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Biomedical subjects

H Rau

Publications and source records attributed to H Rau.

At least 91 records · Page 5Linked to original sources
PubMed1993

Activation of carotid baroreceptors inhibits spinal reflexes in man.

The present study was designed to investigate the effect of baroreceptors on a spinal reflex. The Achilles tendon reflex (T reflex), a monosynaptic spinal reflex, was chosen as an indicator of descending influences of central activation. The baroreceptors are stretch receptors which respond to extensions of the arterial wall. Carotid sinus baroreceptors can be manipulated non-invasively by means of a cuff around the neck. In this study, the phase-related external suction (PRES) neck cuff technique was used. PRES applies short changes in cuff pressure as a function of heart cycle phase, controlling for non-specific effects found in other baroreceptor manipulation methods. The T reflex was reduced when elicited during the highest levels of baroreceptor activation. Reflex amplitude was largest when elicited during the lowest levels of baroreceptor activation. These results are consistent with previous findings that baroreceptor activation reduces CNS excitability.

Adult↗
PubMed1993

Does activation of the baroreceptors reinforce differential Pavlovian conditioning of heart rate responses?

High- and low-pitched tones (CS+ and CS-) signalled baroreceptor stimulation or inhibition (US+ and US-) on 6-s conditioning trials (n = 128). Baroreceptor stimulation was induced by the phase-related external suction (PRES) method of Rau et al. (1992) in which a brief pulse of negative external pressure is applied to the neck at systole and one of positive pressure at diastole within each cardiac cycle (the reverse sequence is used for baroreceptor inhibition). Changes in heart period (R-R intervals) confirmed that PRES manipulated the baroreceptors in the presence of CS+ and CS- without habituation over conditioning trials. However, conditioned heart period responses were not observed on test trials (n = 32) in which CS+ and CS- were presented with the baroreceptor manipulation removed. Subjects were unable to state which CS had signalled baroreceptor stimulation and inhibition when given PRES-alone trials after the conditioning phase (differential attention thus controlled). These results (a) confirm that the differential effect of the two PRES stimuli was specific to the baroreceptors and (b) support earlier studies that have found that differential conditioning is impaired when CS-US relations are not processed in attention. We discuss implications regarding when baroreceptor firing might be discriminable and reinforcing.

Adult↗
PubMed1993

Baroreceptor stimulation alters cortical activity.

The arterial baroreceptors constitute an essential sensory link for the short-term regulation of blood pressure and may also influence higher cortical function. The present study was undertaken to evaluate previous reports of such a cortical influence under conditions of psychologically controlled, mechanical baroreceptor stimulation. This control was achieved by use of PRES (phase-related external suction), a modified neck suction technique. PRES applies short suction bursts that have a different impact on baroreceptors depending on their timing within the cardiac cycle and has the advantage that subjects cannot easily discriminate between conditions of stimulation and inhibition. Electroencephalograms were recorded from 22 subjects during PRES manipulations. A surface-negative shift of about 10 microV developed during the cuff manipulations. Over frontal-central regions, this shift was smaller during baroreceptor stimulation than during inhibition. These data provide support for the proposal that baroreceptor activation influences cortical activity.

Adult↗
PubMed1993

Effects of baroreceptor stimulation on sensorimotor control of the hand.

Finger movements are presumed to be controlled by somatosensory and motor areas of neocortex via the corticospinal tract. Since baroreceptor activation appears to reduce central nervous system activity, an effect on sensorimotor control during precise manual manipulations is expected. To test this hypothesis, motor responses to slow and fast perturbations during grasping of a small object (precision grip) were examined. Baroreceptor activation was manipulated with the phase-related external suction (PRES) technique, which allows the application of baroreceptor stimulation and control conditions in a well-controlled and indiscernible way. Motor reactions following slow perturbations were influenced in the expected way in good-performance subjects. The time to stop slow perturbations was longer and the electromyographic (EMG) activity of the small thumb muscles was lower during baroreceptor stimulation than in the control condition. These effects did not appear in the fast-perturbation task. Fast perturbations were followed by EMG activity onset after about 50 msec, which indicates that a prominent part of the EMG activity must be attributed to a more automatic motor response. EMG activity following slow perturbations began after about 90 msec, and it may be assumed that these motor reactions are primarily under voluntary control. The fact that we found effects of baroreceptor stimulation in slow but not in fast perturbations could have been caused by at least partially different pathways utilized for automatic versus voluntary motor responses, which seem to be differentially vulnerable to baroreceptor activation. An electrocortical sign that precedes voluntary movements is the Bereitschaftspotential, or readiness potential. Since this potential is a slow brain potential, and baroreceptor activation is known to reduce slow brain potentials, it is plausible that baroreceptor activation primarily affects motor responses following slow but not fast perturbations.

Adult↗
PubMed1992

Gallstones in acromegalic patients undergoing different treatment regimens.

