Search PubMed⌕ Search

Biomedical subjects

G J Wilson

Publications and source records attributed to G J Wilson.

At least 109 records · Page 6Linked to original sources

The effect on performance of imposing a delay during a stretch-shorten cycle movement.

Twelve experienced male weight lifters of varying ability completed a series of bench press lifts at 95% of maximum. These lifts included a rebound bench press, which was performed without a delay between the downward and upward components of the lift, a bench press performed without a downward phase, and two bench press movements performed with various pause periods imposed between the downward and upward phases of the lift. Force and cinematographic data were collected during each lift. The augmentation to performance derived from prior stretch was observed to decay as a function of the pause duration. This relationship was accurately described (P less than 0.01) by a negative exponential equation with a half-life of 0.85 s. The nature of this decay is discussed with reference to the implications for stretch-shorten cycle movements that are performed with a period of pause between the eccentric and concentric phases and for stretch-shorten cycle research paradigms.

Adult↗

Calcium and strontium activation characteristics of skeletal muscle fibres from the small marsupial Sminthopsis macroura.

Mechanically skinned skeletal muscle fibres from the soleus and tibialis anterior muscles of the small marsupial Sminthopsis macroura were activated by Ca2+ and Sr2+ so that their isometric force properties could be determined. The properties characterized were the shape, slope and positions of the curves generated by plotting isometric force vs. pCa (-log10[Ca2+]) and pSr (-log10[Sr2+]), the maximum Ca2(+)-activated and Sr2(+)-activated tension (Ncm-2) and the frequency of force oscillations of myofibrillar origin during submaximal activations. The effect of caffeine on force activation was also studied. Apart from the fibres which exhibited physiological characteristics similar to those observed previously in mammalian fibres, a large proportion of fibres exhibited characteristics or combinations of characteristics which have not previously been described from healthy adult mammals. The results from 32 soleus fibres showed that only 23 could be categorized as either typical fast-twitch or slow-twitch fibres. The rest possessed unusual physiological characteristics which suggested the co-existence in the same fibre of Ca2(+)-regulatory and contractile properties from different categories of fast-twitch and slow-twitch fibres. We could distinguish two major fast twitch populations of tibialis anterior fibres which occurred in similar proportions. There were significant differences in the maximum tension produced by some of these groups of fibres. The tibialis anterior population fibres produced the highest maximum tension (ToCa 44.6 +/- 4.6 Ncm-2, n = 7) while the soleus combined type fibres produced the lowest maximum tension (ToCa 18.1 +/- 2.1 Ncm-2, n = 8). Our physiological observations of the Ca2(+)-activation and Sr2(+)-activation properties of soleus fibres in this study provide new evidence that there can be combinations of characteristics in single fibres and a continuum of properties between fibre types in normal mammalian skeletal muscles. These animals can therefore be used as a source of fibres with a wide range of properties.

Animals↗

European versus North American cardioplegia: comparison of Bretschneider's and Roe's cardioplegic solutions in a canine model of cardiopulmonary bypass.

Roe's and Bretschneider's crystalloid cardioplegic solutions were compared in a canine model of total cardiopulmonary bypass with 4.5 hours of hypothermic (27 degrees C) ischemic arrest and 60 minutes of reperfusion. Bretschneider's solution (Group I, six dogs) preserved tissue adenosine triphosphate (ATP) near control levels and maintained coronary effluent pH near 7.0 throughout the ischemic interval, while Roe's solution (Group II, six dogs) allowed progressive acidosis and depletion of ATP (P less than 0.005 versus control). Group I had supranormal left ventricular function during reperfusion (greater than 100% of pre-arrest function) but Group II regained only 40-75% of pre-arrest function. Group I had 2.82% +/- 3.61% necrosis of heart mass and Group II 9.33% +/- 8.26 (P less than 0.10). We conclude that Bretschneider's solution provided better myocardial protection than Roe's solution. The development of acidosis in the Roe group suggests that the more effective buffering of Bretschneider's solution with histidine is the probable basis for its superiority.

Animals↗

Subcellular distribution of peroxidized lipids in myocardial reperfusion injury.

