Respiratory modulation of muscle sympathetic nerve activity in patients with chronic heart failure

Background-Sympathoexcitation and respiratory instability are closely relat ed to worsening of chronic heart failure. To elucidate the dynamic nature o f respiratory modulation of sympathetic activity in patients with heart fai lure, we studied within-breath variation of muscle sympathetic nerve activi ty (MSNA) under various ventilatory volumes. Methods and Results-MSNA, blood pressure, and respiratory flow were recorde d in 23 patients with left ventricular ejection fraction less than or equal to 45%. Within-breath suppression of MSNA (neural silence) was found in I I patients (MSNA bursts: 71 +/- 10/100 heartbeats) but not in the remaining 12 patients (MSNA bursts: 88 +/-8/100 heartbeats). Patients without neural silence had a smaller tidal volume (391 +/- 70 versus 267 +/- 75 mL/m(2) P <0.01) and a higher respiratory rate (15<plus/minus>2 versus 19 +/-4 breath s/min, P<0.01) during spontaneous respiration than those with neural silenc e. The relationship between tidal volume and minimal amplitude of MSNA burs ts in each breath was obtained during random-interval breathing and fitted by an exponential function. The curve of patients without neural silence wa s shifted to the right and upward, which suggests that a greater tidal volu me was required to suppress MSNA (227<plus/minus>70 versus 437 +/- 195 mL/m (2), P<0.01). Conclusions-Sympathoexcitation in patients with chronic heart failure is cl osely related to both a decrease in resting tidal volume and an attenuated sympathoinhibitory effect of lung inflation reflex.