Thoracoabdominal compression and respiratory system compliance in HIV-infected infants

The thoracoabdominal compression technique (TAC) is used to measure expirat ory flow in infants. We investigated whether TAC caused a change in total t horacic compliance (Crs), resistance (Rrs), and respiratory system time con stant (Trs). We studied 41 infants (mean age, 12.4 mo; SD, 7.5) from five c enters studying longitudinal lung and cardiovascular function of infants fr om HIV-infected mothers. We measured Crs, Rrs, and Trs before and after TAC . Changes in Crs, Rrs, and Trs after TAC were not dependent on the length o f time since TAC. Crs and Trs were reduced after TAC, p = 0.013 and p = 0.0 03, respectively, whereas Rrs did not change. When compared with uninfected infants, HIV-infected infants had a larger post-pre TAC percent decline in Crs (p = 0.003) and a post-pre TAC rise in mean Rrs (p = 0.03). These diff erences remained significant after adjusting for sex and age. When per form ing infant pulmonary function testing, TAC itself produces a temporary decr ease in Crs and Trs that is more significant in infants at risk for abnorma l lung volume or compliance. Therefore, the sequence of performing the infa nt lung function parameters should be the same each time the testing is rep eated with TAC as the last parameter tested at each testing session.