Airway distensibility with lung inflation after allogeneic haematopoietic stem-cell transplantation

The ability to reverse induced-bronchoconstriction by deep-inhalation increases after allogeneic haematopoietic stem-cell transplantation (HSCT), despite a decreased total lung capacity (TLC). We hypothesized that this effect may be due to an increased airway distensibility with lung inflation, likely related to an increment in lung stiffness. We studied 28 subjects, 2 weeks before and 2 months after HSCT. Within-breath respiratory system conductance (G(rs)) at 5, 11 and 19 Hz was measured by forced oscillation technique (FOT) at functional residual capacity (FRC) and TLC. Changes in conductance at 5Hz (G(rs5)) were related to changes in lung volume (ΔG(rs5)/ΔV(L)) to estimate airway distensibility. G(rs) at FRC showed a slight but significant increase at all forcing frequencies by approximately 12-16%. TLC decreased after HSCT whereas the ΔG(rs5)/ΔV(L) ratio became higher after than before HSCT and was positively correlated (R2=0.87) with lung tissue density determined by quantitative CT scanning. We conclude that airway caliber and distensibility with lung inflation are increased after HSCT. This effect seems to be related to an increase in lung stiffness and must be taken into account when interpreting lung function changes after HSCT.