Local blood flow in kidney tissue by heat clearance measurement

Abstract

The transient response heat clearance method of Stow & Schieve for measuring local tissue blood flow was tested on dog and rabbit kidney. Heat is injected continuously into a small volume of tissue and the temperature difference between heated and unheated tissue regions is monitored. The blood flow to the tissue is suddenly stopped for a few seconds. A sudden change in time rate of change of the temperature difference is thereby produced, which is a measure of the local blood flow per unit tissue volume just before stoppage. This method was compared with a para-aminohippurate clearance method for total kidney blood flow. Satisfactory agreement was found at low blood flow. A systematically increasing divergence with increasing blood flow could be interpreted as a decreasing extraction ratio for injected heat by the blood flow in the afferent arterioles. It was concluded that the method is capable of absolute and quantitative measurement of local tissue blood flow. The method was used to calibrate in vivo the Gibbs steady state method and the calibration curve was analyzed theoretically.