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Biomedical subjects

R L Hamlin

Publications and source records attributed to R L Hamlin.

At least 127 records · Page 7Linked to original sources
PubMed1978

Echocardiographic diagnosis of endocarditis in a bull.

A 2-year-old Charolais bull was examined because of lameness that developed after infection of a tail laceration. A systolic murmur was auscultated during the routine physical examination. A diagnosis of endocarditis and polyarthritis secondary to septicemia from the tail lesion was made. The diagnosis was supported by echocardiography and blood cultures, which yielded Corynebacterium pyogenes. The clinical diagnosis was confirmed at necropsy.

Animals↗
PubMed1978

Norepinephrine stores in the hypertrophied bovine heart.

Influence of hypertrophy on the cardiac stores of norepinephrine (NE) and epinephrine in different chambers of the heart were studied in calves with experimental left or right ventricular enlargement. In the control calves, concentration of NE was markedly higher in the atrial than in the ventricles, the left atrial body had a lower concentration than the right atrial body. The same was true of the left ventricular tissue compared to the right ventricular tissue. Marked depression of the cardiac NE concentration was observed in all chambers in the groups with right and left ventricular enlargement. The magnitude of changes was roughly related to the severity of the stenosis. Depletions in the concentration of NE were not noticed in the operated nonresponsive calves. By contrast, epinephrine was in small concentrations in control calves, amounting on the average to less than 10% of the amount of NE concentration in the same cardiac tissues. However, alterations in cardiac epinephrine values were not observed in the cardiac tissues obtained from animals with cardiac hypertrophy.

Animals↗
PubMed1978

An invasive procedure for in utero fetal electrocardiology: recording of fetal electrocardiograms by applying electrodes through the uterus.

An in utero technique was developed that allows direct access to the canine fetus for experimentation. This procedure reduces the need for fetal manipulation and umbilical blood flow compromise and reduces fetal fluid loss. In pregnant bitches, uterine horns could be delivered through a ventral midline incision. By manipulating the fetal membranes, and positioning the fetuses through them, electrodes could be inserted subcutaneously in the fetuses. Electrocardiograms satisfactory for interpretation were obtained from as many as 4 fetuses in a bitch for periods up to postoperative week 3.

Animals↗
PubMed1978

Echocardiography in swine.

Twelve clinically normal pigs were anesthetized with fentanyl citrate and sodium pentobarbital and placed in left lateral recumbency. M-mode echograms were recorded from the area of the 4th intercostal space with a 3.5 mmHz transducer. Changes in the internal minor axis diameter %deltaD were measured at 44.8 +/- 3.3 cm. An index of contractility (Vcf) was 1.12 +/- 0.16 cm/s. The caudal wall thickness dimension measured 0.61 +/- 0.04 cm and the aortic root dimension was 1.9 +/- 0.11 cm. To corroborate the echocardiographic findings, echocardiographic, cineangiographic, and postmortem studies were conducted on a 2nd group of 3 pigs. Aortic root, diastolic lumenal dimensions, and wall thickness were compared and the results never differed more than 2 mm. Echograms can conveniently be acquired from restrained, mature swine, and they provide useful, reliable structural and hemodynamic information, without the hazards or expense of invasive techniques.

Animals↗
PubMed1977

Echocardiography in the horse.

Echocardiograms were obtained from 25 standing, clinically normal horses, using an ultrasonic recording device. The echobeam penetrated the right thoracic wall in the area of the 4th to 5th intercostal space, with a frequency of 2.5 mHz. Measurements of left ventricular wall thickness generated a mean value of 3.2 +/- 0.18 (SEM)cm, whereas the left ventricular chamber diameter in diastole was 9.3 +/- 0.30 cm and in systole was 5.7 +/- 0.23 cm. The aortic root dimensions had a mean of 7.7 cm, with a SEM of 0.16. Mitral valve closing slope (E-F) was calculated to be 17.7 +/- 0.87 mm/second, and percentage of delta D, a correlate of ejection fraction, was 38.6 +/- 1.6%.

Animals↗
PubMed1977

Electrocardiographic and vectorcardiographic response to right ventricular hypertrophy in the goat.

