Scintigraphic evaluation of shape of lung and chest in upright and head-down posture

Abstract

We determined the configuration of lungs and chest in six healthy young subjects using anteroposterior and lateral technetium-99m-labeled scintigraphic images obtained in upright and in 90 degree head-down posture at 0, 25, 50, 75, and 100% vital capacity (VC). The lung shape was evaluated from curves relating vertical height vs. cumulative volume of 20 apicodiaphragmatic lung zones of equal height. S-shaped curves were obtained, which, after size normalization, were largely independent of volume or posture (P greater than 0.1). However, the apical zones tended to become relatively wider and the diaphragmatic zones relatively smaller with increasing volume, especially between 0 and 25% VC in upright posture and 0-50% VC in head-down posture. Changing posture from upright to head-down also tended to slightly widen the apical zones and to narrow the diaphragmatic zones, which is in line with a greater intrathoracic penetration of the diaphragm/abdomen. The shape of the chest was evaluated from the ratio of the transverse-thoracic and anteroposterior distances over height. These ratios did not clearly change with posture (P greater than or equal to 0.05) but increased by approximately 30% with decreasing volume (P less than 0.01). The fact that these shape changes of the chest were not accompanied by similar changes in lung shape can be explained mainly by widening of the mediastinum when volume decreases. In conclusion, the shape of the lung and chest are similar in head-down and upright humans, in contrast to the reversal of the apicodiaphragmatic differences in alveolar expansion and in transpulmonary pressure.

Normal thoracoabdominal motions. Influence of sex, age, posture, and breath size.

“…Several authors emphasized that the singleposition MLR method accurately estimates volume partitioning during tidal breathing (13,18,19). During VC maneuvers, however, especially at high volumes, the RC and ABD cross-sectional area changes underestimate the increase in mouth volume because of the predominant expansion of the upper chest located more cranially than the RC coil of the Respitrace; therefore, the two-compartment model with aLlRC and bMBD as the 2 degrees of freedom (LlVOIM = aLlRC + bMBD) is no longer valid (20).…”

“…Because the MLR method aims to optimize the equation LlVolM = aLlRC + bMBD (12) (even when this is not valid), it enhances the VM coefficients of the RC in comparison with those of the ABD when VC maneuvers are used for the calibration, and under these conditions the VM coefficients become unreliable for partitioning the RC-ABD contributions (12)(13)(14). Therefore, we applied the VM coefficients calculated during tidal breathing to the VC maneuvers: these VM coefficients remain reliable during VC maneuvers, but aLlRC + bMBD underestimate LlVoIM, especially at high volumes (13,20).…”

The effect of breath size and posture on calibration of the respiratory inductive plethysmograph by multiple linear regression

“…Calibration factors obtained from quiet breathing a nd VC manoeuvres were studied and their ability to predict momh volume and volume contributions of the rib cage and abdomen was tested. ln this respect we were especially interested in VC manoeuvres because in this condition more than two degrees of freedom are involved [14], a fact which those who apply the Respitrace often neglect to take into consideration.…”