Incomplete Relaxation Research Articles

Investigation of an energy-gap model for photoacoustic O2A-band spectra: H2O calibration near 7180 cm−1

A photoacoustic spectrometer is used to evaluate the accuracy of an energy-gap model for collisional energy transfer. For photoacoustic measurements involving the b1Σg+←X3Σg- transition of molecular oxygen the conversion of photon energy to thermal energy is inefficient and proceeds through the a1Δg state. This results in attenuation of the photoacoustic signal. The magnitude of the attenuation can be predicted with an energy-gap model whose accuracy has been previously confirmed to within 3±5%. However, this prior result does not rule out incomplete rotational relaxation of O2 in the a1Δg state. In this study, high-resolution spectra of H2O in air are used to calibrate the photoacoustic spectrometer. This work binds the relative uncertainty in the energy-gap relaxation factor for O2A-band photoacoustic signals to be approximately 1%. During one acoustic cycle, this result implies negligible collisional relaxation to the X3Σg- state of O2 and nearly complete collisional relaxation to the a1Δg state.

High-Resolution Manometry Patterns of Lower Esophageal Sphincter Complex in Symptomatic Post-Fundoplication Patients

IntroductionThere has been an increase in the number of patients seeking treatment after an anti-reflux surgical procedure. The objective of this study is to describe high-resolution manometry (HRM) topography as it relates to the post-fundoplication anatomy. MethodsRetrospective review of a prospectively maintained database was conducted to identify patients who underwent esophagogastroduodenoscopy and HRM at Creighton University Medical Center (CUMC) between November 2008 and October 2010, for symptoms after a previous fundoplication. Patients were categorized as having intact, intrathoracic, disruptured, twisted, or slipped fundoplication based on endoscopic findings. ResultsSixty-one patients {intact, 17(28%), disrupted, 2(3%), twisted, 3(5%), intra-thoracic, 18(30%), slipped, 21(34%)} are included in this study. A double high-pressure zone (HPZ) configuration was identified in both intra-thoracic and slipped fundoplication. This was not noted in appropriately positioned fundoplications. In intra-thoracic fundoplications, the HPZ below the fundoplication was lower pressure and showed respiratory variations. In slipped fundoplication, the higher HPZ had lower pressure and no respiratory variations. In appropriately positioned fundoplication, the lower esophageal sphincter (LES) pressure and extent of relaxation in the single HPZ correlated with intact (normal pressure and good relaxation), disrupted (low pressure and good relaxation), and twisted (high pressure with incomplete relaxation) fundoplication. Patients with only a recurrent para-esophageal hernia had characteristics of an appropriately positioned fundoplication. ConclusionLES complex HRM findings correlate well with anatomical status of the fundoplication.

A Case of Esophageal Achalasia Compressing Left Atrium Diagnosed by Echocardiography in Patient with Acute Chest Pain

