title: Diaphragmatic force and substrate response to resistive loaded breathing in the piglet.
abstract: Inspiratory resistive loaded (IRL) breathing results in hypoventilation and diaphragmatic fatigue in the piglet. We studied the effects of 6 h of IRL on ten 1-mo-old piglets. The load was adjusted to increase spontaneously generated transdiaphragmatic pressure five to six times baseline. Six 1-mo-old piglets acted as controls and were identically instrumented but were not subjected to IRL. Measurements of ventilation, blood gases and pH, diaphragmatic electromyogram, force-frequency curve, blood flow, and end-expiratory lung volume were obtained hourly. Diaphragmatic muscle samples were obtained after 6 h for determination of ATP, phosphocreatine, lactate, and glycogen levels. No changes occurred in the control animals. IRL resulted in a significant decrease in ventilation, an increase in diaphragmatic EMG, onset of abdominal expiratory muscle activity, and a fall in end-expiratory lung volume by 1 h. The force-frequency curve adjusted for lung volume change fell by 20% at all frequencies of stimulation at 1 h and by 40% at 6 h. Blood flow to the costal and crural diaphragm increased by 51 and 141%, respectively. No differences were noted in ATP, phosphocreatine, lactate, or glycogen between control and IRL animals. It is concluded that submaximal spontaneous contractions of the piglet diaphragm over a 6-h period cause a substantial decrease in its maximal force-generating capacity that is not related to substrate depletion.
authors.affiliation: Department of Pediatrics, University of Washington School of Medicine, Seattle 98195.
authors.forename: D E
authors.initials: DE
authors.lastname: Mayock
authors.forename: T A
authors.initials: TA
authors.lastname: Standaert
authors.forename: T D
authors.initials: TD
authors.lastname: Murphy
authors.forename: D E
authors.initials: DE
authors.lastname: Woodrum
mesh_terms: D000818:Animals; D003964:Diaphragm / Q000098:blood supply / Q000502:physiology*; D004734:Energy Metabolism; D005221:Fatigue / Q000503:physiopathology; D009119:Muscle Contraction / Q000502:physiology; D012039:Regional Blood Flow; D015656:Respiratory Mechanics / Q000502:physiology*; D013552:Swine