title: Effects of lung volume on parasternal pressure-generating capacity in dogs.
abstract: Previous studies have suggested that the optimum length for force generation of the parasternal intercostal (PS) muscles is well above functional residual capacity (FRC). We further explored this issue by examining the pressure-generating capacity of the PS muscles as a function of lung volume in anaesthetized dogs. Upper thoracic spinal cord stimulation (SCS) was used to electrically activate the PS muscles. Changes in airway pressure and parasternal resting length (LR) during airway occlusion were monitored over a wide range of lung volumes during SCS. To assess the effects of parasternal contraction alone, SCS was performed following phrenicotomy and section of the external intercostal, levator costae and triangularis sterni muscles. With increasing lung volume, there were progressive decrements in the capacity of the PS muscles to produce changes in airway pressure. The relationship between PS pressure generation and lung volume was similar to a previous comparable assessment of the external intercostal muscles. The PS muscles shortened during passive inflation and also shortened further (by > 20 % of LR) during SCS. Total shortening (passive plus active) increased progressively with increasing lung volume. Our results indicate that the capacity of the PS muscles to produce changes in airway pressure (a) falls progressively with increasing lung volume and (b) is similar to that of the external intercostal muscles. We speculate that the fall in PS pressure-generating capacity is related, in part, to progressive reductions in end-inspiratory length.
authors.affiliation: Department of Medicine, Division of Pulmonary and Critical Care Medicine, Case Western Reserve University, MetroHealth Medical Center, 2500 MetroHealth Drive, Cleveland, OH 44109-1998, USA. afd3@po.cwru.edu
authors.forename: A F
authors.initials: AF
authors.lastname: DiMarco
authors.forename: J R
authors.initials: JR
authors.lastname: Romaniuk
authors.forename: G
authors.initials: G
authors.lastname: Supinski
authors.forename: K E
authors.initials: KE
authors.lastname: Kowalski
mesh_terms: D000818:Animals; D004285:Dogs; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D007366:Intercostal Muscles / Q000166:cytology / Q000502:physiology*; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D008176:Lung Volume Measurements; D009119:Muscle Contraction / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000502:physiology; D010791:Phrenic Nerve / Q000502:physiology; D011312:Pressure; D013116:Spinal Cord / Q000502:physiology; D013126:Spinal Nerve Roots / Q000502:physiology; D014797:Vital Capacity / Q000502:physiology