A 47-year-old man with squeezing nature chest pain visited the emergency department. His heart sounds were normal without murmurs, and no history of cardiovascular risk factors or previous heart disease. Initial electrocardiogram showed sinus tachycardia with elevation of ST segment in pre-cordial leads, and he complained of continuous chest pain. Emergent coronary angiography was performed but showed no significant coronary artery stenosis. Transthoracic echocardiography (TTE) showed normal left ventricular dimension and systolic function with relaxation abnormality in mitral inflow Doppler. TTE also showed a round shaped echolucent heterogenous mass lesion, approximately 4.2 × 3.6 cm in size, compressing the left atrium (Fig. 1A). The color Doppler image focusing on the mass lesion revealed an absence of flow. Because of the anatomic location and appearance of the mass lesion, a dilated and extended esophagus and other external cardiac tumor were included in differential diagnosis. TTE was performed after drinking of a liquid containing carbon dioxide to differentiate esophagus from tumor or vascular structure. As result, this mass was identified as the esophagus (Fig. 1B). Chest computed tomography scan revealed diffuse esophageal dilatation compressing the left atrium (Fig. 2A). Gastrografin esophagography showed esophageal dilatation with narrowing of lower esophagus, so called 'bird's beak appearance' (Fig. 2B). High-resolution esophageal manometry demonstrated lack of normotensive lower esophageal sphincter with incomplete relaxation after swallowing consistent with achalasia. Balloon dilatation was performed successfully and patient's symptom was improved. During admission, serial electrocardiograms showed persistent ST elevations with saddle back pattern and Brugada syndrome was suspicious. Fig. 1 A: Parasternal long axis view of transthoracic echocardiography showed round shape mass lesion compressing the left atrium (white arrow). B: After drinking a liquid containing carbon dioxide, the esophagus was filled with air contrast (white arrow). LA: ... Fig. 2 A: Dilatation of the esophagus compressing the left atrium was revealed in chest computed tomography (white arrow). B: Esophagography with gastrografin identified achalasia. LA: left atrium, LV: left ventricle, RV: right ventricle, RA: right atrium. Achalasia is a motility disorder characterized by dilatation of distal part of the esophagus with impaired relaxation of the lower esophageal sphincter. Compression of the left atrium leads to various symptoms and signs, which include from mild chest discomfort to hemodynamic instability. There are no previous reports about achalasia compressing left atrium and causes acute chest pain mimicking acute coronary syndrome. TTE is the test of choice for diagnosing the left atrial compression by various etiology.1-3) Furthermore, the esophagus can be identified by the appearance of air contrast during the ingestion of liquid containing carbon dioxide.3) Echocardiography enables clinicians to successfully make the differential diagnosis in patients with chest pain.

Latent Myofascial Trigger Points are Associated With an Increased Antagonistic Muscle Activity During Agonist Muscle Contraction

The aim of this study was to evaluate motor unit activity from a latent myofascial trigger point (MTP) in an antagonist muscle during isometric agonist muscle contraction. Intramuscular activity was recorded with an intramuscular electromyographic (EMG) needle inserted into a latent MTP or a non-MTP in the posterior deltoid muscle at rest and during isometric shoulder flexion performed at 25% of maximum voluntary contraction in 14 healthy subjects. Surface EMGs were recorded from the anterior and posterior deltoid muscles. Maximal pain intensity and referred pain induced by EMG needle insertion were recorded on a visual analogue scale. The results showed that higher local pain was observed following needle insertion into latent MTPs (4.64 ± .48 cm) than non-MTPs (2.35 ± .43 cm, P < .005). Referred pain was reported in 6/14 subjects following needle insertion into latent MTPs, but none into the non-MTPs. The intramuscular EMG activity, but not surface EMG activity, in the antagonist muscle was significantly higher at rest and during shoulder flexion at latent MTPs than non-MTPs ( P < .05). The current study provides the first evidence that increased motor unit excitability is associated with reduced antagonist reciprocal inhibition. Perspective This study shows that MTPs are associated with reduced efficiency of reciprocal linhibition, which may contribute to the delayed and incomplete muscle relaxation following exercise, disordered fine movement control, and unbalanced muscle activation. Elimination of latent MTPs and/or prevention of latent MTPs from becoming active may improve motor functions.

Ambulatory high‐resolution manometry, lower esophageal sphincter lift and transient lower esophageal sphincter relaxation

