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Biomedical subjects

D Parsons

Publications and source records attributed to D Parsons.

18 recordsLinked to original sources
PubMed1992

Characterisation of an infectious bronchitis virus isolated from vaccinated broiler breeder flocks.

Four apparently serologically closely related isolates of infectious bronchitis virus were obtained from two flocks of vaccinated broiler breeders, one mile apart, which were experiencing increased mortality and decreases in egg production. The isolates were serologically distinct from isolates previously described and capable of causing characteristic infectious bronchitis-like respiratory infection in young chicks. In one experiment, the H120 vaccine strain of the virus did not protect the trachea against challenge with the new isolates 21 days later.

Animals↗
PubMed1992

Impedance plethysmography and thrombo-embolic disease.

This study compares the results of impedance plethysmography with lower limb venography in 68 patients referred for investigation of clinical deep vein thrombosis, and with the results of ventilation/perfusion isotope scans in 125 patients with suspected pulmonary embolism. Impedance plethysmography had a sensitivity of 100% and a specificity of 61% for the detection of thromboses involving popliteal or more proximal veins (30 patients), but a sensitivity of 90% and a specificity of 68% in the detection of thrombosis at any level, because of a low sensitivity in the detection of isolated calf vein thrombosis (60% in 10 patients). It is a non-invasive, portable and low-cost technique and, in centres where anticoagulation is only given to patients with popliteal or more proximal thrombosis, venography may only be necessary if impedance plethysmography is positive. It may also be of value in the assessment of patients with suspected pulmonary embolic disease and an indeterminate ventilation/perfusion lung scan.

Humans↗
PubMed1991

Reduced exercise capacity in senescent beagles: an evaluation of the periphery.

This study investigated the effect of age on peripheral factors involved in the systemic response to maximal exercise. Skeletal muscle was analyzed and regional blood flow distribution was determined at rest and during maximal exercise in senescent (old) and in younger mature (young) beagles. Maximal exercise capacity was significantly reduced (P less than 0.05) in old and was associated with a reduction in cardiac output (CO), as well as a tendency for arteriovenous O2 difference to be reduced, with a concomitant reduction in maximal O2 consumption. In each regional circulation evaluated, resting blood flow was similar in young and old. During exercise, blood flow was similar in young and old to the diaphragm, heart, tongue, and six of seven locomotory muscles. Concomitant blood flow reductions in splanchnic regions tended to be more pronounced in old than in young. Skeletal muscle analyses of triceps, semitendinosus, and gastrocnemius muscles disclosed similar percent fiber type distribution in young and old but a reduction in type II fiber area in old. In addition, both muscle capillary density and capillary-to-fiber ratio were reduced in old. These results demonstrate that age-related changes in blood flow distribution during maximal exercise enable skeletal muscle blood flow to be maintained in old, despite reductions in maximal CO and in muscle capillary density. However, this pattern of blood flow distribution only partially compensates for the combined effects of age-related changes in metabolic potential of the periphery, O2 content of arterial blood, and cardiac function during maximal exercise in old.

Aging↗
PubMed1991

Design and implementation of a new computerized system for intraoperative cardiac mapping.

A rapid, portable, yet inexpensive and expandable computer-based system utilizing current technology has been developed from experience in the operating room. An efficient operating system well suited for surgery is defined. New technology recording arrays fabricated from multielectrode flexible Kapton strips were developed and found to be easy to use and highly reliable. Novel arrays are created easily for research or special clinical applications. The system displays all incoming data in real time and transfers 16-s epochs to disk on command. After the user defines a beat for analysis, the computer determines the activation time for each channel, rejects unsatisfactory channels, and displays the results for review and modification before plotting the isochronal map on the monitor. The average time to recall data and produce a map is 16 s; if manual review of 120 channels is included, mapping time is less than 4 min. Clinical data recorded during surgery are discussed. The speed and operational ease demonstrated in the operating room make this computer/electrode system valuable both for surgery and for elucidating basic mechanisms of arrhythmias.

Algorithms↗
PubMed1989

Anoxic hepatocyte injury: role of reversible changes in elemental content and distribution.

