Regulation of blood flow in single capillaries

Abstract

A microphotometric technique recently developed by us was used to measure red cell velocity in individual capillaries of the cat mesentery. The average flow velocities differed drastically between capillaries; mean velocities as low as 0.2 mm/sec. and as high as 2.7 mm/sec. were observed. In most capillaries flow was not constant but changed greatly over the period of observation. In many capillaries (13 of the 27 studied) flow changed in an irregular fashion. In a few capillaries (3 of 27) flow was comparatively constant. In some capillaries (7 of 27) flow was rhythmic, waxing and waning from its mean value by as much as 100%. These periodic capillaries showed autoregulation, which in some cases was so pronounced as to increase mean flow velocity when arterial pressure was reduced. The periodic flow behavior appeared to be controlled by the transmural pressure rather than the flow rate. The irregular flow pattern was little affected by arterial pressure and the mean flow decreased as a function of arterial pressure. The capillaries in which flow was relatively constant showed a high degree of autoregulation and reactive hyperemia.