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Interactions between the two myosin heads were studied in skinned rabbit slow-twitch muscle fibers activated in the presence of vanadate (Vi), a phosphate analog. The strong complex between Vi, MgADP, and myosin trapped the myosin in an inactivated myosin x MgADP x Vi state. Electron paramagnetic resonance spectroscopy was used to quantitate the fraction of myosin heads trapped in the presence of a spin labeled analog of ATP (SLATP). Force was found to depend directly on the fraction of untrapped heads. At high [Vi] (low force), most untrapped heads would have a trapped partner. The equivalence of force with the proportion of untrapped heads shows that the isometric force produced by a single untrapped myosin head on a molecule with a trapped partner is equivalent to that produced by either head of a myosin molecule with neither head trapped. The actin-activated MgATPase activities of one-headed and two-headed skeletal myosin species were inhibited similarly by Vi, suggesting that trapping one head did not preclude trapping its partner. These data indicate that the two skeletal muscle myosin heads can function without interacting during maximal Ca2+-activated force generation.

This study investigated the relationship between musculotendinous stiffness and the ability to perform dynamic stretch-shorten cycle actions involving a range of eccentric loads. Twenty trained male subjects performed a series of quasi-static muscular actions in a supine leg press position, during which a brief perturbation was applied. The resulting damped oscillations allowed the estimation of each subject's maximal musculotendinous stiffness (k) for the lower body musculature. All subjects also performed a countermovement jump (CMJ) and a series of drop jumps (DJs) from heights of 20, 40, 60, 80, and 100 cm. When the jump heights of the nine most compliant (mean k = 11.4 ± 2.7 kN•m−1) and nine stiffest (mean k = 20.5 ± 2.5 kN•m−1) subjects were compared, the stiff subjects demonstrated significantly poorer capacity to perform under the highest (DJ80 and DJ100) eccentric loading conditions. It was hypothesised that the relatively greater forces transmitted from the skeletal system to the musculature of the stiff subjects reduced their ability to attenuate the higher eccentric loads due to less effective contractile dynamics and greater levels of reflex induced inhibition. Key words: series elastic component, compliance, drop jump, muscle elasticity, eccentric contraction

We have developed a multistep detergent-enzymatic extraction process (involving hypotonic and hypertonic solutions, the detergents octyl-phenoxy-polyethoxyethanol and sodium dodecyl sulfate, as well as DNAse and RNAse) which, while inhibiting autolysis, removes all cells from tissues and, with them, cellular antigens together with lipids and more soluble glycosaminoglycans. What remains is acellular matrix with the structural proteins well conserved and normally arranged. Canine arteries extracted to acellular matrix were implanted as coronary artery bypass allografts in a canine model, without the use of cardiopulmonary bypass, and compared with autogenous saphenous veins. Of nine pilot acellular matrix implants, four were patent, as compared with four of seven saphenous vein grafts. All occlusions in both graft types occurred acutely soon after implantation, with almost all patent grafts followed up for 6 months. The acellular matrix allografts showed no inflammation and only minimal cellular repopulation. This model needs further development, but appears promising for preclinical evaluation. Canine aortic and pulmonic valves extracted to acellular matrix using a modification of our extraction process, eliminating the detergent sodium dodecyl sulfate, were implanted heterotopically as allografts in the left main pulmonary artery in dogs, a location chosen to avoid the need for cardiopulmonary bypass. At 1 month, two-dimensional echocardiography of six implants showed leaflet motion and 3-to 5-mm Hg transvalvular gradients. Expiant histology of four valves at 1 month showed no inflammation, cellular repopulation at the base of the valve, and partial endothelialization. Although much remains to be done, the acellular matrix process has the potential to produce a coronary artery bypass graft with performance similar to that of autogenous saphenous vein and a bioprosthetic heart valve with performance similar to cryopreserved homografts, both from an abundant supply of nonhuman tissues

We report four cases of necrotizing fasciitis that occurred following varicella in children ranging in age from 2 to 8 years. The only organism isolated from each of these patients was Streptococcus pyogenes or group A beta-hemolytic Streptococcus (GABHS). Each child recovered; however, three required repeated surgical debridements in addition to therapy with antibiotics. An interesting finding in these patients was the development of hyponatremia and/or hypocalcemia. M-typing and T-typing of the isolates demonstrated that the GABHS strain in two children who attended the same school was M5; M1 and M3 strains were identified in the other two children. In addition to the children described in this series, eleven other cases of children with necrotizing fasciitis following varicella have been reported in the English-language literature since 1970. We believe that these cases provide further evidence that varicella is an important risk factor for necrotizing fasciitis that is caused by more-virulent strains of GABHS.

