title: Some factors of significance for respiratory gas exchange in muscle tissue. A mathematical analysis of a capillary model.
abstract: Morphological dimensions of the Krogh cylinder capillary model were calculated by mathematical simulation of respiratory gas exchange and blood flow in muscle tissue, using experimentally determined values for oxygen consumption (n'O2), blood flow (Q'), a-V O2 difference (a-v O2D) and pressure difference over the capillary (delta P), for resting and exercise conditions up to maximum performance. In the resting state a capillary radius, r1, of 3.5 (3-5) microgram a capillary density (CD) of 35 (30-90) capillaries/mm2 and a capillary length (L) of 900 (400-1000) microgram can satisfy experimentally determined values of the physiological variables. During muscular activity a maintained r1 and L with an increased CD allows higher n'O2. An increase in capillaries to about 600/mm2 can allow an n'O2 uptake 30 times the resting value (maximum performance). This increase cannot be achieved by an increase only in the r1. A shift to the right in the O2Hb dissociation curve during exercise has only a small effect on the O2 delivering capacity of the model, as has an increase in the diffusion constant for O2 in tissue. It is remarkable how limited a range of morphological dimensions, particularly of r1, is compatible with the known range of values for n'O2, O', a-v O2D and delta P, at rest and particularly during maximum performance of the muscle.
mesh_terms: D002199:Capillary Permeability; D006801:Humans; D008433:Mathematics; D008954:Models, Biological; D009132:Muscles / Q000098:blood supply / Q000378:metabolism*; D010101:Oxygen Consumption; D005082:Physical Exertion; D012146:Rest; D014655:Vascular Resistance