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M P Wiedeman

Publications and source records attributed to M P Wiedeman.

At least 19 recordsLinked to original sources
PubMed1986

Considerations in use of microspheres for flow measurements in anesthetized rat.

The results of single injections of different doses of microspheres (60,000, 100,000, and 375,000) demonstrated a significant reduction in measured heart and kidney blood flows as a function of the number of microspheres injected. Measured flow to other organs was unaffected by a single injection of these doses of microspheres. The injection of microspheres at a faster rate (0.8 ml/min microsphere injection; 1.0 ml/min flush) resulted in higher calculated heart flow when compared with the slow rate (0.2 ml/min microsphere injection; 0.25 ml/min flush). A significant decrease (approximately 21%) in measured blood flow to the right side of the brain that was observed in all the groups is due to the occlusion of the right carotid artery by the cannulation procedure. Intra-aortic injection of microspheres resulted in reduced measured brain blood flow when compared with intraventricular injections. Accurate and reliable heart and brain blood flows were not obtained with intra-aortic injection of microspheres. However, intra-aortic injection of microspheres does provide accurate and reliable flow measurements for more distal organs.

Anesthesia↗
PubMed1985

Origin and time course of gas bubbles following rapid decompression in the hamster.

Because conflicting results have been obtained in studies of the hamster (Mesocricetus auratus) microcirculation following rapid decompression, we were interested in the origin of bubbles in the cheek-pouch preparation. The hamster cheek-pouch and surgically exposed femoral vessels were observed under the microscope, before and immediately following rapid decompression. The animals were placed in a hyperbaric chamber and exposed to an increased pressure of 7 ATA for 1 h. They were then decompressed at a rate of 18 m/min until reaching 1 ATA. This hyperbaric exposure produced an LD50 in 100 hamsters examined in this study. In 40% of these animals "bubbles" were seen entering the cheek-pouch artery after a delay of from 3 to 6 min following decompression. Before observing bubbles in the cheek-pouch artery, bubbles were always seen in the femoral vein. Those animals that had observable bubbles in the cheek-pouch usually demonstrated a tachypnea, followed by gasping and apnea. When bubbles were seen in the arterial circulation, few animals survived for more than 10 min following the hyperbaric exposure. Postmortem examination of these animals revealed massive gas emboli in the large venous vessels, right ventricle, and fewer bubbles in the left ventricle. Postmortem examination of surviving animals revealed that the majority of the gas was in the venous vessels and right heart. These data support the hypothesis that bubbles first form on the venous side of the circulation and, if they exceed a certain volume, move through the pulmonary circulation into the systemic arterial vessels.

Animals↗
PubMed1977

Relationship between microvascular blood velocity and pressure distribution.

Red blood cell velocity and diameter were measured in vessels of the wing of the unanesthetized bat (Myotis lucifugus) from the supplying artery to the capillaries. These data were used to determine the manner in which velocity, shear rate, volume flow, and blood pressure depend on the vessel's hierarchical position within the vascular network. The results show that velocity decreases in an almost linear fashion as the capillary is approached but that the shear rate increases as one progresses distally from the supplying artery. Blood volume flow was found to decrease as an exponential function of the branching order. Comparison with available date in some animal species, including man, indicates some agreement in capillary velocity, although significantly lower values have been reported in some preparations. Using a method whereby blood pressure distribution could be obtained from anatomical data and center-line blood velocity, the rheologic alterations accompanying consecutive vessel branching were deduced and found to be in good agreement with data available in the literature.

Animals↗