Altered Respiratory Tissue Mechanics in Asymptomatic Wheezy Infants

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Abstract
Low-frequency forced oscillation (LFOT) and raised volume rapid thoracic compression (RVRTC) techniques were used to measure airways and respiratory tissue mechanics and forced expiratory volumes in 24 asymptomatic infants with recurrent wheeze. Total respiratory impedance spectra (Zrs) (0.5 to 20 Hz) were obtained (n � 22) and a model containing airway (resistance (Raw) and in- ertance (Iaw)) and constant-phase tissue (tissue damping (G) and tissue elastance (H)) compartments fitted to Zrs. Forced expiratory volumes (FEV 0.5 ) were determined (n � 16). Standardized variants (Z scores) were calculated for comparison to a healthy population (Hall et al. , Am J Respir Crit Care Med 2000;162:1397-1402). Wheezy infants had elevated H (Z scores: 0.61 � 0.20; p � 0.007) but not Raw (0.14 � 0.25; p � 0.2), G (0.41 � 0.21; p � 0.066), or FEV 0.5 ( � 0.25 � 0.25; p � 0.2) compared with healthy infants. Infants younger than 1 yr of age were not significantly different from nor- mals, whereas lung function from infants older than 1 yr had devi- ated from normal infants, with Z scores of 0.58 � 0.2 (p � 0.018), 0.79 � 0.31 (p � 0.032), 1.06 � 0.25 (p � 0.002), and � 0.94 � 0.22 (p � 0.007) for Raw, G, H, and FEV 0.5 respectively. We conclude that asymptomatic infants with recurrent wheeze have altered lung function. The abnormalities were more pronounced in respi- ratory tissue mechanics than in airway mechanics or forced vol- umes, highlighting the value of techniques capable of partitioning lung function into airway and respiratory tissue components.

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