Immediate effects of thixotropy conditioning of inspiratory muscles on chest-wall volume in chronic obstructive pulmonary disease.
BACKGROUND
Thixotropy is a passive property of the skeletal muscle that depends on the muscle's immediate history of contraction and length change. Inspiratory-muscle thixotropy affects the end-expiratory position of the rib cage in normal subjects.


OBJECTIVE
To determine whether a reduction in end-expiratory chest-wall volume occurs after thixotropy conditioning of inspiratory muscles in patients with chronic obstructive pulmonary disease.


METHODS
Ten male subjects with chronic obstructive pulmonary disease (mean +/- SD forced expiratory volume in the first second 70+/-20% of predicted) showed an increased ratio of residual volume to total lung capacity (49 +/- 4.7%). The subjects conducted inspiratory muscle thixotropy conditioning maneuvers at 3 different chest-wall volumes (end-expiratory volume of baseline breathing, residual volume plus 40% of expiratory reserve volume, and residual volume) and with 3 levels of inspiratory effort (0%, 30%, and 100% of maximal inspiratory mouth pressure at each volume), with airway-closure, in the sitting position. Using respiratory induction plethysmography, we measured the effect of effort-intensity and volume at the time of the conditioning maneuver on the end-expiratory chest-wall volume of the 5 respiratory cycles immediately following the conditioning maneuver.


RESULTS
There was a reduction in end-expiratory chest-wall volume after the conditioning maneuver, except when conditioning was performed at end-expiratory baseline with 0% effort. The reduction increased as effort intensity increased (p = 0.011) and as volume decreased (p < 0.001), and the reduction was attained by rib-cage movement rather than abdominal movement.


CONCLUSIONS
Thixotropy conditioning of inspiratory muscles, at a reduced chest-wall volume, decreased end-expiratory chest-wall volume in the 5 subsequent breaths in patients with chronic obstructive pulmonary disease.
Izumizaki
Masahiko
M
Department of Physiology, Showa University School of Medicine, Tokyo, Japan. masahiko@med.showa-u.ac.jp
Kakizaki
Fujiyasu
F
Tanaka
Kazumasa
K
Homma
Ikuo
I
D000368:Aged; D000369:Aged, 80 and over; D001945:Breathing Exercises; D005541:Forced Expiratory Volume; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D010991:Plethysmography / Q000379:methods; D029424:Pulmonary Disease, Chronic Obstructive / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics; D012132:Respiratory Muscles / Q000503:physiopathology*; D035441:Thoracic Wall / Q000503:physiopathology