Peri-infarct ischaemia assessed by cardiovascular MRI: comparison with quantitative perfusion single photon emission CT imaging.

OBJECTIVE: To develop a new method for the cardiac MR (CMR) quantification of peri-infarct ischaemia using fused perfusion and delayed-enhanced images and to evaluate this method using quantitative single photon emission CT (SPECT) imaging as a reference. METHODS: 40 patients presenting with peri-infarct ischaemia on a routine stress (99m)Tc-SPECT imaging were recruited. Within 8 days of the SPECT study, myocardial perfusion was evaluated using stress adenosine CMR. Using fused perfusion and delayed-enhanced images, peri-infarct ischaemia was quantified as the percentage of myocardium with stress-induced perfusion defect that was adjacent to and larger than a scar. This parameter was compared with both the percent myocardium ischaemia (SD%) and the ischaemic total perfusion deficit (TPD). The diagnostic performance of CMR in detection of significant coronary artery stenosis (of ≥70%) was also determined. RESULTS: On SPECT imaging, in addition to peri-infarct ischaemia, reversible perfusion abnormalities were detected in a remote zone in seven patients. In the 33 patients presenting with only peri-infarct ischaemia, the agreement between CMR peri-infarct ischaemia and both SD% and ischaemic TPD was excellent [intraclass coefficient of correlation (ICC) = 0.969 and ICC = 0.877, respectively]. CMR-defined peri-infarct ischaemia for the detection of a significant coronary artery stenosis showed an areas under receiver-operating characteristic curve of 0.856 (95% confidence interval, 0.680-0.939). The best cut-off value was 8.1% and allowed a 72% sensitivity, 96% specificity, 60% negative predictive value and 97% positive predictive value. CONCLUSION: This proof-of-concept study shows that CMR imaging has the potential as a test for quantification of peri-infarct ischaemia. ADVANCES IN KNOWLEDGE: This study demonstrates the proof of concept of a commonly known intuitive idea, that is, evaluating the peri-infarct ischaemic burden by subtracting delayed enhancement from first-pass perfusion imaging on CMR.

Towards a computational reconstruction of the electrodynamics of premature and full term human labour.

We apply virtual tissue engineering to the full term human uterus with a view to reconstruction of the spatiotemporal patterns of electrical activity of the myometrium that control mechanical activity via intracellular calcium. The three-dimensional geometry of the gravid uterus has been reconstructed from segmented in vivo magnetic resonance imaging as well as ex vivo diffusion tensor magnetic resonance imaging to resolve fine scale tissue architecture. A late-pregnancy uterine smooth muscle cell model is constructed and bursting analysed using continuation algorithms. These cell models are incorporated into partial differential equation models for tissue synchronisation and propagation. The ultimate objective is to develop a quantitative and predictive understanding of the mechanisms that initiate and regulate labour.

Airway smooth muscle dynamics: a common pathway of airway obstruction in asthma.

Excessive airway obstruction is the cause of symptoms and abnormal lung function in asthma. As airway smooth muscle (ASM) is the effecter controlling airway calibre, it is suspected that dysfunction of ASM contributes to the pathophysiology of asthma. However, the precise role of ASM in the series of events leading to asthmatic symptoms is not clear. It is not certain whether, in asthma, there is a change in the intrinsic properties of ASM, a change in the structure and mechanical properties of the noncontractile components of the airway wall, or a change in the interdependence of the airway wall with the surrounding lung parenchyma. All these potential changes could result from acute or chronic airway inflammation and associated tissue repair and remodelling. Anti-inflammatory therapy, however, does not "cure" asthma, and airway hyperresponsiveness can persist in asthmatics, even in the absence of airway inflammation. This is perhaps because the therapy does not directly address a fundamental abnormality of asthma, that of exaggerated airway narrowing due to excessive shortening of ASM. In the present study, a central role for airway smooth muscle in the pathogenesis of airway hyperresponsiveness in asthma is explored.

Signaling pathways underlying eosinophil cell motility revealed by using caged peptides.

