Effect of pulmonary emphysema on diaphragm capillary geometry

Publisher Website
Google Scholar
Abstract
Poole, David C., and Odile Mathieu-Costello. Effect of pulmonary emphysema on diaphragm capillary geometry. J. Appl. Physiol. 82(2): 599–606, 1997.—In emphysema, the diaphragm shortens by losing sarcomeres. We hypothesized that unless capillaries undergo a similar shortening, capillary geometry must be altered. Without quantifying this geometry, capillary length and surface area per fiber volume, which are critical measurements of the structural potential for blood-tissue exchange, cannot be resolved. Five months after intratracheal elastase (E) or saline (control; C) instillation, diaphragms from male Syrian golden hamsters were glutaraldehyde perfusion fixed in situ at reference lung positions (residual volume, functional residual capacity, total lung capacity) to provide diaphragms fixed over a range of sarcomere lengths. Subsequently, diaphragms were processed for electron microscopy and analyzed morphometrically. Emphysema increased lung volume changes from −20 to 25 cmH2O airway pressure (i.e., passive vital capacity) and excised lung volume (both P < 0.001). In each region of the costal diaphragm (i.e., ventral, medial, dorsal), sarcomere number was reduced (all P < 0.05). Capillary-to-fiber ratio increased (C = 2.2 ± 0.1, E = 2.8 ± 0.1; P < 0.01) and fibers hypertrophied (C = 815 ± 35, E = 987 ± 67 μm2; P < 0.05; both values at 2.5 μm sarcomere length). Capillary geometry was markedly altered by the loss of sarcomeres in series. Specifically, the additional capillary length derived from capillary tortuosity and branching was increased by 183% at 2.5 μm sarcomere length compared with C values (C, 359 ± 43; E, 1,020 ± 158 mm−2, P < 0.01). This significantly increased total capillary length (C, 3,115 ± 173; E, 3,851 ± 219 mm−2 at 2.5 μm, P < 0.05) and surface area (C, 456 ± 13; E, 519 ± 24 cm−1, P < 0.05) per fiber volume. Thus emphysema substantially alters diaphragm capillary geometry and augments the capillary length and surface area available for blood-tissue exchange.