Breathing variability and mechanical ventilation in intensive care

Abstract

Ventilation is not monotonous. In contrast, the breathing pattern components vary with time, not only with respect to homeostatic adjustment needs, but also from one cycle to another (often referred to as the “anharmonic” period). These breath-by-breath variations in tidal volume and its components are a result of the complex and chaotic nature — in mathematical terms — of the central ventilator command that creates the tidal volume. Respiratory variability reflects “healthy’ breathing, whereas decreasing variability of the breathing pattern components is a reflection of “poor health”. This decrease may be due to central command changes or, it may be due to the “filtering” of the central variability changes in regards to the mechanical loads: the complexity of the ventilatory flow and its breath-by-breath variability is related to both the neuro-mechanical coupling and the load-capacity adequacy. Thus, in intensive care, low ventilatory variability predicts mechanical ventilation weaning failure and is also an independent risk factor of death. Moreover, in animal models, the addition of extrinsic variability has shown improvements in both lung mechanics and gas exchange. The restoration of a natural variability through new mechanical ventilation modes may prove beneficial.