Acoustic microscopy system: design and preliminary results.

An acoustic microscopy system was designed to perform 2D imaging in the C-plane with a single-element transducer. The ultrasound transducer was fabricated by polishing bulk lithium niobate (LiNbO(3)) to the required thickness (approximately 60 or 45 micro) for the desired operating frequency (55 or 75 MHz). The polished LiNbO(3) was attached to acoustic backing and matching layers. Finally, an epoxy lens was applied and the transducer mounted in a housing. The transducer was mounted in a 3D motorized positioning stage and operated by a high-frequency pulser/receiver. Received echoes were sampled with a 2 GHz ADC card and displayed on a PC using software developed in the Matlab environment. Transducer frequency and bandwidth were measured off a steel plate positioned at the focal length. A penny was scanned initially to confirm expected performance before acquiring data from liver (n=3) and spleen (n=3) specimens. For the first probe, the peak frequency was 54.05 MHz with a -6 dB bandwidth of 6.76 MHz. The axial and lateral resolutions were estimated to be 114 and 188 microm, respectively. For the second probe, the peak frequency was measured to 82 MHz with a -6 dB bandwidth of approximately 23 MHz. The axial and lateral resolutions were estimated to be around 33 and 81 microm, respectively. C-scans of the penny clearly showed detailed structures on front and back, while the capsule and the trabecular structures of the splenic tissues could easily be separated in different layers. In conclusion, an acoustic microscopy system operating at 55-75 MHz has been constructed and the feasibility of obtaining high-resolution images of tissue specimens demonstrated.

Altered cross-bridge characteristics following haemodynamic overload in rabbit hearts expressing V3 myosin.

1. Our goal in this study was to evaluate the effect of haemodynamic overload on cross-bridge (XBr) kinetics in the rabbit heart independently of myosin heavy chain (MHC) isoforms, which are known to modulate kinetics in small mammals. We applied a myothermal-mechanical protocol to isometrically contracting papillary muscles from two rabbit heart populations: (1) surgically induced right ventricular pressure overload (PO), and (2) sustained treatment with propylthiouracil (PTU). Both treatments resulted in a 100 % V3 MHC profile. 2. XBr force-time integral (FTI), evaluated during the peak of the twitch from muscle FTI and tension-dependent heat, was greater in the PO hearts (0.80 +/- 0.10 versus 0.45 +/- 0.05 pN s, means +/- S.E.M., P = 0.01). 3. Within the framework of a two-state XBr model, the PO XBr developed more force while attached (5.8 +/- 0.9 versus 2.7 +/- 0.3 pN), with a lower cycling rate (0.89 +/- 0.10 versus 1.50 +/- 0.14 s(-1)) and duty cycle (0.14 +/- 0.03 versus 0.24 +/- 0.02). 4. Only the ventricular isoforms of myosin light chain 1 and 2 and cardiac troponin I (cTnI) were expressed, with no difference in cTnI phosphorylation between the PO and PTU samples. The troponin T (TnT) isoform compositions in the PO and PTU samples were significantly different (P = 0.001), with TnT2 comprising 2.29 +/- 0.03 % in PO hearts versus 0.98 +/- 0.01 % in PTU hearts of total TnT. 5. This study demonstrates that MHC does not mediate dramatic alterations in XBr function induced by haemodynamic overload. Our findings support the likelihood that differences among other thick and thin filament proteins underlie these XBr alterations.

Cross-bridge dynamics in the contracting heart.

The mechanical characteristics of the myosin motor is one of the key determinants of ventricular function. In small mammals there are two myosin isoforms, V1 and V3, with profoundly different performance characteristics. We used myothermal and mechanical analysis of intact papillary muscles from thryoxine (V1) and popylthiouracil (V3) treated rabbit hearts to assess the mechanical attributes of the myosin cross-bridge cycle. The average cross-bridge force time integral for V1 papillary muscles is 0.15 +/- 0.02 pNs for the entire isometric twitch and 0.19 +/- 0.03 pNs for the portion of the isometric twitch between 0.9 peak isometric force for the rising and declining portions of the twitch. The ratio of V1/V3 for the cross-bridge force time integral for the entire twitch and at the peak of the twitch is 0.5 (p < 0.05) and 0.4 (p < 0.05), respectively. Since the peak of the twitch measurements minimize internal shortening only these will be presented below. The average unitary force and attachment time during the peak of the twitch for V1 hearts was 1.55 +/- 0.37 pN and 140 +/- 20 msec, respectively. The ratios of V1/V3 for these parameters were 0.6 (p < 0.05) and 0.8 (ns). The cycling rate and duty cycle for V1 were 4.37 +/- 0.81 cycles per head-second and 0.66 +/- 0.22. The ratios of V1/V3 for cycling rate and duty cycle were 2.8 (p < 0.05) and 2.7 (ns). These measurements are consistent with and help explain the energetic and mechanical function of the intact heart.

Molecular motor mechanics in the contracting heart. V1 versus V3 myosin heavy chain.

