Does respiratory motion change with patient posture?

Objectives Changes in the appearance of SPECT cardiac-perfusion studies have been anecdotally observed when patients are imaged sitting upright as compared to the supine position. One possible contributor is a difference in the respiratory motion of the heart with posture. In supine imaging with arms over the head the abdominal component of respiratory motion is known to dominate. We hypothesized that the chest component of respiration contributes more than the abdominal component when patients are sitting upright vs. laying supine, and this may cause a difference in cardiac motion.

Methods The respiratory motion of volunteers positioned for supine imaging on the Philips BrightView XCT and upright imaging on the Digirad Cardius X-ACT was tracked for 5 minutes by bellows wrapped about their chest and abdomen. The average variation between end-inspiration and end-expiration were determined, and the chest-to-abdomen ratio of this variation was calculated for each volunteer. The upright-to-supine ratio of the chest-to-abdomen ratios was then employed to investigate possible changes with posture.

Results There was considerable variation in the chest-to-abdomen ratio between volunteers. However, for every volunteer the chest-to-abdomen ratio was larger in the upright position then supine. The average, lowest, and highest upright-to-supine ratios were 6.02, 24.05 and 1.38 respectively, among 12 volunteers (average BMI 24.5) studied thus far. With IRB approval list-mode acquisitions synchronized with bellows acquisition will be employed to investigate the visual appearance of heart motion in upright vs. supine positions.

Conclusions The chest component of respiration increases from a supine to a sitting posture, in some cases dramatically.

Research Support NIH R01 EB00145