The Use of Airway Occlusion in infants

¹ Research Institute, Hospital for Sick Children, Toronto, Ontario

We now recognize that airway occlusion in infants has a low signal-to-noise ratio. However, the noise is as interesting as the signal and furthermore, most of the noise can be filtered out. The noise is primarily the direct and indirect effect of the curious neurologic state in active sleep. We do not know why respiration is irregular during active sleep. The state is characterized by intense reticular activity accompanied by marked supraspinal inhibition of spinal motor neurons. It has been suggested¹³ that the rapid eye movements are the result of random noise in the vestibular nuclei caused by deprivation of patterning sensory inflow and perhaps something similar is occurring with respiration. Although we do not have direct evidence, the marked distortion of the rib cage strongly suggests that the intercostal muscles are subject to supraspinal inhibition. This distortion is of considerable clinical importance as it impairs load compensation because of both its direct mechanical cost and also indirectly by reflex inhibition of inspiration. Thus, the noise is of considerable importance. What remains unresolved is how these sleep states affect respiratory control in adult man. Also, as anesthesia increases chest wall distortion, this noise may have affected some of the results in animal studies. The noise can be filtered out: studies can be done when respiration is regular, when the pattern of breathing is fixed and when diaphragmatic contraction is isometric and acceptable distortion can be established by monitoring abdominothoracic motion. In general, this means confining studies to quiet sleep. On the other hand, such filtering avoids perhaps the most crucial issue and that is, how is respiration controlled in active sleep; in other words, we may be throwing the baby out with the bath water.