Effects of assisted mechanical ventilation on control of breathing

Abstract

During spontaneous breathing, the respiratory muscle pressure (Pmus) waveform is determined by a complex system consisting of a motor arm, a control center, and various feedback mechanisms that convey information to the control center. During assisted mechanical ventilation, the pressure delivered by the ventilator (Paw) is incorporated into the system and may alter the Pmus waveform, which in turn modifies the function of the ventilator. Thus, the response of Pmus to Paw and the response of Paw to Pmus constitute the two components of patient-ventilator interaction as well as of control of breathing during assisted mechanical ventilation. The response of Paw to Pmus depends on: 1) the mode of ventilatory support; 2) the mechanics of the respiratory system, and 3) the characteristics of the Pmus waveform. On the other hand the response of Pmus to Paw is mediated through four feedback systems: 1) mechanical; 2) chemical; 3) reflex, and 4) behavioral. It follows that the system that controls the act of breathing may be considerably modified by mechanical ventilation. The physician dealing with a mechanically ventilated patient should take into account the interaction between the respiratory effort and the function of the ventilator and be aware that the ventilatory output may or may not reflect the various aspects of control of breathing.