Negative wave reflections in pulmonary arteries

Abstract

The pulmonary arterial branching pattern suggests that the early systolic forward-going compression wave (FCW) might be reflected as a backward-going expansion wave (BEW). Accordingly, in 11 open-chest anesthetized dogs we measured proximal pulmonary arterial pressure and flow (velocity) and evaluated wave reflection using wave-intensity analysis under low-volume, high-volume, high-volume + 20 cmH2O positive end-expiratory pressure (PEEP), and hypoxic conditions. We defined the reflection coefficient R as the ratio of the energy of the reflected wave (BEW [−]; backward-going compression wave, BCW [+]) to that of the incident wave (FCW [+]). We found that R = −0.07 ± 0.02 under low-volume conditions, which increased in absolute magnitude to −0.20 ± 0.04 ( P < 0.01) under high-volume conditions. The addition of PEEP increased R further to −0.26 ± 0.02 ( P < 0.01). All of these BEWs were reflected from a site ∼3 cm downstream. During hypoxia, the BEW was maintained and a BCW appeared ( R = +0.09 ± 0.03) from a closed-end site ∼9 cm downstream. The normal pulmonary arterial circulation in the open-chest dog is characterized by negative wave reflection tending to facilitate right ventricular ejection; this reflection increases with increasing blood volume and PEEP.