Examination of anoxic isolated hepatocytes by light and electron microscopy indicated that initial morphologic changes were largely localized to the periphery of the cells. This early phase consisted of surface bleb formation but was not accompanied by alterations in parameters of plasma membrane integrity (leakage of cellular enzymes, exclusion of trypan blue). The time course of changes in structure was temporally related to alterations in the elemental distribution and content of various subcellular compartments. These studies, which employed electron probe X-ray microanalysis, demonstrated that rapid increases in the sodium and chlorine content and decreases in the potassium content of the cytoplasm, mitochondria and nucleus occurred, whereas no change in the calcium content of any subcellular compartment was detected. Concurrently, two cellular functions known to be dependent upon ion homeostasis, sodium-dependent taurocholate uptake and mitochondrial respiratory control, became markedly impaired. Reoxygenation within 30 min resulted in the restoration of both elemental distribution and the latter two functions to baseline. These data are consistent with the hypothesis that some early functional changes may be mediated by altered ion homeostasis. In contrast, additional studies indicated that sodium and water fluxes could be dissociated from the appearance of plasma membrane blebs. Thus, this study provides direct evidence that the structural and functional changes of early anoxic hepatocyte injury cannot be explained by a single mechanistic cascade, but apparently involve multiple mechanisms which may not be directly linked.

Animals↗
PubMed1989

Tension and electrolyte changes with Na+-K+ pump inhibition in rat papillary muscle.

Myocardial ischemic injury results in altered membrane integrity, energy depletion, and electrolyte shifts leading to accumulation of intracellular Ca. However, analysis of the direct effects of Ca accumulation is complicated by other concomitant cellular changes produced by ischemia. The purpose of this study was to examine the effects of Ca loading in rat papillary muscles produced by Na+-K+ pump inhibition in oxygenated K+-free buffer. Changes in contractile characteristics, high energy phosphate, and elemental concentrations of subcellular compartments were measured. Electron probe X-ray microanalysis was used to assess elemental concentrations in cryosections. After 3 h of Na+-K+ pump inhibition, resting tension (RT) increased to 164% and developed tension (DT) fell to 16.8% of control values. One hour after return to complete buffer, RT and DT partially recovered but remained significantly different from the 180 to 240-min values for the control muscles. Electron probe X-ray microanalysis showed increases in cytoplasmic and mitochondrial Na and Ca and a decrease in K during Na+-K+ pump inhibition. Mitochondrial Ca was greater than 100-fold greater than Ca in control mitochondria. Morphologically, the majority of cells showed ultrastructural damage. The mean ATP level was 20% of control. After 1 h of recovery, the cells appeared more heterogeneous, and the mean mitochondrial Ca decreased, whereas mean cytoplasmic Ca increased. Further statistical analysis showed a bimodal distribution for Na, Ca, K, Mg, and Cl, which coincided with the morphologically mixed population of cells. This suggests that replacement of extracellular K+ was associated with restored electrolyte gradients in some cells and the persistent or further alteration of electrolytes in others. These results suggest that variable Ca accumulation and associated ATP depletion without the compounding effects of ischemia lead to cell injury similar to reperfusion injury reported in ischemic myocardium.

Adenosine Triphosphate↗
PubMed1988

Three-dimensional reconstruction of cells from serial sections and whole-cell mounts using multilevel contouring of stereo micrographs.

A comprehensive computer-graphics-based system (STERECON) is described for tracing and digitizing contours from individual or stereopair electron micrographs. The contours are drawn in parallel planes within the micrographs. Provision is also made for tracing and digitizing in full three-dimensional (3-D) coordinates in any direction along linear structures such as cytoskeletal elements. The stereopair micrographs are viewed in combination with the contours being traced on a graphics terminal monitor. This is done either by projecting original electron micrograph (EM) negatives onto a screen and optically combining these images with contour lines being drawn on the monitor, or by first digitizing the images and displaying them directly on the monitor along with the contour lines. Prior image digitization allows computer enhancement of the structures to be contoured. Correction and alignment routines are included to deal with variable section thickness, section distortion and mass loss, variations in photography in the electron microscope, and terminal screen curvature when combining projected images with contour lines on the monitor. The STERECON system organizes and displays the digitized data from successive sections as a 3-D reconstruction. Reconstructions can be viewed in any orientation as contour stacks with hidden lines removed; as wire-frame models; or as shaded, solid models with variable lighting, transparency, and reflectivity. Volumes and surface areas of the reconstructed objects can be determined. Particular attention was paid to making the system convenient for the biological user. Users are given a choice of three different stereo-viewing methods.

Animals↗
PubMed1988

Anesthetic mishaps and the cost of monitoring: a proposed standard for monitoring equipment.

