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Vol. 84, Issue 3, 971-979, March 1998
1 Department of Physiology, Kirksville College of Osteopathic Medicine, Kirksville, Missouri 63501; and 2 Departments of Kinesiology and Anatomy and Physiology, Kansas State University, Manhattan, Kansas 66506-5602
Chronic
hyperinflation of the lung in emphysema displaces the diaphragm
caudally, thereby placing it in a mechanically disadvantageous position
and contributing to the increased work of breathing. We tested the
hypothesis that total and regional diaphragm blood flows are increased
in emphysema, presumably reflecting an increased diaphragm energetic
demand. Male Syrian Golden hamsters were randomly divided into
emphysema (E; intratracheal elastase 25 units/100 g body wt) and
control (C; saline) groups, and experiments were performed 16-20
wk later. The regional distribution of blood flow within
the diaphragm was determined by using radiolabeled microspheres in
hamsters at rest and during treadmill exercise (walking at 20 feet/min,
20% grade). Consistent with pronounced 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 arterial
PO2 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). At rest, total diaphragm blood flow was not different between C and E
hamsters (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 costal region of the
diaphragm than in the dorsal and medial costal regions and the crural
diaphragm. During exercise in both C and E hamsters, blood flows
increased more in the dorsal and medial costal regions and in the
crural diaphragm than in the ventral costal region. Total diaphragm
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
regions and crural diaphragm. In addition, exercise-induced increases
in intercostal (P < 0.005) and
abdominal (P < 0.05) muscle blood
flows were greater in E hamsters. The finding that diaphragm blood flow
was greater in E hamsters during exercise supports the contention that
emphysema increases the energetic requirements of the diaphragm.
regional blood flow; diaphragm energetics; radiolabeled microspheres
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