Cardiac autonomic responses to volume overload in normal subjects and in patients with dilated cardiomyopathy

This study evaluated the effects of acute isotonic volume expansion on heart rate variability (HRV) in 10 patients with dilated cardiomyopathy (DCM) and in 10 age- and sex-matched normal volunteers. Echocardiographic left ventricular volumes and HRV measurements by continuous Holter recording were assessed at baseline, at 60 and 120 min during intravenous saline load (0.9% NaCl, 0.25 ml·kg^-1·min^-1), and 60 min after infusion was terminated. Data analysis was performed by repeated-measures ANOVA. After volume expansion, left ventricular ejection fraction increased (F = 9.8; P <0.001) in normal subjects and decreased (F = 8.7; P <0.001) in DCM patients. During volume expansion a significant difference was also detectable between the two groups in root-mean-square successive difference (F = 25.2; P <0.001), percentage of differences between successive normal R-R intervals >50 ms (F = 97.6; P <0.001), high-frequency power (F = 50.1; P <0.001), and low- frequency power (F = 41.6; P <0.001), all of which reflect parasympathetic modulation of heart rate; in fact, these measurements increased in normal subjects and decreased in DCM patients. In normal subjects, the increase in HRV measurements during volume expansion suggests a parasympathetic activation, mediated by stimulation of cardiopulmonary and arterial mechanoreceptors. On the contrary, in DCM patients the parasympathetic withdrawal, already detectable at baseline, increases during volume expansion.