Review of insurance data indicates that approximately 1.5 claims are paid per 10,000 anesthetic procedures, a conservative estimate of the incidence of preventable serious injury associated with anesthesia. Insurance data permit estimation of the premium cost for the anesthesiologist and hospital, per operating room per year, of $69,429.00. We propose the use of an enhanced monitoring standard requiring a pulse oximeter, capnograph, spirometer, halometer, automatic sphygmomanometer, breathing circuit oxygen analyzer, stethoscope, electrocardiographic monitor, and temperature monitor. We suggest that this premium cost, together with the estimate that 50% of incidents would be avoided, predicts a resultant saving of over $27,000/operating room/year, a savings equal to the entire cost of the enhanced monitoring system in approximately 8 months, or a yearly savings of over five times the annualized expense of the monitoring system. Thus, in addition to the moral imperative to monitor a patient during anesthesia to avoid injury and death, there is an economic incentive to monitor effectively.

Anesthesia↗
PubMed1987

Cholinergic neurons, learning, and recovery of function.

Two experiments were designed to examine the role of the cholinergic septo-hippocampal projection in spatial and nonspatial learning processes. In Experiment 1 the interaction of individual learning strategies and recovery of function was investigated following medial septal lesions, by assessing individual learning styles and number of trials to recovery on a standard radial eight-arm-maze task. Experiment 2 addressed the relevance of the cholinergic septo-hippocampal pathway in the acquisition of spatially mediated behavior, by employing medial septal lesions, prior to acquisition learning of a modified version of the radial eight-arm-maze task. The data from these two experiments demonstrated that (a) the cholinergic septo-hippocampal projection is important for the acquisition and maintenance of spatial learning strategies, (b) loss of cholinergic function leads to alteration of learning strategies, (c) different learning strategies can be employed to acquire the same behaviors, and (d) the rate of recovery following brain injury can be influenced by preoperative learning strategies.

Animals↗
PubMed1985

Electromechanical changes during electrically induced and maximal voluntary contractions: surface and intramuscular EMG responses during sustained maximal voluntary contraction.

Changes in the electrical activity of the human gastrocnemius and soleus muscles during fatiguing maximal plantar flexions were studied with computer-aided EMG frequency power spectral analysis and intramuscular spike amplitude-frequency histogram analysis. In some experiments, brief supramaximal nerve stimulations of 80 Hz were given at 15-s intervals during sustained maximal voluntary contractions (MVCs). Multiple muscle biopsy samples were also obtained from the gastrocnemius muscle for fiber type determination. The surface EMG frequency spectral analysis showed a highly significant reduction in mean power frequency and root mean square EMG amplitude during sustained MVCs. The intramuscular spike amplitude-frequency histograms showed that the gastrocnemius muscle had a progressive reduction in the motor unit discharge frequency, particularly those with a relatively high amplitude, whereas the soleus muscle hardly showed a reduction in motor unit activity. Reduction in motor unit activity was also found to be more pronounced in gastrocnemius muscles with higher proportions of type II fibers. Brief maximal tetanic stimulations initially matching the MVC failed to increase the contraction force. Similarly, the evoked compound mass action potentials showed little change in the amplitude in subjects with different muscle fiber compositions. Results of this study suggest that during sustained MVCs, force fatigue could not be attributed to a failure of muscle membrane electrical propagation; a progressive reduction in motor unit activation does not result in a functional disadvantage, but may optimize excitation-contraction coupling by avoiding a muscle electrical conduction failure; and the extent of the reduction in motor unit activation seems to be muscle-fiber-type-dependent which may account for the reduction in amplitude and frequency of the surface EMG.

Biomechanical Phenomena↗
PubMed1985

Spina bifida occulta: lesion or anomaly?

Failure of fusion of the posterior arches of the lumbosacral spine above S3 was sought on frontal radiographs of 653 patients attending an accident and emergency (A & E) department. The patients were aged from 2 months to 98 years and represent all those with relevant information discharged as A & E outpatients over a 2-year period. Presenting complaints of backache or enuresis and inadequate radiographs were excluded. Spina bifida occulta was diagnosed in 22% of the whole group. The incidence was much higher in those below the age of 40 years (29.2%) compared with those above (9.8%). The overall age-adjusted incidence was 17.3%. Our study is an attempt to judge the off-the-street' prevalence of spina bifida occulta. It supports the notion that spina bifida occulta is a common anomaly, of no clinical significance on its own.

Adolescent↗
PubMed1985

Dynamic exercise training in foxhounds. II. Analysis of skeletal muscle.

