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Biomedical subjects

A Sances

Publications and source records attributed to A Sances.

At least 109 records · Page 6Linked to original sources
PubMedDate not supplied

Determination of tissue viability in experimental electrical injuries.

Electrical burns or ischemia (induced by vascular ligation) were produced in the legs of 15 anesthetized dogs to study evolution of tissue changes compared with impedance alterations. After the application of 1-ampere currents at 60 Hz, animals were monitored from 1 to 4 days. Muscle impendance was measured with frequency sweeping to determine tissue destruction. Nuclear magnetic resonance spectroscopy (phosphorus 31) was used to assess metabolic activity, and results were compared to impedance measurements. In burned limbs, 70% reduction in muscle impedance was seen, which corresponds to decreased metabolic activity (absent organic phosphates) and suggests necrosis. Visually viable tissue had impedance decreases of 25% and levels of organic phosphates slightly lower than normal. Relaxation frequencies in dogs with severe burns exceeded 80 kHz; in viable tissue, 30 to 40 kHz (normal: 30 kHz). In ischemic muscle, organic phosphates decreased rapidly (1 to 2 hours); impedance changes evolved more slowly (1 day), but they ultimately reached the same degree of severity. Measurement of impedance may be a valuable adjunct in the evaluation of electrical burns, since significant changes strongly suggest nonviability.

Animals↗
PubMedDate not supplied

Evoked potentials in experimental myelopathy.

Evoked potentials recorded from the cerebral cortex and spinal cord secondary to peripheral stimulation are reversibly reduced in amplitude by both pathologic distraction and pathologic flexion of the vertebral column. While the cerebral responses are lost within two minutes after complete occlusion of the ascending aorta, the responses recorded from the spinal cord persist without change for approximately ten minutes and then gradually disappear. During the first few minutes after aortic occlusion, changes produced by spinal distraction and spinal flexion are indistinguishable from those produced when the same maneuvers are made with the aorta patent. The responses mediated by dorsal columns and corticospinal tracts are affected in the same way by flexion and distraction, suggesting that somatosensory evoked potential recordings should be a reliable means of detecting spinal cord dysfunction during surgical procedures affecting the spinal cord. It may also be possible to differentiate a mechanical from a vascular insult by the time required for the evoked potential to become abnormal following a particular surgical maneuver.

Animals↗
PubMedDate not supplied

Exposure of rhesus monkeys to 20 000 G steady magnetic field: effect on blood parameters.

Sixteen monkeys were used in a study to determine the effects, or noneffects, of exposure to a steady magnetic field of 2 T (20 000 G). Arterial and venous blood samples were taken before, immediately after, and several weeks following the test. Blood gas analyses were made of arterial samples, and hemotologic cell data and Technicon SMAC analyses were made of venous samples. Differential and absolute white blood cell counts of segmented neutrophils and lymphocytes were considerably changed during the test, even for monkeys which were not exposed to the magnetic field. These changes have also been observed in monkeys whose environment and daily routine are modified appreciably. Eight of the 16 monkeys were tested twice: first, in the magnet with the magnet turned on, and second, two months later, in the magnet, but with the magnet turned off. A large superconducting magnet (0.63 m i. d. and 1.85 m long warm-air bore) was used, which accommodated two monkeys at one time. Paired-t tests of 45 blood parameters showed no significant differences between the two tests. Exposure to a gradient field compared with exposure to a uniform magnetic field showed no significant differences.

Animals↗
PubMedDate not supplied

The NMR blood flowmeter--design.

Two types of crossed-coil nuclear magnetic resonance (NMR) blood flowmeter detectors have been developed for the noninvasive measurement of blood flow. The first is a cylindrical coil configuration suitable for limb blood measurement. A cylindrical flowmeter (12.5 cm internal diam) operating at a nuclear resonance frequency of 3.2 MHz has been applied to measurement of flow in the forearm. The second type is the flat crossed-coil detector, which retains many of the operational advantages of the cylindrical detector, but is suitable for blood flow measurement of almost any surface of the body. Three flat crossed-coil detectors are described, operating at NMR frequencies of 9, 21.4, and 75 MHz. Two types of intermediate frequency signal processors have been used in the NMR receivers, a simple diode type, and a synchronous detector. The synchronous detector is preferred for its ease of operation and superior stability. Modular detection systems containing transmitter, receiver, post-detector signal conditioning, and power supply have been designed for all of the flat crossed-coil detectors. A self-contained synchronous detector module is included in the 21.4 and 75 MHz systems.

Animals↗
PubMedDate not supplied

The NMR blood flowmeter--applications.

Nuclear Magnetic Resonance (NMR) permits the noninvasive measurement of blood flow signals unimpaired by clothes, bandages, casts, etc. The cylindrical crossed-coil NMR blood flowmeter was used to measure blood flow through a cross-section of the human forearm. Two calibration procedures are described: one for pulsatile flows and the other for flows with a high non-pulsatile component. Flow measurements from normal arms, from limbs with arterial obstruction, arteriovenous hemodialysis fistulas or other conditions are reported. An application of the flow scanning technique for separation of flow signals from individual arteries (e.g., ulnar and radial) is described. The flat crossed-coil NMR flowmeter was applied to detect blood flow from individual arteries (e.g., brachial, popliteal, etc.). Applications of a ranging technique developed to detect signals at predetermined depths are described.

Arteriosclerosis↗