Ronchetti R, Stocks J, Keith I, Godfrey S
Pediatr Res. 1975 Oct;9(10):797-802. doi: 10.1203/00006450-197510000-00011.
Functional residual capacity (FRC) and thoracic gas volume (TGV) were measured in 20 infants, of whom 11 were healthy preterm infants, 5 were recovering from the respiratory distress syndrome (RDS), and 4 had other pulmonary problems. In addition, some of the theoretical aspects of rebreathing techniques, including the lung to bag N2 difference at equilibrium, were studied by constructing a simple digital computer model of the system. In both the normal preterm infants and the post-RDS group, the TGV was significantly greater than the FRC (0.02 greater than P greater than 0.01), indicating the presence of trapped gas (Fig. 2). The mean time taken to reach equilibrium during rebreathng was 44 sec in the normal infants and 52 sec in the post-RDS group (Table 2). In one infant with generalized cystic lung disease, equilibrium was not achieved even after 3 min of rebreathing (Fig. 1). The computer-generated analysis of rebreathing for a normal 3-kg infant is shown in Figure 3, with an in vivo curve for comparison. The rapid equilibration of N2 was completed within 55 sec but, as in the in vivo experiments, there was a change in slope of the line afer 1.7 min. It can be seen from Table 3 that, if a small initial bag volume (11 ml) is used, 30 sec of rebreathing is adequate for equilibration only when FRC and dead space are normal, and errors would occur if either were enlarged. The computer study showed that the gradient for N2 between bag and lung at equilibrium is of the order of 0.2-0.37% which would cause a negligible error when calculating FRC and assuming that lung N2 is equal to the measured bag N2. The combined in vivo and computer studies served to validate the rebreathing technique as a method for measuring FRC, and have enabled it to be modified for use even in small or very sick infants with poor ventilation. The most useful procedure to employ would seem to be to use an initial bag volume of 150-200 ml and to continue the rebreathing for 1.5-2 min, with samples being taken for analysis at approximately 20-sec intervals.
对20名婴儿进行了功能残气量（FRC）和胸腔气体容积（TGV）的测量，其中11名是健康的早产儿，5名正从呼吸窘迫综合征（RDS）中恢复，4名有其他肺部问题。此外，通过构建一个简单的系统数字计算机模型，研究了重复呼吸技术的一些理论方面，包括平衡时肺与袋中氮气的差异。在正常早产儿和RDS后组中，TGV均显著大于FRC（0.02＞P＞0.01），表明存在潴留气体（图2）。正常婴儿重复呼吸过程中达到平衡的平均时间为44秒，RDS后组为52秒（表2）。在一名患有广泛性囊性肺病的婴儿中，即使重复呼吸3分钟后仍未达到平衡（图1）。图3显示了对一名3千克正常婴儿重复呼吸的计算机生成分析，并与体内曲线进行了比较。氮气的快速平衡在55秒内完成，但与体内实验一样，1.7分钟后曲线斜率发生了变化。从表3可以看出，如果使用较小的初始袋容积（11毫升），只有当FRC和死腔正常时，30秒的重复呼吸才足以达到平衡，否则任何一个增大都会产生误差。计算机研究表明，平衡时袋与肺之间氮气的梯度约为0.2 - 0.37%，在计算FRC并假设肺内氮气等于测得的袋内氮气时，这将导致可忽略不计的误差。体内和计算机研究相结合，验证了重复呼吸技术作为测量FRC的一种方法，并使其能够进行改进，甚至可用于通气不良的小婴儿或重病婴儿。最有用的操作似乎是使用150 - 200毫升的初始袋容积，并持续重复呼吸1.5 - 2分钟，每隔约20秒采集样本进行分析。
