[Effect of obstructive sleep apnea on preload of the right heart]. / Der Einfluss der obstruktiven Schlafapnoe auf die Vorlast des rechten Herzens.

Obstructive sleep apnea (OSA) is characterized by a total inspiratory occlusion of the extrathoracic airways with persisting respiratory effort. During obstructive breathing efforts the intrathoracic pressure (ITP) falls below-20 Torr. This should augment venous return by depleting the blood from the extrathoracic veins into the thoracic veins, thus pre- and afterload of the right heart rises. Until now preload of the right heart during OSA was not measured. This study shows the filling pressures (tmPRA) of the right heart during OSA. In five patients the in- and expiratory right atrial pressure and the intrathoracic pressure were measured, beat by beat, during the non REM hour in which the most apnea episodes occurred. The tmPRA values were calculated as follows: tmPRA = PRA-ITP. The rising tmPRA with falling ITP shows that the venous return, during apnea episodes, rises mostly unhampered. Only in one patient did a cut-off of the increasing tmPRA occur. This patient showed a flow limitation of venous return. Two more patients developed different trends. One part of the measurements led to a linear increase of tmPRA, the other part shows a plateau up from a certain ITP. In two patients tmPRA increases linearly, in the extreme, with decreasing ITP. This indicates no flow limitation of venous return. The results of this investigation suggest that the protective mechanism of the limitation of venous return, occurring under artificial conditions, does not regularly appear in patients with OSA. This leads to repetitive volume overloads of the right heart.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.