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Effect of thixotropy conditioning of inspiratory muscles on the chest wall response to CPAP
Masahiko Izumizaki1, Takayuki Nakajima, Michiko Iwase
1Department of Physiology, Showa University School of Medicine, Tokyo, Japan. masahiko@med.showa-u.ac.jp
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 H(2)O was performed under CPAP (10 cm H(2)O) at three Vcw values to change the muscle length at which conditioning occurred: (i) FRC at a CPAP of 10 cm H(2)O (FRC(10)); (ii) FRC at a CPAP of 0 cm H(2)O (FRC(0)); and (iii) RV at a CPAP of 10 cm H(2)O (RV(10)).
Results:
CPAP (10 cm H(2)O) increased FRC by 0.60-0.70 L. Decreases in operating Vcw were noted after conditioning at RV(10), 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 FRC(0) also decreased operating Vcw significantly, but conditioning at FRC(10) did not change operating Vcw.
Conclusions:
Thixotropy conditioning of inspiratory muscles performed below inflated FRC decreased the level of CPAP-induced inflation.
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