Lower esophageal sphincter (LES) lift seen on high-resolution manometry (HRM) is a possible surrogate marker of the longitudinal muscle contraction of the esophagus. Recent studies suggest that longitudinal muscle contraction of the esophagus induces LES relaxation. Our goal was to determine: (i) the feasibility of prolonged ambulatory HRM and (ii) to detect LES lift with LES relaxation using ambulatory HRM color isobaric contour plots. In vitro validation studies were performed to determine the accuracy of HRM technique in detecting axial movement of the LES. Eight healthy normal volunteers were studied using a custom designed HRM catheter and a 16 channel data recorder, in the ambulatory setting of subject's home environment. Color HRM plots were analyzed to determine the LES lift during swallow-induced LES relaxation as well as during complete and incomplete transient LES relaxations (TLESR). Satisfactory recordings were obtained for 16 h in all subjects. LES lift was small (2 mm) in association with swallow-induced LES relaxation. LES lift could not be measured during complete TLESR as the LES is not identified on the HRM color isobaric contour plot once it is fully relaxed. On the other hand, LES lift, mean 8.4 ± 0.6 mm, range: 4-18 mm was seen with incomplete TLESRs (n = 80). Our study demonstrates the feasibility of prolonged ambulatory HRM recordings. Similar to a complete TLESR, longitudinal muscle contraction of the distal esophagus occurs during incomplete TLESRs, which can be detected by the HRM. Using prolonged ambulatory HRM, future studies may investigate the temporal correlation between abnormal longitudinal muscle contraction and esophageal symptoms.

Analysis of phase transformations in shock-compressed potassium chloride and α-quartz in terms of x-ray crystallography

X-ray diffraction patterns of shock-compressed samples of potassium chloride and α-quartz were analyzed in order to estimate the physical state of the substance in the phase coexistence region and the effect of the relaxation process on the location of experimental Hugoniot points in this region. The experimental results are consistent with the interpretation that the state of a substance on the transition curve connecting the Hugoniots of the initial phase and the high-pressure phase can be represented as a state of the substance with an incomplete relaxation process. The degree of incompleteness is determined by the ratio of the residence time of the substance at the shock front to the full time of the relaxation process.

Achalasia With Dense Eosinophilic Infiltrate Responds to Steroid Therapy

A patient presented with chronic substernal discomfort and intermittent dysphagia for solids. High-resolution impedance manometry (HRIM) of the esophagus showed that there was no peristalsis in the esophageal body but incomplete relaxation of the lower esophageal sphincter and incomplete bolus transit, so the patient was diagnosed with achalasia. Moreover, probably because of esophageal stasis, eosinophilic infiltration that mimicked a pattern of eosinophilic esophagitis was observed, on the basis of multiple biopsies of the esophagus. The patient was given 50 mg prednisolone once daily; the symptoms improved dramatically, and HRIM showed complete recovery of esophageal peristalsis, deeper relaxation of the lower esophageal sphincter, and complete bolus transit profile. HRIM can therefore be used to assess dysmotility abnormalities in patients with achalasia and eosinophilic-like esophagitis, and steroids relieve these symptoms. Treatment with a high dose of prednisolone resulted in a complete disappearance of dysphagia because of improved esophageal motility and reduced eosinophilic infiltrate. It is therefore important to control the inflammatory process in patients with idiopathic achalasia, which is likely to result from an autoimmune reaction.

Tachycardia-Induced Diastolic Dysfunction and Resting Tone in Myocardium From Patients With a Normal Ejection Fraction

The purpose of this study is to evaluate tachycardia-induced relaxation abnormalities in myocardium from patients with a normal ejection fraction. Diastolic dysfunction and left ventricular (LV) hypertrophy are closely linked. Tachycardia can induce heart failure symptoms in otherwise asymptomatic patients. To study the effects of tachycardia on myocardial contractility and relaxation, we evaluated the effects of increasing pacing rates in myocardial biopsy samples obtained from patients with a normal ejection fraction. LV biopsy samples were obtained during coronary bypass surgery. Myocardial strip preparations were electrically paced at rates from 60 to 180 beats/min. Diastolic resting tone was assessed by cross-bridge deactivation. Calcium transporting systems were functionally examined, and myofilament calcium sensitivity was studied. Incomplete relaxation developed in 7 preparations, with increased diastolic tension development at increasing pacing rates. This was absent in the remaining 7 preparations. Incomplete relaxation was found to be associated with increased LV mass and left atrial volume. Cross-bridge deactivation showed that these preparations also had a significant resting tone. Additional functional analyses suggest that incomplete relaxation is associated with disproportionately elevated cellular calcium loads due to a reduced sarcolemmal calcium extrusion reserve. Tachycardia-induced incomplete relaxation was associated with increased LV mass and left atrial volumes. We also found a disproportionately increased calcium load at high rates and a substantial resting tone due to diastolic cross-bridge cycling. These observations may play a role in reduced exercise tolerance and tachycardia-induced diastolic dysfunction.

