Can we breathe and swallow at the same time?

The article by Samson et al. (7) in this issue of the Journal of Applied Physiology raises new issues concerning the regulation of nonnutritive swallowing (NNS) and breathing during sleep. The past 10 years have seen a large increase in interest in this field (2, 3). Clearly, NNS is essential for survival. It has been estimated that the combined volume of oral and nasal secretions are well in excess of 2 liters each day. Furthermore, clinical experience has shown that, in the absence of competent NNS, the lungs rapidly fill with these secretions, producing death within a few days. It has been acknowledged that neural mechanisms regulating precise coordination of swallowing and breathing are critically important considering that the pharynx serves as a conduit for air going to and from the lungs and for fluids going to the stomach. This dual pharyngeal function is the basis for the frequently encountered pulmonary aspiration syndromes in clinical medicine (5, 8). Coordination of breathing and swallowing is especially important during sleep when volitional swallowing is absent. It is noteworthy that the NNS mechanism is often frequently imperfect because most of healthy individuals experience nightly aspiration of pharyngeal secretions during sleep (4). In mechanical terms, the function of NNS is analogous to that of a basement sump pump. As pharyngeal fluids accumulate a critical volume is eventually reached such that a regulating mechanism must initiate a swallow to avoid flooding the lungs. It now is clear that the laryngeal chemoreflex is mediated by neural receptors concentrated in the interaryternoid notch. Furthermore, the laryngeal chemoreflex appears to be the principal mechanism that initiates a NNS (6). Again, analogous to a sump pump, it has been suggested that accumulating secretions in the piriform fossae periodically reach a critical volume (6). When this volume is reached, the pooled secretions come into contact with the inner aryteroid receptors, a NNS occurs, and the fossae are emptied. Although each of the various mechanisms envisioned by Samson et al. (7) are potentially relevant, it would seem that the most straightforward explanation for the effect of positive nasal pressures in decreasing NNS would be an increased pharyngeal storage capacity for secretions resulting from dilation of the piriform fossae. Assuming the rate of secretion production remained constant, this would result in decrease swallowing frequency. What of the integration of swallowing and breathing? Sam-son et al. (7) have provided new information here. They …