Altered respiratory tissue mechanics in asymptomatic wheezy infants

Low-frequency forced oscillation (LFOT) and raised volume rapid thoracic co mpression (RVRTC) techniques were used to measure airways and respiratory t issue mechanics and forced expiratory volumes in 24 asymptomatic infants wi th recurrent wheeze. Total respiratory impedance spectra (Zrs), (0.5 to 20 Hz) were obtained (n = 22) and a model containing airway (resistance [Raw] and inertance [law]) and constant-phase tissue (tissue damping [G] and tiss ue elastance [H]) compartments fitted to Zrs. Forced expiratory volumes (FE V0.5) were determined (n = 16). Standardized variants (Z scores) were calcu lated 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: 0.6 1 +/- 0.20; p = 0.007) but not Raw (0.14 +/- 0.25; p > 0.2), G (0.41 +/- 0. 21; p = 0.066), or FEV0.5 (-0.25 +/- 0.25; p > 0.2) compared with healthy i nfants. Infants younger than 1 yr of age were not significantly different f rom normals, whereas lung function from infants older than 1 yr had deviate d 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 FEV0.5 respectively. We conclude that asymptomatic infa nts with recurrent wheeze have altered lung function. The abnormalities wer e more pronounced in respiratory tissue mechanics than in airway mechanics or forced volumes, highlighting the value of techniques capable of partitio ning lung function into airway and respiratory tissue components.