Schulze A, Suguihara C, Gerhardt T, Schaller P, Claure N, Everett R, Bancalari E
University of Miami School of Medicine, Department of Pediatrics, Florida 33101, USA.
Pediatr Res. 1998 Feb;43(2):191-7. doi: 10.1203/00006450-199802000-00006.
Impaired pulmonary mechanics can cause chest wall distortion (CWD) so that work of breathing is dissipated in deforming the rib cage. We hypothesized that respiratory mechanical unloading as a technique of assisted mechanical ventilation would reduce CWD in animals with injured lungs. We studied five piglets and five adult rabbits to test across different ages and chest configurations. As a result of intratracheal meconium instillation, lung compliance decreased from 21 (median; range 17-35) to 9.5 (6.7-14) mL/kPa/kg in rabbits and from 26 (18-31) to 7.9 (4.9-11) in piglets. Airway resistance increased from 5.0 (4.6-6.1) to 6.9 (5.8-7.9) kPa/L/s in rabbits only. Respiratory inductive plethysmography was used to measure the phase shift between the rib cage and abdominal compartment movements and the total compartmental displacement ratio. We aimed at unloading at least three-fourths of lung elastance in all animals and 2.0 kPa/L/s of resistance in rabbits. Elastic unloading decreased the phase shift in all but one animal. It reduced the total compartmental displacement ratio from 1.27 (1.14-3.73) to 1.16 (1.02-1.82) in piglets and from 1.77 (1.45-5.24) to 1.37 (1.11-4.78) in rabbits. The inspiratory rib cage expansion increased, whereas abdominal expansion did not. The tidal esophageal pressure deflection decreased. Tidal volume increased, whereas respiratory rate remained unaffected so that the partial pressure of arterial CO2 decreased. Resistive unloading as an adjunct to elastic unloading further reduced CWD and induced a more rapid, shallower breathing. We conclude that respiratory unloading as a mechanical support to spontaneous breathing reduces CWD. We speculate that the decrease in CWD increases ventilatory efficiency for a given diaphragmatic effort.
肺力学受损可导致胸壁变形（CWD），从而使呼吸功消耗于胸廓变形。我们假设，呼吸机械卸载作为一种辅助机械通气技术，将减少肺损伤动物的CWD。我们研究了5只仔猪和5只成年兔，以测试不同年龄和胸廓结构的情况。由于气管内注入胎粪，兔的肺顺应性从21（中位数；范围17 - 35）降至9.5（6.7 - 14）mL/kPa/kg，仔猪从26（18 - 31）降至7.9（4.9 - 11）。仅兔的气道阻力从5.0（4.6 - 6.1）增加至6.9（5.8 - 7.9）kPa/L/s。呼吸感应体积描记法用于测量胸廓与腹部腔室运动之间的相移以及总腔室位移比。我们的目标是在所有动物中卸载至少四分之三的肺弹性回缩力，在兔中卸载2.0 kPa/L/s的阻力。弹性卸载使除一只动物外的所有动物的相移减小。它使仔猪的总腔室位移比从1.27（1.14 - 3.73）降至1.16（1.02 - 1.82），使兔从1.77（1.45 - 5.24）降至1.37（1.11 - 4.78）。吸气时胸廓扩张增加，而腹部扩张未增加。潮式食管压力偏移减小。潮气量增加，而呼吸频率未受影响，从而动脉二氧化碳分压降低。作为弹性卸载辅助手段的阻力卸载进一步减少了CWD，并导致呼吸更快、更浅。我们得出结论，呼吸卸载作为对自主呼吸的机械支持可减少CWD。我们推测，CWD的降低会提高给定膈肌努力下的通气效率。
