Medical instrumentation最新文献

Intracranial aneurysms have a high prevalence in the adult population; and if they rupture, significant morbidity almost always ensues. However, pulsatile blood flow through aneurysms produces vibrational sound patterns that may be detected extracranially. Thus, an acoustic aneurysm-detector has been developed to detect the sounds produced by intracranial aneurysms prior to rupture. The design is based on the utilization of a hydrophone for signal detection and computational signal processing for signal extraction. Data are examined in the time domain, the frequency domain, and the time-frequency plane. Examples are presented from an animal model and from a patient with a known aneurysm.

This study provides a detailed comparison of 22 digital, blood pressure monitors intended for home use. Blood pressure and pulse-rate readings from each electronic monitor were compared with concurrent measures obtained using the mercury column and auscultation. Correlation coefficients and linear regressions were performed to evaluate accuracy. Separate analyses of variance were used to determine significant calibration errors for each model. The results showed considerable disparity among available home monitors under controlled testing conditions. Variables associated with accuracy and home use by the layperson are discussed.

A Zenith Z-100 PC system was used to control an automated feeding system for determining the angular limits at which a monkey would respond to a food stimulus. Raisins secured to the end of a rotating arm by means of vacuum pressure were delivered to the monkey alternately from clockwise and counterclockwise directions at a fixed radius. The point at which the monkey took a raisin from the end of the arm was determined by an increase in negative pressure. The arm position was measured by using a potentiometer mounted in the arm gear train. The computer system controlled the experiment as well as the on-line recording and plotting of data.

Although the amount and complexity of equipment and supplies used in the practice of anesthesia have sharply increased in the past decade, the role of technical support personnel dealing with this technology has not been assessed. In an effort to determine that role, a questionnaire survey was conducted of the apportionment, direction, duties, and training of anesthesia technicians in teaching departments. Two-thirds of the inquiries were returned, disclosing a typical allocation of three anesthetizing locations (or 2000 annual anesthetics) per technician. A large majority of these departments have direct control of their technicians. Virtually all of these personnel are responsible for the routine upkeep and setup of anesthesia machines and monitors, although about one-third perform more specialized clinical functions. The preparation of these technicians for their duties varies widely, with almost 60% high school graduates and virtually all reporting training as on-the-job. The authors conclude that the term "anesthesia technician" remains poorly defined and unstandardized, and that current diverse efforts to address this issue deserve attention.

A new method is proposed to detect the entrance of a needle into the epidural space. Measuring the changes in electric resistance during the insertion of the needle through different tissues in the interspinal space can help anesthesiologists judge whether and when the needle has entered the epidural space. This preliminary, animal study showed that the proposed method performed quite satisfactorily. The electric resistance of the tissues in the interspinal space varied from 1.57 +/- 1.22 k omega to 2.93 +/- 1.14 k omega, and the resistance of the epidural space varied from 9.00 +/- 1.12 k omega to 14.64 +/- 1.25 k omega. The difference was statistically significant (p less than 0.001). This difference in the resistance can be used to verify placement of the tip of the needle in the epidural space and help anesthesiologists administer epidural anesthesia.

A surge in quantitative muscle physiology began with the mid-nineteenth century introduction of a new instrument capable of measuring contraction events with millisecond resolution. This strictly mechanical device, called a "myograph" by its designer Hermann von Helmholtz, was based on existing technology but included several important innovations that made it suitable for recording accurately the high speed events of muscle contraction. A variety of different myograph designs, each with its own advantages and disadvantages, ultimately came into existence and populated muscle physiology laboratories into the twentieth century.

A novel, noninvasive method to determine simultaneously ophthalmic artery pressure (OAP) and flow direction, called ophthalmomanometry-Doppler, is presented. This technique uses a device consisting of a chamber with an apperture hermetically adaptable to the orbital borders. The chamber is equipped with a Doppler probe and an arrival pipe for compressed air connected to a manometer. The OAP measurement procedure consists of applying a pressure in the chamber while the Doppler probe detects periorbital Doppler signals. The systolic OAP corresponds to the Doppler signal disappearance during chamber pressure increase. Studies performed on normal subjects with direct recording of the internal carotid artery pressure (ICP) and indirect determination of the brachial artery pressure (BAP) demonstrated that OAP values assessed by the ophthalmomanometry-Doppler device were highly correlated with simultaneous ipsilateral intra-arterial systolic ICP measurements (r = 0.95, n = 10) and with simultaneous recordings of the BAP (r = 0.85, n = 40). The ophthalmic pressure index (OAP/ICP and OAP/BAP ratio, respectively) ranged from 0.60-0.77 with a mean (+/- SD) of 0.68 (+/- 0.04) in the 50 normal subjects. Preliminary clinical trials show diminished OAP/BAP ratios in patients with occlusive carotid disease ipsilateral to hemodynamically significant lesions. The values obtained on these normal subjects provide baseline data for further investigation of pathologic conditions. This new procedure is simple, convenient, rapid, and safe and provides reproducible information on both OAP and flow parameters, which are important indices in the evaluation of severe carotid artery disease.

Monitoring of the nervous system using evoked potentials is a developing tool. A new evoked potential, the motor-evoked potential (MEP), based on a traditional test, uses brain stimulation to monitor the motor system. The MEP complements the existing modalities, which are wholly sensory. The MEP can be prompted by direct stimulation of the motor cortex, but, in a more general way, by transcranial stimulation. Electric or magnetic means can be used. One electric system involves placement of an electrode on the scalp over the motor cortex, paired with a cathodal plate on the roof of the hard palate. Recording electrodes are placed over the spinal cord, peripheral nerves, and muscles. Signals are recorded with a standard, evoked-potential, signal-averaging computer. Animal studies indicate that the electric stimulus activates primarily the pyramidal system to produce a descending evoked potential in the ventral and dorsolateral spinal cord. It is more sensitive than the sensory-evoked potential to spinal cord injury produced by the weight-drop method in cats. The peripheral nerve responses, much more sensitive to injury than the cord responses, can be altered by metabolic abnormalities. To date, the MEP has been an accurate indicator of ambulation in chronic spinal cord injury in animals. Parallel clinical development in the operating room has shown that the test is valuable; and it monitors brainstem or cortex manipulation, as well as cord manipulation. Safety studies are encouraging. The MEP is developmentally and technically demanding, but it has produced high quality signals.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies involving 240 fibrillation-defibrillation episodes via epicardial patch electrodes in 21-27-kg dogs and 480 transthoracic episodes in 100-kg calves are reported. In dogs, 120 episodes involving shocks by a 3.7-A, 5-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes of the reverse polarity. When the upper right ventricular patch was positive with respect to the left ventricular apex patch, 85% of the episodes yielded defibrillation; 78% defibrillated with the reverse polarity. In one series in calves, 120 episodes involving shocks by a 42-A, 4-ms unidirectional rectangular wave of one polarity were interlaced with 120 similar episodes involving the reverse polarity. In a second series, 59-A, 4-ms shocks were employed. In the 42-A series, 38% of the episodes were successful when the upper right electrode was positive with respect to the electrode over the apex, and 28% were successful with the reverse polarity. Corresponding results in the 59-A series were 80% and 68%, respectively. On an unpaired basis, the three p values were 0.19, 0.14, and 0.04, respectively. On a paired basis, all three comparisons yielded significant differences (p less than 0.05). We conclude that in these cases, at least, there is a moderate dependence upon electrode polarity and that our results appear to warrant clinical studies.