Effect of thixotropy conditioning of inspiratory muscles on the chest wall response to CPAP.
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.
Izumizaki
Masahiko
M
Department of Physiology, Showa University School of Medicine, Tokyo, Japan. masahiko@med.showa-u.ac.jp
Nakajima
Takayuki
T
Iwase
Michiko
M
Ohshima
Yasuyoshi
Y
Homma
Ikuo
I
D000328:Adult; D045422:Continuous Positive Airway Pressure; D018592:Cross-Over Studies; D045853:Exhalation / Q000502:physiology; D005541:Forced Expiratory Volume / Q000502:physiology; D005652:Functional Residual Capacity / Q000502:physiology; D006801:Humans; D001239:Inhalation / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D010991:Plethysmography; D011175:Positive-Pressure Respiration; D015656:Respiratory Mechanics / Q000502:physiology; D012132:Respiratory Muscles / Q000502:physiology*; D035441:Thoracic Wall / Q000033:anatomy & histology / Q000502:physiology*