Previous studies in our laboratory have demonstrated the peroxidation of myocardial phospholipid in a canine model of reversible global normothermic ischemia and reperfusion while on cardiopulmonary bypass. The present study examines the distribution of phospholipid peroxidation products in three major cellular organelle fractions of myocardium prepared by established centrifugal fractionation procedures (sarcolemma, sarcoplasmic reticulum, and mitochondria). These organelles were isolated from control (nonischemic) and ischemic-reperfused myocardium harvested during early reperfusion (5 min), when previous studies indicated maximal peroxidative injury in whole myocardial biopsies. Utilizing a more rapid analytic procedure for measuring phospholipid containing the conjugated diene chromophore in the polyunsaturated fatty acyl substituents, we were able to establish the fidelity of this procedure by comparing the results obtained with it to the previous more laborious analytic procedure (involving phospholipid hydrolysis with phospholipase A2 and subsequent derivatization for high-pressure liquid chromatography followed by gas chromatographic-mass spectrometric analysis). Analysis of phospholipid extracts from organelle fractions for evidence of peroxidative conjugated diene formation revealed that sarcolemmal membranes had the highest content of oxidized phospholipid containing the conjugated diene chromophore (mean 2.2 +/- 1.2 nmol phospholipid-conjugated diene/mumol phospholipid phosphorus, P less than 0.02 compared with control). Both sarcoplasmic reticulum and mitochondrial membranes were also peroxidized but to a much smaller extent (mean 0.4 +/- 0.2 and 0.3 +/- 0.25 nmol phospholipid conjugated diene/mumol phospholipid phosphorus).

Animals↗

Morphological findings contributing to a failed Fontan procedure. Twelve-year experience.

A group of 37 patients (age range, 3 months to 29 years) who died after the modified Fontan procedure (within 2 months), representing 15% of the 245 patients undergoing this procedure from 1976 through 1988, was reviewed to determine the causes of death. The three morphological groups were 1) univentricular atrioventricular connection (n = 19), 2) tricuspid atresia (n = 9), and 3) other complex malformations (n = 9). Subaortic stenosis was present in 15 patients (40%) in this group compared with 31 of 208 early survivors (15%) (p = 0.008). Pulmonary artery banding, identified as a risk factor in our previous experience, was performed in 14 patients, nine of whom had subaortic stenosis. Nine palliative procedures for subaortic stenosis were performed in eight patients--before the Fontan procedure in three patients and concurrently with the Fontan procedure in five patients. Myocardial hypertrophy and signs of acute ischemic injury were common findings at autopsy (n = 25) and were particularly prominent in all patients with univentricular heart of left ventricular morphology associated with subaortic stenosis and previous pulmonary artery banding (n = 7). We conclude that the present majority of deaths occurring after the modified Fontan procedure are myocardial in nature and attributable to advanced myocardial hypertrophy that is potentiated by previous pulmonary artery banding and subaortic stenosis.

Aortic Valve Stenosis↗

Effects of low perfusate Ca2+ concentration on newborn myocardial function after ischemia.

A greater dependence on transsarcolemmal Ca2+ flux and immaturity of Ca2+ sequestration capacity may potentiate Ca2(+)-mediated reperfusion injury in the newborn myocardium. The effect of serum ionized Ca2+ concentration on left ventricular systolic and diastolic function after ischemia was studied in 5-7-day-old piglets undergoing a 90-minute period of cold-blood cardioplegic arrest. In the control group, Ca2+ was maintained at 1.2 mM (Group A [n = 6]). The cardioplegic solution and bypass perfusate were modified to achieve a low Ca2+ concentration, 0.25 mM, in Group B (n = 6). Left ventricular pressure-volume loops were acquired by using high-fidelity pressure-sensor-tipped and volume-conductance catheters. Ventricular function was assessed from the slope of end-systolic (Ees) and end-diastolic (k) pressure-volume relations during transient caval occlusion. Both groups showed a significant reduction in Ees after ischemia (p less than 0.05). Intergroup comparison of Ees after ischemia demonstrated a better recovery of the systolic function in the low Ca2+ group, 64 +/- 7% versus 49 +/- 6% in the normal Ca2+ group (p = 0.05). There was a significant increase in chamber stiffness index in group A (k, 0.48 +/- 0.06 to 0.65 +/- 0.05 ml-1, p less than 0.01) versus no significant change in group B. This study shows 1) the feasibility of acquiring continuous pressure-volume data in neonatal hearts by using a conductance catheter system, and 2) better preservation of systolic function and diastolic compliance in normal newborn myocardium by low Ca2+ concentration in the peri-ischemic period.