The amount of iron in the low molecular weight pool (LMW) increases during no-flow ischemia and is thought to be essential to oxygen radical-derived damage upon reperfusion. Applying three short ischemic periods (5 min) preconditioning before 15 min ischemia results in an improved contractility compared to a direct 15 min ischemic insult. This raises the question whether preconditioning leads to a decrease in hte LMW iron pool. We therefore investigated the change in in hte LMW iron pool during ischemic insult after applying preconditioning. It is assumed that an increase in LMW iron is dependent on the accumulation of reduction equivalents derived from the anaerobic glycolysis. Therefore the glycogen content was also reduced by administration by anoxia and glucagon administration to study the effect on the LMW iron pool.

Sphenopalatine ganglion block: a safe and easy method for the management of orofacial pain.

The sphenopalatine ganglion (SPG) block is a safe, easy method for the control of acute or chronic pain in any pain management office. It takes only a few moments to implement, and the patient can be safely taught to effectively perform this pain control procedure at home with good expectations and results. Indications for the SPG blocks include pain of musculoskeletal origin, vascular origin and neurogenic origin. It has been used effectively in the management of temporomandibular joint (TMJ) pain, cluster headaches, tic douloureux, dysmenorrhea, trigeminal neuralgia, bronchospasm and chronic hiccup.

Time course of mechanical efficiency during afterloaded contractions in isolated cardiac muscle.

The time course of mechanical efficiency during working contractions in rabbit papillary muscle is presented. Efficiency is found to remain relatively constant during the working portion of the twitch, when the muscle is contracting against a constant load. As afterload was decreased, efficiency increased to 65 +/- 11% (mean +/- SE, n = 3) at 10% developed force at maximum length. This is in contrast to muscle work, which reached a peak of 3.0 +/- 0.3 (n = 6) mJ/g at 50% developed force at maximum length.

Estimated time course of Ca2+ bound to troponin C during relaxation in isolated cardiac muscle.

We present a mechanical assay for estimating the time course of Ca2+ bound to low-affinity sites on troponin C (TnC) in twitching rabbit papillary muscle. The assay is based on a theoretical correlation between the rate of force redevelopment after detachment of all cross-bridges and the amount of Ca2+ bound to TnC. Experimentally, we applied length impulses at different times to detach all cross-bridges; the initial rate of force redevelopment after each impulse was taken as an index of bound Ca2+ at that time. Under control conditions, the magnitude of this index decreased to 10% of its maximum during early relaxation, when force had declined only slightly 78 +/- 12% of its peak isometric value. The time course of this index was examined after addition of either isoproterenol or ryanodine, which are known to shorten and prolong, respectively, the intracellular free Ca2+ transient. As expected, changes previously reported in the free Ca2+ time course were qualitatively reflected in the time course of the bound Ca2+ index. We conclude that this index constitutes a reasonable method for estimating the time course of bound Ca2+ and that bound Ca2+ declines well ahead of force in isometrically contracting rabbit myocardium at 24 degrees C.

Control of segment length or force in isolated papillary muscle: an adaptive approach.

Mechanical studies of isolated cardiac muscle are complicated as a result of damage inflicted on the ends of the muscle during excision and mounting procedures. Inhomogeneities between the healthy central and weakened end portions of the muscle make it difficult to interpret studies where only total muscle length is controlled. Measurement and control of central segment length is clearly desirable but fraught with technical difficulties. We present a novel application of adaptive control methods that minimizes the difficulties encountered with current control techniques. This method, which allows control of either segment length or force, takes advantage of the repetitive, periodic nature of contractions. Here deviations of measured segment length or force signals from a desired response during one twitch are used to modify the muscle length command signal for use on the next twitch. This process continues for successive twitches until either segment length or force is within desired limits. The adaptive method allows greater stability and immunity to noise than classical feedback strategies.

Effect of isoproterenol on force transient time course and on stiffness spectra in rabbit papillary muscle in barium contracture.

To determine whether catecholamines produce alterations in myocardial myosin-actin cycling kinetics, we investigated the effects of isoproterenol upon mechanical characteristics of constantly activated heart muscle thought to reflect crossbridge behavior. In isolated rabbit right ventricular papillary muscles in barium contracture at 24 degrees C, we found that 10 microM isoproterenol caused: (a) a 23% reduction of the 10 to 90% rise time of slow tension recovery in force transients induced by rapid, small amplitude stretches; and (b) a 23% increase in the frequency of sinusoidal length perturbation at which stiffness amplitude exhibited a minimum. Based upon previous mechanistic interpretations of force transients, and on an analysis developed here to relate crossbridge events to the frequency-dependence of stiffness, we argue that our observations provide evidence that isoproterenol induces an acceleration of crossbridge cycling rate. This raises the intriguing prospect that beta-adrenergic stimulation regulates contraction, not only by well-known alterations in calcium metabolism, but also by intrinsic modulation of the force-generating machinery itself.