A simple construction of dual-slit red cell velocimeter

A simple method of building a dual-slit red cell velocimeter is introduced. The basis of this technique is to utilize the body of a 35-mm photomicrography camera as the photometric device, exactly centering a pair of highly sensitive photodiodes on the film plane of the camera. By this arrangement, the microvascular image can be accurately focused on the sensing windows of the photodiodes. Because this velocimeter is not based on videophotometry, it was possible to measure red cell velocity up to 30 mm/s in the benchmark test. The maximum red cell velocity actually measured in the rat mesenteric microvessels (6.0 to 48 microns in diam) was 9 mm/s.