title: Measuring tidal volume and functional residual capacity change in sleeping infants using a volume displacement plethysmograph.
abstract: The noninvasive measurement of infant lung function during unsedated sleep in infants has been a long-standing objective in paediatric respiratory medicine. This note reports on the design and performance of a head-out volume-displacement plethysmograph (VDP) that overcomes some of the limitations of traditional lung function apparatus. The VDP comprises a rigid acrylic box with an integral water-sealed spirometer and a novel neck seal. The bilayer neck seal is of variable compliance and is comfortable and simple to use. The spirometer permits volume resolution of 1.5 mL and a dynamic range in excess of 100 mL. The frequency response extends from 0-7 Hz. Spirometer inertance was measured as 0.0015 kPa.L(-1).s(-2), resistance 0.021 kPa.L(-1).s(-1) and box capacitance 0.18L.kPa(-1). Tidal volume, respiratory rate and changes in functional residual capacity can be recorded during unsedated rapid eye movement and nonrapid eye movement whilst monitoring with conventional polysomnographic methods. The head-out configuration allows additional instrumentation to be implemented with ease, avoids facial stimulation and allows unimpeded access to the upper airway. A polysomnograph illustrating the limitations of respiratory inductance plethysmography signals and typical changes in functional residual capacity are shown.
authors.affiliation: Center for Magnetic Resonance, The University of Queensland, St Lucia, Brisbane, Australia.
authors.forename: S J
authors.initials: SJ
authors.lastname: Wilson
authors.forename: C
authors.initials: C
authors.lastname: O'Brien
authors.forename: M A
authors.initials: MA
authors.lastname: Harris
authors.forename: I B
authors.initials: IB
authors.lastname: Masters
mesh_terms: D005652:Functional Residual Capacity; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D010991:Plethysmography / Q000295:instrumentation*; D017286:Polysomnography / Q000295:instrumentation; D012129:Respiratory Function Tests / Q000295:instrumentation* / Q000379:methods; D012890:Sleep / Q000502:physiology*; D013990:Tidal Volume