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Biomedical subjects

R L Hamlin

Publications and source records attributed to R L Hamlin.

At least 109 records · Page 6Linked to original sources
PubMed1984

Effects of pericardial effusates of various conductivities on body-surface potentials in dogs. Documentation of the eccentric spheres model.

The purpose of this study was to discover the cause and magnitude of changes in the body-surface potentials occurring when: (1) fluids of various conductivity were added to the pericardial sac, or (2) the volume of the blood within chambers of the heart was either increased or decreased. Fluids added to the pericardium were physiological saline, whole-blood, and mineral oil. Magnitudes of body-surface potentials were compared to the predictions based on a mathematical eccentric spheres model of the heart and torso developed previously by Rudy and Plonsey. Data demonstrated conclusively that there is a nonlinear relationship between the body-surface potentials and the conductivity of the pericardial layer. This relationship is one in which the body-surface potentials of the anterior chest were found to decrease when conductivity of the pericardial layer was either increased or decreased. These changes in body-surface potentials were caused solely by alterations in the conductivity and volume of the fluid effusate. It was demonstrated that these changes were not caused by any "stretching" or "compression" of the cardiac tissue caused by the altered fluid volumes in and around the heart. Findings were accurately predicted by the eccentric spheres model, thereby confirming the model's usefulness as a predictive instrument. The model provides an explanation for the nonlinear relationship that was exhibited by the data.

Action Potentials↗
PubMed1984

Genesis of QRS in the ruminant: graphic simulation.

Graphic simulation of ventricular activation for a typical ruminant with complete endocardial-epicardial penetration of Purkinje's fibers was performed. Voltages recorded from points on the torso simulating electrodes V10 and aVF were predicted. These compared favorably in amplitudes and durations with voltages actually recorded from typical ruminants.

Animals↗
PubMed1983

Protection of turkeys against furazolidone-induced cardiomyopathy.

When fed furazolidone, 700 ppm, with their mash, most turkey poults develop dilated cardiomyopathy characterized by gross left ventricular dilatation with thinning of both the left ventricular free wall and ventricular septum. Birds fed propranolol, but not digoxin, did not develop this cardiomyopathy. It is not known what pharmacologic property of propranolol conferred protection or if mammals would receive similar protection.

Animals↗
PubMed1983

Hydralazine pharmacodynamics in the dog.

The pharmacodynamics of hydralazine, an arteriolar dilator, were studied in dogs with induced heart failure. The dogs were studied 5 days after heart failure was induced by injecting microspheres into the left circumflex coronary artery. All dogs had a stroke volume index less than 25 ml/beat/m2 of body surface and a left ventricular filling pressure greater than or equal to 16 mm of Hg. Approximately 1 mg of hydralazine/kg of body weight was administered orally each hour until the total systemic resistance index decreased below 1,700 dynes . s X cm-5 X m2. The drug effect was monitored hemodynamically until it dissipated. Hydralazine increased the cardiac index from 3.06 +/- 0.47 (+/- SD) to 6.81 +/- 0.87 L/min/m2 (P less than 0.01), stroke volume index from 20.9 +/- 1.6 to 36.8 +/- 9.3 ml/beat/m2 (P less than 0.01), and heart rate from 146.2 +/- 17.2 to 187.8 +/- 42.8 beats/min (P less than 0.05). It decreased mean arterial pressure from 111.5 +/- 20.4 to 83.8 +/- 4.7 mm of Hg (P less than 0.05) and total systemic resistance index from 2,903 +/- 149 to 992 +/- 83 dynes . s X cm-5 X m2 (P less than 0.001). It did not affect left ventricular filling pressure or contractility. Peak drug effect occurred at 3 to 5 hours after drug administration and duration of effect was 11 to 13 hours. Recurrence of ventricular dysrhythmias occurred in 2 dogs and 1 dog died during a recurrence. Hydralazine improved cardiac performance in the dog with left ventricular failure.

Animals↗
PubMed1982

Clinical experience with hydralazine for treatment of otherwise intractable cough in dogs with apparent left-side heart failure.

