Laboratory Report The Effects of Drugs on Cardiac Physiology The study of cardio physiology has been divided into five distinct parts, all focusing on the cardiovascular system. The first laboratory was the use 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 calibrated paper graph of these activities. These charts are useful in diagnosing heart disease and cardiac abnormalities. Alongside natural cardiac anomalies there are those induced by chemical substances. The electrocardiogram is useful for showing how these chemicals regulate the electrical impulses they induce. The second part of this lab consisted of a computer simulation program to illustrate a frog's electrocardiogram using various drugs in an isolated environment. The computer program titled “Effects of Drugs on the Frog Heart” made it possible to create experimental conditions for specific drugs. The different drugs used were calcium, digitalis, pilocarpine, atropine, potassium, epinephrine, caffeine and nicotine. Each of these drugs caused a different EKG and beats per minute reading. The calcium-magnesium ratio affects “the permeability of the cell membrane” (Fox). When calcium is placed directly into the heart it results in three physiological functions. The strength of the heart increases as the heart rate decreases. It also causes the appearance of “ectopic pacemakers in the ventricles, which produce abnormal rhythms” (Fox). The effect of digitalis on the heart is very similar to that of calcium. It inhibits the sodium-potassium pump activated by ATP which promotes the absorption of extracellular calcium by the heart. This in turn strengthens myocardial contraction (Springhouse). Pilocarpine on the other hand works to decrease the heart rate. It achieves this by promoting the release of acetylcholine from the vagus nerve. Atropine, on the other hand, blocks acetylcholine receptors, thus decreasing the heart rate. By placing potassium directly into the heart, its extracellular concentration increases, thus decreasing the resting potential. This brings the resting potential closer to threshold and weakens myocardial contractions. The action of adrenaline increases the force of contraction and heart rate. Caffeine is a stimulant that also increases the strength of contraction and heart rate. It inhibits phosphodiesterase which breaks down cyclic AMP thus causing an increase in cAMP levels. Nicotine actively binds to nicotinic receptors causing stimulation of the parasympathetic ganglia.