Physiological factors underlying transthoracic impedance variations in respiration

relationship between the changes in transthoracic impedance w> 3 respired volume (AV), and thoracic circumference (AC) during both spontaneous and forced positive-pressure respiration was studied in anesthesized dogs. By sectioning the phrenic nerves and stimulating them distally to tetanize the diaphragm it was possible to separate the contributions to AZ produced by the diaphragm alone and by the remaining respiratory muscles. The following conclusions were drawn: r) The ratio AZ/AV had essentially the same value for both spontaneous and forced breathing. The magnitude of AZ/AV was maximum at the level of the 8th ribs and decreased rapidly Gth distance (along the midaxillary lines) above and below the 8th ribs. 2) Tetanus of the diaphragm was associated with a sustained increase in AZ which varied in magnitude with rib level in the same manner as during spontaneous or force