Superradiance of cold atoms coupled to a superconducting circuit

We investigate superradiance of an ensemble of atoms coupled to an integrated superconducting LC-circuit. Particular attention is paid to the effect of inhomogeneous coupling constants. Combining perturbation theory in the inhomogeneity and numerical simulations we show that inhomogeneous coupling constants can significantly affect the superradiant relaxation process. Incomplete relaxation terminating in "dark states" can occur, from which the only escape is through individual spontaneous emission on a much longer time scale. The relaxation dynamics can be significantly accelerated or retarded, depending on the distribution of the coupling constants. On the technical side, we also generalize the previously known propagator of superradiance for identical couplings in the completely symmetric sector to the full exponentially large Hilbert space.

Longitudinal Muscle Contraction of the Esophagus & Common Cavity Pressure During Incomplete Transient Lower Esophageal Sphincter Relaxation

Longitudinal Muscle Contraction of the Esophagus & Common Cavity Pressure During Incomplete Transient Lower Esophageal Sphincter Relaxation

Value of preoperative esophageal function studies before laparoscopic antireflux surgery

The value of esophageal manometry and ambulatory pH monitoring before laparoscopic antireflux surgery (LARS) has been questioned because tailoring the operation to the degree of hypomotility often is not required. This study evaluated a consecutive cohort of patients referred for esophageal function studies in preparation for LARS to determine the rates of findings that would alter surgical decisions. High-resolution manometry (HRM) was performed for each subject using a 21-lumen water-perfused system, and motor function was characterized. Gastroesophageal reflux disease (GERD) was evident from ambulatory pH monitoring if thresholds for acid exposure time and/or positive symptom association probability were passed. Of 1,081 subjects (age, 48.4±0.4years; 56.7% female) undergoing preoperative HRM, 723 (66.9%) also had ambulatory pH testing performed. Lower esophageal sphincter (LES) hypotension (38.9%) and nonspecific spastic disorder (NSSD) of the esophageal body (36.1%) were common. Obstructive LES pathophysiology was noted in 2.5% (achalasia in 1%; incomplete LES relaxation in 1.5%), and significant esophageal body hypomotility in 4.5% (aperistalsis in 3.2%; severe hypomotility in 1.3%) of the subjects. Evidence of GERD was absent in 23.9% of the subjects. Spastic disorders were more frequent in the absence of GERD (43.9% vs. 23.1% with GERD; p<0.0001), whereas hypomotility and normal patterns were more common with GERD. Findings considered absolute or relative contraindications for standard 360º fundoplication are detected in 1 of 14 patients receiving preoperative HRM. Additionally, spastic findings associated with persistent postoperative symptoms are detected at esophageal function testing that could be used in preoperative counseling and candidate selection. Physiologic testing remains important in the preoperative evaluation of patients being considered for LARS.

