Mechanisms of the inspiratory action of the diaphragm during isolated contraction

• Published in: Journal of applied physiology (1985) Vol. 107; no. 6; pp. 1736 - 1742
• Main Authors: De Troyer, Andre, Leduc, Dimitri, Cappello, Matteo, Mine, Benjamin, Gevenois, Pierre Alain, Wilson, Theodore A
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.12.2009; American Physiological Society
• Subjects: Algorithms; Analysis of Variance; Animals; Biological and medical sciences; Computed tomography; Diaphragm - physiology; Dogs; Electromyography; Fundamental and applied biological sciences. Psychology; Lung - physiology; Lung Volume Measurements; Lungs; Measurement; Models, Biological; Muscle Contraction - physiology; Muscular system; Neurons; Phrenic Nerve - physiology; Respiration, Artificial; Respiratory Mechanics - physiology; Ribs - physiology; Supine Position; Tomography; action of diaphragm; Vertebrata; Mammalia; Respiratory muscle; chest wall mechanics; Diaphragm; Mechanism of action; Chest wall; Respiratory system; Muscle contraction; respiratory muscles
• ISSN: 8750-7587; 1522-1601; 1522-1601
• DOI: 10.1152/japplphysiol.00753.2009

1 Laboratory of Cardiorespiratory Physiology, Brussels School of Medicine; ; 2 Chest Service and ; 3 Department of Radiology, Erasme University Hospital, Brussels, Belgium; and ; 4 Department of Aerospace Engineering and Mechanics, University of Minnesota, Minneapolis, Minnesota Submitted 14 July 2009 ; accepted in final form 30 September 2009 The lung-expanding action of the diaphragm is primarily related to the descent of the dome produced by the shortening of the muscle fibers. However, when the phrenic nerves in dogs are selectively stimulated at functional residual capacity, the muscle insertions into the lower ribs also move caudally. This rib motion should enhance the descent of the dome and increase the fall in pleural pressure ( Ppl). To quantify the role of this mechanism in determining Ppl during isolated diaphragm contraction and to evaluate the volume dependence of this role, radiopaque markers were attached to muscle bundles in the midcostal region of the muscle in six animals, and the three-dimensional location of the markers during relaxation at different lung volumes and during phrenic nerve stimulation at the same lung volumes was measured using computed tomography. From these data, accurate measurements of muscle length, dome displacement, and lower rib displacement were obtained. The values of dome displacement were then corrected for lower rib displacement, and the values of Ppl corresponding to the corrected dome displacements were obtained using the measured relationship between Ppl and dome displacement. The measurements showed that phrenic stimulation at all lung volumes causes a caudal displacement of the lower ribs and that this displacement, taken alone, contributes 25% of the Ppl produced by the diaphragm. To the extent that this lower rib displacement is itself caused by Ppl, the lung-expanding action of the diaphragm during isolated contraction may therefore be viewed as a self-facilitating phenomenon. respiratory muscles; chest wall mechanics; action of diaphragm Address for reprint requests and other correspondence: A. De Troyer, Chest Service, Erasme Univ. Hospital, 808, Route de Lennik, 1070 Brussels, Belgium (e-mail: a_detroyer{at}yahoo.fr ).