Insights into structure-function relations of many proteins opens the possibility of engineering peptides to selectively interfere with a protein's activity. To facilitate the use of peptides as probes of cellular processes, we have developed caged peptides whose influence on specific proteins can be suddenly and uniformly changed by near-UV light. Two peptides are described which, on photolysis of a caging moiety, block the action of calcium-calmodulin or myosin light chain kinase (MLCK). The efficacy of theses peptides is demonstrated in vitro and in vivo by determining their effect before and after photolysis on activities of isolated enzymes and cellular functions known to depend on calcium-calmodulin and MLCK. These caged peptides each were injected into motile, polarized eosinophils, and when exposed to light promptly blocked cell locomotion in a similar manner. The results indicate that the action of calcium-calmodulin and MLCK, and by inference myosin II, are required for the ameboid locomotion of these cells. This methodology provides a powerful means for assessing the role of these and other proteins in a wide range of spatio-temporally complex functions in intact living cells.

Calcium signalling during chemotaxis.

The role of Ca2+ in chemotaxis of eosinophils from the newt Taricha granulosa was investigated using fluorescent indicators and digital imaging microscopy. In response to serum chemoattractant, cytoplasmic Ca2+ concentration ([Ca2+]i) rises prior to polarization. In polarized locomoting cells [Ca2+]i gradients (tail-high-front-low) are always seen, and when cells turn [Ca2+]i rises transiently and falls fastest and furthest in the new direction of cell motion. These Ca2+ signals, which are required for polarization and locomotion, arise from Ca2+ derived from internal stores released in response to inositol 1,4,5-trisphosphate (InsP3) (because microinjected heparin fully blocks them). 1,2-Diacyl-sn-glycerol (DAG), which is co-produced with InsP3, has an inhibitory effect on Ca2+ signals, an effect apparently mediated by protein kinase C. Studies with caged InsP3 reveal that InsP3-responsive stores appear to be concentrated in the nuclear and microtubule-organizing centre regions and that InsP3 moves so rapidly within the cell that it is effectively a global secondary messenger. Thus, stable [Ca2+] gradients observed during unidirectional migration appear to result from the concentration of InsP3-responsive Ca2+ stores in the rear of the cell. By contrast, we propose that reorientation of the [Ca2+] gradient prior to a change in direction of motion results from the joint actions of InsP3 and DAG, with InsP3 acting as a global secondary messenger stimulating Ca2+ release and DAG, through protein kinase C, acting as a spatially restricted secondary messenger inhibiting [Ca2+] increases locally near the site of chemotactic stimulation.

Mediation of chemoattractant-induced changes in [Ca2+]i and cell shape, polarity, and locomotion by InsP3, DAG, and protein kinase C in newt eosinophils.

During chemotaxis large eosinophils from newts exhibit a gradient of [Ca2+]i from rear to front. The direction of the gradient changes on relocation of the chemoattractant source, suggesting that the Ca2+ signal may trigger the cytoskeletal reorganization required for cell reorientation during chemotaxis. The initial stimulatory effect of chemoattractant on [Ca2+]i and the opposite orientations of the intracellular Ca2+ gradient and the external stimulus gradient suggest that more than one chemoattractant-sensitive messenger pathway may be responsible for the generation of spatially graded Ca2+ signals. To identify these messengers, Ca2+ changes were measured in single live cells stimulated with spatially uniform chemoattractant. On stimulation spatially averaged [Ca2+]i increased rapidly from < or = 100 nM to > or = 400 nM and was accompanied by formation of lamellipods. Subsequently cells flattened, polarized and crawled, and [Ca2+]i fluctuated around a mean value of approximately 200 nM. The initial Ca2+ spike was insensitive acutely to removal of extracellular Ca2+ but was abolished by treatments expected to deplete internal Ca2+ stores and by blocking receptors for inositol-trisphosphate, indicating that it is produced by discharge of internal stores, at least some of which are sensitive to InsP3. Activators of protein kinase C (PKC) (diacyl glycerol and phorbol ester) induced flattening and lamellipod activity and suppressed the Ca2+ spike, while cells injected with PKC inhibitors (an inhibitory peptide and low concentrations of heparin-like compounds) produced an enhanced Ca2+ spike on stimulation. Although cell flattening and lamellipod activity were induced by chemoattractant when the normal Ca2+ response was blocked, cells failed to polarize and crawl, indicating that Ca2+ homeostasis is required for these processes. We conclude that InsP3 acting on Ca2+ stores and DAG acting via PKC regulate chemoattractant-induced changes in [Ca2+]i, which in turn control polarization and locomotion. We propose that differences in the spatial distributions of InsP3 and DAG resulting from their respective hydrophilic and lipophilic properties may change Ca2+ distribution in response to stimulus reorientation, enabling the cell to follow the stimulus.

