Statistics. p values < 0.05 were considered to indicate statistical significance. Values are presented as mean ± SD when not otherwise indicated.
Causes the new 16 infants receive when you look at the Desk step one, therefore the differences when considering the brand new RDS category and you may sky-vented organizations was described in Table 2.
The coefficient of variation (range with median in parentheses) of repeated measurements was 0-20% (6%) for FRCp, 0-13% (6%) for FRCz, 0-15%(5%) for IC, and 0-14% (5%) for Crs-max. The most marked intraindividual variation was usually seen in infants with RDS. Crs-max increased between the first and last measurement in seven infants in the RDS group, and in six of these the increase was more than 10% of the initial value. The major part of the increase occurred between the first and second P-V maneuver and was thought to represent recruitment of lung volume after deep inflation. Therefore the last two P-V curves in each infant were used when calculating IC, TLC, and Crs-max. In the air-ventilated group, the first and last P-V curves were similar.
The shape of the P-V curves varied most between individuals in the RDS group. FRCz, IC, and TLC, normalized to body weight, were significantly less in the RDS group than in the air-ventilated group(Table 2, Figs. 2 and 3). However, FRCz/weight in the two groups overlapped, whereas IC/weight did not(Fig. 3). Crs-max and Cdyn were less in the RDS group, a relation that remained after the data had been normalized to weight (Table 2). When the compliance values were normalized to volume (TLC), only Crs-max was significantly less in the RDS group (Table 2). The steepest slope of the P-V curve occurred at a higher alveolar pressure in the RDS group (range 2-8, median 6 cm H2O) than in the air-ventilated group (range 3-6, median 5 cm H2O).
FRCz/TLC was greater (p < 0.05) in the RDS group (46± 10%) than in the air-ventilated group (35 ± 8%)(Table 2, Fig. 2). PCD in the group with RDS was not significantly different from PCD in the air-ventilated group (53 ± 24 versus 41 ± 32%).
This study confirms that FRC and compliance are low in mechanically ventilated neonates with severe RDS (3, 5) . In addition we found that TLC was reduced, mainly due to a markedly reduced IC. Thus, the P-V curves in RDS had smaller amplitude and were less steep(implying a lower Crs-max) than those of air-ventilated infants with normal chest radiograms.
IC and Crs-max discriminated distinctly between infants with severe RDS and those ventilated with air (Fig. 3). These measures can be obtained without knowledge of absolute lung volumes; only the readily available equipment in Fig. 1 is needed. The computerized interrupter technique has previously been used in animal RDS models (15, 16) and in a modified dating dabble version to obtain P-V diagrams in anesthetized infants and children (23) . The occlusion period of 0.08 s was chosen to obtain a high resolution of the P-V curve (20-60 data points), while still achieving an accurate pressure plateau at the end of each occlusion, indicating equilibration with the alveolar pressure (15, 24) . The short-term muscle relaxation that is necessary for performing the P-V maneuver is not harmful if there is a reasonable fit between the tracheal tube and the trachea, as was the case in the present study. However, if the tube is too small, there is the risk that relaxation of muscles in the larynx and pharynx will produce an increased leak around the tracheal tube and, especially in the sickest neonates with stiff lungs, difficulty in achieving adequate alveolar pressures during mechanical ventilation.