Medical instrumentation最新文献

We compared the parameters describing the defibrillation threshold in patients with normal hearts and in patients with ischemic heart disease, using a special electrode system and sequential pulses of current. Twenty-eight patients consented to the study (mean age: 36.6 +/- 10.1 years; mean mass: 80.7 +/- 13.8 kg). Twenty-one patients underwent surgery for Wolff-Parkinson-White syndrome (relatively normal hearts). Six patients had a history of previous myocardial infarction and aneurysm or coronary artery disease; and one patient had been resuscitated from an episode of sudden death, without evidence of consequent myocardial damage. For 26 patients, defibrillation thresholds were determined intraoperatively by passing sequential pulses through a catheter electrode and epicardial mesh electrode. For 2 patients defibrillation thresholds were determined during electrophysiologic study, after ventricular fibrillation was induced by programmed stimulation, by passing sequential pulses through a catheter and skin-patch electrode. Parameters for sequential pulse defibrillation thresholds between the two groups did not differ appreciably. Total energy for patients with normal hearts averaged 9.9 +/- 6.3 J compared to 8.9 +/- 4.6 J for patients with cardiac disease. No patient with cardiac disease had defibrillation parameters that exceeded the range of the normal patients. These results suggest that the presence of cardiac disease may not significantly alter the parameters necessary for successful defibrillation when using sequential pulses for delivery of energy.

There are many clinical situations that present the need for special purpose electrocardiography using standard equipment. These include monitoring cardiac activity from temporary myocardial leads implanted following cardiac surgery, detecting signals from intracardiac catheter leads, and noninvasive atrial recording from the esophagus. It is often difficult to connect nonstandard leads and access the individual amplifiers. In this article, we present the case for an esophageal electrode such as the Pill Electrode (Arzco Medical Electronics, Inc., Chicago, IL). We describe several configurations for connecting this electrode to electrocardiographs and comment on the merits and shortcomings of each method.

Most commercially available aerosol generators widely used in medical applications produce aerosols characterized by a large mass median diameter in the 4-8 micron range and the particle size in the 0.1-10.0 microns range. The desirable size of therapeutic and diagnostic aerosols, however, is about 2-4 microns mass median diameter, and less than 2.0 geometric standard deviation; this size increases the reproducibility of inhalation tests and enhances drug efficacy. We combined the commercially available DeVilbiss Model 65 nebulizer with a dilution/mixing chamber developed in our laboratory. The characteristics of this aerosol generator system were examined over a range of operating conditions and concentrations of solutions of three bronchoconstrictive agents--histamine, carbachol, and methacholine. The aerosol generator system produced a polydispersed aerosol with a mass median diameter range of 1.7-2.4 microns and geometric standard deviation of 1.5. The reliable and reproducible operation of the aerosol generator system greatly increases the power of bronchial challenge tests with bronchoconstrictive drugs.

A new continuous-wave Doppler device is described, which has the capability of measuring peak aortic blood velocity and acceleration noninvasively in the ascending aorta of patients. To test the accuracy of the device, blood velocity and acceleration in the ascending aorta were compared with measurements obtained using an electromagnetic flowmeter in 16 open-chest anesthetized dogs. The Doppler probe was hand held directly on the aorta. Aortic flow was measured with a cuff electromagnetic flow transducer placed at the root of the aorta. Isoproterenol and propranolol, sometimes in combination with lidocaine, were administered intravenously to augment or reduce left ventricular contractile performance. Values of peak velocity, measured with the Doppler, corresponded closely to values measured with the electromagnetic flowmeter (r = 0.95). Values of peak acceleration also corresponded closely with the electromagnetic flow measurements (r = 0.96). The results indicate that valid measurements of blood acceleration in the ascending aorta, as well as blood velocity, can be obtained with continuous-wave Doppler.

A quantity termed the "threshold" has been used to describe the results of electrical ventricular defibrillation studies, with the implication of a clear distinction between ineffective and effective shock intensities. Although several definitions of the threshold have been suggested, and various methods have been used to quantify it, no comparison of the accuracies of the various methods could be found in the literature. This article, after presenting a method of applying basic probability theory to an assumed distribution relating probability of successful defibrillation to current amplitude, uses the method to examine several popular algorithms for defibrillation-threshold determination. The results show that where a sharp transition exists from ineffective to effective current amplitudes, most algorithms yield fairly good results. Where that transition is gradual (as it appears to be in all of the published reports examined), the algorithms are shown to be inadequate.

A communication instrument has been developed for use by a quadriplegic person who is limited solely to eye motion as a control input. The instrument uses an infrared-emitting diode/phototransistor sensor mounted on the frame of a pair of eyeglasses to transform deliberate lateral eye motion into a contact-closure output form. A software program has also been developed for use with this instrument to display letters of the alphabet in a series of six lines. The lines are slowly scrolled until the desired line is reached, then stopped by a lateral eye motion. The scrolling then continues for each character in that line until the desired character is reached. Again, lateral eye movement causes the scrolling to stop and the character becomes part of a string. This process continues until a command character is selected whereby the string can be sent to a printer, spoken through a speech synthesizer, or erased.

The efficacy of defibrillation using the damped sine and constant-tile (60%) truncated exponential waveforms was determined in each of nine dogs. Two measures of efficacy were used to compare the two waveforms: 1) threshold defibrillation current and 2) percent successful defibrillation. For both measures of efficacy, shock strength was expressed in terms of delivered energy. Mean threshold energy was 0.98 J/kg for the damped sine wave and it was 1.24 J/kg for the truncated exponential waveform. Percent successful defibrillation versus energy/kg curves were constructed for each of the waveforms and were found to be essentially the same. Percent successful defibrillation increased with increasing shock intensity. For 50% success, the energy for the damped sine wave was 1.16 J/kg; for the truncated exponential wave, the corresponding value was 1.15 J/kg. A shock of threshold intensity successfully defibrillated in approximately 50% of the defibrillation attempts, i.e., defibrillation threshold corresponds to about 50% successful defibrillation.

Hyperthermia, the intentional elevation of tissue temperature above 41 degrees C, is being intensely researched as a therapeutic modality for cancer, especially when used in combination with radiation therapy and/or chemotherapy. A serious impediment to laboratory progress in this area has been the lack of affordable equipment providing control and reproducibility when faced with highly variable factors including tumor size and shape, blood flow, heat conduction, and tissue dielectric discontinuity. Our solution has been the development of a laboratory microwave hyperthermia system, dedicated to the treatment of small, superficial tumors. This system uses a 2.45-GHz microwave generator and custom applicator to noninvasively heat a mass of tissue about 2 cm in diameter and 1.5 cm in depth. Tissue temperature at up to four locations is measured using miniature. Teflonencased thermocouples. The microwave generator and the thermometry are interfaced to a personal computer which provides fully automated hyperthermia treatment reproducible to +/- 0.2 degrees C.