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Biomedical subjects

J W Buchanan

Publications and source records attributed to J W Buchanan.

At least 37 records · Page 2Linked to original sources
PubMed1987

Relationship between extracellular potassium accumulation and local TQ-segment potential during acute myocardial ischemia in the porcine.

Depolarization of resting membrane potential during acute myocardial ischemia is strongly correlated with the accumulation of extracellular potassium ([K+]e). Also, diastolic currents of injury flowing across the ischemic border that occur as a result of local differences in resting membrane potentials cause changes in the TQ-segments of unipolar, DC-coupled, extracellular electrograms. Further, the changes in [K+]e and TQ-segment potentials during acute ischemia and reperfusion follow a similar time course. For these reasons, a predictable relationship between [K+]e and TQ potentials might be expected to exist. If found, easily obtainable local TQ potential measurements could serve as an index of the resting membrane depolarization induced by [K+]e accumulation and, by extension, as an index of ischemic injury. We measured local [K+]e and TQ potentials from 30 mid-myocardial sites in central and marginal ischemic zones in 2 isolated, Langendorff-perfused porcine hearts during a single, 10-min ligation of the left anterior descending coronary artery. In general, we found a linear relationship between [K+]e and TQ potential for both ischemic zones when data was taken as a whole, but the slopes (S) and correlation coefficients (R) were markedly different between the two locations (-2.24 vs -1.28 and -0.73 vs -0.51 for central and marginal zones, respectively). Further, we found a time dependent change in both S and R that was biphasic. Both were low during the first minutes, attained their maximum values at 4 mins, and then fell during the remainder of the occlusion. We conclude, therefore, that local TQ potentials cannot be used as an index of the severity of ischemic changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1987

Enhancement of procainamide-induced rate-dependent conduction slowing by elevated myocardial extracellular potassium concentration in vivo.

Procainamide, a type 1A antiarrhythmic drug, blocks sodium channels and reduces the maximum rate of rise of the cardiac action potential (Vmax) in a rate-dependent fashion. In vitro, the magnitude of this rate-dependent reduction in Vmax is greater in tissue that is partially depolarized at rest than in tissue with a normal resting potential. Reductions in Vmax produced by drugs that block sodium channels are also directly related to the reductions in longitudinal conduction velocity of action potential propagation in papillary muscle preparations. We therefore sought to determine whether the rate-dependent conduction slowing induced by procainamide in the intact canine heart is enhanced in myocardial tissue abnormally depolarized by an elevated myocardial extracellular potassium concentration, [K+]o. QRS duration and epicardial activation times were measured as indexes of myocardial conduction. QRS duration and epicardial activation times were measured at control (4.0 mM) and at intermediate (6.5 mM) and high (9.2 mM) myocardial [K+]o in the presence or absence of a clinically relevant procainamide concentration (12.2 +/- 2.6 g/ml) at the longest obtainable interstimulus interval of 440 msec and at 330, 280, and 250 msec. Intermediate and high myocardial [K+]o alone induced rate-dependent conduction slowing as the frequency of stimulation increased (cycle length 440 msec to 330, 280, and 250 msec). In the presence of procainamide, rate-dependent conduction slowing was observed at all levels of myocardial [K+]o, and the amount of rate-dependent change in conduction time increased as the myocardial [K+]o was increased.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1987

Skeletal muscle ventricles in circulation. One to eleven weeks' experience.

Skeletal muscle ventricles were constructed from canine latissimus dorsi and connected to the thoracic aorta in six dogs. These ventricles were stimulated to contract synchronously during diastole. The skeletal muscle ventricles were capable of continuous stroke work when placed within the arterial circulation for several weeks. Effective synchronous diastolic counterpulsation was produced. These results demonstrate that diastolic counterpulsators can be constructed from skeletal muscle and in the future may provide a feasible therapeutic alternative for the treatment of end-stage cardiac failure.

Animals↗
PubMed1986

A method for measurement of internal longitudinal resistance in papillary muscle.

We have modified the original Weidmann method for the measurement of internal longitudinal resistance in ventricular muscle by using air rather than silicon oil to insulate guinea pig papillary muscles and by omitting the tetrodotoxin inactivation of a portion of the preparation and have examined the requirements necessary for the theoretical assumptions to be satisfied by this or similar preparations. We found a homogeneous depolarization wavefront beyond about 1 mm from the stimulating electrodes. The adequacy of the interelectrode spacing was identified by a discrete plateau in the extracellular potential recording. The extracellular resistance in this preparation was sensitive to changes in the volume of the extracellular compartment, which we manipulated by changing inflow and outflow rates, and to changes in total ionic content of the superfusate. Our results establish the essential nature of maintaining constant flow rates and total ionic content and suggest that changes in volume and ionic content of a restricted extracellular space could conceivably influence conduction in vivo.

Action Potentials↗
PubMed1985

The effects of antiarrhythmic drugs, stimulation frequency, and potassium-induced resting membrane potential changes on conduction velocity and dV/dtmax in guinea pig myocardium.

