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Biomedical subjects

H R Weiss

Publications and source records attributed to H R Weiss.

At least 217 records · Page 12Linked to original sources
PubMed1980

Oxygen consumption in subepicardial and subendocardial regions of the canine left ventricle. The effect of experimental acute valvular aortic stenosis.

Moderate and severe levels of experimental valvular aortic stenosis (VAS) were produced in anesthetized, open-chest dogs to determine the effects of VAS on subepicardial (EPI) and subendocardial (ENDO) blood flow, O2 extraction, and O2 consumption (MVO2). Regional flow was determined by microspheres, and O2 saturation and extraction were analyzed by a three-wavelength absorbance microspectrophotometric method. Left ventricular pressure-volume work increased by 49% in moderate and 135% in severe VAS. The ENDO:EPI flow ratio averaged 1.21 +/- 0.09 in controls and decreased to 0.90 +/- 0.16 in moderate and 0.89 +/- 0.09 in severe VAS, and coronary flow increased by 40% and 58%, respectively. O2 extraction increased with both moderate and severe VAS, with extraction being higher in the ENDO than the EPI. MVO2 increased more in severe VAS than in moderate VAS. The ENDO:EPI MVO2 ratios fell to 1.10 (moderate) and to 0.84 (severe) from 1.44 in controls. We conclude that the O2 supply and consequently the MVO2 became limited in the ENDO relative to that in the EPI by simultaneous limitation of the O2 extraction reserve and the blood flow to this region during the increased O2 requirements imposed by experimentally induced VAS.

Acute Disease↗
PubMed1979

Regional oxygen consumption and supply in the dog heart: effect of atrial pacing.

The effects of atrial pacing on the relationship of O2 supply to demand were studied on a regional basis in the dog heart. Experiments were conducted on fourteen hearts, seven in control pentobarbital-anesthetized, open-chest dogs and seven in dogs paced at 225 beats/min. Regional O2 extraction was determined by a microspectrophotometric method, and coronary blood flow was measured with radioactive microspheres. There was an 89% increase in coronary blood flow, a small but significant decrease in O2 extraction, and an increase in O2 consumption with atrial pacing. With pacing the increase in blood flow and the decrease in O2 extraction were uniform throughout the heart. In control hearts, right ventricular blood flow and O2 consumption were lower than the mean in the septal or left ventricular free wall. In the left ventricular free wall in control, the subepicardial region had a lower O2 consumption and O2 extraction than the subendocardial region. These differences were also preserved during pacing. Due to the large increase in coronary blood flow, the relationship of oxygen supply to demand was improved by atrial pacing.

Animals↗
PubMed1979

Graded flow reductions and O2 consumption of small partially ischemic region of dog left ventricle.

The relationship of O2 supply and demand was studied in a small region of a normally functioning left ventricle in 11 pentobarbital anesthetized open chest dogs. A small myocardial vein was catheterized for flow and venous O2 content measurements. An electromagnetic flow probe and screw-type occluder were placed on the supply artery. Arterial flow reductions produced a lesser decrease in venous outflow. This indicated that collateral channels were functional even with relatively small reduction in arterial flow. Even with complete arterial blockage, venous flow never fell below 13.7% of control. Supply had to be reduced to 80.8% of control before we could predict with 95% confidence that O2 demand would fall. Using this technique, it would be possible to test antianginal agents' actions on the O2 supply and demand relation in a region of flow restricted myocardium.

Animals↗
PubMed1979

The effects of mild normovolemic hemodilution on regional flow, oxygenation, and small vessel blood content in the rabbit heart subjected to acute coronary occlusion.

The effect of mild hemodilution (hematocrit, 19%) on ischemic and nonischemic regions of myocardium during acute coronary occlusion was studied in 41 pentobarbital-anesthetized, open-chest New Zealand white rabbits. Blood flow in the control area determined with radioactive microspheres was unaffected by occlusion and increased 61.8% following hemodilution. The endo/epi ratio remained at about 1.0. Occlusion decreased flow in the affected region to 41% of the control myocardium, and endo/epi ratio decreased significantly to 0.76. Hemodilution raised flow in this area 84.3%. Occlusion increased small vessel blood content (a measure of open capillary density) in the ischemic region significantly. Hemodilution further significantly increased this volume in the occluded area, although the increase in the control region was not significant. Relative tissue pO2, measured polarographically, declined significantly following occlusion in the affected area. Isovolemic hemodilution did not affect relative O2 tension in either area. The data indicate that during mild hemodilution, the O2 supply-demand status of both the occluded and nonoccluded myocardial regions is maintained.