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Objective: It has recently been suggested that conductance catheter parallel conductance (αVc) is a function of left ventricular volume. To confirm this, αVc was measured in this study over a wide range of steady state volumes. In addition, conductance derived volumes were compared to those obtained by radionuclide angiography to determine if the conductance catheter can be used to measure absolute left ventricular volume accurately in the intact dog heart. Methods: Seven dogs were anaesthetised and instrumented with left ventricular conductance and pressure tip catheters, a flow through rho cuvette to continually measure blood resistance, a thermodilution catheter, and a venous catheter for volume infusion/withdrawal. Conductance and angiographic data were acquired at 8(SD 1) variably loaded states. Parallel conductance was measured twice at each state using a saline dilution technique and a new non-linear algorithm that allows variability in the observations of both maximum and minimum conductance volumes. Results: The mean value of αVc was 89.1(18.0) ml (71.8 to 111.3 ml) with a mean within-animal coefficient of variation of 7.3(3.4)%. Multiple linear regression using dummy variables to account for the large interanimal variability did not reveal any relationship between αVc and either maximum or minimum left ventricular volume. Furthermore, no difference was found when αVc values measured at the lowest and highest loading levels in each dog were compared. Linear regression showed good agreement between conductance and radionuclide derived end diastolic volumes (slope = 0.94, R = 0.9, p

Objective: The aim was to compare the effects of ischaemic preconditioning in the buffer perfused and parabiotic blood perfused Langendorff rabbit heart models. Methods: Isolated hearts were perfused with either Krebs-Henseleit buffer solution or blood from a support rabbit. Hearts were subjected to an initial 30 min stabilisation period followed by 30 min of global ischaemia and 60 min of reperfusion. Ischaemic preconditioned (IP) hearts were also subjected to one cycle of 5 min global ischaemia and 10 min of reperfusion before the 30 min ischaemia. For each experiment, left ventricular function and necrosis were measured. Results: Necrosis, as measured by tetrazolium staining and expressed as a percentage of the left ventricular area, was significantly different between the buffer perfused control [42.5%(SEM 6.9), n=7] and buffer perfused IP group [22.2%(5.4), n=7, p

An initial numerical/experimental investigation has been done to better understand multi-dimensional flow phenomena inside pulse facilities. Time-dependent quasi-one-dimensional and axisymmetric numerical simulations of complete shock tube flow are compared with experimental pressure traces recorded at the NASA Ames electric-arc driven shock tube facility (from cold driver shots). Of particular interest is the interaction between the reflected shock wave and the boundary layer. Evidence of the shock bifurcation caused by this interaction is clearly seen in the present experimental data. The axisymmetric simulations reproduce this phenomenon and demonstrate how this interaction can provide a mechanism for driver gas to contaminate the stagnation region. The simulations incorporate finite-rate chemistry, a moving mesh and laminar viscosity.

A numerical methodology is presented for simulating the time-dependent reacting flow inside the entire length of high enthalpy pulse facilities. The methodology is based on a finite-volume TVD scheme for the quasi-1D Euler equations coupled with finite-rate chemistry. A moving mesh and tracking of gas interfaces are used to overcome certain numerical difficulties associated with these types of flows. Simulation results of a helium driven shock tube show that computations can be used to predict the off-tailored behavior of shock tubes and tunnels. Particular attention is given to computations of the flow through the NASA Ames 16-inch combustion driven shock tunnel which show the influence of nonuniformities in the driver section on the reservoir conditions; and the effect of finite secondary diaphragm opening times on the chemical composition of the test flow in the HYPULSE expansion tube.

