a comparison with 12 train drivers who were well acquainted with SIFA. Alertness was determined by means of EEG evaluations. Heart rate was monitored as the parameter for physical load, and the precoded SIFA tasks as the active response parameter. In spite of significantly more frequent and more distinct decreases in alterness, the SIFA-trained subjects (TS) performed better. Nine out of 12 TS reached the stage of light sleep at least once during the experimental run, as compared to 4 out of 12 untrained subjects (US). Nevertheless, the ratio acoustic warnings/occurrence of light sleep was significantly lower in TS (P less than 0.01), and there were three operational errors (equivalent to emergency braking) in US. Whereas US received fewer acoustic warnings in the stages of slightly reduced altertness, this trend was reversed as soon as low frequency theta-activity appeared in the EEG. A time-related calculation of the cross-correlation coefficients between SIFA operation, alpha-activity, theta-EEG-activity, and heart rate showed that timing of SIFA operation interrupting phases of light sleep correlated significantly and positively with increases in heart rate. The results suggest that a mechanism of rhythmic central nervous arousal interrupting phases of decreased alertness/drowsiness can be learned, whereas the physiological consequences of the effort to prevent the deterioration of performance under conditions of monotony are not reduced by professional adaptation.

Automobile Driving↗
PubMed1990

MESAM: a heart rate and snoring recorder for detection of obstructive sleep apnea.

The high prevalence of sleep-related breathing disorders demands the development of ambulatory recording devices that can handle data with a high degree of selectivity and are easy to use and to interpret. A digital device based on the recording of heart rate and breathing sounds was developed. Patients with sleep-related breathing disorders can be preselected before they undergo sleep laboratory investigations. Treatment control can be achieved ambulatory, having an initial recording.

Ambulatory Care↗
PubMed1989

[Snoring and sleep apnea syndrome].

Sleep apnea and obstructive snoring are sleep related breathing disorders (SRBD). Nevertheless, there is only a quantitative difference between snoring and the obstructive form of sleep apnea. Snoring occurs in at least 20% of the population; 50% of the 50 year old male snore. Although in most of the cases only harmless snoring is concerned. It becomes serious if it leads as the independent SRBD "obstructive snoring" to a continuous oxygen desaturation and a sleep disturbance or, if in cases of sleep apnea a postapnoic snoring is concerned. The snoring pattern "loud and irregular" is always a sign for a serious SRBD. Still, no exact statement can be given concerning the frequency of obstructive snoring. However, the prevalence of sleep apnea in men of the mean age group has been determined to 10%. By the so-called sleep apnea syndrome are summarized clinical pictures with symptoms and findings caused by sleep apnea, respectively with those which can be reduced by sufficiently early introduced therapy. Most frequent symptoms and findings are: hypertension, loud and irregular snoring, daytime sleepiness and nocturnal cardiac arrhythmias. Especially hypersomnia has always to be taken seriously. In relation with other symptoms and findings associated with apnea it is always an indication for the examination for sleep apnea and obstructive snoring.

Brain↗
PubMed1989

[Diagnosis of sleep apnea: required equipment for staged diagnosis].

In view of the high prevalence of sleep apnoea (SA) a stepped concept for diagnosis and therapy is needed. Such a concept requires appropriate instrumentation. The apparative requirement for a five-stage concept, and the experience gained with it, are presented, in particular these newly introduced stages: screening instrument, based on an analysis of heart rate and breathing sounds, and a mobile sleep laboratory based on oxygen saturation measurement combined with inductive plethysmography and four further parameters. Experience obtained with such a stepped concept demonstrates its efficiency and necessity in the diagnosis of sleep-related breathing disturbances.

Electrocardiography, Ambulatory↗
PubMedDate not supplied

Correction of endothelial dysfunction in coronary microcirculation of hypercholesterolaemic patients by L-arginine.

Hypercholesterolaemia impairs endothelial function, possibly by interference with the intracellular formation of endothelium-derived relaxing factor from its precursor L-arginine. Whether L-arginine reverses hypercholesterolaemia-induced endothelial dysfunction in the coronary circulation was thus investigated. Epicardial artery cross-sectional area and coronary blood flow velocity were measured in 8 hypercholesterolaemic patients (mean serum cholesterol 7.8 [SE 0.3] mmol/l) and 7 age-matched controls before and after graded intracoronary infusions of the endothelium-dependent agent acetylcholine (0.036, 0.36, 3.6 micrograms/min). The effect of intracoronary infusion of L-arginine (160 mumol/min via the guiding catheter) on these measurements was then examined. In controls, acetylcholine induced a moderate dose-dependent constriction of the epicardial artery segment of the left anterior descending artery and increased coronary blood flow (by 239% [SE 57] at the highest dose). In patients with hypercholesterolaemia, the vasoconstrictive effect of acetylcholine on epicardial segments was similar to that in controls, but the increase in coronary blood flow with acetylcholine was significantly attenuated (highest dose: 61%, p less than 0.02 vs controls). L-arginine restored the acetylcholine-induced increase in blood flow in patients with hypercholesterolaemia (198% [61] vs baseline) but did not affect coronary blood flow in controls. The findings suggest that hypercholesterolaemia impairs endothelium-dependent dilatation of the coronary microcirculation and that this impairment can be restored by short-term administration of L-arginine. The possibility that L-arginine might form the basis of treatment for coronary endothelial abnormalities induced by hypercholesterolaemia could be worth investigating.

Acetylcholine↗