Animals↗
PubMed1978

Blood flow and relative tissue PO2 of brain and muscle: role of carotid chemoreceptors.

The effects of inspiration of low O2 and/or high CO2 gas mixtures on relative tissue PO2 and perfusion of brain and muscle were studied in 60 pentobarbital-anesthetized spontaneously respiring rats. These animals were studied in intact condition, after administration of phenoxybenzamine hydrochloride, 2 mg/kg, or after bilateral denervation of their carotid bodies. In the intact rats, the relative tissue PO2 ratio of biceps brachii to cerebral white matter always decreased after exposure to the above gas mixtures. This indicated a better maintenance of O2 supply to demand in the brain than in muscle. After either carotid denervation or alpha adrenergic blockade, this change in the ratio was no longer significant. Further, cerebral blood flow responses to these gas mixtures were attenuated (avg + 5.3%) compared to previous work in intact rats. It is concluded that the brain is best protected against hypoxia and/or hypercapnia when the carotid chemoreflex is intact.

Animals↗
PubMed1978

Changes in small vessel blood content of the rat heart induced by hypercapnic, hyperoxic or asphyxic conditions.

The small vessel blood content (SVBC) of the ventricular walls of the heart of anesthetized closed chest rats was determined using 59FeC13 to label the plasma siderophilin. SVBC was measured breathing air, 100% O2, 5% CO2 in 21% O2 and during asphyxia. The average SVBC could be ranked: air less than 100% O2 less than 5% CO2 less than asphyxia. Only the '100% O2' values were not significantly above the 'air' values. Under control conditions, SVBC of the rat heart averaged 6.77 +/-(SE) 0.23 ml blood/100 g tissue. Inhalation of 5% CO2 increased this to 8.68 +/- 0.34, while asphyxia produced a maximal response to 14.40 +/- 0.77. Comparison of SVBC were made between various regions of the ventricular walls. The only significant difference was that the right side of the septum had a lower SVBC than the left ventricular subepicardium under all conditions except CO2. These differences in SVBC are related to the number of open capillaries in the myocardium. Thus inhalation of CO2 decreases intercapillary distance while 100% O2 has no effect.

Animals↗
PubMed1978

Regional oxygen saturation of small arteries and veins in the canine myocardium.

Oxygen saturation of small arteries and veins (20-500 micron) was determined microspectrophotometrically in the hearts of 12 pentobarbital-anesthetized open-chest dogs. Hearts were removed, quick frozen in liquid propane, and O2 saturation was determined in blood vessels on a regional basis between and within ventricular walls. No significant differences existed in arterial O2 saturation between right, left, and septal walls or regionally within any wall by depth or in base-to-apex comparisons. Although there was variation in arterial saturation, it was independent of vessel size. Arteries were followed by serial section into the left ventricular wall for distances up to 7.5 mm without significant saturation change. The average venous saturations of the right, septal, and left ventricular walls were not significantly different. No regional differences in venous saturation were found within any ventricular wall in comparisons between base and apex. In the left ventricle, subepicardial venous saturation (29.8%) was significantly higher than subendocardial saturation (16.4%). In veins traced from the surface, saturation decreased with depth. Greater variability of saturation was found in small compared to large veins. The greater O2 extraction in the subendocardium may indicate a higher O2 consumption than in the subepicardium.

Animals↗
PubMed1978

Quantitative determination of regional oxygen consumption in the dog heart.

A micro-Fick method has been developed to measure the O2 consumption of different regions of an organ. The method was tested in isolated dog gracilis muscle and consisted of microspectrophotometric determination of arterial and venous O2 saturation in quick frozen tissue to determine O2 extraction and flow measured with 85Sr-labeled microspheres, with O2 consumption calculated from the product. This was compared to electromagnetically measured flow and O2 extraction determined by Van Slyke or CO-oximeter. The accuracy of the new measurement was at worst 8.7% for O2 consumption over the range tested in a single muscle. In the hearts of anesthetized open-chest dogs, right ventricular O2 consumption, 7.1 +/- 0.9 ml O2/min per 100 g, was significantly lower than left, 11.0 +/- 0.4. This gradient was related to a blood flow difference. Right ventricular base had a 51% lower O2 consumption than right ventricular apex. In the left ventricle, subepicardial O2 consumption, 9.5 +/- 0.7, was lower than that of the subenocardium, 12.1 +/- 0.7. This difference was related to a difference in O2 extraction.