Animals↗

Calcium paradox in an in vivo model of multidose cardioplegia and moderate hypothermia. Prevention with diltiazem or trace calcium levels.

The production and prevention of calcium paradox injury in myocardium was studied in a canine model of cardiopulmonary bypass with multidose, moderately hypothermic, crystalloid cardioplegic solution. During 4 1/2 hours of global ischemia, three groups of six dogs each received one of three histidine-buffered cardioplegic solutions (500 ml initially and 250 ml every 30 minutes) at 27 degrees C. Group 1 cardioplegic solution was calcium free, group 2 solution contained a trace amount of calcium chloride (70 mumols /L), and group 3 cardioplegic solution was calcium free but contained diltiazem (150 micrograms/kg body weight). Left ventricular function measured as percent control of developed pressure revealed significantly greater (p less than 0.05) recovery in groups 2 and 3. Triphenyltetrazolium chloride staining showed 35% +/- 9% (mean +/- standard error) of heart mass necrosis in group 1 versus 0% and 0.5% +/- 0.4% in groups 2 and 3, respectively (p less than 0.001). Electron microscopy revealed ultrastructural changes characteristic of calcium paradox injury in group 1 myocardium. Calcium paradox injury was produced in an in vivo model of global myocardial ischemia and multidose cardioplegia despite moderate hypothermia and non-coronary collateral flow. The addition of either trace levels of calcium or diltiazem to the cardioplegic solution was effective in preventing this injury.

Animals↗

Comparison of blood-based and asanguineous cardioplegic solutions administered at 4 degrees C. An ultrastructural morphometric study in the dog.

Although several studies have shown better myocardial preservation with blood-based than asanguineous cardioplegic solutions at myocardial temperatures above 15 degrees C, one might suspect that blood would become unsafe at lower temperatures because of increased oxygen-hemoglobin affinity and viscosity. We compared myocardial preservation in dogs subjected to 6 hours of aortic crossclamping and treated with modified Roe's asanguineous cardioplegic solution at 4 degrees C (group CA), blood cardioplegic solution at 4 degrees C (CB), or blood cardioplegic solution at 27 degrees C (WB, four dogs per group). Myocardial preservation was assessed by triphenyltetrazolium staining of whole hearts, and by analysis of ultrastructure and morphometric analysis of mitochondria in myocardial biopsies from three sites in each heart (left ventricle subepicardium and subendocardium and right ventricle). Tetrazolium staining showed no difference in preservation among the three treatment groups (no necrosis in any heart). For two of the three biopsy sites (left ventricular subepicardium and right ventricle), ultrastructural and morphometric analyses demonstrated signs of more severe subcellular injury in group CA than in CB (p = 0.013 to 0.004), whereas equivalent preservation with all treatments was observed in the left ventricular endocardial site. Functional recovery also appeared to be equivalent between treatments, to the extent that all dogs were successfully weaned from bypass after 20 minutes of reperfusion. We conclude that the safety and effectiveness of blood cardioplegia is not compromised by infusion at 4 degrees C compared with 27 degrees C and that myocardial preservation is not improved by using asanguineous cardioplegia instead of blood cardioplegia at 4 degrees C.

Animals↗

Asanguineous reperfusion in a canine model of cardiopulmonary bypass and controlled postischemic work.

