Charles L. Soule

Isolated four-chamber working swine heart model

BACKGROUND Isolated heart models separate cardiac characteristics from systemic characteristics with subsequent findings used in cardiac research, including responses to pharmacologic, mechanical, and electrical components. The model objective was to develop the ability to represent in situ physiologic cardiac function ex vivo. METHODS Swine hearts were chosen over rat or guinea pig models due to their notably greater anatomical and physiologic similarities to humans. An in vitro apparatus was designed to work all four chambers under simulated in situ physiologic conditions. Using standard cardiac surgical techniques, 12 porcine hearts (mean weight 331 +/- 18 g) were explanted into the apparatus. Preload and afterload resistances simulated in situ input and output physiologic conditions. Hemodynamic characterizations, including cardiac output, max +/- dP/dt, and heart rate, were used to determine in situ function leading to explantation (prethoracic operation, postmedial sternotomy, and postperidectomy) and during in vitro function (t = 0, 60, 120, and 240 minutes). RESULTS In vitro performance decayed with time, with statistical differences from base line (t = 0) function at t = 240 minutes (p > 0.05). CONCLUSIONS An isolation and in vitro explantation protocol has been improved to aid in the study of isolated cardiac responses, and to determine cardiac hemodynamic function during open chest operation, transplantation, and in vitro reanimation with a crystalloid perfusate. The resulting model offers similar working physiologic function, with real-time imaging capabilities. The resulting model is advantageous in representing human cardiac function with regard to anatomic and physiologic functions, and can account for atrial and ventricular interactions.

Hibernation induction trigger reduces hypoxic damage of swine skeletal muscle

A link between the cardioprotective benefits of pharmacological preconditioning and natural mammalian hibernation is considered to involve the cellular activation of opioid receptors and subsequent opening of KATP channels. In previous studies, we have demonstrated the protective effects of specific δ‐opioid agonists against porcine cardiac ischemia/reperfusion injury. We hypothesize here that preincubation with hibernation induction trigger (HIT) should confer a similar protection in skeletal muscles. Therefore, muscle bundles from swine were pretreated with plasma from hibernating woodchucks (HWP) for 30 min, then exposed to hypoxia for 90 min and reoxygenation for 120 min. Stimulated twitch forces were assessed. The functional effects of pretreatment with nonhibernation (summer) woodchuck plasma, a KATP blocker, or opioid antagonist were also studied. During the reoxygenation period, significantly greater force recoveries were observed only for bundles pretreated with HWP; this response was blocked by naloxone (P < 0.05). We conclude that HIT pretreatment could be used to confer protection against hypoxia/reperfusion injury of skeletal muscles of nonhibernators; it could potentially be utilized to prevent injury during surgical procedures requiring ischemia.

Lactic acid restores skeletal muscle force in an in vitro fatigue model: are voltage-gated chloride channels involved?

High interstitial K(+) concentration ([K(+)]) has been reported to impede normal propagation of electrical impulses along the muscle cell membrane (sarcolemma) and then also into the transverse tubule system; this is one considered underlying mechanism associated with the development of muscle fatigue. Interestingly, the extracellular buildup of lactic acid, once considered an additional cause for muscle fatigue, was recently shown to have force-restoring effects in such conditions. Specifically, it was proposed that elevated lactic acid (and intracellular acidosis) may lead to inhibition of voltage-gated chloride channels, thereby reestablishing better excitability of the muscle cell sarcolemma. In the present study, using an in vitro muscle contractile experimental setup to study functionally viable rectus abdominis muscle preparations obtained from normal swine, we examined the effects of 20 mM lactic acid and 512 μM 9-anthracenecarboxylic acid (9-AC; a voltage-gated chloride channel blocker) on the force recovery of K(+)-depressed (10 mM K(+)) twitch forces. We observed a similar muscle contractile restoration after both treatments. Interestingly, at elevated [K(+)], myotonia (i.e., hyperexcitability or afterdepolarizations), usually present in skeletal muscle with inherent or induced chloride channel dysfunctions, was not observed in the presence of either lactic acid or 9-AC. In part, these data confirm previous studies showing a force-restoring effect of lactic acid in high-[K(+)] conditions. In addition, we observed similar restorative effects of lactic acid and 9-AC, implicating a beneficial mechanism via voltage-gated chloride channel modulation.