Animals↗
PubMed1978

Alterations in brain and muscle oxygenation during hypovolemia and replacement with plasma substitutes in rats.

A study was conducted on the effects of mild hemorrhage-induced hypovolemia and subsequent replacement with lactated Ringer's dextran or hemoglobin solution in 52 pentobarbital-anesthesized rats. Blood loss of 1.25% of body weight had no significant effect on the blood flow or relative tissue PO2 of the white matter of the cerebral cortex. Blood flow and relative tissue PO2 of the biceps brachii muscle were lowered during hypovolemia. Volume replacement with any of the three plasma substitutes had no effect on blood flow or relative tissue PO2 of cortical white matter. They all caused partial restoration of blood flow and relative tissue PO2 in the biceps brachii muscle. Full return in the muscle was not achieved, nor were there any significant differences between the treatment groups.

Animals↗
PubMed1978

Effect of mild hypovolemia and fluid replacement on regional oxygenation, flow, and small vessel blood content in the rabbit heart.

A study was conducted on the effects of mild hemorrhage-induced hypovolemia and subsequent fluid replacement with lactated Ringer's or dextran solution on the hearts of 61 pentobarbital anethetized open-chest New Zealand white rabbits. After a blood loss equivalent to 1.25% of body weight, blood flow in the subepicardial and subendocardial regions of the left ventricular free wall was unaffected, relative tissue PO2 fell, and small vessel blood content, a measure of open capillary density, increased. No regional differences were seen after one hour. With fluid replacement, small vessel blood content returned toward control; coronary blood flow and myocardial relative tissue PO2 were unaltered. These results are best explained by an increased myocardial metabolism and a loss of blood oxygenation in hypovolemia and a return of metabolism toward control with fluid replacement. The lack of regional effects indicated that the subendocardium was no more adversely affected than the subepicardium during the experimentally induced mild hypovolemia.

Animals↗
PubMed1976

Blood flow and relative tissue PO2 of brain and muscle: effect of various gas mixtures.

The effects of inspiring low O2 or high CO2, or low-O2-high-CO2 gas mixtures on tissue perfusion and tissue Po2 of brain and muscle were studied in 76 anesthetized rats. Under control conditions, relative tissue Po2 of cerebral white matter measured polarographically averaged 16.4 mmHg and 18.7 mmHg in the biceps brachii. With low-O2 gas mixtures, tissue Po2 declined in both brain and muscle, but more in muscle. Tissue Po2 increased under high-CO2 conditions, with the brain increasing to a greater extent. Control cerebral cortex tissue perfusion averaged 23.5 ml/min per 100 g and muscle was 18.3 ml/min per 100 g measured by H2 clearance. Brain perfusion increased under all experimental conditions. Muscle perfusion did not change with low O2 alone, but increased with low-O2-high-CO2 or high-CO2 gas mixtures. Brain perfusion increased under all conditions significantly more than muscle. The brain appeared better protected compared to skeletal muscle in terms of tissue Po2 and perfusion under the stress of hypoxia and hypoxic-hypercapnia. The effects of hypercapnia are also greater on the brain.

Animals↗
PubMed1976

Effect of alpha and beta adrenergic blockade on oxygen transport in rat skeletal muscle and brain.

The effects of phenoxybenzamine HCl and propranolol HCl, 2 mg/kg, on tissue oxygen tension (PO2), perfusion and small vessel blood content of the cerebral cortex and biceps brachii muscle of anesthetized rats were determined. Perfusion and PO2 were measured polarographically and small vessel blood content was measured with 59Fe-siderophilin-labeled blood. Under control conditions PO2, perfusion and small vessel blood content averaged 15.1 mm Hg., 15.6 ml/min/100 g and 0.91 ml/100 g in brain and 15.6 mm Hg, 13.1 ml/min/100 g and 1.63 ml/100 g in muscle. After phenoxybenzamine adminstration, there was a significant increase in muscle perfusion (17.4%) and decrease in cortical PO2 (9.2%). No other factors changed significantly. Propranolol caused no significant changes in any of the above factors. Arteriolar resistance in skeletal muscle decreased after phenoxybenzamine. Small vessel blood content measurements (an estimate of open capillary density) indicate no effects on precapillary sphincters with either agent. Since some changes in metabolism were indicated with these agents, regional oxygen consumption was calculated from this data.

Animals↗