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A method for plaque dissolution has been identified that percutaneously delivers a pulsatile high-velocity stream of saline to the site of an atheromatous lesion within a coronary or peripheral artery. In vitro evaluation and in vivo canine and porcine testing were performed using this 'rheolytic' system to deter mine its feasibility in ablating calcified plaque and soft thrombotic tissue. A prototype rheolytic guidewire capable of providing 30,000 psi of internal pressure was designed to fit within the guidewire lumen of a standard percutane ous transluminal coronary angioplasty catheter. An additional over-the-wire rheolytic catheter was fabricated to follow a standard .014-inch guidewire. The rheolytic devices were tested in vitro with simulated atheromatous and thrombotic lesions to evaluate the size and quantity of the particulate effluent. The particulate was then sterilized, mixed with saline, and introduced percutaneously into the animal kidney and heart for evaluation. The in vitro studies demonstrated that the rheolytic catheter and guidewire were able to follow both a coronary and femoral arterial model and successfully ablate the simulated lesions. The particle size for osseous, muscular, and car tilagenous tissue. ranged from 2 to 6 micrometers; for fresh human plaque the particles ranged from 2 to 15 micrometers. Injection of cartilagenous and plaque particles into the animal model caused very slight regions of necrosis but no clinical sequelae . Applications of the rheolytic devices to the animal femoral artery demonstrated that both devices could ablate and cross calified or soft thrombosed lesions without damage to the vessel wall; the rheolytic catheter provided a debulking of the plaque. The ability to cut through calcified and soft lesions with the rheolytic devices without thermal damage may provide this system with advantages over current atherectomy methods. Its flexibility suggests that it may have applications in the coronary position.

To assess whether steroid therapy influenced the clinical course of myocarditis in a pediatric population, findings in 13 consecutive infants and children (8 female, 5 male) with biopsy-proved myocarditis were reviewed. The mean age was 5.7 +/- 4.8 years (range 1.1 to 14.8). Congestive heart failure was present in all as were ST-T wave changes, cardiomegaly and pulmonary edema on chest roentgenogram. Echocardiography demonstrated pericardial effusion in five patients and mitral regurgitation in eight. Mean left ventricular ejection fraction was 34 +/- 12%. Prednisone was administered to all patients; one patient also received azathioprine. There was one death. All survivors showed clinical improvement with normalization of ECG changes, heart size and systolic function. No significant side effects occurred. Repeat myocardial biopsy in eight patients demonstrated improvement in all eight and elimination of the inflammatory infiltrate in six. Immunosuppressive therapy in this pediatric population appeared useful in improving the clinical course and cardiac function in acute myocarditis with no adverse side effects.

Dr Wilson is a Research Scientist in the CSIRO Division of Energy Technology. He completed his B.AppSci.(Hons) in 2001 and received his Ph.D. in 2006 from the Queensland University of Technology under Dr Geoffrey D. Will in the field of heterosupramolecular assembly. His current research interests are focussed on novel nanostructured materials for application in electrochemical energy storage devices. Manuscript received: 13 August 2007. Final version: 17 October 2007.

Mass-transfer properties of a continuously reciprocating paddle reactor are investigated using computational fluid dynamic simulations. The flow induced by the paddle motion is modeled with a moving mesh assuming laminar flow. Spatial and temporal mass-transfer data are gathered over many paddle cycles under diffusion-limited conditions. Transient, numerical simulations of this type are computationally expensive, but can add insight into flow phenomena that are difficult to observe experimentally. It is shown that a major source of the agitation in a paddle cell is vortices shed from the paddle. This results in a mass-transfer limit that is periodic in nature and that may exhibit spatial variations related to the paddle wake. A simulation-based, mass-transfer correlation is presented that relates various design and operating parameters within a generic paddle reactor. The mass-transfer trends predicted by the numerical simulations are compared with experimental mass-transfer correlations found in the literature.

A tracer study was conducted on a low-energy beach in Delaware Bay to determine how the nutrient washout rate is affected by the tidal cycle. When tracer was applied during spring tide, it was reduced to background levels following a single high tide; but when it was applied during neap tide, tracer persisted in the bioremediation zone for a much longer time. The washout rate was found to be related to the extent of water coverage during high tide.

