REGIONAL CHEST-WALL IMPEDANCE DURING NONRESPIRATORY MANEUVERS

To assess changes in total and regional chest wall properties during nonrespiratory maneuvers, we measured electromyographic activity of various chest wall muscles, esophageal pressure, and rib cage and abdominal surface displacements in six subjects before and during various static tasks. Subjects were seated at functional residual capacity, and quasi-sinusoidal forcing at the mouth (0.4 Hz, 500 ml) was imposed during the maneuver in the absence of active breathing. Magnitude of total chest wall impedance ([Zw[) increased with effort during all maneuvers; changes in phase were small. Maneuvers involving primarily muscles of the neck and rib cage - holding a 10-kg weight, 10 kg of isometric tension between the arms, and isometric neck flexion - roughly doubled the magnitude of rib cage impedance ([Zrc[) and, to a lesser degree, increased magnitude of diaphragm-abdomen impedance ([Zd-a[). Unilateral and bilateral leg lifts, in addition to increasing [Zd-a[, increased [Zrc[. Passive 90-degrees rotation of the torso caused approximately 25% increases in [Zrc[ and [Zd-a[; if the rotation was actively maintained by the trunk muscles, both regional impedances increased over 100%. Increases in magnitude of regional impedance were correlated to increases in regional electromyographic activity; changes in phase were small. Passive restriction of rib cage displacement by strapping increased [Zrc[ and [Zw[ but not [Zd-a[, whereas abdominal strapping increased [Zd-a[ but did not affect [Zrc[ or [Zw[. We speculate that, when respiratory muscles contract during a nonrespiratory muscles contract during a nonrespiratory maneuver, breathing will be more difficult unless contraction of various muscles contract during a nonrespiratory maneuver, breathing will be more difficult unless contraction of various muscles is coordinated in some complex way to minimize [Zw[.