The frequency of gallstones during long-term treatment with the somatostatin analogue octreotide reported in different studies varies from 0% to 50%, the reason for this variation being unknown. Therefore, we examined 58 acromegalic patients undergoing different treatment regimens for the frequency of gallstones. Thirteen were treated with octreotide, 20 with bromocriptine, and 25 had no medical treatment after successful neurosurgery. Also, 58 patients without known gallbladder disease served as controls. The postprandial gallbladder contraction was also investigated in 27 acromegalic patients (10 with octreotide, 10 with bromocriptine, and 7 with no medical therapy). Ten of the 58 acromegalic patients were found to have gallstones, 4 of 25 receiving no medical treatment, 4 of 20 treated with dopamine agonists, and 2 of 13 treated with octreotide. In 9 of the 58 control patients, gallstones were detected. Although in the octreotide group the gallstones were newly formed under therapy, there was no difference in gallstone prevalence between the different treatment regimens and the control group. However, the postprandial gallbladder contraction was significantly more often inhibited during octreotide therapy, and this effect was most pronounced during the first hours following injection. Differences in the timing of injections therefore may be an explanation of the variable incidence of cholelithiasis in the different studies.

Acromegaly↗
PubMed1992

Physiological and psychological differentiation of bidirectional baroreceptor carotid manipulation in humans.

We investigated a phase-related-external-suction (PRES) method of bidirectional carotid stimulation which, unlike other methods, is not readily discriminable for direction (excitation vs. inhibition). Thirty-two subjects were first given 128 6-s PRES trials (64 each excitatory and inhibitory) which were signaled by two tones of differing frequency. There followed a 20-trial discrimination phase where subjects' task was to identify excitatory and inhibitory PRES trials (randomly presented) in terms of the two tone signals. Physiological (HR) discrimination was bidirectional (deceleration and acceleration for excitatory and inhibitory PRES trials, respectively), reflex-like (no habituation), but asymmetrical in magnitude (larger decelerations than accelerations), and topography (e.g., presence of a short latency deceleration). Group psychological discrimination was absent, although two subjects had a 100% hit rate on the discrimination test. There were, however, no systematic HR changes associated with these two subjects. Finally, the small-magnitude (2-3 bpm) physiological HR reflex was markedly augmented by what appeared to be a psychological, attentional factor. Accordingly, while the results indicated a dissociation between physiological and psychological differentiation, there was also evidence of a psychological factor (attention) influencing a physiologically induced reflex.

Adult↗
PubMed1992

PRES: the controlled noninvasive stimulation of the carotid baroreceptors in humans.

To study physiological and psychological effects of baroreceptor activity, the cervical neck cuff technique has been frequently used to stimulate the carotid baroreceptors mechanically. Using this technique, no satisfying control conditions to date have been available. Because the carotid stretch receptors are sensitive not only to the pressure level, but also to the rate of change, it is possible to manipulate the receptor firing through changes in carotid pulse amplitude. The device described here relies on the application of short changes in cuff pressure tied to different phases within the cardiac cycle (phase related external suction (PRES)). A brief external suction during systole has potent stimulatory effects on baroreceptors whereas the application of the very same pressure pulse during diastole inhibits the firing burst associated with the pulse wave. To allow an ongoing period of stimulation, a sequence of alternating negative/positive pressure pulses is applied. In the stimulation condition, the R-wave of the electrocardiogram triggers a negative pulse which is followed by a positive one during diastole. In the control condition this relationship is reversed. Two experiments are reported confirming different baroreceptor effects of the two conditions. PRES allows for blind or double-blind experiments to investigate effects of baroreceptor activity on physiology and behavior.

Adult↗
PubMed1992

Bromocriptine treatment over 12 years in acromegaly: effect on growth hormone and prolactin secretion.

It is not known whether bromocriptine treatment in acromegaly can be implemented for a life-long period. To elucidate this problem, the secretory GH and PRL states of 12 patients with acromegaly were determined, before bromocriptine treatment, under therapy (15.0 +/- 6.8 mg/day for 12 +/- 3 years; mean +/- SD) and during two-weeks long drug withdrawal after long-term treatment, respectively. Before therapy, all patients showed a non-sufficient GH suppression after oral glucose load (greater than 2 micrograms/l), whereas under dopaminergic treatment the post-glucose GH levels of three patients fell below 2 micrograms/l; normal IGF-I concentrations were found in five patients. However, under bromocriptine, only two patients showed GH suppressions below 2 micrograms/l following glucose, accompanied with normal IGF-I levels. During bromocriptine withdrawal, GH secretion at 60 min in the oral glucose tolerance test increased significantly (17.0 +/- 15.5 vs 5.7 +/- 5.2 micrograms/l; p less than 0.01); the mean IGF-I level rose from 2.1 +/- 0.8 to 4.9 +/- 2.2 kU/l (p less than 0.01). IGF-I was normal during bromocriptine cessation in only one patient; none of the 12 patients showed a GH suppression below 2 micrograms/l after oral glucose load. Under dopaminergic treatment hyperprolactinemia could not be detected. In conclusion, bromocriptine led to a stable suppression of both GH hypersecretion and--if present--concomitantly elevated PRL levels. Severe side effects or a further tumor growth could not be observed. Thus, the data of the longest follow-up investigation that has so far been published indicate that effective life-long bromocriptine therapy seems to be possible in selected patients with acromegaly.

