Biomedical subjects

E Zerbst

Publications and source records attributed to E Zerbst.

18 recordsLinked to original sources

PubMed1990

Changes in blood pressure and heart rate during passive upright tilt upon electrical carotid sinus nerve stimulation.

Electrical carotid sinus nerve stimulation was applied in three normotensive anginal patients and one hypertensive patient during upright tilting. Despite a base-line depressor response to continuous stimulation, orthostatic hypotension was not augmented. In individual patients stimulation slightly enhanced the fall of systolic pressure and delayed the increase of diastolic pressure immediately after tilting. Base-line heart rates and cardio-acceleration upon tilting remained almost uninfluenced by stimulation. It is concluded that a moderately enhanced carotid baroreceptor afferent nerve traffic did not interfere with the regular orthostatic response.

Blood Pressure↗

PubMed1989

Temporal and spatial summation caused by aortic nerve stimulation in rabbits. Effects of stimulation frequencies and amplitudes.

Frequency-modulated stimulus patterns, controlled by heart rate or blood pressure feed-back, are proposed for therapeutic use of electrical stimulation of the carotid sinus nerves (CSNS). Continuous CSNs with equidistant pulses is applied in hypertensive or angina pectoris patients who are refractory to therapy. Frequency modulation simulates transmission properties of single baroreceptors, while modulation of stimulus amplitudes simulates recruitment of baroreceptors by pressure pulses in the carotid sinus. Using aortic nerves in the anesthetized rabbit as a model, it was investigated if amplitude modulation could substitute frequency modulation in electrical stimulation. First, 'step stimulation' was applied (protocol 1): starting from a basal low frequency with the basal amplitude set at a level of 10% between threshold and the maximum, either the frequency or the amplitude of pulses was increased in a single step for 20 s (frequency step, FS; amplitude step, AS). The blood pressure response and its course of recovery was analyzed. Fifteen different basal stimulus frequencies (1, 2, ...15 Hz) were investigated. For FS, each given frequency was increased 10-fold (10, 20, ...150 Hz) while the basal amplitude level was kept constant. For AS, the basal amplitude level was increased to the maximum, while each given frequency was kept constant. Depressor responses to AS were equivalent to FS at a 10-fold higher frequency. After step stimulation it was either stopped immediately (type A), or was resumed for 90 s with a basal low frequency and the basal low amplitude level (type B). After type A and B stimulations, the recovery time of blood pressure response was found to be longer after cessation of AS, compared to FS. In further experiments (protocol 2), an 'electronic baroreceptor analog' generated stimulus patterns which were feed-back controlled by the blood pressure signal. Either frequencies (FM) or amplitudes (AM) of stimuli were modulated by the pressure pulse signal. Since in feed-back controlled stimulation the mean electrical current flow is reduced by depressor responses, stimulus current flow in relation to the blood pressure response served to compare the efficacy of different stimulus patterns. Equidistant stimulation (EDS) was also applied for comparison. Both feed-back controlled stimulus patterns (FM and AM) were more effective than EDS. It is suggested that AS predominantly activated C-fibers, whereas low level stimulation predominantly excited A-fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1989

Blood pressure and heart rate changes during physical activity upon heart rate feedback-controlled electrical carotid sinus nerve stimulation.

The effect of feedback-controlled electrical carotid sinus nerve stimulation on changes in blood pressure and heart rate during interventions simulating usual daily activity was studied in four anginal patients. Frequency or amplitude of stimulation was modulated pulse-synchronously and controlled by heart rate. While individual responses differed between both types of modulation, stimulation attenuated predominantly increases in blood pressure during walking and staircase climbing. Heart rate changes remained almost unaffected.

Adult↗

PubMed1989

Search for optimal frequencies and amplitudes of therapeutic electrical carotid sinus nerve stimulation by application of the evolution strategy.

In humans, electrical, bipolar, bilateral carotid sinus nerve stimulation (CSNS; impulse duration 0.35 ms) was applied, using frequencies between 10 and 110 Hz and voltages between individual thresholds and maximal amplitudes of stimulation. Ten anginal patients and two hypertensive patients were studied at an interval of up to 12 years after implantation of electrodes and a radiofrequency receiver for chronic therapeutic CSNS. In search of combinations of frequency and voltage of CSNS, eliciting largest ("optimal") depressor responses of blood pressure and heart rate in the individual patient, Rechenberg's evolution strategy was applied. This strategy simulates mutation and selection of biological evolution. In each patient and on each test stimulation, a value of quality was computed from actual heart rate and blood pressure values as a selection criterion for the strategy. Either responses to uninterrupted CSNS were investigated, while stimulation parameters were adjusted every 3 min, according to the strategy, or responses to 3 min of CSNS after a change in stimulation parameters were compared to intercalated 3-min control periods. In each patient, one or more combined settings of frequency and voltage elicited "optimal" responses. In principle, "optimal" CSNS frequencies ranged between 35 and 105 Hz with large interindividual differences. Due to chronic implantation of electrodes and technical features of radiofrequency transmitted stimulation energy, interindividually different voltages led to an optimal response to CSNS. Also according to the present results, the frequency of CSNS has to be determined individually. It is concluded that the evolution strategy was applied successfully, because voltage and frequency settings leading to "optimal" responses were found within 90-180 min, whereas intraindividual systematic investigations would not be feasible due to their necessarily very long duration. So far, only short-term responses have been evaluated. A broader use of the strategy in other applications is encouraged, as for example in pacemaker optimization and especially in functional electrostimulation.

Adult↗

PubMed1988

Cardiovascular responses to time delays of electrocardiogram-coupled electrical stimulation of carotid sinus nerves in dogs.

In search of improved patterns for electrical stimulation of the carotid sinus nerves (CSNs), which is applied therapeutically in patients with previous therapy refractory hypertension or angina pectoris, the timing of stimulation trains within the cardiac cycle was investigated in anesthetized dogs. Blood pressure responses and prolongations of heart beat intervals upon CSNs were analyzed. Electrocardiogram (ECG)-coupled trains of electrical stimuli were applied to bilateral intact CSNs. Pulses of 1 ms duration and the maximal (5-10 V) and 50% maximal stimulus amplitude were applied. The onset of stimulation trains (150 ms long, 15 impulses/train) was delayed from ECG-R-wave synchronous periods in units of 30 ms to maximally 150 ms. The timing of stimulus trains within the cardiac cycle did not influence the responses. Heart rate and blood pressure reductions upon CSNs were entirely dependent on the amplitudes of stimuli. In conclusion, a phase-dependency of such responses to CSNs, supposedly due to coincidence of electrically induced carotid sinus nerve activity with endogenous signals centrally converging from other cardiovascular afferents, could not be supported, using such stimulation trains. The observed responses did not show the known phase-dependency of sensitivity of the sino-atrial node to changes in effernt vagal activity. In experimental and therapeutic electrical CSNs (baropacing) for obtaining stronger cardiovascular responses with similar parameters, a preferential timing of stimuli relative to the cardiac cycle cannot be recommended.

Animals↗

PubMed1981