Related Experiment Videos
Modification of the baroreceptor control of atrio-ventricular conduction induced by digitalis in man
Insights
Digitalis significantly enhances baroreceptor control of atrio-ventricular conduction in humans. This potentiation of the baroreflex sensitivity is primarily observed during stimulation of arterial baroreceptors.
Area of Science:
- Cardiology
- Pharmacology
- Neuroscience
Background:
- Baroreceptors modulate heart rate and circulation, an effect potentially enhanced by digitalis.
- The atrio-ventricular node is a key site for digitalis action.
- Understanding digitalis's impact on baroreceptor control of atrio-ventricular conduction is clinically relevant.
Purpose of the Study:
- To investigate how therapeutic doses of digitalis modify baroreceptor control of atrio-ventricular conduction in humans.
- To quantify the effect of digitalis on baroreflex sensitivity related to atrio-ventricular conduction.
Main Methods:
- Eight subjects underwent atrial pacing to maintain constant heart rate.
- Arterial baroreceptors were stimulated using phenylephrine or nitroglycerine to alter blood pressure.
- Baroreflex sensitivity was measured as the change in the atrial stimulus-Q interval per mmHg change in systolic blood pressure, before and after digitalis administration.
Main Results:
- Digitalis significantly increased baroreflex sensitivity during baroreceptor stimulation from 2.9 +/- 1.1 to 5.6 +/- 1.5 ms/mmHg.
- Baroreflex sensitivity during baroreceptor deactivation was not significantly affected by digitalis.
- The potentiation by digitalis was most evident at higher levels of baroreceptor stimulation.
Conclusions:
- Digitalis strikingly potentiates baroreceptor control of atrio-ventricular conduction in humans.
- This potentiation is dose-dependent and primarily affects the upper range of baroreflex activation.
- The findings highlight a significant interaction between digitalis and the baroreflex system impacting cardiac conduction.
Abstract:
Several studies in animals and in man have suggested that the inhibitory influence of baroreceptors on heart rate and peripheral circulation is enhanced by digitalis. Because the atrio-ventricular node represents a key site for the clinical action of digitalis we studied how baroreceptor control of atrio-ventricular conduction is modified by digitalis at therapeutical doses. In eight subjects heart rate was kept constant by atrial pacing to assess neural influences on atrio-ventricular conduction rate without the modifications caused by simultaneous changes in cardiac cycle length. Arterial baroreceptors were stimulated by increasing or reducing blood pressure (intra-arterial recording), via an iv bolus of phenylephrine or nitroglycerine. The baroreflex sensitivity was assessed in ms . mmHg-1 as the slope of the linear regressions relating the rise or fall in systolic blood pressure to the lengthening or shortening in St- (atrial stimulus artifact) Q interval (ECG recording). The study was performed before and 45 min after iv administration of digitalis (0.8 mg of Lanatoside C). Baroreflex sensitivity during baroreceptor stimulation was 2.9 +/- 1.1 ms . mmHg-1 (mean +/- SE) before digitalis, whereas after digitalis a significantly and markedly greater value of 5.6 +/- 1.5 ms . mmHg-1 was found. Baroreflex sensitivity during baroreceptor deactivation was 0.9 +/- 0.1 ms . mmHg-1 before digitalis, and was not significantly affected by the drug. Thus in man the baroreceptor control of atrio-ventricular conduction is strikingly potentiated by digitalis although this potentiation is only evident in the upper portion of the stimulus-response curve of the reflex.(ABSTRACT TRUNCATED AT 250 WORDS)