The supply of oxygen to the tissues and the regulation of the capillary circulation

Estimated contribution of hemoglobin and myoglobin to near infrared spectroscopy

“…Further, they found more than 80% of the capillaries at rest supported RBC flow. This increase in Hct cap may be what is interpreted in many studies (Krogh, 1919, Renkin, 1983, Honig et al, 1980and Clark et al, 2008 as capillary recruitment. Consistent with these observatons, Richardson et al (2003) measured RBC velocity and flux in skeletal muscle and calculated capillary hematocrit from these two measurements in rats with chronic heart failure (CHF) and a healthy control group.…”

“…Capillary recruitment has been proposed for close to a century as one of the mechanisms that may explain the increase in diffusing capacity (DO 2 ) from rest to exercise in skeletal muscle (Krogh, 1919, Renkin, 1983, Honig et al, 1980and Clark et al, 2008. Many of the methods used by those that support the concept of capillary recruitment have several flaws such as using opaque dye which makes it difficult to see RBCs, underestimating the complexity of the tortuous three dimensional capillary network or not actually viewing the capillary network, which may lead to inaccurate conclusions.…”

The Gradient of Vascular Permeability

“…This can be attributed, in part, to posture,--for the muscles we examined bore much of the weight when the frog was qulet,--but mostly to the poor normal circulation. Krogh states that in resting frog muscle the capillary circulation is very variable and as a rule feeble, especially in the limbs (2). So often was the blood flow found to be highly irregular or nearly at a standstill on exposure of the muscle that we were forced to sacrifice frog after frog in order to obtain individuals in which, for reasons unknown, flow was good.…”

August Krogh

“…4 The study of diffusion of gases into and through tissues 8 led August Krogh to another area of research that eventually resulted in his winning the Nobel prize. He studied the capillaries 9,10 in striated muscles and found that they were arranged with such a regularity along the muscle fibers that each capillary supplied a definite cylinder of tissue (Fig. 2).…”

“…He provided evidence "pointing to the arteriomotor and capillariomotor systems being able to act in opposite direction." 10 August Krogh won the Nobel Prize in Physiology or Medicine in 1920 "for his discovery of the capillary motor regulating mechanism." The Nobel prize made August Krogh internationally famous, and he and his wife traveled to the United States in 1922.…”