A novel non-invasive technique for measuring the residual lungvolume by nitrogen washout with rapid thoracoabdominal compression ininfants

摘要

BACKGROUND—The functional residual capacity (FRC), the only lung volume to be routinely measured in infants, is an unreliable volume landmark. In addition to FRC, the residual volume (RV) was measured by nitrogen washout using rapid thoracoabdominal compression (RTC) in nine infants with cystic fibrosis aged 5-31 months.
METHODS—A commercial system for nitrogen washout to measure lung volumes and a custom made system to perform RTC were used. Lung volume was raised to an airway opening pressure of 30 cm H2O (V30). RTC was performed from V30. The jacket pressure (Pj; 65-92 cm H2O) which generated the highest forced expiratory volume (mean 40.2 ml/kg; 95% confidence interval (CI) 33.03 to 47.33) was used during the RV manoeuvre. The infants were manually hyperventilated to inhibit the respiratory drive briefly. RTC was initiated during the last passive expiration. RV was estimated by measuring the volume of nitrogen expired after end forced expiratory switching of the inspired gas from room air to 100% oxygen whilejacket inflation was maintained at the time of switching into oxygen during the post-expiratory pause.
RESULTS—In each infantRV and FRC measurements were reproducible and did not overlap; thedifference between mean values, which is the expiratory reserve volume,was statistically significant (p<0.05). Mean RV was 21.3 (95% CI 18.7 to 24.0), FRC was 25.5 (95% CI 22.8to 28.1), and TLC30(total lung capacity at V30) was 61.5 (95% CI 54.4 to68.7) ml/kg. These values were dependent on body length, weight andage. When measuring RV the period between switching to oxygen and theend of the Pj plateau was 0.301 (95% CI 0.211to 0.391) s. Thewashout duration was longer for RV than for FRC measurement (80.9 s(95% CI 71.3 to 90.4) versus 72.4 s (95% CI 64.9 to 79.8))(p<0.001).
CONCLUSIONS—A newnon-invasive and reliable technique for routine measurement of RV ininfants is presented.