The effect of upper chest wall restriction on diaphragmatic function

Abstract

[Purpose] The purpose of the present study was to determine whether transient upper chest wall restriction would enhance diaphragmatic contribution to tidal volume in healthy subjects. [Methods] Changes of diaphragm thickness (ΔTdi) were studied by ultrasound in 24 healthy male subjects in the supine position. Tidal volume (Vt) and respiratory rate were measured by spirometer. ΔTdi with each breath was expressed as percentage of the thickness at the end of expiration (ΔTdi%) and the ratio of ΔTdi% to tidal volume was calculated (ΔTdi%/Vt). The upper rib cage was compressed with a sphygmomanometer cuff to restrict its motion. All parameters were measured in three conditions: during rib cage compression, prior to the compression, and subsequent to the compression. [Results] When upper rib cage compression was applied, ΔTdi% significantly increased, whereas it returned to baseline levels upon release of the compression. ΔTdi%/Vt tended to increase, however there was no significant difference. Subjects were divided into those who showed an increase in ΔTdi%/Vt (group 1: n=16) and those who showed a decrease (group 2: n=8). Prior to the compression, ΔTdi% and ΔTdi%/Vt of group 1 were higher than those of group 2. [Conclusion] These results suggest that in healthy male subjects transient upper rib cage ristriction may enhance diaphragmatic contribution to tidal volume, particularly in those subjects with low initial diaphragm recruitment.