Eleven dogs with mitral regurgitation and severe cough were given hydralazine for reduction of systemic arterial pressure. The treatment was stopped and then restarted. Heart rates were measured and cough was assessed subjectively by the clients during each period. While the dogs were receiving hydralazine, heart rate and severity of cough decreased, when compared with periods either before or between treatments. Clinical improvement may have resulted from increased cardiac output or reduction in regurgitation. The improvement also may have resulted from effect on pulmonary function inasmuch as we had no evidence that the signs were a result of heart disease.

Animals↗
PubMed1982

Intramyocardial pressure and distribution of coronary blood flow during systole and diastole in the horse.

Transmural myocardial blood flow was measured with microspheres in systole and in diastole, along with intramyocardial pressure, in seven anaesthetised horses. Intramyocardial pressures were measured with a miniature manometer implanted in the tip of a 16-gauge needle. Peak systolic intramyocardial pressure decreased from subendocardium to subepicardium and never exceeded intraventricular pressure. Systolic blood flow decreased from epicardium to endocardium where it did not differ from zero. Diastolic blood flow increased from epicardium to subendocardium, but then decreased in the most endocardial layer to a level not different from the immediate subepicardial layer. The horse was a useful model for studying these parameters because the ventricular walls are so thick and the heart rate is so slow that injections may be made during various phases of the cardiac cycle. These results of transmural myocardial blood flow and intramyocardial pressure measured in the same animal are identical with those of others, except for the reduction in subendocardial blood flow compared with the layers just epicardial to that.

Animals↗
PubMed1982

The anatomic relationship of the esophageal lead to the left atrium.

This study was undertaken to establish the "in vivo" anatomic relationship of the esophageal catheter to the left atrium. Fourteen patients, seven of whom had enlarged left atria, were included in the study. During cardiac catheterization, a bipolar recording catheter was placed in the esophagus; left atrial cineangiograms were then obtained in the posterior-anterior (PA), left anterior oblique (LAO), and lateral views. The distance of the esophageal catheter, in each of four commonly used positions, to the interatrial septum-right atrium was measured in the PA and LAO cineangiograms. The distance from the same catheter positions to the posterior left atrial wall was measured from the lateral view. In all positions and regardless of left atrial size, the catheter clearly lay behind the left atrium and was closer to the left atrial wall than any other cardiac structure, including the interatrial septum. Bipolar electrograms were recorded from the four commonly used esophageal locations; atrial wave amplitude and other parameters of the electrogram deflection did not vary significantly in the different lead positions. We conclude that esophageal electrograms reflect left atrial activity by virtue of the recording electrode's clear proximity to this structure. The amplitude and configuration of the atrial wave itself is generally not useful in determining the position of the esophageal lead.

Adult↗
PubMed1982

Noninvasive measurement of systemic arterial pressure in dogs by automatic sphygmomanometry.

Mean, systolic, and diastolic systemic arterial blood pressures were recorded by indirect automatically inflating and deflating sphygmomanometry, using an oscillometric principle in 9 anesthetized dogs whose blood pressures were varied by infusions of sodium nitroprusside and phenylephrine. Blood pressures fluctuated between a diastolic pressure of 40 mm of Hg and a systolic pressure of 210 mm of Hg. A total of 147 blood pressures, measured by indirect sphygmomanometry, were compared with those obtained from a cardiac catheter within the artery of the contralateral limb. The device also indicated heart rate. Correlation coefficients between actual pressures from the cardiac catheter and those registered by the oscillometric device were greater than 0.9 for all pressures, and correlation coefficient for heart rate was 0.827. The lower correlation for heart rate was a consequence of (i) the slow sinus arrhythmia produced in response to phenylephrine and (ii) the device recognizing catacrotic waves as primary pulsations. In the anesthetized dog, this device is reliable, simple to use, and may be of value for monitoring dogs during surgery. Preliminary subjective evaluation indicated that the device is useful for measuring systemic arterial pressures in unanesthetized dogs as well, as long as motion of the limb around which the cuff is placed is minimal.

Animals↗
PubMed1980

Clinical use of echocardiography in the domestic cat.

