[Method for the determination of local intracapillary hemoglobin saturation]

[Determination of intracapillary HbO2 saturation with a cryo-microphotometric method, applied to the rabbit myocardium (author's transl)]

We succeeded in determining the O2 saturation of Hb in capillaries of the rabbit myocardium with a cryo-microphotometric method. Myocardial samples (2-3 mm) were removed in situ with a pair of nitrogin-cooled copper tongs, and rapidly frozen in Freon 13. The samples were sectioned into 10-12 mum slices in a cryotome at about minus 60 degrees C. Hemoglobin absorption spectra were measured on the capillary sections of the frozen slices at minus 100 degrees C in a vacumm-isolated microscope cooling chamber which we developed for the UMSP 1 (C. Zeiss, Oberkochen). The spectra were subdivided into three basic components (oxygenated Hb, desoxygenated Gb, and desoxygenated dehydrated Hb) with a weighted multi-component analysis (Lübbers and Wodick, 1969). The basic components were measured in Hb solutions. The accuracy of the method was tested both with Hb solutions inserted into glass capillaries, and Hb droplets. O2 saturations of the Hb solutions were measured at room temperature. Subsequently, both test solutions were frozen, HbO2 saturation measured in the glass capillaries at low temperatures agreed well with those recorded at room temperature. HbO2 saturation of the sectioned hemoglobin droplets was found to be systematically increased with low Hb32 saturations as compared with the records made at room temperature. The systematic error was determined and the intracapillary HbO2 saturations were corrected accordingly. Measurements on samples of the rabbit myocardium showed that the histogram of capillary HbO2 saturations has a maximum at saturations of 20-30%. The lowest saturation values were found to be between 0 and 10%, but these values were recorded less frequently. The arterial HbO2 saturation in the femoral artery was about 98%.