Intracellular cyclic AMP produces effects opposite to those of cyclic GMP and calcium on shape and motility of neuroblastoma cells.

We have directly evaluated the effects of various intracellular second messengers including cyclic nucleotides, calcium ion, and inositol polyphosphates on shape and motility of differentiating mouse neuroblastoma cells. The messengers were microinjected into cells and the responses of the soma, neurite, and growth cone were monitored using time-lapse video microscopy. Each messenger altered cell shape and motility in a characteristic manner. Cyclic AMP promoted lamellipodial expansion, neurite outgrowth, and motility. The other injected messengers opposed motility. Cyclic GMP caused motile structures to freeze and to retract permanently, while the inhibitory effects of calcium injection were concentration-dependent. Small calcium injections affected specifically actin-containing motile structures which froze and retracted temporarily. Intermediate calcium injections caused a strong contraction at the site of injection in all cells. With large injections, cells retracted long neurites, rounded up, and frequently began vigorous blebbing that continued to cell death. Injections of the inositol polyphosphates IP3(1,4,5) and IP4(1,4,5,6) mimicked the effects of small calcium injections, as did electrical stimulation that elicited action potentials. The results suggest that in mouse neuroblastoma cells, intracellular cAMP elevation increases cytoskeletal organization and promotes neurite extension perhaps through an enhancement of cell-substratum adhesion. On the other hand, a rise of intracellular cGMP or intracellular calcium interferes directly with the function and organization of the actin-microfilament system. The integrated action of these second messenger systems may, therefore, operate in vivo to allow substances released from neighboring cells to regulate neuronal architecture.

Analysis of diffusion delay in a layered medium. Application to heat measurements from muscle.

An analysis is presented of diffusional delays in one-dimensional heat flow through a medium consisting of several layers of different materials. The model specifically addresses the measurement of heat production by muscle, but diffusion of solute or conduction of charge through a layered medium will obey the same equations. The model consists of a semi-infinite medium, the muscle, in which heat production is spacially uniform but time varying. The heat diffuses through layers of solution and insulation to the center of the thermal element where heat flow is zero. Using Laplace transforms, transfer functions are derived for the temperature change in the center of the thermopile as a function of the temperature at any interface between differing materials or as a function of heat production in the muscle. From these transfer functions, approximate analytical expressions are derived for the time constants which scale the early and late changes in the central temperature. We find that the earliest temperature changes are limited by the diffusivities of the materials, whereas the approach to steady state depends on the total heat capacity of the system and the diffusivity of muscle. Hill (1937) analyzed a similar geometry by modeling the layered medium as a homogeneous system with an equivalent half thickness. We show that his analysis was accurate for the materials in his system. In general, however, and specifically with regard to modern thermopiles, a homogeneous approximation will lead to significant errors. We compare responses of different thermopiles to establish the limits of time resolution in muscle heat records and to correct them for diffusional delays. Using numerical techniques, we invert the Laplace transforms and show the time course of the temperature changes recorded by different instruments in response to different patterns of heat production.

Heat changes during transient tension responses to small releases in active frog muscle.

Tension and heat production were measured in frog sartorius muscles in response to small shortening ramps (releases) at high and moderate speed. Transient tension responses to fast releases (0.1 to 0.4 mm in 1 or 4 ms) were similar to the tension transients length-clamped single fibers. Tension time courses during releases at 25 mm/s were like fiber responses calculated from the first two phases of the step responses (Ford et al., 1977). We conclude that similar crossbridge transitions produce tension transients observed in whole muscles and single fibers. Heat was absorbed during rapid tension recovery after fast releases and during the later part of releases at 25 mm/s. Variation of heat absorption with release size was compared with that of crossbridge movement predicted by the Huxley-Simmons hypothesis of force generation (Huxley and Simmons, 1971). Agreement between the two supports the conclusion that heat is absorbed by the crossbridge transitions responsible for rapid tension recovery after release. The results indicate that the entropy change of these transitions is positive.