Preclinical Assessment of a Tissue-Engineered Vasomotive Human Small-Calibered Vessel Based on a Decellularized Xenogenic Matrix: Histological and Functional Characterization

Tissue-engineered arterial vessels (TEAV) offer substantial advantages in small-calibered human-bypass-grafting and vascularized scaffold applications. However, histological composition of TEAV must allow for functional properties, such as vasomotoricity. Aim of this study was to characterize human TEAVs regarding morphology and vasomotoricity. Three groups containing segments of porcine carotid artery < 5 mm in diameter (native [NA, n = 6], decellularized [DA, n = 6], and decellularized/reseeded in a bioreactor [RA, n = 7] with human vascular endothelial [hvECs] and smooth muscle cells [hvSMCs]) were examined. Light and scanning electron microscopy were applied, and hvSMCs- and hvECs-associated Vasomotoricity Test conducted in Krebs-solution was used for characterization of revitalized TEAVs. Morphologic examination showed cell-free extracellular matrix in DAs. Light microscopy demonstrated intact extracellular matrix components in circle-layered formation in cross sections of DAs. RAs showed small cells migrating along the remaining medial fiber structures and flat cell layers at the luminal site, identified as hvECs and hvSMCs with lower CD-31 and α-actin signaling than controls. Scanning electron microscopy showed intact flat cell layers on luminal surfaces of RAs and dense hvSMCs at their media site. DAs showed decreasing strain after stimulation. RAs retrieved vasomotoricity compared to DAs, but showed reduced contraction and incomplete relaxation compared to NAs. This study shows that revitalization of DA with human vascular cells resembles NA-like morphology and can ensure vasomotoricity of TEAVs.

Further Consideration of Viscoelastic Two Glass Transition Behavior of Nanoparticle-Filled Polymers

Tsagaropoulos and Eisenberg [Macromolecules 1995, 28, 396; Macromolecules 1995, 28, 6067] reported a second loss tangent (tan δ) peak in temperature-dependent viscoelastic data for various un-cross-linked polymers filled with nanometer-sized silica particles. This peak, occurring at temperatures as much as 100 °C above the primary tan δ peak (glass-to-rubber softening transition), was ascribed to the glass transition of immobilized chains near the particles. This research is often cited as support for the existence of severely retarded segmental motion of polymer near the surfaces of small particles (glassy polymer shell). We offer a different interpretation of the results from Tsagaropoulos and Eisenberg, reinforced by our recent measurements on particle-filled polybutadiene and consideration of other literature data. Particles restrict the flow of some polymer chains, thus resulting in incomplete terminal relaxation, and partial cross-linking of unfilled polymers produces the same higher temperature tan δ peak. Polymer chains which are adsorbed onto filler surfaces are immobilized from a flow relaxation (chain diffusion/reptation) standpoint, but segmental relaxation (glass transition) is not substantially altered by small particles as a general rule.

Gastro‐intestinal Chagas disease in migrants to Spain: prevalence and methods for early diagnosis

Each year in Spain, the number of Latin American immigrants who present with chronic Trypanosoma cruzi infection increases. Although gastro-intestinal abnormalities are not as common as cardiomyopathy in such infection, they can still lead to an impaired quality of life. In a recent study based in Madrid, the frequencies of gastro-intestinal involvement in a cohort of Latin American immigrants infected with T. cruzi, and the role of early diagnostic techniques in the detection of such involvement, were explored. Between January 2003 and April 2009, all Latin Americans who attended the Tropical Medicine Unit of the Hospital Universitario Ramón y Cajal were tested for T. cruzi infection, in IFAT and ELISA. Each subject found both IFAT- and ELISA-positive was considered to be infected (chronically) and checked for symptoms indicative of Chagas disease. Each infected subject giving informed consent was investigated further, using an electrocardiogram, an echocardiogram and oesophageal manometry. Between January 2003 and June 2008, every infected subject who consented was also explored using a barium swallow and barium enema. After July 2008, however, only subjects showing oesophageal and/or colonic symptoms were investigated in this manner. Of the 248 patients found infected with T. cruzi, 118 underwent oesophageal manometry, 75 a barium enema and 48 a barium swallow. Thirteen (11%) showed evidence of oesophageal involvement (incomplete relaxation of the lower oesophageal sphincter; three cases) or bowel involvement (five cases of dolichosigma, three of dolichocolon and two of megacolon). Only six of these 13 had any gastro-intestinal symptoms (all six were suffering from constipation). None of the barium swallows revealed any pathology. It appears that oesophageal manometry can reveal mild abnormalities not detected by barium swallow, even in asymptomatic patients, while barium enemas are useful in the detection of colonic involvement.

