Microvascular blood flow distribution in skeletal muscle. An intravital microscopic study in the rabbit.

: Distribution patterns of the microvascular blood flow and interactions of various microvascular elements were studied in the tenuissimus muscle of the rabbit with the aid of intravital microscopy. The modified technique employed permitted observation, with high resolution, of the microcirculation in the tenuissimus muscle in situ, with only minor surgical preparation and incision. Preparation and exposure of the muscle for vital microscopy did not alter the resting blood flow and did not limit the normal range of vascular control. Microvascular flow data agreed well with the whole organ blood flow and the vascular smooth muscle reacted vigorously to various stimuli. In the resting state one-third to one-half of the total number of capillaries were considered to be perfused, with a homogeneous spatial distribution. The average capillary red cell velocity at rest was less than 20% of the average maximal velocity. Alterations in the ambient oxygen tension to which the muscle tissue was exposed resulted in profound changes in capillary perfusion. These were mainly attributed to changes in the number of perfused capillaries, whereas changes in red cell velocity were of less significance. However, an increase in red cell velocity was considered to contribute substantially to the capillary flow response in situations with a markedly increased blood flow. The proportion of capillaries being perfused seemed to be a passive function of the pressure gradient over the capillary bed, in combination with a yield stress in the capillaries controlled by the arteriolar resistance. Apparently the active control of functional capillary was not anatomically separated from that of capillary flow velocity. The ultimate control of the capillary perfusion resided in the terminal arterioles, although the capillary flow was influenced also by the resistance in the proximal arteriolar segments. Vascular connections between the muscle tissue proper and adjacent connective tissue were a regular and frequent phenomenon. A majority of the transverse arterioles also supplied, in addition to the muscle capillaries, the connective tissue. The distribution of the arteriolar flow between these two vascular areas was determined by the interaction between the larger transverse and smaller terminal arterioles and their relative contributions to the vascular resistance. The terminal arterioles were clearly more responsive than the transverse arterioles to changes in ambient oxygen availability.(ABSTRACT TRUNCATED AT 400 WORDS)