Distribution of the myocardial tissue PO2 in the rat and the inhomogeneity of the coronary bed.

The structural inhomogeneity of the myocardial capillary bed is stimulated by microcirculatory units (MCU's) in a diffusion model. This stimulation is based on MCU's in which the arrangement of the capillary ends (concurrent structure, partial and total countercurrent (structure, helical structure) as well as the structure and supply parameters are varied. The variation of these parameters is based on own measurements of the intracapillary HbO2 saturation as well as on the following parameters from the literature: frequency distribution of capillary distance and capillary radius, mean capillary length or capillary section length respectively, arterial and mean venous PO2, mean coronary blood flow, mean O2 consumption and diffusion conductivity. The analysis of O2 supply of the normoxic rat heart shows that an O2 diffusion shunt is obligatory except of MCU's with an extremely large capillary distance or with a concurrent capillary structure. Therefore the minimal tissue PO2 lies at the level of the capillary venous PO2 of a MCU. The maximum of the total PO2 frequency distribution in the normoxic rat myocardium lies at 25 +/- 5 mm Hg, i.e. above the mean venous PO2 (20 mm Hg). Tissue PO2 values between 0 and 5 mm Hg amount to 0.5% i.e. they are extremely rare. Tissue PO2 values of 0-1 mm Hg represent less than 0.2%.

Myoglobin-O2-saturation profiles in muscle sections of chicken gizzard and the facilitated O2-transport by Mb+.

It has been shown that the oxygen transport in intact muscle can be quantitatively determined using Mb as an oxygen indicator in the cryomicrophotometric method. 1) The influence of the parameters such as time, temperature, boundary PO2 and metabolism on the oxygen transport in sections of chicken gizzard could be quantitatively determined from measured MbsO2-profiles; 2) The MbsO2-profiles measured under various conditions can be reproduced using a mathematical model which considers not only the diffusion of dissolved O2 but also the facilitated diffusion as well as O2 consumption. From this mathematical results it can be concluded that the mobility of the Mb in the muscle cells is limited and that Mb in the PO2-region between 5 and 0 mmHg contributes to at most 40% to the total O2-transport in chicken gizzard.

Intracapillary HbO2 saturation in tumor tissue of DS-carcinosarcoma during normoxia.

The measurements of the intravascular HbO2 saturation in tumor capillaries using the cryophotometric micromethod reveal that very low HbO2 saturation values predominate in malignant tumors. Under normoxic conditions only 8% of the measured values exceed 50% saturation. 53% of the intracapillary HbO2 saturation values are in the range of 0-10% HbO2 saturation. Great regional differences are seldom and can be found only in areas where a sufficient vascularization still exists. Taking into account the data of morphometric analysis of tumor vascularization and the parameters of respiratory gas exchange, the measured frequency distribution of HbO2 saturation values in tumor capillaries is simulated by means of different three-dimensional capillary structures; On the basis of these microcirculatory units, tissue pO2 values are computed in the intercapillary regions. As a result of these calculations it can be stated that the computed data derived from intracapillary HbO2 saturations are in sufficient agreement with pO2 values measured polarographically using gold- microelectrodes.

[Determination of intracapillary HbO2 saturation with a cryo-microphotometric method, applied to the rabbit myocardium (author's transl)]. / Die Bestimmung der intracapillären HbO2-Sättigung mit einer kryo-mikrofotometrischen Methode angewandt am Myokard des Kaninchens

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%.