Case report: Achalasia-like dysmotility secondary to oesophageal involvement of sarcoidosis

We present a case of a patient with sarcoidosis and who subsequently developed dysphagia for solids, and some difficulty in swallowing liquids. High-resolution manometry of the oesophagus showed absent peristalsis...

Mechanism of the Swern Oxidation: Significant Deviations from Transition State Theory

Deprotonation of the alkoxysulfonium intermediate has been shown to be rate-determining in the Swern oxidation of benzyl alcohol. Directly following this rate-determining step is the intramolecular syn-β-elimination of the ylide. In the present study, intramolecular (2)H kinetic isotope effects (KIEs) are used to gain insight into this syn-β-elimination step. As a result of the stereogenic sulfur center in the ylide intermediate, two diastereomeric transition states (endo-TS1 and exo-TS1) must be assumed to contribute to the intramolecular KIE. The intramolecular (2)H KIE determined at -78 °C is 2.82 ± 0.06. Attempts to reproduce this measurement computationally using transition state theory and a Bell tunneling correction yielded a value (1.58) far below that determined experimentally. Computational analysis is complicated by the existence of two distinct transition structures owing to the stereogenic center. Two extremes of Curtin-Hammett kinetics are explored using energies, vibrational frequencies, and moments of inertia from computed transition structures. Neither Curtin-Hammett scenario can reproduce the observed KIE to any acceptable degree of fidelity. Evidence based upon previous kinetics measurements and calculations upon a model system suggests that the stereogenic sulfur center is not likely to undergo inversion to a significant degree at the temperatures at which the Swern oxidation is performed here. Proceeding under the assumption of no stereoinversion at the sulfur center, calculations predict a nearly linear Arrhenius plot for the KIE--even with the inclusion of a one-dimensional tunneling correction. By contrast, the experimentally determined temperature dependence shows a significant concave upward curvature indicative of the influence of tunneling. Notably, KIEs measured in CCl(4), CHCl(3), CH(2)Cl(2), dichloroethane, and chlorobenzene at -23 °C showed little variance. This finding discounted the possible influence from dynamical effects due to incomplete vibrational relaxation. An ad hoc amplification of the imaginary frequencies corresponding to the first-order saddle points corresponding to endo-TS1 and exo-TS1 allowed us to reproduce the experimental temperature dependence of the KIE using only two adjustable parameters applied to a kinetic scenario that involves four isotopomeric transition states. The cumulative data and computational modeling strongly suggest that, even though the intramolecular (2)H KIE observed in these experiments is small, this reaction requires a multidimensional description of the tunneling phenomenon to accurately reproduce experimental trends.

Serendipitous Diagnosis of Achalasia Cardia on a Radionuclide Study

Achalasia cardia is a motility disorder, involving the distal esophagus, resulting in elevated lower esophageal sphincter pressure, increased intraesophageal pressure, incomplete relaxation of lower esophageal sphincter in response to deglutition and loss of esophageal peristalsis. It usually presents between third and fifth decades of life with the most common symptom of dysphagia. We present a case of middle-aged lady who complained of intermittent vomiting after meal and excessive postprandial sense of fullness in abdomen. It was suspected to be related to delayed gastric emptying. Therefore, a gastric emptying time study was requested. The solid bolus of radioactive meal was held up in the lower end of esophagus, thereby suggesting achalasia. Barium meal examination confirmed the diagnosis.

