The study of cardio physiology was broken up into five distinct parts all centering on the cardiovascular system. The first lab was utilization of the electrocardiogram (ECG). This studied the electrical activities of the heart by placing electrodes on different parts of the skin. This results in a graph on calibrated paper of these activities. These graphs are useful in the diagnosis of heart disease and heart abnormalities. Alongside natural heart abnormalities are those induced by chemical substances. The electrocardiogram is useful in showing how these chemicals adjust the electrical impulses that it induces. The second part of this lab was a computer simulation program to illustrate a frog’s electrocardiogram using various drugs in an isolated setting. The computer program entitled “Effects of Drugs on the Frog Heart” allowed experimental conditions to be set for specific drugs. The different drugs used were calcium, digitalis, pilocarpine, atropine, potassium, epinephrine, caffeine, and nicotine. Each of these drugs caused a different electrocardiogram and beats per minute reading. The calcium-magnesium ration affects “the permeability of the cell membrane”(Fox). When calcium is placed directly on the heart it results in three physiological functions. The force of the heart increases while the cardiac rate decreases. It also causes the appearance of “ectopic pacemakers in the ventricles, producing abnormal rhythms” (Fox). Digitalis’ affect on the heart is very similar to that of calcium. It inhibits the sodium-potassium pump activated by ATP that promotes the uptake of extracellular calcium by the heart. This in return strengthens myocardial contraction (Springhouse). Pilocarpine on the other hand
acts to decrease the heart rate. It achieves this by assisting in the release of acetylcholine from the vagus nerve. Atropine on the other hand block acetylcholine receptors thus decreasing cardiac rate. By placing potassium directly on the heart, its extracellular concentration increases thus decreasing the resting potential. This brings the resting potential closer to threshold and weakens myocardial contractions. Epinephrine’s action increases the strength of contraction and of the cardiac rate. Caffeine is a stimulant that also increases the strength of contraction and of the cardiac rate. It inhibits phosphodiesterase that breaks down cyclic AMP thus causing an increase in cAMP levels. Nicotine actively binds to the nicotinic receptors causing stimulation of the parasympathetic ganglia. This in returns slows the heart rate. By listening to chest one can hear the actual mechanical contraction of the heart. Upon the closure of the valves a lub can be heard and the semilunar valves shut a dub is heard. Using this technique, diagnosis of a heart murmur can be made. The relative opening of the foramen ovale can cause this condition. Adding a device known as a sphygmomanometer and listening to the brachial artery is how blood pressure is taken. Blood pressure is highly dependent on cardiac output and peripheral resistance. Cardiac output is the amount of blood pumped by the heart per minute. The resistance the blood receives flowing through the arterioles is peripheral resistance. As a result of this, blood pressure can be controlled by dilation and constriction of arterioles. Upon measuring blood pressure, on should be able to hear five phases of sound. These phases are:
1. A loud clear tapping.
A sequence of murmurs.
Cardiac Physiology 4
A loud thumping following the murmurs.
The sound becomes muffled.
In determining how fit we are a number of test can be used. This can include but is not limited to the ECG, blood pressure, and/or pulse rate. By taking the pulse under various conditions the maximum cardiac rate can be estimated. Trend wise, a non-athlete will reach their maximum cardiac output at a lower workload than an athlete. Although not completely accurate, this can be a very...
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Tuen, Charles M.D. Neuroland. 22 July 1998. 1 Apr. 2000
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