EFFECTS OF EMPHYSEMA ON DIAPHRAGM BLOOD-FLOW DURING EXERCISE

Chronic hyperinflation of the lung in emphysema displaces the diaphrag m caudally, thereby placing it in a mechanically disadvantageous posit ion and contributing to the increased work of breathing. We tested the hypothesis that total and regional diaphragm blood flows are increase d in emphysema, presumably reflecting an increased diaphragm energetic demand. Male Syrian Golden hamsters were randomly divided into emphys ema (E; intratracheal elastase 25 units/100 g body wt) and control (C; saline) groups, and experiments were performed 16-20 wk later. The re gional distribution of blood flow within the diaphragm was determined by using radiolabeled microspheres in hamsters at rest and during trea dmill exercise (walking at 20 feet/min, 20% grade). Consistent with pr onounced emphysema, lung volume per unit body weight was greater in E hamsters (C, 59.3 +/- 1.8; E, 84.5 +/- 5.0 ml/kg; P < 0.001) and arter ial Po-2 was lower both at rest (C, 74 +/- 3; E, 59 +/- 2 Torr; P < 0. 001) and during exercise (C, 93 +/- 3; E, 69 +/- 4 Torr; P < 0.001). A t rest, total diaphragm blood flow was not different between C and E h amsters (C, 47 +/- 4; E, 38 +/- 4 ml.min(-1).100 g(-1); P = 0.18). In both C and E hamsters, blood flow at rest was lower in the ventral cos tal region of the diaphragm than in the dorsal and medial costal. regi ons and the crural diaphragm. During exercise in both C and E hamsters , blood flows increased more in the dorsal and medial costal regions a nd in the crural diaphragm than in the ventral costal region. Total di aphragm blood flow was greater in E hamsters during exercise (C, 58 +/ - 7; E, 90 +/- 14 ml.min(-1).100 g(-1); P = 0.03), as a consequence of significantly higher blood flows in the medial and ventral costal reg ions and crural diaphragm. In addition, exercise-induced increases in intercostal (P < 0.005) and abdominal (P < 0.05) muscle blood flows we re greater in E hamsters. The finding that diaphragm blood flow was gr eater in E hamsters during exercise supports the contention that emphy sema increases the energetic requirements of the diaphragm.