Botulinum toxin injection in dysphagia syndromes with preserved esophageal peristalsis and incomplete lower esophageal sphincter relaxation

Botulinum toxin injection into the lower esophageal sphincter (LES) treats dysphagia syndromes with preserved peristalsis and incomplete LES relaxation (LESR). We evaluated clinical and esophageal motor characteristics predicting response, and compared duration of efficacy to similarly treated achalasia patients. Thirty-six subjects (59 ± 2.2 years, 19F/17M) with incomplete LESR on high resolution manometry (HRM) treated with botulinum toxin injection were identified. Individual and composite symptom indices were calculated, and HRM characteristics extracted. Symptom resolution for 6 months was a primary outcome measure, and repeat botulinum toxin injection, dysphagia recurrence or employment of alternate therapeutic approaches were secondary outcome measures. Duration of response was compared using Kaplan-Meier survival curves to a historical cohort of similarly treated achalasia subjects. Response lasted a mean of 12.8 ± 2.3 months. Symptom relief for >6 months was seen in 58.3%; short (<6 months) response was associated with younger age, higher chest pain index, and esophageal body spastic features (P ≤ 0.04). On multivariate logistic regression, chest pain, younger age and contraction amplitudes >180 mmHg independently predicted <6 months relief (P < 0.05 for each). On survival analysis, relief with a single injection extended to 1 year in 54.8% and 1.5 years in 49.8%, statistically equivalent to that reported by 42 similarly treated achalasia subjects (59 ± 3.2 years, 24F/18M). Symptom relief was more prolonged compared to achalasia when repeat injections were performed on demand (P = 0.003). Botulinum toxin injections can provide lasting symptom relief in dysphagia syndromes with incomplete LESR. Prominent perceptive symptoms and non-specific spastic features may predict shorter relief.

Chemical Shifts and Lifetimes for Nuclear Magnetic Resonance (NMR) Analysis of Biofuels

Determination of the molecular composition of biofuels is critical to process development. Because biofuels, such as pyrolysis oil, contain hundreds of compounds, quantitative determination of the mixtures is a formidable task and is often not necessary for routine development work. 13C and 1H nuclear magnetic resonance (NMR) offer a reasonable trade-off between functional group identification and analytical measurement effort. However, accuracy depends upon selection of chemical-shift regions, baseline compensation, and correction for incomplete longitudinal relaxation effects. We propose chemical-shift assignments and T1 correction factors based on 13C and 1H NMR measurements of over 50 compounds that have been previously identified in pyrolysis oils and several plant natural products, especially terpenes. The results are intended to allow for a semiquantitative assessment of molecular composition of bio-oils on a time scale of 1−8 h to provide feedback for process development.

Energetics of stress production in isolated cardiac trabeculae from the rat

The heat liberated upon stress production in isolated cardiac muscle provides insights into the complex thermodynamic processes underlying mechanical contraction. To that end, we simultaneously measured the heat and stress (force per cross-sectional area) production of cardiac trabeculae from rats using a flow-through micromechanocalorimeter. In a flowing stream of O(2)-equilibrated Tyrode solution (∼22°C), the stress and heat production of actively contracting trabeculae were varied by 1) altering stimulus frequency (0.2-4 Hz) at optimal muscle length (L(o)), 2) reducing muscle length below L(o) at 0.2 and 2 Hz, and 3) changing extracellular Ca(2+) concentrations ([Ca(2+)](o); 1 and 2 mM). Linear regression lines were adequate to fit the active heat-stress data. The active heat-stress relationships were independent of stimulus frequency and muscle length but were dependent on [Ca(2+)](o), having greater intercepts at 2 mM [Ca(2+)](o) than at 1 mM [Ca(2+)](o) (3.5 and 2.0 kJ·m(-3)·twitch(-1), respectively). The slopes among the heat-stress relationships did not differ. At the highest experimental stimulus frequency, pronounced elevation of diastolic Ca(2+) resulted in incomplete twitch relaxation. The resulting increase of diastolic stress, which occurred with negligible metabolic energy expenditure, subsequently diminished due to the time-dependent loss of myofilament Ca(2+)-sensitivity.