This study was designed to test the hypothesis that asanguineous reperfusion with a standard crystalloid cardioplegic solution results in improved myocardial salvage after a period of global ischemia. Four groups of 6 dogs each were placed on cardiopulmonary bypass. Control group A (work only) performed two hours of controlled work by contracting against a saline-filled left intraventricular balloon. Control group B (ischemia only) underwent 45 minutes of global normothermic ischemia before simple blood reperfusion while supported on bypass. Groups C and D were subjected to ischemia and reperfusion as in group B, followed by controlled work stress as in group A. Group D, however, received 500 mL of St. Thomas' Hospital solution immediately before blood reperfusion. Morphological analysis showed no significant injury in groups A and B, whereas group C had 11.4% +/- 2.4% necrosis of heart mass versus 2.5% +/- 1.1% in group D (p less than 0.001). Biochemical data from left ventricular biopsies showed no significant differences between groups B, C, and D. Functional analyses showed deterioration of diastolic compliance in group C (p less than 0.05), although a significant difference in systolic functional indexes could not be detected. Myocardial protection and salvage was improved by initial reperfusion with an asanguineous cardioplegic solution versus reperfusion with blood alone.

Animals↗

A simplified concept for a bileaflet atrioventricular valve that maintains annular-papillary muscle continuity.

We have developed a simplified concept for a bileaflet atrioventricular prosthesis that can be constructed from a simple sheet of glutaraldehyde preserved pericardium. The valve has no rigid ring or stent and no cloth sewing ring. Insertion of the valve reestablishes normal continuity between the annulus and the papillary muscles. We have replaced the mitral valve in nine dogs using this prosthesis. All valves have been competent with excellent valve opening areas as confirmed by echo-Doppler assessment. Studies up to 4 1/2 months have confirmed excellent hemodynamics and there has been no evidence of early tissue failure. Possible advantages of this simple valve design are improved hemodynamics, ease of construction and insertion, and low cost.

Animals↗

Dissociation of force from myofibrillar MgATPase and stiffness at short sarcomere lengths in rat and toad skeletal muscle.

1. Single fast-twitch fibres from the extensor digitorum longus muscle of the rat, Rattus norvegicus, and single twitch fibres from the iliofibularis muscle of the cane toad, Bufo marinus, were mechanically skinned and then used to measure maximally Ca2+-activated [( Ca2+] greater than 0.03 mmol l-1) isometric force production, myofibrillar MgATPase activity and fibre stiffness at different sarcomere lengths. MgATP hydrolysis was linked by an enzyme cascade to the oxidation of NADH (nicotinamide adenine dinucleotide, reduced form) and was monitored by a microfluorimetric system. Fibre stiffness was measured from the amplitude of force oscillations generated by small sinusoidal length changes. 2. At sarcomere lengths which were optimal for isometric force production (around 2.7 microns for rat and 2.2 microns for toad fibres) the myofibrillar MgATPase activity (mean +/- S.E.M.) at 21-22 degrees C was found to be 3.80 +/- 0.53 molecules MgATP hydrolysed s-1 per myosin head for eight rat fibres and 6.35 +/- 0.77 s-1 per myosin head for four toad fibres. 3. At sarcomere lengths shorter than 2.7 microns in rat fibres and 2.2 microns in toad fibres, MgATPase and stiffness remained elevated and close to their respective values at 2.7 microns in rat fibres and 2.2 microns in toad fibres even when the isometric force decreased to near zero levels. 4. The dissociation at short sarcomere lengths of myofibrillar MgATPase activity and fibre stiffness from isometric force suggests that the cross-bridge cycle is not greatly affected by double actin filament overlap with the myosin filaments at short sarcomere lengths. Moreover, the results suggest that cross-bridges can be formed by myosin with actin filaments projecting from the nearest Z-line and from the Z-line in the other half of the sarcomere. 5. These results help to reconcile energetic and mechanical data obtained by others at short sarcomere lengths and can be explained within the framework of the sliding filament theory.

Adenosine Triphosphate↗

A biomechanical analysis of the sticking region in the bench press.

