Comprehensive Integrated Spirometry Using Raised Volume Passive and Forced Expirations and Multiple-Breath Nitrogen Washout in Infants

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With the rapid somatic growth and development in infants, simultaneous accurate measurements of lung volume and airway function are essential. Raised volume rapid thoracoabdominal compression (RTC) is widely used to generate forced expiration from an airway opening pressure of 30 cmH2O (V30). The (dynamic) functional residual capacity (FRCdyn) remains the lung volume most routinely measured. The aim of this study was to develop comprehensive integrated spirometry that included all subdivisions of lung volume at V30 or total lung capacity (TLC30). Measurements were performed on 17 healthy infants aged 8.6-119.7 weeks. A commercial system for multiple-breath nitrogen washout (MBNW) to measure lung volumes and a custom made system to perform RTC were used in unison. A refined automated raised volume RTC and the following two novel single maneuvers with dual volume measurements were performed from V30 during a brief post-hyperventilation apneic pause: (1) the passive expiratory flow was integrated to produce the inspiratory capacity (IC) and the static (passive) FRC (FRCst) was estimated by initiating MBNW after end-passive expiration; (2) RTC was initiated late during passive expiration, flow was integrated to produce the slow vital capacity (jSVC) and the residual volume (RV) was measured by initiating MBNW after end-expiration while the jacket (j) was inflated. Intrasubject FRCdyn and FRCst measurements overlapped (p = 0.6420) but neither did with the RV (p < 0.0001). Means (95% confidence interval) of FRCdyn, IC, FRCst, jSVC, RV, forced vital capacity and tidal volume were 21.2 (19.7-22.7), 36.7 (33.0-40.4), 21.2 (19.6-22.8), 40.7 (37.2-44.2), 18.1 (16.6-19.7), 40.7 (37.1-44.2) and 10.2 (9.6-10.7) ml/kg, respectively. Static lung volumes and capacities at V30 and variables from the best forced expiratory flow-volume curve were dependent on age, body length and weight. In conclusion, we developed a comprehensive physiologically integrated approach for in-depth investigation of lung function at V30 in infants.