Interrelationships between mechanical ventilation and the autonomic nervous system

Abstract

The assessment of autonomic nervous system (ANS) efficiency is mainly based on baroreflex gain and heart rate variability, which both have a prognostic value in cardiovascular diseases and critically ill patients. Newly developed software, allowing automatic calculation of heart rate variability, could improve the ANS assessment in critical care patients. Mechanical ventilation has been shown to increase baroreflex gain and heart rate variability in several respiratory diseases associated with an impaired autonomic function (obstructive sleep apnea, chronic obstructive pulmonary disease), mostly during long-term application. Due to methodological considerations, this beneficial effect has not been demonstrated in critical care patients, in whom the use of high levels of PEEP could even worsen the ANS by decreasing baroreflex gain and heart rate variability, possibly through hemodynamic effects. The development of new ventilatory modes could be beneficial in terms of ANS: NAVA (neurally adjusted ventilatory assist) improves the physiological respiratory variability, and fractal ventilation enhances respiratory sinus arrhythmia, which could, according to some authors, improve gas exchanges. In contrast, ANS assessment could make easier the weaning from mechanical ventilation, as a decrease in heart rate variability during weaning trials seems predictive of weaning failure.