Blood flow switching among pulmonary capillaries is decreased during high hematocrit.
Pulmonary capillary perfusion within a single alveolar wall continually switches among segments, even when large-vessel hemodynamics are constant. The mechanism is unknown. We hypothesize that the continually varying size of plasma gaps between individual red blood cells affects the likelihood of capillary segment closure and the probability of cells changing directions at the next capillary junction. We assumed that an increase in hematocrit would decrease the average distance between red blood cells, thereby decreasing the switching at each capillary junction. To test this idea, we observed 26 individual alveolar capillary networks by using videomicroscopy of excised canine lung lobes that were perfused first at normal hematocrit (31-43%) and then at increased hematocrit (51-62%). The number of switches decreased by 38% during increased hematocrit (P < 0.01). These results support the idea that a substantial part of flow switching among pulmonary capillaries is caused by the particulate nature of blood passing through a complex network of tubes with continuously varying hematocrit.
Baumgartner
William A
WA
Department of Anesthesia, Indiana University School of Medicine, 635 Barnhill Dr., Indianapolis, IN 46202-5120, USA.
Peterson
Amanda J
AJ
Presson
Robert G
RG
Tanabe
Nobuhiro
N
Jaryszak
Eric M
EM
Wagner
Wiltz W
WW
D000818:Animals; D001794:Blood Pressure / Q000502:physiology; D002196:Capillaries / Q000502:physiology; D004285:Dogs; D006400:Hematocrit; D066298:In Vitro Techniques; D008168:Lung / Q000098:blood supply*; D008297:Male; D010477:Perfusion; D011652:Pulmonary Circulation / Q000502:physiology*