Video courtesy of the Journal of Applied Physiology.
The Krogh cylinder is a useful model to explain the effect that changes in perfused capillary density have on capillary gas transfer and the development of the lethal corner. However except for muscle tissue, capillary configuration in other tissues is usually completely random and redundant like twigs on a tree branch. This video demonstrates how the concept of a lethal corner can exist outside of the Krogh cylinder model. In the center of the screen is an amorphic tissue mass. Capillary blood flow can be seen moving around the periphery of this mass. The central area of the tissue mass is relatively distant from the capillary blood flow. So oxygen concentration would be lowest and carbon dioxide concentration would be highest in this central area; constituting the lethal corner. If this were a glomerulus in a kidney, the patient would not be making much urine. Or if this were an area of gray matter in the brain, the patient might be stuperous or unconscious. If the situation were allowed to continue, serious complications like kidney failure or brain infarction could occur. However at a certain point when conditions are appropriate, capillaries within the tissue mass spontaneously open (perfused capillary density increases), dividing the mass into much smaller areas, thus eliminating the lethal corner.
This concept is called the compartment model ( as opposed to the Krogh cylinder model) because as perfused capillary density changes larger or smaller compartments of tissue are formed. With low perfused capillary density the compartments are big with greater potential for development of a lethal corner. With high perfused capillary density the compartments are smaller with less potential for development of a lethal corner.
This video is actually of a living lung alveolus. It dramatically illustrates how quickly capillary recruitment can change for the better or for the worse in patients with pulmonary disease.
Perfusion Theory is an educational platform for the Oxygen Pressure Field Theory (OPFT). August Krogh’s theoretical concept of the oxygen pressure field is explained and then applied to clinical applications in perfusion practice.