Radiolabeled (15-microns) microspheres were used to measure blood flow to upper airway muscles [alae nasi (AN), intrinsic laryngeal, tongue, cervical strap, and hyoid musculature], diaphragm (DI), and parasternals (PS) during spontaneous breathing in 24 anesthetized tracheotomized supine dogs. Six dogs were also studied while -28 +/- 3 (SE) cmH2O tracheal airway pressure was generated against an inspiratory resistance (IR) (upper airway bypassed). Blood flow to posterior cricoarytenoid muscle (PCA) [24.0 +/- 2.1 (SE) ml.min-1.100 g-1] was greater than that to 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 muscles, and cricothyroid (CT). Average blood flow to these muscles was only 8.0 +/- 0.8 ml.min-1.100 g-1. With the exception of CT, blood flow to these upper airway muscles was less than that to DI and PCA. Relative to blood flow during spontaneous breathing, IR loading increased blood 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 during loading. Our results show that at rest blood flow to main glottic dilator (PCA) is similar to that to main inspiratory muscles. Furthermore, in response to an IR load, blood flow to PCA and AN increased by an equivalent or greater amount than that to DI.(ABSTRACT TRUNCATED AT 250 WORDS)