e. 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. Epinephrines 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.2.A sequence of murmurs.Cardiac Physiology 43.A loud thumping following the murmurs.4.The sound becomes muffled. 5.Silence. 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...
