Thickness of the diaphragm during active straight leg raise: an investigation with ultrasound

Abstract

The diaphragm is considered as the main inspiratory muscle, which also plays an important role in trunk control during postural tasks. This latter may be disturbed in certain patient populations for example low back pain. Thickening of the diaphragm can be measured directly and non-invasively with ultrasound measurement (US). The main purpose of this study was to investigate whether there is a change in thickness of the diaphragm during a postural task compared to thickness in rest, when investigated with US. In addition, the intra- and inter-rater reliability for this measurement is assessed in healthy subjects and whether there is a correlation between the maximal inspiratory pressure (MIP) and diaphragm thickness. Inter-rater reliability during rest, ipsilateral and bilateral ASLR was fair to good (ICC=0.458, 0.474, 0.518) and intra-rater reliability was excellent (ICC=0.875, 0.875, 0.889). There was no significant difference in diaphragm thickness between rest and ASLR (p<0.05). There was a correlation between MIP and diaphragm thickness (r> 0.41, p< 0.05). Discussion and conclusion: The findings in this study suggest that there is no change in thickness of the diaphragm during this specific postural task (ASLR). Also, the reliability of the US measurement could be further improved with a more standardized procedure. Further research is needed to investigate the postural function of the diaphragm with other, more functional postural tasks.