THE EFFECT OF INCREASING THE COMPLIANCE OF THB MUSCULO-TENDINOUS SYSTEM ON THE PERFORMANCE OF A STRETCH SHORTEN CYCLE MOVEMENT Gregory J. Wilson*, Bruce C. Elliott+ and Graeme A. Wood+ *Centre for Human Movement Science & Sport Management, The University of New England-Northern Rivers, Lismore NSW 2480, Australia. +Department of Human Movement, The University of Western Australia, Nedlands, WA 6009, Australia. Sixteen experienced male powerlifters served as subjects in a training study designed to examine the effect of flexibility training on: (i) the stiffness of the series elastic components (SEC) of the upper body musculature and (ii) rebound and purely concentric bench press performance. in two sessions of flexibility training twice a week for eight weeks. Nine of the subjects participated Prior to and after the training period the subjects’ static flexibility, SEC stiffness, rebound bench press (RBP) and purely concentric bench press (PCBP) performance were recorded. The flexibility training induced a signiticant reduction in the maximal stiffness of the SEC. Further, the experimental subjects produced significantly more work during the initial concentric portion of the RBP lift enabling a significantly greater load to be lifted in the post-training testing occasion. The benefits to performance achieved by the experimental group consequent to flexibility training were greater during the RBP lift as compared to the PCBP lift. The control subjects exhibited no change in any variable over the training period. These results implied that the RBP performance enhancement observed consequent o flexibility training were directly caused by a reduction in SEC stiffness increasing the utilization of elastic strain energy during the RBP lift.

WILSON, G. J., B. C. ELLIOTT, and G. A. WOOD. Stretch shorten cycle performance enhancement through flexibility training. Med. Sci. Sports Exerc., Vol. 24, No. 1, pp. 116–123, 1992. Sixteen experienced male powerlifters served as subjects in a training study designed to examine the effect of flexibi

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.

The safe period of anoxic arrest of the heart is related to its individual metabolic activity rather than to a specific time interval. The capacity of the heart to produce energy through anaerobic metabolism, on which survival depends, has been assessed in this study by continuous monitoring of intramyocardial carbon dioxide tension (Pco2). Two groups of 12 dogs each were placed on total cardiopulmonary bypass at 38° C. and 28° C., respectively. Anoxic arrest of the heart was produced by cross-clamping of the ascending aorta and venting of the left ventricle. Intramyocardial Pco2 was measured by a mass spectrometer, and carbon dioxide accumulation curves were plotted. An initial period during which the Pco2 increased in a linear fashion was followed by a period during which the rate of rise gradually decreased until a plateau was reached. If the arrest was terminated at the transition point between these two periods, all hearts could be resuscitated. If the arrest was terminated when the carbon dioxide accumulation curve had reached a plateau, none of the hearts could be resuscitated. These results are given in the text. Our technique defines a point at which anoxic arrest can be safely terminated. This point can be significantly extended by reducing the metabolic activity of the heart by moderate hypothermia.

Twenty-four rectangular metal plates were fabricated with surface regions in three different pore size ranges (5-20 microns, 20-50 microns, 50-200 microns). The plates were implanted into the dorsal subcutaneous tissue of 12 adult mongrel dogs for periods of 4, 8, 12, and 16 weeks. After animal sacrifice, the fibrous tissue which adhered to the porous-surfaced regions of each plate was mechanically peeled off to give an indication of the strength of tissue attachment. The tissue was examined by both transmitted light and scanning electron microscopy. At each time period, the tissue that contacted the porous regions was found to be collagenized fibroconnective tissue. The mechanical tests indicated an increasing strength of tissue attachment with increasing implantation time and pore size range. The largest pore size range of approximately 50-200 microns produced a mean peel strength of attachment of 27.5 g/mm at the 16-week period.

