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Biomedical subjects

Z Turek

Publications and source records attributed to Z Turek.

At least 55 records · Page 3Linked to original sources
PubMed1985

The effect of heterogeneity of capillary spacing and O2 consumption--blood flow mismatching on myocardial oxygenation.

The effect of heterogeneity of capillary spacing on myocardial oxygenation was estimated for various sizes of tissue cylinder radii ranging from 8 to 18 microns, which are the values expected from the histological measurements. Similarly, the effect of mismatching between myocardial oxygen consumption and capillary blood few was analyzed. The results are summarized in charts which demonstrate that both heterogeneities are important independent tissue oxygen determinants irrespective of the mean values of these parameters. Therefore they should be included in any future evaluation of the oxygen supply to tissue.

Animals↗
PubMed1985

Protamine inhibits capillary formation in growing rat hearts.

Various indices of capillary supply to the rat heart were studied in neonatal rats injected for 2 or 4 weeks with protamine sulfate in saline (subcutaneously, 60 mg/kg body weight, 2 times/day). Cardiac capillarization was evaluated not only by traditional indices for the capillary supply, such as mean capillary density and myocyte-to-capillary ratio, but also by a more advanced morphometric method of capillary domains. This method allows the estimation of both the average radius of the Krogh tissue cylinder and its variability, which reflects the heterogeneity of capillary spacing found to be an independent morphological determinant of oxygen diffusion in the tissue. The results were evaluated with respect to regional differences (subendocardial vs. middle section), age differences, and the effect of protamine. No regional differences in capillary supply were found in this experimental situation. Hearts from older rats had significantly decreased capillary supply, expressed as lower capillary density, larger capillary domains, and greater radius of the tissue cylinder. On the other hand, the heterogeneity of capillary spacing decreased significantly with age. Protamine-injected animals, when compared to their control littermates, had a significantly higher cell-to-capillary ratio, lower capillary density, larger capillary domains, greater radius of the tissue cylinder, and larger variability in capillary spacing. Thus, protamine was effective in impeding rapid capillary growth in the hearts from rats in the early postnatal period. Close to half of all the existing capillaries in the adult rat hearts are formed during the first 3-4 postnatal weeks.

Animals↗
PubMed1984

The effect of blood O2 affinity on the efficiency of O2 transport in blood at hypoxic hypoxia.

An index of the efficiency of O2 transport in blood and delivery to tissues, the capacitance coefficient beta, was theoretically analyzed as a function of the position of the blood O2 dissociation curve (ODC). The P50 at which beta reaches its maximum is high at normoxia and decreases with lowering the ambient PO2. At very deep hypoxia this value becomes lower than the normal P50 of human blood. An increase of blood O2 capacity enlarges beta, particularly at deep hypoxia, and also increases the P50 at which maximal beta is reached. Changes of (a-v)O2 have ambivalent effects, depending on both P50 and PaO2. The capacitance coefficient beta was further calculated as a function of PaO2 at three values of P50, simulating the effect of a shift of the ODC. The capacitance coefficient is several times higher at deep hypoxia than at normoxia at all values of P50 used. A shift of the ODC to the left results in a moderate decrease of beta at mild hypoxia but in a large increase at severe hypoxia; a shift to the right has a reverse effect.

Animals↗
PubMed1984

The effect of cell size and capillary spacing on myocardial oxygen supply.

Recently, we collected basic morphometric data from normal and hypertrophic rat hearts: median and mean values of the cell diameter and of the intercapillary distance as well as their variabilities. In the present communication we used these data, first for analysis of the effect of the heterogeneity of capillary spacing on the myocardial tissue PO2. Comparison of tissue PO2 histograms calculated for a situation in which the capillaries are evenly distributed as in the Krogh model, with a situation based on the same capillary but variable intercapillary distances clearly demonstrates the importance of heterogeneity of the capillary spacing as a separate oxygen determinant. This is even more important in the hypertrophic hearts which are characterized by longer and more variable intercapillary distances. In the second part, we compared the classical Krogh model with a model of concentric diffusion in which the oxygen consumption was either uniform or divided into two zones of distinctive rates. Oxygen profiles calculated for the Krogh model with excentric diffusion were similar to those derived for the two models of concentric diffusion.

Animals↗
PubMed1981

[Thermodynamic analysis of oxygen/transport to the turtle heart].

Isolated turtle hearts were perfused, at constant flow, with human erytrocytes suspensions containing different levels of 2,3-DPG. PO2 measurements, in the blood leaving the heart, resulted in lower figures when the tissue was perfused with low affinity blood compared with perfusion of high affinity blood. Thermodynamic analysis was, also, carried out at four different levels of temperature. The results suggest that, in severe hypoxia, oxygen delivery to the tissue is increased when perfusion is performed with high oxygen affinity blood.

