Continuously accelerating decay limbs in indicator dilution curves

¹ Thorndike Memorial Laboratory and the Second and Fourth (Harvard) Medical Services, Boston City Hospital; and Department of Medicine, Harvard Medical School, Boston, Massachusetts

Indicator dilution curves with continuously accelerating decay limbs have been produced in a model and in man by increasing flow during the dilution process. Curves of similar configuration were obtained in a model when two sequential chambers with large ratios of residual to total volume were traversed by indicator. Flow estimates computed from curves distorted by large volumes had only a small error, but those from curves distorted by increasing flow were unreliable. An analysis of 30 curves in cardiovascular normals and of 24 curves in 19 patients with mitral or pulmonic stenosis revealed continuously accelerating decay limbs in one and 13 curves, respectively. This high incidence was attributed to the large volumes occurring with valvular stenosis. A mathematical relationship is presented which defines both the contour of any dilution curve from single or double chamber unidirectional flow systems and the magnitude or the change in magnitude of the ratios of residual to total volume required to produce continuously accelerating decay limbs.