Comprehensive integrated spirometry using raised volume passive and forced expirations and multiple-breath nitrogen washout in infants

Abstract

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 cm H 2 O (V 30 ). The (dynamic) functional residual capacity (FRC dyn ) 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 V 30 or total lung capacity (TLC 30 ). Measurements were performed on seventeen 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 V 30 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 (FRC st ) 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 ( j SVC) and the residual volume (RV) was measured by initiating MBNW after end-expiration while the jacket (j) was inflated. Intrasubject FRC dyn and FRC st measurements overlapped (p= 0.6420) but neither did with the RV (p<0.0001). Means (95% confidence interval) of FRC dyn , IC, FRC st , j SVC, 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 V 30 and variables from the best forced expiratory flowvolume 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 V 30 in infants. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access

Nasal versus oronasal raised volume forced expirations in infants—A real physiologic challenge

“…Clearing the nose of the sleeping infant of inspissated mucus before initiating the tests was important 5, 6, 14. Their oxygen saturation and heart rate were monitored with a pulse oximeter during testing and until they were fully awake after 5, 6, 24. The ethics committee of the institution approved the testing protocol and informed written parental consent was obtained prior to each infant test.…”

“…Whereas in cooperative older children and adults a mouth piece and a nose‐clip are used during forced expiration (FE) in order to bypass the nasal resistance, raised volume RTC requires an infant sleeping supine, sedated with chloral hydrate and the use of a facemask which covers the mouth and nose. Hence, both nasal and oral airways contribute to the forced expiratory airflow in infants 1–12. Infants are obligatory or preferential nose breathers, yet their average nasal resistance is 13 cm H 2 O/L/sec, which is nearly 50% of the total airway resistance as in adults 13.…”

“…Cold ambient temperature and rhinitis could swell the nasal turbinates which increases nasal expiratory resistance 21, 23. Hence, testing has been recommended three weeks after an upper respiratory tract infection 5–7, 24, 25. Consequently, changes in lower airway resistance with disease or therapeutic interventions may be masked unless the sensitivity of the infant lung function test employed is increased by dissociating the upper from the lower airways 6, 7, 26.…”

“…Hence, testing has been recommended three weeks after an upper respiratory tract infection 5–7, 24, 25. Consequently, changes in lower airway resistance with disease or therapeutic interventions may be masked unless the sensitivity of the infant lung function test employed is increased by dissociating the upper from the lower airways 6, 7, 26. Taken together, we thought that maintaining an opened mouth during raised volume RTC from an airway opening pressure (Pao) of 30 cm H 2 O (V 30 ) was crucial 6.…”

“…Consequently, changes in lower airway resistance with disease or therapeutic interventions may be masked unless the sensitivity of the infant lung function test employed is increased by dissociating the upper from the lower airways 6, 7, 26. Taken together, we thought that maintaining an opened mouth during raised volume RTC from an airway opening pressure (Pao) of 30 cm H 2 O (V 30 ) was crucial 6. We hypothesized that the known higher nasal than pulmonary airway resistance would decrease the forced expiratory flows (FEF % ) during a nasal (FE n ) forced expiration, even in an infant who was an obligatory or preferential nose breather, which an opened mouth, that is (oronasal) FE o , would resolve.…”