Diaphragm curvature modulates the relationship between muscle shortening and volume displacement

Brad J. Greybeck, Matthew Wettergreen, Rolf D. Hubmayr, Aladin M. Boriek

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

During physiological spontaneous breathing maneuvers, the diaphragm displaces volume while maintaining curvature. However, with maximal diaphragm activation, curvature decreases sharply. We tested the hypotheses that the relationship between diaphragm muscle shortening and volume displacement (VD) is nonlinear and that curvature is a determinant of such a relationship. Radiopaque markers were surgically placed on three neighboring muscle fibers in the midcostal region of the diaphragm in six dogs. The three-dimensional locations were determined using biplanar fluoroscopy and diaphragm VD, curvature, and muscle shortening were computed in the prone and supine postures during spontaneous breathing (SB), spontaneous inspiration efforts after airway occlusion at lung volumes ranging from functional residual capacity (FRC) to total lung capacity, and during bilateral maximal phrenic nerve stimulation at those same lung volumes. In supine dogs, diaphragm VD was approximately two- to three-fold greater during maximal phrenic nerve stimulation than during SB. The contribution of muscle shortening to VD nonlinearly increases with level of diaphragm activation independent of posture. During submaximal diaphragm activation, the contribution is essentially linear due to constancy of diaphragm curvature in both the prone and supine posture. However, the sudden loss of curvature during maximal bilateral phrenic nerve stimulation at muscle shortening values greater than 40% (ΔL/LFRC) causes a nonlinear increase in the contribution of muscle shortening to diaphragm VD, which is concomitant with a nonlinear change in diaphragm curvature. We conclude that the nonlinear relationship between diaphragm muscle shortening and its VD is, in part, due to a loss of its curvature at extreme muscle shortening.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Regulatory Integrative and Comparative Physiology
Volume301
Issue number1
DOIs
StatePublished - Jul 2011

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Diaphragm
Muscles
Phrenic Nerve
Posture
Respiration
Dogs
Total Lung Capacity
Functional Residual Capacity
Lung
Fluoroscopy

Keywords

  • Chest wall
  • Kinematics
  • Mechanics
  • Respiratory muscles
  • Rib cage

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

Cite this

Diaphragm curvature modulates the relationship between muscle shortening and volume displacement. / Greybeck, Brad J.; Wettergreen, Matthew; Hubmayr, Rolf D.; Boriek, Aladin M.

In: American Journal of Physiology - Regulatory Integrative and Comparative Physiology, Vol. 301, No. 1, 07.2011.

Research output: Contribution to journalArticle

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