The effects of diffusion and ultrafiltration on cardiac output and organ blood flows.

The effects of diffusion and ultrafiltration on cardiac output (CO) and organ blood flow (BF) in the uraemic dog were studied by a modified microsphere technique. In the diffusion phase of sequential therapy, a decrease in mean arterial pressure (MAP) and total peripheral resistance (TPR) was noted despite no change in circulatory plasma volume (CPV) and CO. In the ultrafiltration (UF) phase, MAP recovered with an increase in TPR despite the decrease in CPV and CO. Muscle vascular resistance increased in UF phase but not in the diffusion phase. The results suggest that the decrease in CPV through UF resulted in CO decrease, but that the compensation mechanism for the decrease is impaired by diffusion.