Acromegaly↗
PubMed1992

[Modification of autoregulation of intrinsic physical processes in field-dependent subjects: a study of performance in heart rate biofeedback].

Witkin, the founder of the concept of "field dependence", assumed that there is a relationship between field dependence and body perception. However, this hypothesis was never investigated experimentally in a well-controlled study. Twenty healthy subjects learned to increase and decrease their heart rate dependent upon two discriminative stimuli. In order to increase and decrease their heart rate they received exteroceptive feedback (movements of a rocket-ship on a video screen). Each trial lasted 6 s. The distance of the rocket-ship from a certain point indicated the amount of the achieved increase or decrease. Field dependent subjects scoring higher in field dependency as measured by the Embedded Figures Test were poorer at heart rate control on feedback and transfer trials (test trials with feedback removed) than were subjects scoring low in field dependency. This result may be of therapeutic interest in the application of behavioral medicine to psychosomatic and psychiatric disorders.

Adult↗
PubMed1992

[Minimally invasive interventions in solitary liver cysts].

Large intrahepatic cysts need surgical intervention when becoming symptomatic. In case of non-parasitic solitary cysts different surgical treatments are available. We performed three different minimal-invasive procedures in 8 patients. Good results were obtained by laparoscopic extended deroofing of the cyst. Indications and technical performance are presented.

Adult↗
PubMed1991

Responses of the T-wave amplitude as a function of active and passive tasks and beta-adrenergic blockade.

This paper presents evidence that phasic changes in T-wave amplitude vary as a function of task conditions and beta-adrenergic drugs. Three experiments were designed to test the sensitivity of T-wave amplitude to manipulations in sympathetic arousal. In the first experiment, T-wave amplitude was recorded during an active behavioral task in which 32 subjects believed that they could control the duration of an aversive white noise and during a passive behavioral task in which another 30 subjects knew that they had no control. T-wave amplitude decreased to a greater extent in the active behavior group than in the passive group. In the second experiment, 9 subjects receiving one of two beta-adrenergic blockers and 10 subjects receiving placebo completed the active task. Task-induced reductions in T-wave amplitude were systematically blocked by the beta blockers. In the third experiment, 5 subjects received placebos and 15 received one of two different beta blockers. All subjects performed a mental arithmetic task. Subjects receiving a placebo, but not those receiving beta blockade, exhibited a significant reduction in T-wave amplitude during mental arithmetic.

Adaptation, Psychological↗
PubMed1991

Effect of bromocriptine withdrawal in acromegaly on body composition as assessed by bioelectrical impedance analysis.

To evaluate the effect of bromocriptine withdrawal after dopaminergic long-term treatment (15.0 +/- 6.8 mg/day, mean +/- SD) in 12 acromegalic patients on body composition, bioelectrical impedance was measured before and at the end of two weeks of drug withdrawal. During withdrawal basal hGH and IGF-I increased from 2.5 +/- 1.9 micrograms/l and 2.1 +/- 0.8 kU/l to 9.1 +/- 11.7 micrograms/l and 4.9 +/- 2.2 kU/l, respectively, and the hGH secretion deteriorated significantly both after oral glucose load and in the TRH test, indicating recurrence of active acromegaly. Reactance and resistance decreased by 5 +/- 4 and 23 +/- 19 omega, respectively (p less than 0.01), whereas body weight remained constant (+0.4 +/- 2.1 kg). Bioelectrical impedance analysis indicated evident shifts in body composition, i.e. a significant reduction of body fat (-2.0 +/- 1.7 kg) and a simultaneous increase in both lean body mass (+2.4 +/- 2.2 kg) and total body water (+1.8 +/- 1.6 l). The changes in body composition were related to a combined effect of unsuppressed hypersomatotropism and the lack of bromocriptine actions other than inhibition of hGH secretion (for example stimulation of the renin-angiotensin-aldosterone system by both the recurred hypersomatotropism and the absence of dopaminergic bromocriptine effects). We conclude that bioelectrical impedance analysis is a good additional tool to assess the pathophysiological effects of bromocriptine withdrawal in long-term treated acromegalic patients.

Acromegaly↗
PubMed1986

Reaction of platinum cytostatics of the second generation with deoxyribonucleic acid.

Adducts of native calf thymus DNA with several platinum compounds with or without antitumour activity were prepared and their chiroptical and renaturation properties investigated. It was found that at high levels of binding cis-dichlorodiammineplatinum(II) and all other substances with antitumour activity induced changes in circular dichroic spectra of DNA which were attributed to formation of "premelted" regions in the double-stranded DNA. On the other hand, the substances with no antitumour effect induced changes corresponding to formation of single-stranded regions in DNA molecules, even at low levels of binding.

Animals↗