Echocardiograms were obtained from unanesthetized cats positioned in left lateral recumbency. Information regarding chamber wall thickness, lumen dimensions, valve motion, and indices of contractility was obtained. In three cases, echocardiographic manifestations typical of cardiac dilatation, cardiac hypertrophy, and pericardial effusion were recorded. Unlike thoracic radiographs, which portray pulmonary features as well as a cardiac silhouette, the echocardiogram provided an opportunity to measure each component comprising the cardiac silhouette--namely, the pericardial sac, cardiac musculature, and the cardiac chambers.

Animals↗
PubMed1980

Effects of furosemide on cardiovascular function and performance when given prior to simulated races: a double-blind study.

In a double-blind study under simulated racing conditions, six Standardbred horses, which had been trained for 12 weeks, were given 1 mg of furosemide/kg of body weight or saline solution IV 15 minutes before the first of two warm-up workouts (1.6 km at 60-minute intervals). Sixty minutes later, 135 minutes after drug or placebo injection, these horses were driven 1.6 km at maximum speed. Heart rate, respiratory rate, cardiac output, pulmonary trunk pressure, body temperature, PCV, arterial oxygen, and plasma lactic acid were recorded during and after the first warm-up workout and after a simulated race (1.6 km). Values increased compared with values determined at rest whether saline solution or furosemide was given. There were decreases in arterial CO2 and pH. When furosemide was given, the pulmonary trunk pressure was significantly lower (P < 0.05) during the first warm-up workout (1.6 km). There were no significant differences in the other values. The average times of the simulated races were not significantly (P < 0.05) different after the use of furosemide compared with average times after use of saline solution.

Animals↗
PubMed1980

Sound transfer function of the congested canine lung.

Alterations of sound transfer function of the lung in pre-congested and congested states were studied in a canine model as an index of the accumulation of lung liquids. Pulmonary congestion was produced by graduated inflations of a balloon in the left atrium. Different degrees of pulmonary congestion were documented by post-mortem wet to dry lung weight ratios. Sound transfer function of the lung was determined utilizing passive sound transmission in the audio freqency range consisting of sinusoidal oscillations swept from 50 Hz to 2 kHz. Sound transfer function in dB was defined as 20 times the logarithm of sound output divided by sound input. These functions were computed for pre-congested and congested states of the lung and the differential values correlated with the post-mortem wet to dry weight ratios of the lung. The magnitude of sound transfer function of the lung correlated well with increasing accumulation of intravascular and extravascular lung liquids and provided a quantitative index of pulmonary congestion.

Animals↗
PubMed1979

Ventricular wall thickness in the fetal dog.

Ventricular wall thickness of 21 50-to 60-day canine fetuses was determined by direct measurement with calipers. Measurements were made of the left and right ventricular walls and of the interventricular septum, perpendicular to the apico-basilar axis at the location just below the aortic valve, and midway between the coronary sulcus and the apex. Mean determiniations were used to characterize the wall thickne-s at the various levels. The right wall was found to be thickpreciable thickness differences between the septal and left wall at this location. At the level of the midventricular wall, the septal wall thickness exceeded that of the left and right wall. Left and right wall thickness at this level were similar.

Animals↗
PubMed1979

Echocardiography in the domestic cat.

Echocardiographic examinations were performed on 25 normal healthy cats placed in left lateral recumbency. The cats were representative of serveral breeds, consisted of 12 males and 13 females, and weighed between 2 and 6.5 kg. Twelve measurements from the echocardiograms of each cat were made for the purpose of compiling a small data base (reference values). These measurements included wall thicknesses, luminal dimensions, and contractile indices. Left ventricular wall thickness averaged 0.37 +/- 0.08 cm, and the septal wall thickness averaged 0.45 +/- 0.09 cm. The average left ventricular lumen in diastole was 1.48 +/- 0.26 cm, and in systole, it was 0.88 +/- 0.24 cm, which resulted in an average shortening fraction of 41 +/- 7.3%. Velocity of circumferential shortening, an index of contractility, averaged 2.86 +/- 0.78 cm. In eight additional cats, both ventricles were catheterized for echographic chamber identification and then cineangiographic procedures. Then these cats were euthanatized, and postmortem measurements were compared with echocardiographic and cineangiographic measurements. According to the three methods of determining wall thickness, differences were less than 15%, where the range of deviations was between 0 and 0.5 mm and the average deviation was -0.01 +/- 0.26 mm.

Animals↗