Mechanical ventilation results in progressive contractile dysfunction in the diaphragm.
These experiments tested the hypothesis that a relatively short duration of controlled mechanical ventilation (MV) will impair diaphragmatic maximal specific force generation (specific P(o)) and that this force deficit will be exacerbated with increased time on the ventilator. To test this postulate, adult Sprague-Dawley rats were randomly divided into one of six experimental groups: 1) control (n = 12); 2) 12 h of MV (n = 4); 3) 18 h of MV (n = 4); 4) 18 h of anesthesia and spontaneous breathing (n = 4); 5) 24 h of MV (n = 7); and 6) 24 h of anesthesia and spontaneous breathing (n = 4). MV animals were anesthetized, tracheostomized, and ventilated with room air. Animals in the control group were acutely anesthetized but were not exposed to MV. Animals in two spontaneous breathing groups were anesthetized and breathed spontaneously for either 18 or 24 h. No differences (P > 0.05) existed in diaphragmatic specific P(o) between control and the two spontaneous breathing groups. In contrast, compared with control, all durations of MV resulted in a reduction (P < 0.05) in diaphragmatic specific tension at stimulation frequencies ranging from 15 to 160 Hz. Furthermore, the MV-induced decrease in diaphragmatic specific P(o) was time dependent, with specific P(o) being approximately 18 and approximately 46% lower (P < 0.05) in animals mechanically ventilated for 12 and 24 h, respectively. These data support the hypothesis that relatively short-term MV impairs diaphragmatic contractile function and that the magnitude of MV-induced force deficit increases with time on the ventilator.
Powers
Scott K
SK
Department of Exercise and Sport Sciences, University of Florida, Gainesville 32611, USA. spowers@hhp.ufl.edu
Shanely
R Andrew
RA
Coombes
Jeff S
JS
Koesterer
Thomas J
TJ
McKenzie
Michael
M
Van Gammeren
Darin
D
Cicale
Michael
M
Dodd
Stephen L
SL
D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure; D001831:Body Temperature; D001835:Body Weight; D003964:Diaphragm / Q000503:physiopathology*; D004195:Disease Models, Animal; D018450:Disease Progression; D005260:Female; D006706:Homeostasis; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D007537:Isometric Contraction; D009119:Muscle Contraction; D051381:Rats; D017207:Rats, Sprague-Dawley; D012121:Respiration, Artificial / Q000009:adverse effects*; D012131:Respiratory Insufficiency / Q000209:etiology* / Q000503:physiopathology*