Airways and lung parenchyma are distensible anatomical structures and in healthy subjects dilate with each inspiration. This process is even more evident during deep inhalations (DI). The bronchodilatory and bronchoprotective effect of a DI depends on the tethering forces on the airway wall by the expanding parenchyma, and the loss of this function appears to be associated with airway hyperresponsivenes - a characteristic feature of asthma. Models have assumed that the peribronchial parenchyma expansion (EPB) equals that of the subtended parenchyma (ESL). However, the changes in EPB during bronchoconstriction and its relationship with ESL have not yet been characterized. In this thesis, EPB and ESL were measured at baseline and then studied as they changed during bronchoconstriction and DI, and a novel distensibility measurement was proposed. HRCT scans from subjects with mild-to-moderate asthma (AS) and healthy controls (NA) were acquired in 3 conditions in supine position: at baseline, following a methacholine challenge, and with a DI to TLC. ESL and EPB were quantified as the average of the regional voxel-gas-to-tissue-ratio for each segmental region, and for a spherical region around each of the corresponding segmental airways. The difference in parenchymal expansion (E), the vertical-distance between airway’s center point and the respective segment’s center-of-gravity, and the relative distensibility were also measured. E varied among segments with a systematic vertical-distance dependency for all conditions and subjects, significantly higher in NA than AS (P < 0.05). At baseline average segmental E adjusted by vertical-distance was near zero and increased monotonically with bronchoconstriction and after a DI, following closely a linear relationship with average expansion of the lung (ELung) for all AS and NA subjects and conditions. No significant differences were found in this relationship between AS and NA but E adjusted tended to be higher for AS at TLC. We found that EPB, adjusted for the relative-vertical-distance, was lower than ESL (E > 0) with a difference that increased with average-lung-expansion. The spontaneous increase in lung volume following bronchoconstriction or DI increased peribronchial expansion up to a half of the increase in segmental expansion at the same height. This difference represents a type of airway-parenchyma-uncoupling that has not been described, can have important mechanistic implications on the effects of a DI on airway distensibility, and suggests that in clinical asthma a lack of homogeneous parenchymal stiffening may also contribute to airway hyperresponsiveness.