Effects of Ablation (Radio Frequency, Cryo, Microwave) on Physiologic Properties of the Human Vastus Lateralis

Objective: Ablative treatments can sometimes cause collateral injury to surrounding muscular tissue, with important clinical implications. In this study, we investigated the changes in muscle physiology of the human vastus lateralis when exposed to three different ablation modalities: radiofrequency ablation, cryoablation, and microwave ablation. Methods: We obtained fresh vastus lateralis tissue biopsy specimens from nine patients (age range: 29–73 years) who were undergoing in vitro contracture testing for malignant hyperthermia. Using leftover waste tissue, we prepared 46 muscle bundles that were utilized in tissue baths before and after ablation. Results: After ablation with all the three modalities, we noted dose-dependent sustained reductions in peak force (strength of contraction), as well as transient increases in baseline force (resting muscle tension). But, over the subsequent 3-h recovery period, peak force improved and the baseline force consistently recovered to below its preablation levels. Conclusion: The novel in vitro methodologies we developed to investigate changes in muscle physiology after ablation can be used to study a spectrum of ablation modalities and also to make head-to-head comparisons of different ablation modalities. Significance: As the role of ablative treatments continues to expand, our findings provide unique insights into the resulting changes in muscle physiology. These insights could enhance the safety and efficacy of ablations and help individuals design and develop novel medical devices.

Assessment of Ablative Therapies in Swine: Response of Respiratory Diaphragm to Varying Doses

Ablation is a common procedure for treating patients with cancer, cardiac arrhythmia, and other conditions, yet it can cause collateral injury to the respiratory diaphragm. Collateral injury can alter the diaphragm’s properties and/or lead to respiratory dysfunction. Thus, it is important to understand the diaphragm’s physiologic and biomechanical properties in response to ablation therapies, in order to better understand ablative modalities, minimize complications, and maximize the safety and efficacy of ablative procedures. In this study, we analyzed physiologic and biomechanical properties of swine respiratory diaphragm muscle bundles when exposed to 5 ablative modalities. To assess physiologic properties, we performed in vitro tissue bath studies and measured changes in peak force and baseline force. To assess biomechanical properties, we performed uniaxial stress tests, measuring force–displacement responses, stress–strain characteristics, and avulsion forces. After treating the muscle bundles with all 5 ablative modalities, we observed dose-dependent sustained reductions in peak force and transient increases in baseline force—but no consistent dose-dependent biomechanical responses. These data provide novel insights into the effects of various ablative modalities on the respiratory diaphragm, insights that could enable improvements in ablative techniques and therapies.

Measurement of Biomechanical Properties of Tissues Under Uniaxial Stress

• Knowledge of biomechanical properties of tissues is necessary for credible description of their constitutive behavior in physiological conditions of normality and stress • A comprehensive and comparative understanding of tissue properties is of prime importance from the perspectives of device-tissue interactions • Moreover, ablation has become a common medical procedure, which alters both the structure and function of the ablated tissue; and in small percentage of cases, it can cause collateral damage of surrounding vital structures, which can have severe clinical implications • In order to maximize the efficacy of ablative procedures and minimize collateral damage, it is important to understand the biomechanical properties of all tissues that may be potentially affected by ablation • We have developed unique methodologies to assess the biomechanical properties of various tissues under uniaxial stress that include measurement of force-displacement graphs, stress-strain characteristics, calculations of avulsion forces, avulsion strains, energies associated with avulsions, and the elastic moduli of various tissue samples

Effect of tissue dehydration on smooth muscle cell contractility, collagen matrix structure and overall artery biomechanics

Applications involving freeze-thaw in arteries such as cryoplasty and cryopreservation alter the arterial biomechanics significantly [1]. Tissue dehydration or bulk water loss is observed following freeze-thaw in native arteries as well as other artificial tissues [1, 2]. It is hypothesized that tissue dehydration observed during freeze-thaw is an important mechanism underlying the biomechanical changes in arteries. In order to test this hypothesis, dehydration was induced in arteries (without changing temperature or phase) by treating them with different concentrations of hyperosmotic mannitol solutions. Changes to smooth muscle cell (SMC) contractility, collagen matrix structure and overall artery biomechanics were studied following tissue dehydration. SMC contractility and relaxation were measured by studying the response of arteries to norepinephrine (NE) and acetylcholine (AC) respectively. Collagen matrix structure was assessed by studying the thermal denaturation of collagen due to heating using Fourier transform infrared (FTIR) spectroscopy and the overall artery biomechanics through uniaxial tensile tests.© 2008 ASME