Influence of respiratory motor neurone activity on human autonomic and haemodynamic rhythms.

Although humans hold great advantages over other species as subjects for biomedical research, they also bring major disadvantages. One is that among the many rhythmic physiological signals that can be recorded, there is no sure way to know which individual change precedes another, or which change represents cause and which represents effect. In an attempt to deal with the inherent complexity of research conducted in intact human subjects, we developed and used a structural equation model to analyse responses of healthy young men to pharmacological changes of arterial pressure and graded inspiratory resistance, before and after vagomimetic atropine. Our model yielded a good fit of the experimental data, with a system weighted R2 of 0.77, and suggested that our treatments exerted both direct and indirect influences on the variables we measured. Thus, infusions of nitroprusside and phenylephrine exerted all of their direct effects by lowering and raising arterial pressure; the changes of R-R intervals, respiratory sinus arrhythmia and arterial pressure fluctuations that these drugs provoked, were indirect consequences of arterial pressure changes. The only direct effect of increased inspiratory resistance was augmentation of arterial pressure fluctuations. These results may provide a new way to disentangle and understand responses of intact human subjects to experimental forcings. The principal new insight we derived from our modelling is that respiratory gating of vagal-cardiac motor neurone firing is nearly maximal at usual levels of arterial pressure and inspiratory motor neurone activity.

Acute effects of alcohol on divided and covert attention in men.

RATIONALE: While several studies identified divided attention to be sensitive to alcohol effects, the impact of alcohol on covert visual attention is still not clear, despite the latter's important role in perception. OBJECTIVES: The study tests the effect of acute moderate doses of alcohol on divided and covert attention in right-handed, male volunteers. METHODS: The design of the study involved a double-blind trial with an alcohol and a placebo condition; measurements were taken before and after an oral dose of 0.6 g/kg alcohol versus placebo. In the divided-attention task, simultaneous visuo-spatial and auditory stimulation was applied. In a test of covert attention, subjects had to shift their attentional focus according to a central cue, from one location in the visual field to another. RESULTS: Under the divided-attention condition, reaction times were significantly prolonged after alcohol ingestion compared to placebo. Covert attention pre-post change was also significantly different between the alcohol and placebo groups. There is a reduction of false-cueing disturbance for left-appearing stimuli under moderate alcohol but an increase of disturbance for rightward stimuli, i.e. we found a lateralised pattern of reaction for spatial orienting. In the placebo group, no significant differences in right-left performance were obtained. CONCLUSION: The results suggest that sensory-attentional mechanisms play a key role in altered visual perceptual performance after alcohol ingestion. Furthermore, differences between the right and left visual field in the cued target-detection task indicate that alcohol exerts an influence on right-hemispheric attentional priming.

Effects of carotid sinus nerve stimulation at different times in the respiratory and cardiac cycles on variability of heart rate and blood pressure of normotensive and renal hypertensive dogs.

It was the purpose of the present study to determine (1) whether or not there exists a common respiratory and cardiac cycle time effect of the baroreceptor control of heart rate (HR) and blood pressure (BP) in spontaneously breathing anaesthetized dogs and (2) whether this effect, if present, is abnormal in dogs with renal hypertension. The baroreflex responses were evoked by brief low-intensity electrical carotid sinus nerve stimulation (CSNS) triggered by the R-wave in the electrocardiogram with an adjustable delay (0-210 ms) and positioned in either inspiration or expiration. All baroreceptor afferent nerves were intact. Brief CSNS had no noticeable effect on breathing. The responses of means of HR, respiratory sinus arrhythmia (RSA), and systolic and diastolic respiratory blood pressure waves (RBPWsyst, RBPWdiast) to CSNS were not different for normotensive and hypertensive dogs. No cardiac, but a small respiratory cycle time effect on means of HR, BPsyst and BPdiast was observed. The magnitude of RSA and RBPWdiast was markedly enhanced for expiratory CSNS at each delay after the R-wave. Inspiratory CSNS diminished the magnitude of RSA and RBPW only if applied during systole, and become ineffective for delays greater than 200 ms after the R-wave. During both respiratory phases, CSNS was elevated at times of central presentation of the natural sinoaortal baroreceptor discharges (120 ms and 70 ms, respectively). The magnitudes of RSA and RBPW were influenced simultaneously and in the same way by CSNS throughout. It is concluded that, under the present experimental conditions, RSA and RBPW have a common central origin.

Long-term implantation of a system of electrical stimulation of paralyzed laryngeal muscles in dogs.

Electrical stimulation of the posterior cricoarytenoid muscle, synchronized with inspiration, was achieved in dogs utilizing a radio frequency stimulus triggered by a chest wall expansion transducer. This system brings about abduction of the paralyzed vocal cord for the entire duration of inspiration, which allows a normal flow of air through the larynx. The implantable part of that system was tested successfully in chronic experiments (up to 11 months) in dogs with experimental paralysis of the recurrent laryngeal nerve. We feel that the system may be suitable for pacing the paralyzed human larynx.

Respiratory variations in arterial blood pressure and heart rate in normotensive and renal hypertensive dogs.

Respiratory sinus arrhythmia (RSA), systolic and diastolic respiratory blood pressure waves (RBPWsyst, RBPWdiast), mean heart rate (HR), mean respiratory frequency (RF) and the heart beat to respiratory cycle ratio (HB/RC) were measured in 23 spontaneously breathing, normotensive or renal hypertensive dogs under light anaesthesia. No significant differences were found between conditions of normal and chronically elevated blood pressure. All these parameters were analyzed statistically by means of linear regression analysis and rank correlation coefficient (rs). A correlation was found to exist between RSA and mean systolic blood pressure (negative), RF (negative), RBPWsyst (positive), RBPWdiast (positive). RF correlated with both HB/RC (negative) and RBPWsyst (negative). A correlation was also seen between PA and both BPsyst (positive) and BPdiast (positive), BPsyst and BPdiast (positive) and between HR and RBPWdiast (negative); however, all the remaining, theoretically possible correlations were not significant. The results may be referred to resonance mechanisms in a common nervous oscillator system.

