THEOPHYLLINE ALTERS DISTRIBUTION OF BLOOD-FLOW TO RESPIRATORY MUSCLES

This study was designed to examine the effects of theophylline on resp iratory muscle blood flow in 11 lightly anesthetized and spontaneously breathing dogs using the radioactive microsphere tracer technique. Du ring quiet breathing, blood flow to the costal diaphragm (25.1 +/- 13. 9 ml/100 g/min) exceeded blood flow to the parasternal intercostals (1 8.0 +/- 10.2 ml/100 g/min, p < 0.05). Inspiratory resistive loading ab olished these differences by increasing blood flow to the parasternal intercostals more than to the diaphragm. Aminophylline (40 mg/kg) sign ificantly increased minute ventilation and tidal transdiaphragmatic pr essure (Pdi) swing during quiet breathing but not during inspiratory r esistive loading. Theophylline did not affect diaphragmatic blood flow during inspiratory resistive loading while the same Pdi swing and ten sion-time index (TTdi) were reached. During quiet breathing, however, theophylline significantly (p < 0.05) increased blood flow to the tria ngularis sterni from 7.9 +/- 5.6 to 18.1 +/- 25.6 ml/100 g/min and to the transversus abdominis from 10.8 +/- 8.4 to 14.6 +/- 10.5 ml/100 g/ min and tended to increase blood flow to the costal diaphragm and the parasternals. We conclude that (I) during quiet breathing, but not dur ing inspiratory resistive loading, blood flow to the costal diaphragm exceeded flow to the parasternal intercostals; (2) during quiet breath ing, theophylline increased blood flow to the expiratory muscles as it promoted recruitment of expiratory muscles; and (3) theophylline did not affect diaphragmatic blood flow for a given TTdi.