Blood flow in respiratory muscles during maximal exertion in ponies with laryngeal hemiplegia

Laryngeal hemiplegia increases the respiratory effort required during exercise. By use of 15-micron-diam radionuclide-labeled microspheres, respiratory muscle blood flows were studied at rest, submaximal exercise (SE), maximal exercise (ME), and ME + adenosine (3 mumol X kg-1 X min-1) in nine healthy laryngeal hemiplegic (LH) ponies to ascertain whether vasodilator reserve in these tissues may be exhausted during SE, which caused maximal respiratory frequency (f) to be reached. Blood flows were also studied in the limb muscles, and data were compared with normal ponies (M. Manohar, J. Appl. Physiol. 60: 1571-1577, 1986). The heart rate, f, and change in pleural pressure in LH ponies during SE were 205 +/- 5 beats/min, 91 +/- 10 breaths/min, and 61.2 +/- 8.7 cmH2O. Corresponding values for ME were 223 +/- 2 beats/min, 90 +/- 7 breaths/min, and 75.1 +/- 5.2 cmH2O. The treadmill speed for SE was set at 75% of that for ME. Mean aortic pressure (161 +/- 9 mmHg), diaphragmatic (206 +/- 27 ml X min-1 X 100 g-1), and intercostal muscle (124 +/- 12 ml X min-1 X 100 g-1) blood flows in LH ponies increased markedly with SE and these values were not different from ME (170 +/- 5 mmHg, 293 +/- 40 ml X min-1 X 100 g-1, 167 +/- 15 ml X min-1 X 100 g-1, respectively). This suggested that maximal vasodilation in the respiratory muscles was achieved during SE. Vascular resistance in the diaphragm and intercostal muscles of LH ponies also remained similar for SE, ME, and ME + adenosine.(ABSTRACT TRUNCATED AT 250 WORDS)