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Biomedical subjects

D J Doyle

Publications and source records attributed to D J Doyle.

At least 19 recordsLinked to original sources
PubMed1994

An interface to display special physiologic signals on patient monitors.

OBJECTIVE: The objective of this study was to develop an interface to allow special physiologic signals (e.g., in a research setting) to be displayed on the invasive pressure channel of conventional clinical monitors. The interface accepts single-ended high-level signals for display using the pressure channel of patient monitors, which use strain-gauge transducers employing direct current (DC) excitation. METHODS: By studying the electronic circuitry common to most clinical invasive pressure measurement systems (Wheatstone bridge, differential input instrumentation amplifier) it was possible to develop an interface to convert high-level single-ended signals into the low-level differential signal needed for input to an invasive pressure channel. RESULTS AND CONCLUSIONS: The device is useful when it is desired to display signals from special transducers on regular patient monitors. Schematic diagrams and sample results are provided.

Humans↗
PubMed1992

Analysis of intracranial pressure.

Methods for the acqusition and analysis of intracranial pressure (ICP) signals are reviewed from clinical and technical perspectives. The clinical importance of ICP monitoring is presented, and methods for ICP transduction are briefly discussed. These methods include intraventricular catheters, subarachnoid screws, epidural techniques, and the new fiberoptic ICP measurement systems. Approaches to the visual analysis of the ICP waveform are presented, with special emphasis on the relationship between the ICP waveform and the arterial blood pressure signal. Methods of computer-based ICP analysis are also reviewed, including histogram and "systems analysis" methods. Methods to predict ICP pressure rises and to estimate intracranial compliance are also discussed. Finally, ICP monitoring is reviewed from the point of view of patient outcome. It is concluded that advanced ICP waveform analysis methods warrant further clinical evaluation to demonstrate their clinical usefulness.

Humans↗
PubMed1992

PUMPSIM: a software package for simulating computer-controlled drug infusion pumps.

Advances in microcomputer technology have lead to the development of volumetric infusion pumps which can be controlled by a remote computer. Such pumps offer powerful capabilities for the administration of medications and fluids. Complex control strategies can be preprogrammed and the pump allowed to run with a minimum of supervision. The safety of patients is of the utmost importance. Therefore, great care must be taken to implement robust error avoidance, detection and correction protocols in the host control program. This paper describes a software simulator of a commercial infusion pump (Abbott Lifecare Model 4). Using the simulator in the development and debugging of control programs has several advantages over using the real pump: it provides detailed pump status information and it can stimulate various error and alarm conditions to comprehensively test the error recovery procedures of the control program.

Computer Simulation↗
PubMed1992

Spinal cord tissue pressure during spinal cord distraction in dogs.

Spinal column distraction is a known cause of spinal cord injury. Laplace's law predicts that cord interstitial pressure will elevate during spinal cord distraction. To determine the significance of the Laplace predictions a series of in vitro and in vivo experiments examining spinal cord distraction were performed. In vitro experiments were carried out on 10 dog spinal cords in a specially designed distraction apparatus. These experiments verified the Laplace's law demonstrating a close correlation (R(avg) = 0.99) between the tension applied to the cord, and cord interstitial pressure. Cord interstitial pressure strain (elongation) curves show that initial elongation is accompanied by negligible elevations of cord interstitial pressure; the final 20% elongation being responsible for 80% of the elevation in cord interstitial pressure. In vivo experiments were carried out on five beta-blocked dogs. Significant elevations in cord interstitial pressure were obtained during stepwise spinal column distraction. Spinal cord blood flow and somatosensory evoked potentials were well maintained during distraction until cord interstitial pressure reached 47 mm Hg. At this point a simultaneous fall in spinal cord blood flow and somatosensory evoked potentials was noted. Release of the distracting force resulted in return of spinal cord blood flow, somatosensory evoked potentials, and cord interstitial pressure to baseline. The authors conclude that significant elevations in cord interstitial pressure occur with spinal cord distraction and that these cord interstitial pressure elevations are associated with a reversible ischemic response in the cord.

Animals↗
PubMed1991

Design and evaluation of a pneumatic pulse monitor for use during magnetic resonance imaging.

We describe a portable, battery-operated instrument designed to monitor pulsations in the finger or toe. The monitor is based on pneumatic principles and is suitable for use in the electromagnetically harsh environment of magnetic resonance imaging. A compliant Silastic chamber is deformed with each cardiac pulsation; the resulting pressure wave is then transmitted along a 25-ft (7.5-m) microbore tube to a pressure sensor in a remote electronic monitor.

