Quantification of thoracic volumes by three-dimensional imaging

Abstract

End-expiratory thoracic cavity volume (Vthx) was measured in eight volunteers lying supine by three-dimensional X-ray computed tomography using the Dynamic Spatial Reconstructor. Untrapped end-expiratory pulmonary gas volume at functional residual capacity (FRC) was determined by nitrogen clearance. Both measurements were done before and after induction of anesthesia-paralysis. After induction of anesthesia-paralysis, Vthx and FRC were consistently and significantly (P less than 0.01) reduced by 0.28 +/- 0.22 (SD) and 0.59 +/- 0.24 liter, respectively. The reduction of FRC was larger than the reduction of Vthx (delta Vthx) in six of the eight subjects, a finding suggesting that intrathoracic fluid (blood) plus trapped gas volume (Vtt) increased. Changes in Vthx were partitioned into volume changes from the thoracic rib cage (delta Vrc) and from shape and/or position changes of the diaphragm (delta Vdi). delta Vrc contributed significantly (0.17 +/- 0.15 liter, P less than 0.02) to delta Vthx, whereas delta Vdi contributed only in four of the eight subjects. We conclude that delta Vrc, delta Vdi, and delta Vtt contribute to the reduction of FRC after induction of anesthesia-paralysis in humans; the relative contribution of them varies among subjects.

The effect of propofol on airway pressures generated by magnetic stimulation of the phrenic nerves

“…These values are close to our findings. Nitrogen washout produced higher figures of 600-700 ml [26], possibly due to absorption atelectasis.…”

“…Bergman found a fall in resting end expiratory volume 30 s after induction, stabilising at a lower level after another 1545 s [8]. Some of this volume change may also be due to other factors [25], such as movement of blood into the thorax during spontaneous breathing or out during mechanical ventilation [26,27]. However, results so far are extremely variable.…”

Pathophysiology of changes in absolute lung volumes

“…Decreases in inspiratory muscle tone, airway closure and subsequent atelectasis, cephalad movement of the diaphragm, and decreases in compliance of both the lung and chest wall have also been suggested as causes [130][131][132]134]. The smaller changes in thoracic cage dimensions after anaesthesia, observed utilizing measures of thoracic dimensions [135] and computed tomography (CT) estimates of thoracic cage volume [136], suggest that increases in intrathoracic fluid may play a contributory or dominant role.…”

Static Versus Prospective Gated Non–breath Hold Volumetric MDCT Imaging of the Lungs1

“…This measurement has a high level of repeatability considering that the measurements were made using 5 different scans (FRC, 2 static and 2 dynamic scans) at three different volumes (FRC, 7 and 15 cmH2O) and using three different acquisition methods (spiral, non-gated axial and gated axial scanning). The slightly higher non-significant tissue volume at FRC could be explained by shifts in blood volume due to breath hold at FRC after a recruitment to TLC as suggested by Beck et al [21] and Krayer et al [22].…”

“…The comparison shows that the dynamic and static histogram means were significantly different (p < 0.05) with the means of the dynamic images being higher indicating greater partial volume effects on air filled areas of the lung. In addition, the blood volume present in the imaged regions could be different between the two conditions [22].…”