Inferring Diaphragm Activation And Electromechanical Effectiveness From

The Rahn, Campbell, Konno-Mead, and Macklem diagrams allow the inference of respiratory muscle activity via departures from the relaxed pressure-volume, motion-relaxation, or pressure-pressure relationships. The major limitation of

Figure 5. Macklem diagram. The pleural pressure-abdominal pressure relationship for a variety of breaths is shown, emphasizing the use of certain chest wall muscles: mainly rib cage (RC) muscles (upper girdle, in-tercostals), normal breath, or mainly diaphragm contraction. Dotted lines: Iso Pdi isopleths show loci of constant transdiaphragmatic pressure.

Figure 5. Macklem diagram. The pleural pressure-abdominal pressure relationship for a variety of breaths is shown, emphasizing the use of certain chest wall muscles: mainly rib cage (RC) muscles (upper girdle, in-tercostals), normal breath, or mainly diaphragm contraction. Dotted lines: Iso Pdi isopleths show loci of constant transdiaphragmatic pressure.

these methods is that both esophageal and gastric pressures are affected by the action of many muscles, and the analysis of their individual actions is indirect and qualitative. "Relaxation" is often difficult to obtain.

The use of the electromyogram (EMG) displayed in the time domain allows the evaluation of the level and timing of activation of an individual muscle (28-31) The frequency domain analysis of the EMG allows the evaluation of center frequency or centroid parameter sensitive to changes in the velocity of conduction of membrane potentials. Center frequency decreases when the muscle fatigues (32, 33) (and see Frequency Domain Analysis in Section 3 of this Statement).

Simultaneous measurement of integrated EMG of the diaphragm (Edi), the Pdi, and muscle configuration (length) allows the estimation of activation pressure ratio, as shown in Figure 7 (28, 31, 34). The strength of Edi can be measured as the root mean square (RMS) (34). Because absolute RMS values are subjected to many variables, normalization is done to the maximal voluntary RMS obtained by holding an inspiration at TLC. This test could be used to evaluate the relative activation during resting breathing. It was found that the percentage of RMS swings measured during resting breathing was 8% of maximal in healthy subjects and 43% in chronic obstructive pulmonary disease, whereas there were nonsignificant differences in Pdi swings (34).

From studies of normal subjects, it was established that the RMS, expressed as a percentage of its maximal activation at TLC, varies as a function of chest wall configuration as measured by a Konno-Mead diagram (28, 31). The RMS/Pdi ratio has the highest slope at lung volumes near TLC (short muscle) and smaller slopes at low lung volumes, at which the diaphragm is contracting against active abdominal muscles. The force of the diaphragm (for a given percentage of maximum RMS) is strongly dependent on its length and configuration (Figure 7).

Advantages

The advantage of this method is that it makes possible the evaluation of the effectiveness of the muscle, that is, amount of force generated per stimulation units.

Disadvantages

The disadvantage of this method is the rather complex method of EMG analysis, which may be made easier by multielectrode recording technology (33). In addition, this method requires evaluation of the configuration of the diaphragm via the Konno-Mead method, as well as the velocity of shortening. This method is still under development, and remains an interesting research tool.

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