Conclusion Respiratory Muscles

This Section of the Statement has considered the mechanical properties and function of the chest wall, assessed by volume

Figure 6. Abdominal displacement (Vab) gastric pressure (Pga) characteristic during relaxation and contraction of abdominal muscles.

displacements, chest wall motion, and respiratory pressures.

Important techniques include the following:

Assessment of the passive properties of the chest wall (Rahn diagram): the chest wall is a contractile musculoskeletal structure that changes volume to accommodate the ventila-tory function of the lung. Its passive characteristics are those of an elastic body, and have been defined by Rahn diagram (the relationship between the passive relaxation pressure at the closed mouth and lung volume). The relaxation characteristics of the lung are measured by the relationship between volume and esophageal pressure. By subtraction, the passive relaxation properties of the chest wall are calculated. The Rahn diagram is of considerable conceptual importance, although seldom constructed outside a research context.

Assessment of the active chest wall (Campbell diagram): lung volume is plotted against pleural pressure and the diagram permits calculation of respiratory muscle work, both elastic and resistive. The measurement of work and oxygen consumption helps calculate muscle efficiency. If pressure data from maximum efforts against a closed airway (Pi,max, PE,max), across the range of lung volume, are plotted on the Campbell diagram a useful comparison can be made with the pressures achieved during maximum dynamic inspiration and expiration or resting ventilation.

Estimation of ventilation by chest wall motion (Konno-Mead diagram): the technique allows noninvasive measurement of ventilation and the assessment of the contribution of the diaphragm and rib cage to tidal volume. The diagram plots rib cage and abdomen diameters (magnetometers) or perimeters (respiratory inductive plethysmograph). If calibrated, the technique can measure tidal volume without the need

Figure 7. Static progressive contraction of the diaphragm held at three configurations, as shown in Figure 4 (solid circles). The transdiaphragmatic pressure is plotted against the integrated electrical activity of the diaphragm, obtained from the crural region via an esophageal electrode and an RC integrator. FRC: The contraction held at FRC configuration. 85% VC: Notice a considerable loss of Pdi per percent Edi (shorter diaphragm). FRC volume and abdominal muscle contraction [FRC (ab in)]: Notice the increase in Pdi for any given level of Edi (longest diaphragm). The slopes are an index of the effectiveness of the diaphragm to convert stimulation to pressure. Reprinted by permission from Reference 28.

Figure 6. Abdominal displacement (Vab) gastric pressure (Pga) characteristic during relaxation and contraction of abdominal muscles.

Figure 7. Static progressive contraction of the diaphragm held at three configurations, as shown in Figure 4 (solid circles). The transdiaphragmatic pressure is plotted against the integrated electrical activity of the diaphragm, obtained from the crural region via an esophageal electrode and an RC integrator. FRC: The contraction held at FRC configuration. 85% VC: Notice a considerable loss of Pdi per percent Edi (shorter diaphragm). FRC volume and abdominal muscle contraction [FRC (ab in)]: Notice the increase in Pdi for any given level of Edi (longest diaphragm). The slopes are an index of the effectiveness of the diaphragm to convert stimulation to pressure. Reprinted by permission from Reference 28.

of a mouthpiece. Initially magnetometers, and later RIP, have allowed the concept embodied in the Konno-Mead diagram to develop into a clinically useful and widely used noninvasive measure of ventilation. Inferring respiratory action from esophageal and gastric pressures (Macklem diagram): the diagram plots esophageal against gastric pressure and allows breaths that are achieved mainly by rib cage muscles or diaphragm to be distinguished. Assessing activation and electromechanical effectiveness of the diaphragm from EMG (Edi/Pdi diagram): At FRC the diaphragm can generate much more Pdi for a given Edi than at high lung volumes. EMG is measured with an esoph-ageal electrode and activity is expressed as a percentage of EMG at active TLC. At rest, patients with chronic obstructive pulmonary disease have much higher Edi/Pdi ratios than normal subjects.

The measurements listed above have been widely used in clinical research and have advanced importantly our understanding of chest wall function. However, relatively little work has been undertaken in the clinical arena, an important challenge to be met.

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