Responses of the posterior cricoarytenoid and alae nasi muscles to increased chemical drive in man.

We examined the electromyographic activity of the posterior cricoarytenoid (PCA) simultaneously with the alae nasi (AN) in response to increasing chemical drive in 5 normal, awake human subjects. During progressive isocapnic hypoxia the peak of the integrated PCA activity (EPCA) increased as a function of tidal volume (VT), and in 3 of the 5 subjects the residual variance of an exponential fit (of the form EPCA = A - Be-KVT, where A, B and K are constants) was significantly less than that of a linear regression. In the other 2 subjects the data were too noisy to detect a difference although a positive relationship was present. In contrast, during progressive hyperoxic hypercapnia we found a linear relationship between EPCA and VT (r = 0.84 +/- 0.14) in all subjects over a comparable ventilatory range. The peak of the integrated AN activity (EAN) increased linearly with increasing VT during both hypoxia (r = 0.90 +/- 0.08) and hypercapnia (r = 0.89 +/- 0.12). Tonic EPCA also increased as a function of VT during both hypoxia and hypercapnia and at a VT of 1.6 L constituted 26 +/- 6% and 24 +/- 8% of the respective maximal peak EPCA. During hypoxia the relative increase in tonic EPCA occurred at a lower VT than during hypercapnia. Our results suggest that there are qualitative differences in the response of the PCA to increased chemical drive between hypoxia and hypercapnia. This is consistent with differing inputs to some upper airway motoneurones from central and peripheral chemoreceptors.