The kinetics of heat production in response to active shortening in frog skeletal muscle.

1. Tension and heat production were measured at 0 degree C in sartorius muscles from Rana temporaria in response to two extents of shortening at five velocities. Shortening was from approximately 2.4 to 2.2 microns, 2.4 to 2.3 microns and 2.3 to 2.2 micron at velocities per half-sarcomere from 0.2 to 1.56 micron s-1. 2. Tension became approximately constant at all velocities. Records of heat rate obtained by differentiating traces from which thermoelastic heat had been subtracted became negative early in shortening and then rose. Heat rate became constant during shortening only at the lowest velocity and was still rising at the end of shortening at higher velocities. The highest heat rate occurred at the end of shortening at the two highest velocities. At the end of shortening at all velocities heat rate gradually approached the isometric level measured at the short length, the half-time for decline being largest following the slowest larger shortening. 3. Heat produced as a consequence of shortening but not associated with tension recovery was determined by subtracting shortening heat measured in response to two extents of shortening to the same muscle length. The differences in shortening heat continued to increase after shortening ended, and more of the extra heat produced in response to shortening appeared after the end of rapid shortening than during shortening itself. 4. Shortening heat coefficients calculated in different ways were similar to coefficients determined in previous studies. Coefficients calculated from measurements that excluded heat produced by tension recovery and allowed for continued production of heat by processes initiated by shortening were found to increase linearly with the force maintained during shortening. 5. The results show that the kinetics of heat production during and after shortening are very sensitive to the speed of shortening and that steady rates of energy liberation are not attained during shortening of less than or equal to 10% of muscle length at velocities greater than or equal to 12% of maximum velocity.

The effect of length range on heat rate and power during shortening near in situ length in frog muscle.

Heat rate and tension were measured during the steady state of isovelocity shortening in frog sartorius muscles at two speeds (7.5 and 2.0 mm s-1) through two ranges of the length-tension curve: 1.11 to 1.01 L0 and 1.01 to 0.91 L0. Both heat rate and mechanical power were higher at short length than at long length. The ratio of mechanical power to total energy rate was smaller at short length. The difference in heat rates in the two length ranges was greatest during shortening at 7.5 mm s-1 and least during isometric contractions. Calculations were made for two extreme interpretations of the results, based on the assumption that 30% of the isometric maintenance heat rate at optimum length is produced by processes related to activation: that all the difference in heat rate results from effects of length on activation processes and that all the difference results from effects on contractile processes. The rate of heat production by activation processes would have to be 1.5 times higher at short than at long length in an isometric contraction, 1.7 times higher during shortening at 2mm s-1 and 2.0 times higher at 7.5 mm s-1 to explain the differences in heat rate. The rate of contractile processes would have to be only 1.2 times higher at short than at long length. The results favour the interpretation that the contractile process itself is sensitive to sarcomere length near the plateau of the length-tension curve.(ABSTRACT TRUNCATED AT 250 WORDS)

The thermoelastic effect in rigor muscle of the frog.

Small length changes were imposed on pairs of sartorius muscles from Rana temporaria and Rana pipiens in rigor and the mechanical and thermal responses studied. Rigor was induced by soaking the muscles overnight at 0 degrees C in a physiological salt solution containing 1.5 mM sodium azide and 0.4 mM sodium iodoacetate. Tension was measured at both the tibial and the pelvic ends of the preparation. Muscles were held at a steady tension of 20 to 76 kN m-2 and stretches or releases of 0.02 to 0.6 mm applied in pairs, with the initial change reversed several hundred milliseconds later. Single stretches resulted in heat absorption and releases in heat production by the preparation. Net heat production resulted from complete cycles of length changes larger than 0.1 mm, whether the initial change was a stretch or a release. The heat produced by the complete cycle was attributed to the movement of the muscles over the thermopile. It was proportional to the difference in tension between the tibial and pelvic ends of the preparation and increased with the size and speed of the length change. Half the heat produced by a complete cycle of length changes was subtracted from the thermal response recorded in the first half-cycle to obtain the reversible component of the response. The reversible component was linearly related to the tension change for all sizes and speeds of length change which were studied, with the heat:tension ratio ranging from -0.0093 to -0.0179 in eleven muscles (mean -0.0128 +/- 0.0009). The constancy of the heat:tension ratio in rigor muscles over a wide range of mechanical conditions indicates that the source of the thermal changes is the normal elasticity of the preparation. Since the size of the ratio is approximately the same as that measured in active muscles, the tension-dependent component of the thermal response to length changes applied to active muscles is probably also of elastic origin.