For one-dimensional propagation, a nonlinear relationship between Vmax and conduction velocity is predicted by cable theory, and, under experimental conditions, Vmax and conduction velocity may change in opposite directions. Using standard microelectrode techniques, we have measured Vmax and conduction velocity in guinea pig papillary muscles exposed to tetrodotoxin and low sodium (agents expected primarily to decrease, directly, the rapid inward current), increased extracellular potassium (an agent which decreases the rapid inward current at least partially by inactivation mediated by depolarization of the resting membrane potential), and, over a wide range of stimulation frequencies, the antiarrhythmic drugs, quinidine, lidocaine, and procainamide. In all cases, except for the region of potassium-induced "supernormal conduction" between 5.4 and 9 mM, Vmax and conduction velocity varied as predicted by one-dimensional cable theory; that is, changes in Vmax were always proportional to changes in the square of conduction velocity. We conclude that the relationship between Vmax and conduction velocity predicted by cable theory occurs experimentally in guinea pig papillary muscle subjected to commonly used antiarrhythmic drugs and other interventions expected to reduce the sodium inward current. This relationship may be useful in applying known effects of drugs on Vmax to action potential propagation.

Animals↗
PubMed1985

Morphological observations of mineralizing pericardium cardiac grafts.

Pericardial patch grafts were implanted in the hearts of young sheep for periods ranging from two to 120 days. Explants seven to 21 days old revealed the formation of a "pseudoneointima" (PNI) on the blood contacting surface of the pericardium. The PNI was more heavily mineralized than the pericardium. Mineralization was most intense on the blood contacting surface of the PNI and on the chamber surface of the pericardium. After three weeks of implantation, the PNI was much thinner and was organized into a thin fibrous capsule without any signs of mineralization. In the pericardium, mineral deposits were seen in fibroblasts. Moreover, cell-related mineralization was evident prior to calcification of the surrounding collagen matrix.

Animals↗
PubMed1984

Mineralization of short term pericardial cardiac patch grafts.

Glutaraldehyde fixed patch grafts of bovine pericardium were implanted in myocardial windows in young (3-4 months old) sheep. The samples were retrieved after one to three weeks for study with scanning electron microscopy (SEM) and energy dispersive x-ray microanalysis (EDX). A layer of porous material (pseudoneointima, PNI), consisting mostly of a dense mesh of fibers interspersed with blood cells, was noted to form on the blood contacting surface of the graft. Four distinct sets of mineralization were noted in the retrieved grafts: (1) at the blood contacting surface of the PNI; (2) within the PNI at the junction between layers of PNI with differing densities; (3) near the junction of PNI and pericardium (but in the PNI); and (4) within the pericardium. In both the PNI and pericardium the mineral was shown by EDX analysis to contain both calcium and phosphorous indicating the mineral to be a calcium phosphate. Mineralization in the PNI differed from that in the pericardium; in the PNI it was deposited in discrete regions and apparently in association with thrombi while in the pericardium it was distributed diffusely within the collagen matrix, which may influence its formation.

Animals↗
PubMed1981

Patent ductus arteriosus: anatomy and surgery in a cat.

A 5-month-old cat with patent ductus arteriosus (PDA) and probable small ventricular septal defect had severe cardiomegaly and congestive heart failure. The cat improved slightly with medical therapy and markedly after surgical closure of the ductus. A 4th left intercostal space thoracotomy gave good exposure. The external anatomy of the PDA was similar to that of a short, wide PDA in dogs; however, the internal aortic orifice was situated more cranial than in dogs, as evidenced by preoperative cardiac catheterization. Examination 1 year later showed marked reductions in heart size and electrocardiographic amplitude. The cat was 1 of 3 with clinically diagnosed PDA at the University of Pennsylvania from 1968 to 1980. The prevalence of PDA in 14,224 cats (0.2/1,000) was significantly less than in 68,049 dogs (4.7/1,000).

Animals↗
PubMed1980

Monitoring cardiac function with nuclear techniques.

Noninvasive imaging with radioactive tracers has become widely used since its introduction in the early 1970s. Improvements continue to be made in the techniques and the clinical applications. Much of the information provided by these techniques is new. The first transit studies are used mainly in the evaluation of pulmonary transit time, detection of intracardiac shunting, evaluation of right ventricular function, measurement of ejection fraction and detection of wall motion abnormalities at rest and after exercise. The gated blood pool study is found to be most useful in assessment of global left ventricular function, regional wall motion, valve regurgitation and right ventricular function. The techniques of nuclear cardiac imaging are noninvasive, simple, successfully performed in almost 100 percent of cases. They are easy to interpret, able to be quantified and able to be almost totally automated. Their use is likely to become more widespread in the future.

Coronary Disease↗
PubMed1980

Radioactive tracers and the heart.

The most widely used tracer for the study of the heart muscle is thallium-201. The principal advantage of radioactive tracers in the study of the heart is that they tell us about regional as well as a overall function. In some cases a regional abnormality may be detected before the overall function of the heart is impaired.

Aortic Valve Insufficiency↗
PubMed1977

Comparison of toadfish-serum competitive binding and microbiologic assays of vitamin B12.

Toadfish serum (TFS) offers several advantages over other proteins as the binder in a competitive-binding assay for vitamin B12. It is unaffected by pH changes in the range 5.6-9.4 or by the addition of human serum albumin. Prolonged incubation with charcoal does not disrupt the TFS-cyanocobalamin bond, and the addition of albumin as a protein source in the standard tubes was proven unnecessary. The binding capacity of TFS does not increase significantly with increasing concentrations of cyanocobalamin as does the binding capacity of intrinsic factor, normal serum, or transcobalamin I. A single extract was prepared from each of 44 sera and measured for vitamin B12 content simultaneously by the TFS assay and the conventional microbiologic method using Lactobacillus leichmannii. The values obtained with TFS were in each instance higher than those obtained by the microbiologic assay (p less than 0.001).

Animals↗