Effect of thixotropy conditioning of inspiratory muscles on the chest wall response to CPAP

Background and objective:  Thixotropy conditioning of inspiratory muscles changes the end-expiratory position of the respiratory system during resting breathing. We examined the immediate effects of thixotropy conditioning of inspiratory muscles on chest wall inflation induced by CPAP.

Methods:  A cross-over design study was performed in 13 healthy men. Operating chest wall volume (Vcw) was measured by respiratory inductive plethysmography. Conditioning consisting of a 5 s inspiratory effort at a mask pressure of −20 cm H₂O was performed under CPAP (10 cm H₂O) at three Vcw values to change the muscle length at which conditioning occurred: (i) FRC at a CPAP of 10 cm H₂O (FRC₁₀); (ii) FRC at a CPAP of 0 cm H₂O (FRC₀); and (iii) RV at a CPAP of 10 cm H₂O (RV₁₀).

Results:  CPAP (10 cm H₂O) increased FRC by 0.60–0.70 L. Decreases in operating Vcw were noted after conditioning at RV₁₀, which decreased end-expiratory Vcw by 0.16 ± 0.12 L and end-inspiratory Vcw by 0.20 ± 0.14 L at 180 s (P < 0.01). Inspiratory capacity (1.59 ± 0.45 L) and inspiratory reserve volume (1.18 ± 0.40 L) were greater than preconditioning values (1.44 ± 0.49 L and 0.99 ± 0.41 L, respectively; P < 0.01). Conditioning at FRC₀ also decreased operating Vcw significantly, but conditioning at FRC₁₀ did not change operating Vcw.

Conclusions:  Thixotropy conditioning of inspiratory muscles performed below inflated FRC decreased the level of CPAP-induced inflation.