Basic differences were observed in the elctrocardiographic and vectorcardiogrpahic response to RVH in goats when compared to man and dogs. Instead of RVH inducing a redistribution of major fronts of electrical activity which result in profound QRS complex alterations as in man and dogs, it appears to produce no significant alteration of the QRS complex or major vector orientation in goats. Although slight reorientation of sagittal and horizontal vector forces occurred during development of RVH, no statistically significant changes could be detected.

Animals↗
PubMed1977

Respiratory parameter estimation using forced oscillatory impedance data.

The frequency dependency of the magnitude and phase angle of total respiratory impedance was measured in apneic dogs at functional residual capacity during forced oscillation by a special electronics unit. Regression analysis of these data yielded estimates of total respiratory resistance (RFO), inertance (IFO), and compliance (CFO). After correcting for the effects of the endotracheal tube, mean control values (+/-SE) of RFO, IFO, and CFO for the clinically normal dogs were 1.30+/-0.10 cmH2O-1-1-s, 0.0114+/-0.0022 cmH2O-1-1-s2, and 0.0306+/-0.0009 1-cm H2O-1, respectively. Estimates obtained with added resistance, a less dense gas, and abdominal weighting were consistent with predicted effects. In four dogs with mild respiratory symptoms, mean RFO was significantly elevated with no change in IFO or CFO. Independent measurements of resistance and compliance during tidal ventilation correlated well with RFO (r=0.87) and CFO (r=0.80), but RFO and CFO were, on the average, 71% of the tidal breathing values. Thus, the method provides precise estimates of RFO, IFO, and CFO, and allows detection of small changes in these parameters.

Airway Resistance↗
PubMed1976

Effects of angiotensin and prostaglandin A2 in perfused isolated kidneys of dogs.

Simultaneous recordings of pressure and flow were made from the renal artery in perfused isolate canine kidneys. The system was perturbated by the administration of angiotensin and prostaglandin A2. The data were recorded on frequency-modulated analog tape and converted to digital form, and a Fast Fourier Transform program was used to calculate input impedance. Changes in total renal volume and renal arterial pressure data were used to determine compliance values. in compliance were found, along with changes in both magnitude of impedance and phase angle, as a result of the perturbations introduced. Seemingly, renal vascular compliance has an important role in the autoregulatory mechanisms of the kidney.

Angiotensin II↗
PubMed1976

Systolic time intervals for left and right ventricles of swine.

Because swine are used often in cardiovascular research, and because systolic time intervals (durations of preejection and ejection) are useful in evaluating the ventricular function in health and disease and the effects of drugs on ventricular function, systolic time intervals for left and right ventricles were obtained from 12 healthy anesthetized shoats. Catheter-tip micromamonmeters were placed just distal to the semilunar valves, and pressure pulses from these positions in the ascending aorta and pulmonary trunk were simultaneously recorded with an electrocardiograph at paper speed of 200 mm/second on a photographic oscillograph. Equations of regression relating preejection period (PEP) and ejection time (ET) for the left ventricle (L) to heart rate (HR) are as follows: PEPL = 53 + 0.56 HR ETL = 329 -- 0.94 HR Systolic time intervals for the right ventricle did not relate to heart rate.

Animals↗
PubMed1975

Ventricular activation process in minipigs.

Because the form of QRS from the body surface of pigs is different from that of carnivores or ungulates, and because that form is dependent upon pathways of ventricular activation, this study was designed to study pathways of ven tricular activation in pigs. Twelve pigs were anesthetized and right or left hemithoracotomies were performed to expose the heart. Contiguous bipolar electrograms were recorded from button electrodes on the epicardium and from both faces of the interventicular septum, and from multipolar plunge electrodes introduced into the intramural regions of both ventricles. Electrograms were recorded simultaneous with the Z-axis ECG at 625 mm/sec paper speed on a photographic oscillograph. Times of arrival of waves of activation at numerous points in the ventricle were referenced to the peak of the R-wave in the Z-axis ECG. During the initial 10 msec of QRS, the apical-third of the interventricular septum is activated from left to right. During the next 40 msec of QRS, waves of activation originating at the cranial portion of the right ventricle and the caudal portion of the left ventricle engulf the epicardium toward the interventricular septum and slightly in an apico-basilar direction. Activity begins slightly earlier at the caudal aspect of the left ventricular free-wall and terminates on the pulmonary conus region. During the terminal 30 msec of QRS, the basilar third of the interventricular septum is activated in a general apico-basilar direction. Through regions of either right or left ventricular free-walls was a general endocardial to epicardial activation observed. These pathways of ventricular activation may be explained by the rather complete penetration of Purkinje fibers through both ventricular free-walls in a manner similar to that of ungulates but different from carnivores and primates.