The purpose of this study was to determine whether 8-12 wk of endurance training produces biochemical and histochemical adaptations in skeletal muscle in foxhounds. Analyses were performed on samples removed from gastrocnemius, triceps, and semitendinosus muscles of foxhounds before and after a treadmill running program. Biochemical analysis showed that training did not alter the activities of phosphofructokinase, beta-hydroxyacyl-CoA dehydrogenase, succinate dehydrogenase, or total phosphorylase. Histochemical analysis of myofibrillar actomyosin ATPase demonstrated three distinct classes of type II fibers and one type I fiber in the semitendinosus and triceps muscles and two type II and two type I fibers in the gastrocnemius muscle. Fiber type distribution and oxidative and glycolytic potentials, as indicated by nicotinamide adenine dinucleotide tetrazolium reductase or alpha-glycerophosphate dehydrogenase staining intensity, were unaltered by training. Similarly, capillary density, capillary-to-fiber ratios, and capillary area-to-fiber area ratios did not change with training. Thus, unlike humans and other mammals (i.e., rat), these foxhounds did not manifest biochemical or histochemical adaptations in skeletal muscle as the result of endurance training. This is consistent with the results of the study in which endurance training produced a 27% increase in maximal cardiac output and a 4% increase in maximal arteriovenous O2 extraction in foxhounds.

3-Hydroxyacyl CoA Dehydrogenases↗
PubMed1985

Alterations of ultrastructure and elemental composition in cultured neonatal rat cardiac myocytes after metabolic inhibition with iodoacetic acid.

The purpose of this study was to document changes in cellular fine structure and elemental composition, and their relationship to progression of cell injury, in cultured neonatal rat cardiac myocytes in which impaired energy metabolism was produced by the metabolic inhibitor, iodoacetic acid (IAA). In order to quantitate changes in the concentrations of elements and their subcellular distribution in individual myocytes, electron probe x-ray microanalysis was performed on freeze-dried cryosections of rapidly frozen cells. After 1 hour of exposure to IAA, ATP level was not significantly reduced. Most cells exhibited minimal ultrastructural alterations and had normal elemental profiles, whereas some cells (10 to 25%) had increased sodium and calcium in mitochondria and cytoplasm. After exposure to IAA for 1.5, 2, or 4 hours, the ATP level was reduced to below one third of control, and remained decreased 24 hours after removal of IAA, indicating irreversible depression of this variable. After exposure to IAA for 1.5 hours no longer, many cells showed severe ultrastructural alterations, including contraction or swelling of mitochondria and distortion of the cristae, myofibrillar hypercontraction, and formation of fluid-filled blebs. At 1.5 and 2 hours, approximately 75% or more of the myocytes had increased sodium and calcium and decreased potassium and magnesium in mitochondria, nuclei, and cytoplasm. Thus, the development of an increased calcium concentration in cytoplasm as well as mitochondria of most myocytes was a feature of this transitional period. These data indicate that progressive alterations in the levels and distribution of elements accompany the development of severe ultrastructural changes and irreversible injury in response to impaired energy metabolism in cultured myocytes. These elemental alterations include accumulation of calcium in cytoplasm and mitochondria of myocytes in this model.

Adenosine Triphosphate↗
PubMedDate not supplied

Distal tracheal compression.

The consultants concur that distal tracheal stenosis is a challenging problem in the pediatric patient but don't all agree on the presentation or management. Drs. Cotton and Crysdale agree that these children are usually seen with biphasic stridor. Dr. Parsons believes that biphasic stridor is not particularly common but inspiratory stridor is. The experts divide the differential diagnosis into intrinsic and extrinsic categories. Dr. Cotton lists tracheomalacia, complete tracheal rings and masses, such as an isolated hemangioma or granuloma. The usual extrinsic lesion is a vascular anomaly, the most common being an innominate artery. Dr. Crysdale's differential diagnosis includes tracheal stenosis, either congenital or acquired, and tracheomalacia. Vascular compression is most common as an extrinsic cause. Dr. Parsons includes tracheomalacia, complete tracheal rings, segmental tracheal stenosis, isolated masses, and vascular anomalies, such as an aberrant innominate artery. He also states that a tracheoesophageal fistula must be considered. Dr. Cotton prefers MRI and possibly a barium swallow for assessing vascular architecture. Even finding an air bronchogram on a chest x-ray can pinpoint an area of stenosis. The best test is direct laryngoscopy with video-photography. While Drs. Parsons and Crysdale agree that direct laryngoscopy is the best, Dr. Crysdale also suggests MRI or CT and adds that a contrast bronchogram is a most useful test.(ABSTRACT TRUNCATED AT 250 WORDS)

Airway Obstruction↗