Variation in the isometric maintenance heat rate with muscle length near that of maximum tension in frog striated muscle.

1. Tension and heat rate were measured as a function of muscle length in the range 0.75--1.25 lO in 10-sec isometric tetani in frog striated muscle at 0 degrees C in seven experiments. lO was defined as the length at which maximal tension was developed. 2. The length at which the stable maintenance heat rate (hB) was maximal was 7--16% lO shorter than the length at which tension was maximal (Pmax). 3. The range of hB at the length at which tension was maximal was 0.82-0.97 times the maximum value of hB. 4. For equal values of tension of 0.9 Pmax on each side of lO, hB was almost 40% greater at the shorter muscle length. 5. The results show that h(B) varies considerably with muscle length near lO, where tension varies little, and imply that tension is not the sole determinant of energy liberation in this little region.

Echocardiographic assessment of normal and abnormal valvular function in Beagle dogs.

Echocardiograms were obtained from 5 young Beagles (4 to 5 years of age) and from 4 old Beagles (12 to 14 years of age). Ultrasound surface transducers and esophageal transducers were used on all animals during anesthesia. Triplicate studies were performed on the 5 young Beagles over a 2-week period. The left atrioventricular valve and aortic root were identified by both procedures, whereas the right atrioventricular valve dynamics could be viewed with difficulty by the transcutaneous approach. Suitable recordings of the pulmonary valve were not obtainable with either technique. Abnormal left atrioventricular valve dynamics, characterized by a decreased closing velocity of the left atrioventricular septal cusp and increased valve thickness, were observed in 2 of the 4 aged dogs, using echocardiography. Excellent correlation between the 2 methods was evident, and minimal variation in results from one recording session to another occurred.

Tension and heat production during isometric contractions and shortening in the anterior byssus retractor muscle of Mytilus edulis.

1. Tension and heat production were measured during phasic isometric contractions and isovelocity shortening in the anterior byssus retractor muscle (ABRM) of Mytilus edulis at 20 degrees C. 2. Isometric tension at lo was 550 +/- 40 mN/mm2 (S.D. for 173 observations in nine muscles), while the isometric maintenance heat rate was 1.0 +/- 0.2 mW/g wet wt. (S.D. for seventy-eight observations in eight muscles). 3. Isometric tension and heat production were measured as functions of muscle length over a range of 0.79--1.14 lo and were found to bear a linear relation to each other. 4. The force-velocity relation was determined in isovelocity releases imposed during tetanic stimulation and was found to fit the Hill equation with parameters alpha/Po = 0.07 +/- 0.01 and b/lo = 0.016 +/- 0.0007 sec-1 (S.E. from non-linear least-squares regression of the pooled data from seven experiments). 5. Heat production measured in the same experiments showed that shortening heat is produced with a shortening heat coefficient alpha/Po of 0.15. Shortening heat does not appear to be force-dependent, and separate experiments confirmed that it is a linear function of the amount of shortening.

A reexamination of the thermoelastic effect in active striated muscle.

Isolated Rana pipiens sartorius muscles at 0degreeC were stimulated via their nerves and small stretches or releases applied during the plateau of the isometric tetanus at lo. Extra heat above the isometric maintenance heat was produced during the drop in tension caused by release and, for very small releases (delta less than or equal to 0.5% lo), was completely reabsorbed during tension recovery. The extra heat was always directly proportional to the tension change. Heat absorption proportional to the tension change was also observed during the increase in tension produced by small stretches in the range 0.5% lo less than or equal to deltal less than or equal to 3.0% lo. The mean heat:tension ratio R in seven experiments was -0.0084, which is within the range of values reported previously by Woledge. In addition, it was found that during tension recovery after small releases of 1.0% lo less than or equal to deltal less than or equal to 3.0% lo the "contractile" component seems able to shorten about 1% lo without producing shortening heat.