title: Cumulative effects of aging and mechanical ventilation on in vitro diaphragm function.
abstract: OBJECTIVE
  Unloading the diaphragm, via mechanical ventilation (MV), results in significant diaphragmatic atrophy, contractile dysfunction, and oxidative stress in young adult animals. Since aging increases skeletal muscle susceptibility to atrophy and injury, we tested the hypothesis that MV-induced diaphragmatic contractile dysfunction would be exacerbated in aging rats.
  
  
  METHODS
  Fisher 344/Brown Norway hybrid rats (4 months old [young] and 30 months old [old]) were assigned to either control or MV groups. MV rats were anesthetized, tracheostomized, and ventilated with 21% O(2) for 12 h. Arterial BP, pH, and blood gas homeostasis were maintained in the MV animals throughout the experimental period. Animals in the control group were acutely anesthetized, and the diaphragms were immediately removed. Muscle strips from the mid-costal diaphragm were removed from each experimental animal, and contractile properties were studied in vitro.
  
  
  RESULTS
  Compared to young control animals, aging (old control animals) was associated with a 13% decrease in maximal isometric tension (24.5 N/cm(2) vs 21.3 N/cm(2)). Although, MV induced similar relative losses (24%) in diaphragmatic isometric tension in both young and old animals receiving MV, the combined effects of aging and MV resulted in a 34% decrement in diaphragmatic isometric tension compared to young control animals (24.5 N/cm(2) vs 16.1 N/cm(2)).
  
  
  CONCLUSIONS
  These data do not support the hypothesis that aging exacerbates the relative MV-induced impairment in diaphragmatic isometric tension. Nonetheless, the additive effects of aging and MV have dramatic effects on diaphragmatic force reserve. This could exacerbate weaning difficulties in older individuals receiving MV.
authors.affiliation: Department of Exercise and Sport Sciences, Center for Exercise Science, University of Florida, Gainesville, FL 32611, USA. dcriswell@hhp.ufl.edu
authors.forename: David S
authors.initials: DS
authors.lastname: Criswell
authors.forename: R Andrew
authors.initials: RA
authors.lastname: Shanely
authors.forename: Jenna J
authors.initials: JJ
authors.lastname: Betters
authors.forename: Michael J
authors.initials: MJ
authors.lastname: McKenzie
authors.forename: Jeff E
authors.initials: JE
authors.lastname: Sellman
authors.forename: Darin L
authors.initials: DL
authors.lastname: Van Gammeren
authors.forename: Scott K
authors.initials: SK
authors.lastname: Powers
mesh_terms: D000375:Aging / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D003964:Diaphragm / Q000378:metabolism / Q000502:physiology*; D004558:Electric Stimulation; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D012121:Respiration, Artificial