The performance of ten elite powerlifters were analyzed in a simulated competition environment using three-dimensional cinematography and surface electromyography while bench pressing approximately 80% of maximum, a maximal load, and an unsuccessful supramaximal attempt. The resultant moment arm (from the sagittal and transverse planes) of the weight about the shoulder axis decreased throughout the upward movement of the bar. The resultant moment arm of the weight about the elbow axis decreased throughout the initial portion of the ascent of the bar, recording a minimum value during the sticking region, and subsequently increased throughout the remainder of the ascent of the bar. The electromyograms produced by the prime mover muscles (sternal portion of pectoralis major, anterior deltoid, long head of triceps brachii) achieved maximal activation at the commencement of the ascent phase of the lift and maintained this level essentially unchanged throughout the upward movement of the bar. The sticking region, therefore, did not appear to be caused by an increase in the moment arm of the weight about the shoulder or elbow joints or by a minimization of muscular activity during this region. A possible mechanism which envisages the sticking region as a force-reduced transition phase between a strain energy-assisted acceleration phase and a mechanically advantageous maximum strength region is postulated.

Acceleration↗

Balloon electric shock ablation. Effects on ventricular structure, function, and electrophysiology.

We have recently developed a transatrial balloon approach for intraoperative endocardial mapping of ventricular tachycardia, which can be performed in the intact ventricle. In selected patients, we have eliminated the arrhythmia by passing a series of electric currents through specific beads on the balloon array. The goal of this new technique, balloon electric shock ablation, is to create a homogenous scar in the subendocardial target area identified by mapping. Experimental data exist on the effects of catheter delivery of electric discharges to the myocardium, but no data are available on the effects of balloon electric shock ablation. We have performed balloon electric shock ablation in animals (nine cathodal shocks of 100 J given through a 4 cm2 electrode grid). Ventricular function was assessed at 6 weeks and compared with function after a simple ventriculotomy and with function in control animals having no operation. Gated nuclear ventriculograms were obtained during volume loading. Myocardial performance and diastolic pressure volume relationships were determined for the three groups. After balloon electric shock ablation or ventriculotomy, left atrial pressures were increased at similar end-diastolic volumes, which indicated decreased ventricular compliance. The trend reached statistical significance (compared with data from control animals) only in the group undergoing balloon electric shock ablation. Myocardial performance (stroke work index/end-diastolic volume relationship) was unchanged in the three groups. In the long-term balloon electric shock ablation preparation, an electrophysiologic study (including burst pacing) failed to induce ventricular arrhythmias. At 6 weeks, the lesion created by balloon electric shock ablation was a layer of homogenous mature scar with sharply defined borders. There was no evidence of additional injury to the surrounding myocardium or to the mitral valve apparatus. These studies show that delivery of a series of electric shocks through a 1 cm balloon grid of electrodes can create an area of homogeneous, electrically inert scar and that this procedure when performed in healthy dog hearts has no significant effect on the structure and function of the rest of the left ventricle.

Animals↗

Cardiac manifestations in disorders of fat and carnitine metabolism in infancy.

The prognosis of patients with cardiomyopathy associated with hypocarnitinemia is uncertain. Cardiac hemodynamics, histologic findings and response to oral L-carnitine therapy were retrospectively evaluated in 11 children with cardiomyopathy associated with abnormal carnitine metabolism. Three had systemic carnitine deficiency, two familial hypocarnitinemia with neutropenia, three transient neonatal hypocarnitinemia and three a carnitine insufficiency syndrome. Six had a hypertrophic and five a dilated cardiomyopathy. Hypotonia was present in seven (64%). The cardiothoracic ratio was greater than 0.60 in eight (73%). The most frequent abnormality on the electrocardiogram was ST-T wave inversion in the left precordial leads with various degrees of left ventricular hypertrophy. Echocardiographically, two patients with hypertrophic cardiomyopathy had decreased left ventricular function and two patients with dilated cardiomyopathy had increased thickness of the left ventricular wall. Histologic evaluation (two autopsies and one endomyocardial biopsy) revealed striking lipid accumulation within hypertrophied myocytes. Six of eight patients on carnitine replacement therapy had improvement echocardiographically during a 3 month to 2 year follow-up period. In summary, both hypertrophic and dilated cardiomyopathy can result from abnormal carnitine metabolism. The determination of plasma carnitine concentrations and fatty acid metabolism by-products should be performed in all patients with either form of cardiomyopathy of unknown etiology because carnitine supplementation may lead to improvement.

