Site of autoregulatory reactions in the vascular bed of cat skeletal muscle as determined with a new technique for segmental vascular resistance recordings.

An arterial and venous microcannulation technique was developed for circulatory studies in the cat gastrocnemius muscle which, based on detailed morphological and functional observations of the microvascular arrangement, seems to permit continuous recordings of pressure in arterioles (diameter approximately 25 microns) and capillary pressure. These variables in combination with measurements of arterial and venous pressure and blood flow provided a means of continuous simultaneous recordings of total as well as segmental resistances in defined sections of the vascular bed, viz. in large arterial vessels (diameter greater than 25 microns), arterioles (less than 25 microns), and on the venous side. This new technique was applied to a study of the site(s) of autoregulatory reactions along the vascular bed evoked by changes of arterial pressure over the range 50-150 mmHg. The results indicated that active autoregulation mainly occurred within arterioles smaller than about 25 microns. In larger arterial vessels concomitant moderate active smooth muscle adjustments barely balanced out the pressure-induced passive calibre changes, and the venous vessels did not seem to contribute actively to autoregulation, but exhibited a passive change in postcapillary resistance (Rven). The described pattern of response results in quite effective autoregulation of blood flow and capillary pressure (PC). The observed passive Rven change, via its effect on the pre- to postcapillary resistance ratio, seems to explain the fact that autoregulation of PC can be more efficient than flow autoregulation. The study also provided quantitative data for the level of active intrinsic vascular tone in defined consecutive sections of the muscle vascular bed at normal arterial pressure and for segmental redistributions of tone evoked by pressure alterations.