Animals↗
PubMed1981

Lognormal distribution of intercapillary distance in normal and hypertrophic rat heart as estimated by the method of concentric circles: its effect on tissue oxygenation.

The inhomogeneity of the capillary net in the cardiac muscle was estimated using our morphometric measurements in normal and hypertrophic rats hearts. As entry data we used the distribution of tissue at different distances from the nearest capillary as measured by the method of concentric circles and the mean intercapillary distance independently calculated from the capillary density. The derived distribution of intercapillary distances was approximated by lognormal distribution in which the spread can be characterized by a single parameter, namely the log standard deviation. The effect of the log standard deviation on tissue oxygenation was evaluated in normal and hypertrophic hearts, at normoxia and at hypoxia. The mean tissue PO2 and the percentage of anoxic tissue at the venous end of the tissue cylinder were calculated using Krogh's model. Two boundary situations were considered: A) the end-capillary PO2 was assumed to be equal in all capillaries due to compensatory adjustment in blood flow; B) the same flow in all capillaries was assumed resulting in varying end-capillary PO2. The real situation is expected to be between situations A and B. Increased variability of intercapillary distance proved to impair considerably the tissue oxygenation, especially when the results were expressed as a percentage of anoxic tissue. The percentage of anoxic tissue turned out to be a better index of tissue oxygenation than the mean PO2 particularly at hypoxia. The results suggest the presence of at least a partial adjustment of blood flow with respect to the width of tissue cylinder. Without such adjustment, a large part of tissue would become anoxic already in normal hearts at normoxia and this would be further aggravated by hypertrophy and/or hypoxia.

Animals↗
PubMed1981

Myocardial capillaries in guinea pigs native to high altitude (Junin, Peru, 4,105 m).

Quantitative evaluation of the myocardial left ventricular capillarity was performed in three groups of guinea pigs: a) animals native to high altitude collected in Andean mountains, b) animals born at sea level and subjected to a stimulated high altitude postnatally, c) animals born and kept at sea level. The number of capillaries and muscle fibers/mm(2) as well as the fiber capillary ratio and the diffusion distance were similar in all three experimental groups. The only difference found during the detailed analysis of the myocardial capillarity was a slightly lower percentage of the myocardial tissue in the extreme distance from the capillary found in the hearts of high altitude natives when compared to sea level animals. From these morphometric data the distribution of diffusion distances was derived which can be approximated by lognormal distribution. Capillary inhomogeneity expressed as log standard deviation was found to be similar in all three groups.

Adaptation, Physiological↗
PubMed1981

Effect of shifts of the O2 dissociation curve upon alveolar-arterial O2 gradients in computer models of the lung with ventilation-perfusion mismatching.

The effect of a shift of the blood O2 dissociation curve (ODC) on the alveolar-arterial O2 gradient was studied in computer models of the lung with several degrees of VA/Q inequality during air breathing. A shift to the left decreases and a shift to the right increases not only the mixed-venous but also the arterial PO2. Consequently the alveolar-arterial O2 gradient is larger with a left and smaller with a right shift of the ODC. This effect of a shift of the ODC on the alveolar-arterial O2 gradient is negligible in a healthy lung but becomes quite considerable in a diseased lung with a severe mismatching of VA/Q.

Animals↗
PubMed1979

Effect of variations in blood hydrogen ion concentration on pulmonary gas exchange of artificially ventilated dogs.

The effect of variation of blood hydrogen ion concentration on arterial and mixed venous PO2, ideal alveolar-arterial O2 pressure difference (PAiO2--PaO2), venous admixture (Qs/Qt), arterio-alveolar CO2 pressure difference (a--A)DCO2, physiological dead space to tidal volume ratio (VD/VT), cardiac output (Qt) and mean pulmonary arterial pressure (PAP) has been studied. Arterial and mixed venous PO2 increased and (PAiO2--PaO2) decreased with increasing blood hydrogen ion concentration. No change in Qs/Qt, (a--A)DCO2, VD/VT, Qt and PAP was observed. The effect of hydrogen ion concentration on arterial and mixed venous PO2 and on (PAiO2--PaO2) is mainly due to a shift of the blood oxyhemoglobin dissociation curve (ODC), i.e. due to the Bohr effect. The upper part of the ODC is more flat in alkalosis (shift to the left) than in acidosis (shift to the right). Therefore the same end-capillary to arterial O2 content difference results in a greater (PAiO2--PaO2) in alkalosis than in acidosis. Any factor influencing the slope of the upper part of the ODC is expected to affect the arterial PO2 and the (PAiO2--PaO2) by this mechanism. Similarly any factor shifting the steep part of the ODC is expected to affect the PO2 of the mixed venous blood.

Animals↗