This study compared interactive videodisc-simulated laboratories with two types of traditional labs: a traditional general cardiovascular physiology participation lab and a traditional fibrillation/positive pressure ventilation demonstration lab. The two laboratory sections (a total of 85 first-year veterinary medical students) were divided into 12 lab groups of 3-4 students per lab section. These groups were randomly assigned to either a traditional live animal laboratory or an interactive videodisc-simulated laboratory to compare the effectiveness and efficiency of these methods in teaching physiology. A 22-item, multiple-choice/short answer test was given to all students after the laboratories. In both the participation and the demonstration laboratories, there were no significant differences between group test scores of the interactive videodisc groups and the live animal laboratory groups, but there were differences in time spent by both students and instructors. It was concluded that the interactive videodisc-simulated lab was as effective as the traditional live-animal labs and was more time efficient than the traditional participation lab.
SUMMARYSyncope and sudden death occurs in certain purebred Pug dogs which have been found to have intermittent sinus pauses and paroxysmal second degree heart block on electrocardiographic (ECG) study. We have established a colony of such dogs to study this problem and here report the results of histological examination of the cardiac conduction system in twenty-one of them. These include a dam which may be considered the proband, three of her offspring (two littermates) and three fetal pups in an unborn litter of one of these; three of the four adult dogs died suddenly and unexpectedly. Two groups of puppies descendants of these lines were also studied after they all died within three days of birth. The first group of puppies (8) made on some of the Pug dogs with syncope demonstrated various forms of electrical instability of the heart. A colony of Pug dogs has now been established for the purpose of careful investigation into the anatomical and physiological basis for the electrical instability and into the pathogenesis of the syncope and sudden death. This report will present the result of some of those investigations. Material and MethodsSeveral years ago a five-year-old purebred female Pug dog (to be designated Dog A) was examined because of a history of syncopal attacks. An electrocardiogram made with Dog A lying quietly awake (no sedation) is shown in figure 1 and is typical of a number of such records. The syncopal attacks had a characteristic course which began with a few seconds of excitement and hyperactivity ending in an abrupt collapse. Dog A was observed during several attacks, which consisted of dyspnea, cyanosis, disorientation and the absence of any audible heartbeat. Within the next few minutes the dog would gradually recover. This sequence, including the onset with a period of excitement, is remarkably similar to the observed spells of syncope in congenitally deaf children.2' 4 In the second year of observation Dog A died suddenly and unexpectedly after being observed a few minutes earlier in apparent good health.
Ten hypertensive (hyper) and hypotensive (hypo) turkeys of both sexes were used to evaluate the effect of various stimuli on blood pressure (BP) and heart rate (HR). Blood pressures were recorded from the brachial artery via a catheter and radio telemetric system. After a 48 hr baseline monitoring, the birds were subjected to exercise, fright, and mating and the BP and HR changes recorded. Mean arterial BP was 4.5 mm Hg less during night than day, and the BP of the hyper strain was significantly (P less than or equal to .05) higher than the hypo strain. Tracings from quiescent birds revealed fluctuations in BP that varied by 100 mm Hg. These were unexplainable fluctuations and occurred in both hyper and/or hypo birds at various times. The application of various stressful situations, such as exercise and fright, had little effect on BP but appeared to cause marked changes in HR. The highest recorded BP occurred during one of the mating exercises where systolic BP approached 350 mm Hg and HR increased by approximately 100%. Noises created with dog whistles and a .22 caliber pistol shot did not cause marked changes in BP and HR.
This study was undertaken to evaluate the relative sensitivity of the canine sinus and atrioventricular (AV) nodes to acetylcholine (Ach). A dose-dependent increase in both A–A and R–R intervals occurred when Ach (5–320 μg/kg) was injected into the left ventricle of both conscious and anesthetized dogs. Comparison of the ED50 values for Ach (derived by weighted nonlinear least squares regression analysis of the dose-dependent changes in the A–A and R–R intervals) revealed the AV node to be 1.9-fold more sensitive to the effect of Ach than the sinus node in the conscious dogs and 3.3-fold more sensitive than the sinus node in the anesthetized group. The results imply that the greater sensitivity of the AV node to Ach is, at least in part, responsible for the occasional second degree block commonly observed in clinically normal dogs.
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