Total and local impedances of the chest wall up to 10 Hz.
To understand how bical mechanical chest wall (CW) properties are related to those of the CW as a whole, we measured esophageal and gastric pressures, CW volume changes (measured with a head-out body plethysmograph), and anteroposterior and transverse CW diameter changes (measured with magnetometers attached to the surface) during sinusoidal forcing at the mouth (2.5% vital capacity, 0.5-10 Hz) in four healthy subjects. Total CW resistance decreased sharply as frequency rose to 3-4 Hz and remained relatively constant at higher frequencies. Total CW reactance became less negative with increasing frequency but showed no tendency to change sign. Above 2 Hz, diameters measured at different locations changed asynchronously between and within the rib cage and abdomen. "Local pathway impedances" (ratios of esophageal or gastric pressure to a rate of diameter change) showed frequency dependence similar to that of the total CW less than 3 Hz. Local pathway impedances increased during contraction of respiratory muscles acting on the pathway. We conclude that 1) total CW behavior is mainly a reflection of its individual local properties at less than or equal to 3 Hz, 2) local impedances within the rib cage or within the abdomen can change independently in some situations, and 3) asynchronies that develop within the CW during forcing greater than 3 Hz suggest that two compartments may be insufficient to describe CW properties from impedance measurements.
Barnas
G M
GM
Department of Anesthesiology, University of Maryland, Baltimore 21201.
Yoshino
K
K
Fredberg
J
J
Kikuchi
Y
Y
Loring
S H
SH
Mead
J
J
D000009:Abdominal Muscles / Q000502:physiology; D003964:Diaphragm / Q000502:physiology; D004553:Electric Conductivity; D004947:Esophagus; D006801:Humans; D008297:Male; D011312:Pressure; D015656:Respiratory Mechanics; D013270:Stomach; D013909:Thorax / Q000033:anatomy & histology / Q000502:physiology*