Vagus nerve stimulation decreases left ventricular contractility in vivo in the human and pig heart
Corresponding author J. H. Coote: Department of Physiology, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK., Email: firstname.lastname@example.org
- 1Studies of the effect of vagus nerve stimulation on ventricular myocardial function in mammals are limited, particularly in the human.
- 2The present study was designed to determine the effect of direct electrical stimulation of the left vagus nerve on left ventricular contractile state in hearts paced at 10 % above the natural rate, in anaesthetised pigs and anaesthetised human subjects undergoing open chest surgery for coronary artery bypass grafting.
- 3Contractility of the left ventricle was determined from a series of pressure-volume loops obtained from a combined pressure and conductance (volume) catheter placed in the left ventricle. From the measurements a regression slope of the end-systolic pressure-volume relationship was determined to give end-systolic elastance (Ees), a load-independent measure of contractility.
- 4In six anaesthetised open chest pigs, stimulation of the peripheral cut end of the left cervical vagus nerve induced a significant decrease in Ees of 26 ± 14 %.
- 5In nine patients electrical stimulation of the left thoracic vagus nerve close to its cardiac branch resulted in a significant drop in Ees of 38 ± 16 %.
- 6The effects of vagal stimulation were blocked by the muscarinic antagonist glycopyrronium (5 mg kg−1).
- 7Administration of the β-adrenoreceptor antagonist esmolol (1 mg kg−1) also attenuated the effect of vagal stimulation, indicating a degree of interaction of vagal and sympathetic influences on contractility.
- 8These studies show that in the human and pig heart the left vagus nerve can profoundly decrease the inotropic state of the left ventricular myocardium independent of its bradycardic effect.