Biopsy↗

Loss of the somatosensory evoked response as an indicator of reversible cerebral ischemia during hypothermic, low-flow cardiopulmonary bypass.

We assessed somatosensory evoked response (SSER) as a monitor of cerebral protection during nonpulsatile, hypothermic cardiopulmonary bypass (CPB). In 13 dogs under CPB, extracorporeal flow rate (EFR) thresholds for loss of SSER were determined by stepwise reduction of the EFR from 2.0 to 0.25 L/min/m2 at perfusion temperatures of 35 degrees C, 30 degrees C, 25 degrees C, and 20 degrees C. Testing began at 35 degrees C in Group 1 (N = 6) and at 20 degrees C in Group 2 (N = 7). Immediately on loss of SSER (denoted as a decrease of 80% or more in the amplitude of the somatosensory evoked potentials), EFR was restored to 2.0 L/min/m. Thresholds for loss of SSER ranged between 0.75 and 0.25 L/min/m2. SSER was always restored on return of EFR to 2.0 L/min/m2; thus loss of SSER was a reversible ischemic change. Both groups had similar threshold values at 35 degrees C, but at lower temperatures, Group 1 thresholds were significantly higher than those in Group 2. Since 35 degrees C was the first test temperature for Group 1 but the last for Group 2, EFR reduction at 35 degrees C apparently caused neurophysiological changes (depletion of cortical energy reserves), which diminished subsequent tolerance to ischemia, but EFR reduction at 20 degrees C did not. Our findings show that loss of SSER warns of reversible cerebral ischemia, and support SSER monitoring as a useful measure of cerebral function during low-flow, hypothermic CPB.

Animals↗

A new technique of experimental heterotopic cardiac transplantation.

Heterotopic cardiac transplantation is a useful method for studying allograft rejection. In this study a new technique of cardiac transplantation was carried out, which involved retroperitoneal anastomoses of the donor ascending aorta and main pulmonary artery with the recipient abdominal aorta and inferior vena cava respectively. The procedure was simple and effective and was accomplished with minimal operative mortality and postoperative morbidity. The method allows better access to the allograft for repeated open myocardial biopsies, obviating the limitations of transvenous fluoroscopically directed endomyocardial biopsy. This technique of retroperitoneal heterotopic cardiac transplantation has important advantages compared with similar procedures performed in the neck, abdomen, or thorax.

Animals↗

Telemetric detection of cardiac allograft rejection. Correlation of electrophysiological, histological, and biochemical changes during unmodified rejection.

Intra-abdominal mismatched heterotopic cardiac allograft transplantation without immunosuppression was performed in eight pigs. Postoperatively, daily electrophysiological studies were carried out either with exteriorized temporary epicardial pacing wires (n = 4) or by a telemetrically controlled implanted pacemaker connected to permanent epicardial pacing leads (n = 4). Electrophysiological studies data were correlated with histopathologic and biochemical findings from daily myocardial biopsies. Electrophysiological studies revealed no significant alteration of sinus or atrioventricular node function, refractoriness, or ventricular pacing threshold. However, ventricular voltage amplitude, measured through the electrodes, decreased steadily with time in all donor hearts and was significantly correlated with histopathologic rejection grade (p less than 0.001) and with adenosine 5'-triphosphate (ATP) depletion (p less than 0.001). Ventricular voltage amplitude less than 75% of baseline occurred 4.5 +/- 1.5 days after transplantation, and this decreased voltage amplitude coincided with a moderate to severe (Grade 2 or 3) histological rejection pattern with a sensitivity of 89% (17 of 19) and a specificity of 77% (17 of 22). Similar changes in voltage amplitude were not found in control hearts. Myocardial tissue ATP values fell significantly from control values with early (Grade 1) rejection (p less than 0.05). Evidence for oxygen free radical injury was indicated by a rise in conjugated dienes of free fatty acids; this increase in diene level occurred 4.3 +/- 1.2 days postoperatively and then regressed during the terminal stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