Blood Pressure Determination↗
PubMed1991

Time constant-related capnograph distortion: a theoretical analysis.

A theoretical analysis of time constant-related distortion in side-stream capnographs was carried out using two models of respiratory patterns. It is demonstrated that under circumstances likely to be encountered clinically, significant distortion may occur. This distortion may produce both spurious rebreathing and under estimation of the true end-tidal CO2 concentration.

Carbon Dioxide↗
PubMed1991

Spinal cord distraction: an in vitro study of length, tension, and tissue pressure.

Since the Scoliosis Research Society released a report on cord injury related to Harrington rod instrumentation for scoliosis, little has been published on the pathophysiology of this disorder. Dolan et al. (4) described diminished cord blood flow associated with spinal distraction in a cat model, but failed to demonstrate its cause. In this article, we describe a series of in vitro experiments performed on dog and sheep cadaver spinal cords. Controlled distractive forces were applied to spinal cords while monitoring both cord interstitial pressure and cord elongation. A close (Ravg = 0.986) correlation was noted between applied tensile forces and cord interstitial pressure. At 1,000-g loads, the average tissue pressure obtained was 29.5 cm H2O, ranging from 17 to 47 cm H2O. However, it was noted that the cord demonstrated nonlinear tensile elastic properties that appeared exponential in the range examined. These properties are consistent with those described for collagen-containing compounds. We conclude that spinal cord distraction is capable of generating cord tissue pressures that could cause a spinal cord compartment syndrome and thereby seriously impair spinal cord blood flow causing spinal cord injury.

Animals↗
PubMed1990

Inexpensive temperature monitor for heated humidifiers.

A commercially available indoor/outdoor electronic thermometer has been adapted to monitor both airway gas temperature and operating room temperature when heated humidifiers are used. Heated humidifiers that do not have temperature monitoring capabilities pose a risk of dangerously high inspired gas temperatures.

Environmental Monitoring↗
PubMed1990

Continuous measurement of central venous pressure by manometry.

An alternative method is described for measurement of central venous pressure by insertion of a right atrial catheter with a connection to a fluid-column manometer. With this method, the central venous pressure can be monitored by visual inspection of the manometer column; the stopcock does not need turning; the manometer column does not need refilling; and the catheter is always being flushed, eliminating the risk of clotting.

Catheterization, Central Venous↗
PubMed1990

Reflex bradycardia during surgery.

Reflex bradycardia and sinus arrest may occur in a variety of surgical procedures, from neurosurgery to general abdominal, laparoscopic, ophthalmic and facial surgery and even procedures such as liver biopsies and electroconvulsive therapy. In most cases a vagally-mediated reflex has been implicated, although experimental support for this is often lacking. Drugs such as vecuronium, atracurium, halothane, fentanyl and succinylcholine may predispose to this reflex. Premedication with an anticholinergic is usually effective in preventing its occurrence.

Bradycardia↗
PubMed1989

Comparison of high-dose with low-dose subcutaneous heparin to prevent left ventricular mural thrombosis in patients with acute transmural anterior myocardial infarction.

We performed a double-blind randomized trial comparing high doses of subcutaneous heparin (12,500 units every 12 hours) with low doses (5000 units every 12 hours) for 10 days in the prevention of left ventricular mural thrombosis in 221 patients with acute anterior myocardial infarction. Left ventricular mural thrombosis was observed by two-dimensional echocardiography on the 10th day after infarction in 10 of 95 patients (11 percent) in the high-dose group and in 28 of 88 patients (32 percent) in the low-dose group (P = 0.0004). One patient in the high-dose group and four in the low-dose group had nonhemorrhagic strokes (P = 0.17). One patient in the low-dose group had a fatal pulmonary embolism. There was no difference in the frequency of hemorrhagic complications, which occurred in six patients in the high-dose group and four in the low-dose group. The mean (+/- SEM) plasma heparin concentration was 0.18 +/- 0.017 U per milliliter in the high-dose group and 0.01 +/- 0.005 U per milliliter in the low-dose group (P less than 0.0001). In the high-dose group, the mean plasma heparin concentration was 0.10 +/- 0.029 U per milliliter among patients with abnormal two-dimensional echocardiograms, as compared with 0.19 +/- 0.019 U per milliliter among patients with normal echocardiograms (P = 0.01). We conclude that heparin administered subcutaneously in a dosage of 12,500 units every 12 hours to patients with acute anterior transmural myocardial infarction is more effective than a lower dosage (5000 units every 12 hours) in preventing left ventricular mural thrombosis.

Aged↗