Introduction

Part 2

Part 3

Part 4

Basic Cardiology...(cont)

Ohm's law explains the relationship between current, resistance and potential (voltage) in a DC circuit. The formula is V=IR, where V is potential (in volts), I is current (in Amps), and R is resistance (in Ohms). This relationship can be used in association with Kirchoff's voltage and current laws to find various parameters within a DC circuit. Kirchoff's Current Law states that the sum of the currents entering and exiting a single node must equal zero (ie. current in = current out of a node). Kirchoff's Voltage Law states that the sum of all changes in potential within a closed loop must equal zero.

Since the heart, arteries and veins comprise in integrated cardiovascular system, problems in the conduit vessels can obviously impact the function of the heart. Coronary arteriosclerosis, or cholesterol-blocked arteries in the heart muscle, can injure the heart muscle by failing to provide necessary oxygen and nutrients to the cardiac muscle. When blood flow is completely and acutely blocked, typically by formation of a blood clot in a coronary artery, the heart muscle dies (a heart attack). A chronic subtotal blockage may not actually kill the heart muscle because some hypertension increases the work required to circulate blood to the vital organs such as the brain, kidneys and even the heart itself. Interestingly, this relationship between cardiac function and blood pressure is precisely described by the electrical equation, Ohm's law (E=IR), which states that the pressure gradient across a circuit (potential or E) is equal to the product of flow through the circuit (current or I) and the resistance in the circuit (R). Increased blood pressure (E) therefore must occur as a result of increased resistance in the arteries (R), assuming that the heart continues to pump the same volume of blood per minute (I). In fact, this is known to be the case and hypertension is routinely treated with vasodilator drugs which increase the size of arteries, decrease vascular resistance, and protect the heart.

Hypertrophy
A critically important feature of cardiac muscle is that, like the brain, it has no capacity to regenerate. Shortly after birth the number of cardiomyocytes in a heart stabilises and further growth of the heart can only occur by enlargement of existing cells, or hypertrophy. As noted previously, hypertrophy in response to valvular disease or increased blood pressure has limited ability to compensate for the increased work needed in these conditions, and ultimately fails. However, the type of cardiac hypertrophy which develops as a consequence of athletic training is purely beneficial, and even protective against heart failure. Therefore, in addition to risk factor modification for coronary atherosclerosis, such as not smoking and observing a low fat and cholesterol diet, aerobic physical training is an important preventative measure for heart disease, and a vital part of the therapeutic regime during cardiac rehabilitation. An exciting area of medical investigation in the cardiovascular field is the attempt to develop methods of regenerating cardiac muscle, or to modify the hypertrophic response to more resemble athletic hypertrophy, perhaps using gene transfer technology.

Reference sites:
http://www.e-cardiovascular.net/
http://www.innerbody.com/image/cardov.html
http://cardiovascular.cx/
http://www.carle.com/OldSite/HeartCenter/heartworks.htm
http://www.ecglibrary.com/

Article updated by John Sandham