Animals↗
PubMed1975

Ventilatory alterations in normal horses in response to changes in inspired oxygen and carbon dioxide.

The influence of various concentrations of CO2 and O2 in the inspired gases on minute volume (V), tidal volume (VT), and respiratory rate (breaths per min; BPM) was examined in nonanesthetized, nonsedated normal horses. The VT and BPM increased linearly in response to increases in inspired CO2 concentration and curvilinearly in response to decreases in inspired Os concentration. The V increased curvilinearly in response to both increases in inspired CO2 concentration and decreases in inspired O2 concentration.

Animals↗
PubMed1975

Effects of xylazine and acetylpromazine upon induced ventricular fibrillation in dogs anesthetized with thiamylal and halothane.

Ventricular arryhythmias including ventricular fibrillation were produced with epinephrine in dogs induced to an anesthetic state with thiamylal and maintained with halothane. In dogs given (premedicated) xylazine 20 minutes prior to anesthesia, ventricular arrhythmias, including ventricular fibrillation, were induced with much smaller doses of epinephrine than in nonpremedicated dogs. Dogs premedicated with acetylpromazine 20 minutes prior to anesthesia with thiamylal and halothane displayed protection from epinephrine-induced arrhythmias. Caution is advised from using xylazine in the presence of halothane if epinephrine is to be administered.

Anesthesia↗
PubMed1975

Effects of acetylpromazine on ventilatory variables in the horse.

The influence of breathing various concentrations of carbon dioxide and oxygen upon minute volume, tidal volume, and respiratory rate were examined in acetylpromazine-tranquilized horses. Responses in the horses before (control period) and after tranquilization were qualitatively similar to increases in carbon dioxide and to alterations in oxygen. The quantitative responses to these changes were less in tranquilized horses than in the same horses studied in the untranquilized state. Tranquilization had its most prominent effect upon respiratory rate in horses breathing room air.

Acepromazine↗
PubMed1975

Antiarrhythmic effects of diazepam during coronary artery occlusion in dogs.

The ventral interventricular branch of the left coronary artery was ligated in a 2-step operation in 10 dogs whose electrocardiograms and systemic arterial blood pressures were then monitored during the next 7 days. Monitoring was done in awake dogs given 1 mg of diazepam per kilogram of body weight (intravenously administered in 3 dogs and orally in 7). Because ventricualr ectopic activity was greatest during the interval of 10 to 48 hours after ligation, the antiarrhythmic activity of diazepam was recorded during this 38-hour interval. After administration of diazepam by either route, frequency of ventricular ectopic beats decreased from 98 to 80%. THIS REDUCTION BETAN IMMEDIATELY AFTER THE INTRAVENOUS ADMINISTRATION AND PERSISTED FOR ONLY 5 MINUTES; REDUCTION BEGAN APPROXIMATELY 1 HOUR AFTER THE ORAL ADMINISTRATION AND PERSISTED 4 TO 6 HOURS. Systemic arterial blood pressure decreased only after the intravenous administration. It is concluded that diazepam is effective in reducing the frequency of ventricular ectopic activity after occlusion of major branches of coronary arteries, that diazepam works independent of alterations in systemic arterial blood pressure, and that orally administered diazepam prolongs antiarrhythmic activity. Possibly, the adjuvants present in the parenteral form of diazepam reduce antiarrhythmic activity by being, themselves, arrhythmogenic.

Administration, Oral↗