The positional change in vital capacity as a tool to identify diaphragm dysfunction: A qualitative systematic review

Sitting to supine fall in vital capacity (∆VC) is commonly used to screen for diaphragmatic dysfunction (DD), but the predictive threshold value varies. This systematic review aimed to compare the position-dependent change in vital capacity (VC) in patients with objectively confirmed DD.

What is the optimal predictive value of ∆VC to diagnose DD.

We searched Medline/PubMed, Embase and Scopus, including backward citations, for studies from database inception to December 5, 2023. Included trials measured position change in VC in adult patients with DD, confirmed independently by a parameter other than ∆VC. Risk of bias was assessed using the Downs and Black checklist.

Of 497 records identified, 10 studies were included, totalling 393 adults, of which 284 had DD. In patients with confirmed unilateral diaphragmatic paralysis, mean change in VC ranged from 7 to 23%, and in those with bilateral diaphragmatic paralysis, from 19 to 37%. In studies providing only values for DD without specifying unilateral or bilateral involvement, it ranged from 31 to 42%. In control groups, it ranged from 3 to 9%.

The change in VC appears to be a valid test for confirming DD when using a cut-off value of 20%, though this approach results in very low sensitivity. A cut-off value of 15% should be used in a screening setting as an initial approach of a multimodal strategy, without being sensible enough to exclude milder forms of DD.