Morphometric characterization of the capillary network in the cat's brain cortex: A comparison of the physiological state and hypovolemic conditions

Summary

Histotopochemical and morphometric investigations were used to determine the following average values of capillary parameters in the cat's brain cortex: diameter$\bar D_i$, percentage of the projected area${{\bar A^0 } \mathord{\left/ {\vphantom {{\bar A^0 } {_{0^{Ai} } }}} \right. \kern-\nulldelimiterspace} {_{0^{Ai} } }}$, surface-to-volume ratio${{\bar S_i } \mathord{\left/ {\vphantom {{\bar S_i } {\bar V_i }}} \right. \kern-\nulldelimiterspace} {\bar V_i }}$, free distances between capillary surfaces$\bar \lambda$ and length per unit brain volume$\bar L_{Vi}$. These overall average values per stereotaxically defined brain region of 6 control and 6 hypovolemic animals were calculated by a computer.

The hypovolemic condition was achieved by reducing the systemic arterial blood pressure to 50 mm Hg. The resulting hypovolemia caused a significantly diminished diameter$\bar \bar D_i$, a highly increased length per unit brain volume$\bar \bar L_{Vi}$ and an improved surface-to-volume ratio${{\bar \bar S_i } \mathord{\left/ {\vphantom {{\bar \bar S_i } {\bar \bar V_i }}} \right. \kern-\nulldelimiterspace} {\bar \bar V_i }}$ of cortical capillaries. The behaviour of these 5 morphometric parameters during hypovolemic oligemia in the cat's brain cortex leads to the conclusion, that an adapted state of the capillary network may be a response to a reduced blood volume and blood pressure.