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 hear t rate variability (HRV) in 10 patients with dilated cardiomyopathy (DCM) a nd in 10 age- and sex-matched normal volunteers. Echocardiographic left ven tricular volumes and HRV measurements by continuous Holter recording were a ssessed 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. D ata analysis was performed by repeated-measures ANOVA. After volume expansi on, left ventricular ejection fraction increased (F = 9.8; P < 0.001) in no rmal subjects and decreased (F = 8.7; P < 0.001) in DCM patients. During vo lume expansion a significant difference was also detectable between the two groups in root-mean-square successive difference (F = 25.2; P < 0.001), pe rcentage 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-freq uency power (F = 41.6; P < 0.001), all of which reflect parasympathetic mod ulation of heart rate; in fact, these measurements increased in normal subj ects 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 d etectable at baseline, increases during volume expansion.