Cardiac arrhythmias induced by transient hypertension during sleep-waking states

Effects of transient hypertension on cardiac rhythm during sleep and waking states in unrestrained cats were investigated. Blood pressure elevation, produced either by phenylephrine injection or by aortic occlusion, was followed by progressive bradycardia in all cats during each sleep-waking state. With phenylephrine, the heart rate response to induced hypertension consisted solely of reflex sinus bradycardia in 67% of the trials, whereas non-sinus cardiac arrhythmias developed during the period of reflex bradycardia in 33% of the trials. In all trials where hypertension was produced by aortic obstruction, non-sinus cardiac arrhythmias occurred. The observed non-sinus rhythms included both atrioventricular junctional and ventricular escape beats. The occurrence of non-sinus arrhythmias after phenylephrine injection was more frequent during sleep states than during waking. Overall, the incidence of escape rhythms varied from a brief burst of non-sinus beats at the onset of bradycardia to repeated trains of non-sinus beats occurring over the span of blood pressure elevation. Respiratory gating of cardiomotor activity was manifested both as respiratory sinus arrhythmia and as inspiratory 'gating' of escape rhythms. Both forms of respiratory gating continued during periods of induced hypertension.