BLOOD-FLOW DISTRIBUTION TO UPPER AIRWAY MUSCLES

Radiolabeled (15-mum) microspheres were used to measure blood flow to upper airway muscles [alae nasi (AN), intrinsic laryngeal, tongue, cer vical strap, and hyoid musculature], diaphragm (DI), and parasternals (PS) during spontaneous breathing in 24 anesthetized tracheotomized su pine dogs. Six dogs were also studied while -28 +/- 3 (SE) cmH2O trach eal airway pressure was generated against an inspiratory resistance (I R) (upper airway bypassed). Blood flow to posterior cricoarytenoid mus cle (PCA) [24.0 +/- 2.1 (SE) ml.min-1.100 g-1] was greater than that t o DI (18.0 +/- 2.3 ml.min-1.100 g-1) and comparable to that to PS (21. 4 +/- 2.9 ml.min-1.100 g-1). Blood flow per unit weight did not differ between AN, tongue muscles, laryngeal adductors, cervical strap muscl es, and cricothyroid (CT). Average blood flow to these muscles was onl y 8.0 +/- 0.8 ml.min-1.100 g-1. With the exception of CT, blood flow t o these upper airway muscles was less than that to DI and PCA. Relativ e to blood flow during spontaneous breathing, IR loading increased blo od flow to AN by a factor of 7.5, to PCA by 3.4, to DI by 3.2, and to PS by 1.9. There was no change in blood flow in the other muscles duri ng loading. Our results show that at rest blood flow to main glottic d ilator (PCA) is similar to that to main inspiratory muscles. Furthermo re, in response to an IR load, blood flow to PCA and AN increased by a n equivalent or greater amount than that to DI. Insofar as changes in blood flow reflect changes in metabolic demand and hence muscle activa tion, mechanical loading applied to the lower airway is a more potent stimulus to AN and PCA muscle activity than to laryngeal adductors, CT , tongue, and strap muscles.