Cessation of capillary blood flow induced by localized application of carbon dioxide

A small test area of the pulmonary capillary bed of frog's lung was exposed to carbon dioxide. The capillary bed was observed by means of a dark field episcopal microscope and recorded on video tapes via a TV-camera. Swollen capillaries forming a hexagonal network surrounded concave alveolar cells. The flow velocity of red blood cells through capillaries was reduced to 17.5% of the flow velocity during the control condition by the application of the moistened gas mixture containing 30% CO2. The blood flow in capillaries ceased when wet 100% CO2 was applied to the test area. Red blood cells were packed in capillaries. They disaggregated by the introduction of air in five seconds and were quickly flowing in an elongated leaflet shape in 30 seconds after the introduction of air.