Abstract
In more severe types of SMA the intercostal muscles are weakened, while the diaphragm is relatively preserved. We studied chest wall asynchronies in SMA type II patients and in a recently proposed sub-classification of SMAIIIA and SMAIIIB to study chest wall distortion and respiratory muscle coordination.
4 SMAII (age 24.0±14.2), 4 SMAIIIA (age 25.0±14.9) and 9 SMAIIIB (age 21.5±10.2) patients and 16 healthy age-matched controls (CTR, age 22.3±11.4) were considered. In each subject pulmonary rib cage, abdominal rib cage and abdominal volumes (VRCp, VRCa and VAB respectively) were measured in seated (ST) and supine (SP) positions by opto-electronic plethysmography. Rib cage distortion was quantified as the phase shift between VRCp and VRCa (θRC) and respiratory muscle coordination between VRCp and VAB (θTA).
In ST chest wall asynchronies in all SMA were similar to CTR. The major differences were found in SP with SMAII showing highly negative values both in θRC and in θTA when compared to SMAIIIB and CTR (see fig). The change in posture had an effect on θRC and θTA in SMAII and SMAIIIA, with more negative values in SP.
In SMAII the diaphragm strongly anticipates intercostal muscles action. This marked direct action of the diaphragm on RCa induces rib cage distortion especially in supine. Changing posture highlights a more similar behavior of SMAIIIA to SMAII confirming the suitability of sub-classification of SMAIII.
- © 2013 ERS