Regional variations in lung expansion in rabbits: prone vs. supine positions

Abstract

We studied the vertical gradient in lung expansion in rabbits in the prone and supine body positions. Postmortem, we used videomicroscopy to measure the size of surface alveoli through transparent parietal pleural windows at dependent and nondependent sites separated in height by 2-3 cm at functional residual capacity (FRC). We compared the alveolar size measured in situ with that measured in the isolated lungs at different deflationary transpulmonary pressures to obtain transpulmonary pressure (pleural surface pressure) in situ. The vertical gradient in transpulmonary pressure averaged 0.48 +/- 0.16 (SD) cmH2O/cm height (n = 10) in the supine position and 0.022 +/- 0.014 (SD) cmH2O/cm (n = 5) in the prone position. In mechanically ventilated rabbits, we used the rib capsule technique to measure pleural liquid pressure at different heights of the chest in prone and supine positions. At FRC, the vertical gradient in pleural liquid pressure averaged 0.63 cmH2O/cm in the supine position and 0.091 cmH2O/cm in the prone position. The vertical gradients in pleural liquid pressure were all less than the hydrostatic value (1 cmH2O/cm), which indicates that pleural liquid is not generally in hydrostatic equilibrium. Both pleural surface pressure and pleural liquid pressure measurements show a greater vertical gradient in the supine than in the prone position. This suggests a close relationship between pleural surface pressure and pleural liquid pressure. Previous results in the dog and pony showed relatively high vertical gradients in the supine position and relatively small gradients in the prone position. This behavior is similar to the present results in rabbits. Thus the vertical gradient is independent of animal size and might be related to chest shape and weight of heart and abdominal contents.

An improved technique for studying pleural fluid pressure and composition in rabbits

“…The end-expiratory P1iq values from the present study are similar to those previously obtained in rabbits with intrapleural cannulae (Miserocchi et al 1982) and micropipettes (Miserocchi et al 1988a), yet they are significantly more negative than those obtained with the 'rib capsule' technique in the rabbit (Yang et al 1989 (Albertine, Wiener-Kronish, Bastacky & Staub, 1991) they are likely to occur on a functional basis (Grotberg & Glucksberg, 1994). In fact simultaneous measurements of Pliq and Pp1 (Miserocchi,Nakamura & Agostoni,198 la), indicate that the former is more subatmospheric than the latter at any height.…”

“…Another non-invasive method, originally developed for larger animals, involves the use of capsules fixed to a rib through which holes are drilled (Wiener-Kronish, Gropper & Lai-Fook, 1985; Olson & Lai-Fook, 1988;Urmey, De Troyer, Kelly & Loring, 1988;Yang, Kaplowitz & Lai-Fook, 1989;Yang & Lai-Fook, 1991). This technique represented a major step forward since it allowed dynamic recording without being invasive, however, there was one major drawback: the potential lack of hydraulic continuity between the capsule and the pleural fluid.…”

Effect of low-xenon and krypton supplementation on signal/noise of regional CT-based ventilation measurements

“…Hoffman and colleague (14,15) found a significant vertical gradient of air content (3.3% air/cm at functional residual capacity) in the supine position, but a minimal gradient (Ϫ0.36% air/cm) in the prone position. Other studies found similar gradients of subpleural alveolar size (44), pleural pressure (41), and alveolar volume by PET (38) in the supine position, but no or minimal gradient in the prone position.…”

Atelectasias durante anestesia: fisiopatologia e tratamento

“…Em posição supina, o coração e as estruturas do mediastino repousam sobre as partes mediais dos lobos inferiores exercendo pressão em torno de 5 cmH 2 O.cm -2 em pacientes adultos sem doença cardíaca, e em torno de 7 a 8 cmH 2 O.cm -2 nos pacientes com lesão pulmonar aguda 27 . Nos pacientes submetidos à anestesia e ventilação mecâ-nica, é provável que a compressão mecânica das regiões pulmonares dependentes e caudais seja o fator mais importante para o colapso pulmonar observado no intra-operató-rio 26,28,29 . Estudando pacientes submetidos à operação abdominal sob anestesia geral por meio de tomografia computadorizada de tórax, Brismar e col. encontraram densidades pulmonares maiores nos segmentos mais caudais e menores nas regiões mais cefálicas 30 .…”

“…In the supine position, the heart and other mediastinal structures rest on the medial regions of the inferior lobes, exerting a 5 cmH 2 O.cm -2 pressure in adult patients without cardiac diseases, and approximately 7 to 8 cmH 2 O.cm -2 in patients with acute pulmonary lesion 27 . In anesthetized patients on mechanical ventilation, the mechanical compression of dependent and caudal lung regions is probably the most important factor in the development of intraoperative pulmonary collapse 26,28,29 . In a study by Brismar et al of patients undergoing abdominal surgery under general anesthesia, CT scan of the chest demonstrated pulmonary densities that were more pronounced in caudal regions than in the upper areas of the lungs 30 .…”