Effects of carotid sinus nerve stimulation on respiratory sinus arrhythmia and respiratory blood pressure waves of the dog.

The effect on the amplitudes of RSA and RBPW of the time of the stimulus in the cardiac cycle, and also of continuous stimulation were studied. When the stimulus train was applied near peak systole the amplitudes of RSA and RBPW decreased. Stimulation in late systole increased both RSA and RBPW. Continuous stimulation did not exert any effects on RSA and RBPW.

Respiratory rhythmically regulated electrical stimulation of paralyzed laryngeal muscles.

Electrical stimulation of the posterior cricoarytenoid muscle, synchronized with inspiration, was achieved in dogs, utilizing a radio frequency stimulus triggered by a chest wall expansion transducer. This system brings about the abduction of the paralyzed vocal cord for the entire duration of inspiration, which allows a normal flow of air through the larynx. The stimulation system could be tested successfully in actual experiments in dogs with artificial paralysis of the recurrent laryngeal nerve. Its effectiveness could be proved through observation of the vocal cord movements (photographic documentation) and recording subglottic pressure variations. Transmission of stimulation energy is effected by electrical induction.

Effects of auditory stimulus timing in the respiratory cycle on the evoked cardiac response in man at rest.

The present experiments were carried out in 21 healthy adults to study the effects of auditory stimulus timing within the respiratory cycle on evoked cardiac response. The stimulus (80 dB white noise) was started by the first and finished by the second R-wave after change in respiratory phase, and presented in different series in either early inspiration or early expiration. The spirogram and eight sequential interbeat intervals (IBI) after respiratory phase change were recorded. The mean of IBI and standard deviation (SD) were calculated separately for each IBI of 20 trials for each subject, during both the prestimulus and poststimulus phases. The stimulus effects were expressed as changes from prestimulus conditions, in terms of delta IBI and delta SD. The mean of each of the eight IBI and its SD were found to vary consistently in the same direction, i.e., SD increased with increasing mean IBI. Stimulation during early inspiration did not produce any effect during this respiratory phase. It was not before the beginning of the following expiration that a significant deceleration was evoked, which was associated with an enhanced delta SD, whereas stimulation during early expiration promptly evoked a biphasic cardiac response of the deceleration - acceleration pattern and an increase and decrease in delta SD, respectively. While SD was found to be a function of age, no such finding was obtained for delta IBI and delta SD. These results are discussed in terms of the "vagal gating" hypothesis.

[Respiration rhythm-controlled electric stimulation of paralyzed laryngeal muscles--animal experiment findings]. / Die atemrhythmusgesteuerte Elektrostimulation der gelähmten Kehlkopfmuskulatur--tierexperimentelle Grundlagen.

Patients with bilateral paresis of the recurrent laryngeal nerves have primarily breathing difficulties. But on the other hand the common operations for widening the glottis produce voice problems. To overcome these difficulties a muscle stimulation device was developed, which is triggered by the inspiratory motion of the thorax. With this device impulses are transmitted by radiofrequency from a transmitter located outside the body to a receiver implanted into subcutaneous tissue of the neck and thence by electrode wires to the posterior cricoarytenoid muscle (PCA). In the dogs with one cut recurrent laryngeal nerve the paralyzed vocal cord (VC) moved regularly with abductions at inspiration by stimulating the PCA. The efficiency of that stimulating device was proved by taking photographs of the VC-motion and by recording the subglottal air pressure changes.

[Heart cycle related sensitivity of the pressor receptor reflex before and after dissection of the carotid sinus nerves]. / Herzzyklusbezogene Empfindlichkeit des Pressorezeptorenreflexes vor und nach Durchtrennung der Karotissinusnerven.

Both carotid sinus nerves of anesthetized, spontaneously breathing dogs were stimulated, before and after dissection, with brief, R-wave-triggered, submaximal electric impulses during different phases of the heart cycle. The resulting decrease of blood pressure and heart rate, related to the initial level and stimulation intensity is, respectively, about 2.5- and 4.5fold higher after denervation. Stimuli applied 90 ms after the R-wave provoke maximal lowering of mean arterial pressure. After dissection this maximum reappears, enhanced by the factor of 1.4, with stimuli delayed by 70 ms. Also, the initial decrease of heart rate in the first respiration cycle after onset of stimulation shows a maximum of 90 ms, which does not, however, change its position after dissection. Two mechanisms are discussed for the heart cycle related sensitivity of the pressor-receptor reflex: 1. Time-selective inhibition of the sympathetic activity controlling the smooth vascular muscles because of a central coincidence of the afferent signals from the sinus and aorta nerves with the electric stimuli, and 2. the heart cycle related sensitivity of the heart against efferent vagal control signals.

[The inhibition of efferent sympathetic activity by means of pressure stimulation of the carotid sinus pressoreceptors]. / Die Hemmung efferenter sympathischer Aktivität durch Druckreizung der Karotissinuspressorezeptoren

The influence of pressure stimulation of a barorecptor upon the activity of the sympathetic nerve branch terminating in the wall of the contralateral carotid bifurcation was studied on narcotized dogs. The potential activity of this branch is of efferent nature. On the average, 570 msec after the pressure load applied to the opposite carotid sinus preparation, a silent period occurred. The duration of this silent period and the activity of the sympathetic nerve branch depend on the internal pressure of the preparation. The influence of different structures (central and peripheral) on latency, total and partial inhibition of the sympathetic activity are discussed.