Medical instrumentation最新文献

A rapid, inexpensive, portable technique has been developed for the qualitative and semiquantitative evaluation of in vitro flow characteristics through prosthetic heart valves. The technique combines a cardiac pulse duplicator and any diagnostic, linear sequential array, ultrasonic imaging system. The pulse duplicator has been modified to include an acoustically transparent aortic section which contains the prosthetic valve to be evaluated. The acoustically transparent section is fabricated from Rho-c rubber and enables direct flow-imaging for several centimeters on both sides of the prosthesis. Aerated tap water is used as a contrast medium. Forward and reverse flow, laminar flow complex eddy patterns, regurgitation, and jets are easily observed in real time over a wide field of view. Time-exposure photography of sequential images and subsequent off-line calculations enable point-by-point determinations of flow velocities. This work allowed preliminary evaluations of four cardiac valves: Bjork-Shiley, St. Jude, caged disk, and Starr-Edwards.

Electrosurgical return electrodes can produce heating, and occasionally burns, of cutaneous and subcutaneous skin layers. Up to now, only limited aspects of modern, dispersive, polymer electrodes have been studied using infrared thermography and thermocouples. This report presents new results on a quantitative infrared study, and adds the aspects of subcutaneous effects using microwave thermography as a third dimension. In agreement with previous work in infrared thermography, average cutaneous temperature increases observed in a dozen human volunteers were 1.5 degrees C for the normal mode, and 5.7 degrees C at near-fault (with partial contact). The intradermal and/or subcutaneous microwave thermographic images exhibited slightly lower, but still significant temperature elevations which were located at a more leading location, and were more widespread. This significant heating of subcutaneous layers, particularly of the sensitive stratum germinativum, clearly suggests the need for multiple-depth (microwave and infrared) thermography in order to evaluate the thermal performance of dispersive electrosurgical return electrodes.

Zero stability tests were performed on contrasting, commercially available, blood pressure-transducer systems. One system was based on a brand of disposable transducer. The others employed one brand of reusable transducer with and without samples of two different brands of compatible disposable domes. Drift was measured at atmospheric pressure over 3-hr periods. Drifts with the disposable transducers and with the bare reusable transducers were small, ranging from -2 to +2 mm Hg over 3 hr. However, the drifts of the reusable transducers with domes were significantly greater, ranging from -11 mm to +5 mm Hg. The disposable transducers did not drift significantly after the first half hour, although the reusable transducers with domes continued to drift. In addition, one brand of disposable dome produced inaccurate calibrations with the reusable transducer. The methodology of drift measurement and analysis should be practical and useful in other settings and with other brands of transducers. In general, the results indicate that periodic zeroing is still a clinically important procedure, and it is a worthwhile effort prior to treatment decisions based on pressure readings.

Although much additional work is needed to accurately define the physics of thermal transfer between a baby and the environment, especially with respect to convection and evaporation, it is currently possible to calculate estimates of the quantities in many conditions. These estimates are valuable in predicting the effect various design changes will have on the performance of an incubator or warmer. They also allow us to define what many of the important parameters of an infant are for heat exchange. This brings us closer to designing appropriate infant models for efficiently testing incubator or radiant warmer designs both in the factory and in medical equipment evaluation facilities and perhaps in government regulatory facilities.

The preterm newborn, although a homeotherm in the true sense of the word, has increased heat and water losses when compared to the adult and these large losses necessitate providing a thermal environment which can allow a minimal resting metabolic rate. The physician who cares for newborn infants must direct special attention to the maintenance of "normal" body temperature of the low-birth-weight infant, whose survival may depend on such careful management. However, the physiology of temperature control is important for almost every aspect of the management of these infants; the immediate adaptation to extrauterine life, requirements for oxygen and calories, growth and development, and the diagnosis of infection. An understanding of these interrelated areas is highly relevant to the successful management of a wide variety of clinical problems in the newborn period.