Multidose administration of cardioplegic solution during cardiac operation is intended to maintain both electromechanical arrest of the heart and myocardial hypothermia as well as to remove accumulated metabolites of anaerobic glycolysis. This study was conducted to assess the effect of multidose infusion of three different types of cardioplegic solution on tissue acidosis during global myocardial ischemia. Three groups of five dogs each were placed on cardiopulmonary bypass and the aorta was cross-clamped for 3 hours. The hearts were maintained at a constant temperature (20° C) and cardioplegic solution was infused at an initial dose of 500 ml and five supplementary doses of 250 ml administered every 30 minutes. Group 1 received a crystalloid solution weakly buffered with sodium bicarbonate, Group 2 received a blood-based solution, and Group 3 received a crystalloid solution strongly buffered with histidine (Bretschneider's solution). The buffering capacities of the solutions used in Groups 2 and 3 were 40 and 60 times, respectively, that of the solution used in Group 1. The average myocardial tissue pH at the end of 3 hours of ischemia was 6.54 ± 0.07 in Group 1, 7.23 ± 0.05 in Group 2, and 7.19 ± 0.06 in Group 3 (Group 1 significantly lower than Groups 2 and 3). Multidose infusion of a cardioplegic solution with low buffering capacity was unable to prevent the progressive development of tissue acidosis during 3 hours of ischemia. However, the multidose infusion of either blood-based or crystalloid solutions with high buffering capacity completely prevented any further reduction of tissue pH after the first 30 minutes of ischemia.

Although endocardial excision and encircling endocardial ventriculotomy are being performed in patients with extensive triple-vessel disease and compromised ventricular function, long-term effects of the operative intervention on structure and function of the left ventricle have not been determined. These procedures were performed in healthy dogs in three groups: control (ventriculotomy alone), endocardial excision, and encircling endocardial ventriculotomy (five dogs per group). Six weeks later, through a left thoracotomy, an arterial line, left atrial line, and Swan-Ganz catheter were inserted. Cardiac output measurements permitted calculation of left ventricular stroke work index, and gated nuclear ventriculograms permitted calculation of left ventricular volume indices. Myocardial performance (stroke work index/end-diastolic volume index relation), systolic elastance (systolic blood pressure/end-systolic volume index relation) and diastolic pressure-volume relationship (left atrial pressure/end-diastolic volume index relation) were determined from volume loading studies. In the endocardial excision group, the left atrial pressures were increased at similar end-diastolic volumes (p

The early recognition and reversal of ischemic spinal cord injury have not been successfully accomplished during the conduct of surgical procedures requiring temporary occlusion of the thoracic aorta. Using a model of spinal cord infarction, we evaluated (1) a technique of perfusion cooling of the spinal cord designed to protect against the development of perioperative ischemic injury and (2) the utility of somatosensory cortical evoked potentials (SCEP) elicited by peripheral nerve stimulation in the detection of spinal cord dysfunction during normothermic and hypothermic ischemia. Six dogs (Group I) subjected to proximal and distal occlusion of the thoracic aorta for a 30 minute period at normothermia uniformly-sustained complete neurologic lesions confirmed by functional and histologic assessment. In a second group of six animals (Group II) likewise subjected to 30 minutes of aortic occlusion, regional cooling of the spinal cord was accomplished by perfusion of the thoracic intercostal arteries in the isolated aortic segment with an asanguineous hypothermic solution. The latter intervention substantially protected against the development of irreversible spinal cord injury; only one animal in this group had temporary postoperative paraparesis, and all animals had only minor abnormalities on histologic examination of the spinal cords (Group I versus Group II, p

Failure to reestablish blood flow to the subendocardium of the left ventricle may occur after prolonged myocardial ischemia and it has been suggested that edema may be responsible for this “noreflow” phenomenon. However, the process of ischemic contracture is also associated with prolonged myocardial ischemia and an inability to reperfuse the subendocardium. This study was designed to clarify the relative roles of edema and contracture in the pathogenesis of subendocardial “no-reflow.” This objective was achieved by determining the transmural distribution of tissue blood flow and water content across the wall of the left ventricle, in both the presence and absence of contracture, during the reperfusion phase after global myocardial ischemia of sufficient duration to exhaust myocardial anerobic metabolism. We made use of the fact that ischemic contracture can be inhibited in the intact canine heart by decreasing the temperature to a level of moderate hypothermia (28°C) in order to separate the variables of contracture and edema. We found that the subendocardial “no-reflow” phenomenon was present when contracture was present, but absent when contracture was absent. While edema, assessed by tissue water contents in excess of control values, was much greater in the deeper layers of the left ventricular wall in the absence of contracture than in its presence, there was no evidence that it impeded myocardial blood flow. Edema was indeed found to be greater in regions of greater flow. These findings challenge the concept that myocardial edema following ischemic arrest in cardiac surgery is directly responsible for inadequate reperfusion leading to necrosis.

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.