Cardiac Function And Physiology - Research Paper Example

Cardiac Function and Physiology Effects on homeostasis and organ function John Doe Biology 164 St. Augustine North Dakota N. Utter October 21, 2011 Abstract This paper explains the function, physiology, and effects on homeostasis for other organ systems. The interrelationships between the organs and how vital the cardiac system is to providing those crucial elements needed by the other organs is explained in detail as well as highlighting the breakdown in other organs when the cardiac system begins the process of failure, weakening, or anomalous pattern. Further, the understanding of the cardiac cycle and its function will be discussed as well as the important ElectroCardiac (EKG) readings which show electrical activity. Cardiovascular mechanics will be discussed and how it maintains whole person homeostasis along with general features of the cardiac cycle and the electrolytes involved in the action potential. Some basic alterations of cardiac activity will also be covered here, as well as a few primary pathologies that will affect other organ systems such as tumors, congestive heart failure, ischemic heart disease, among others as well as how pharmaceuticals are involved and help compensate for any loss of function. As such the 3 sections of this paper will include normal physiology, pathology of the organ and associated affects on the body, and conclusions from discovery. The appendix will include all graphic information mentioned in this paper at the end. Keywords: cardiac function, pathology, EKG, physiology, cycle, vascular homeostasis I. FUNCTION OF THE HEART AND VASCULAR SYSTEM The heart lies in the thorax of the body in an area called the mediastinum. This area is further divided into inferior and superior parts by a plane passing from the sternal angle anteriorly to the intervertebral disc between T4 and T5 posteriorly (Harrisons 2008). The inferior mediastinum is classically subdivided into middle, anterior and posterior parts. The heart is contained within a sac called the pericardium which is fibrous in the outer part and also has a double membraned serous sac between the parietal and visceral layers. The right border of the heart is formed by the right atrium and the left ventricle and left atrium form the left border. The apex is the tip of the ventricle. The blood flow into the heart begins and ends at the superior/inferior vena cava which brings deoxygenated blood back to the heart to be transported through the pulmonary artery and vein to and from the lungs where gas exchange occurs. Oxygenated blood flows then from the pulmonary vein into the left atrium to the left ventricle and out to the body in the aorta and following arteries and veins. The heart is a functioning pump which forced blood throughout the body and obviously all necessary organs and structures to supply the body with oxygenated blood and nutrients. The heart is the beginning and ending of life. Without the heart pumping blood through the body, there is no life. Subsequently, any discussion of life after heart failure is pointless and will not be discussed. In terms of heart mechanics, systolic function is a measurement of the overall force generated by the ventricular muscle during systole, which is determined by the number of cross bridges cycling during a contraction. The number of cross bridges is determined by the amount of preload on the heart and level of contractility. The factors work together in general to determine the overall force. As with skeletal muscle, preload is the load on the muscle in a relaxed state (diastole). More accurately, it is the pre-stretch of the heart ventricle before the beginning of contraction. The end of the paper will show indices of cardiac function, preload, contractility indexes and a host of physiology related information in support of the mechanics of the heart and how the above is measured. The hearts action as a pump supplies blood to all sectors of the body. The most important organs in order of blood flow are the brain, kidney, and liver. The obvious need of the body is to control blood flow to the central computer, if you will, of the body. Control of the heart rate is intrinsic and set at around 110beats/min (Harrisons 2008). This is the spontaneous firing rate of the SA node in complete absence of the influence of the parasympathetic nervous system and sympathetic nerves. Increased or decreased blood volumes can also influence the heart rate making it go down or up depending on the brains signaling and needs (Kumar 2006). A decrease in blood flow to the brain, however will signal an increase in the heart rate to maintain neural function. Blood pressure is maintained by many inputs and counter regulations. Baroreceptor reflexes maintain short term control of blood pressure while the endocrine based renin-angiotensin-aldosterone system maintains long term control. (This is illustrated later in the appendix.) In short, the mean arterial pressure is the result of the cardiac output times the total peripheral resistance (MAP = CO x TPR). The main receptors are found in the carotid sinus which monitor the stretch of the vessel. (Runge 2009) Organs are affected by a decrease in blood pressure (BP). A decrease in BP will cause a decrease in the stimulation of the stretch receptors which will increase sympathetic activity, which therefore will increase the heart rate. This is most commonly due to a loss of blood, for example in hemorrhage. (Runge 2009) A subsequent loss of blood would automatically trigger an increase in heart rate, but other organs affected would have blood flow shunted from them, for example the kidneys, which would then decrease the processing of blood and creation of urine. So urine flow would therefore necessarily decrease. The liver would also see a decrease in flow and digestive functioning would cease until the body returned to normal functioning and flow was returned to normal. If the heart is functioning at a regular rate and rhythm the blood flow it provides encourages normal utility in the whole body. The kidneys function regularly cleansing the blood of excess electrolytes, toxins, and fluids. The liver stores fats and lipids and helps remove toxins as well which are transported by the vascular system. Without adequate blood flow, the liver fails and the body fills with toxins and causes poisoning of the brain leading to death. The digestive system, likewise, helps process food and liquids and once it has done that and broken down the food product into smaller transportable molecules the blood flow transports it to the liver where its being processed as mentioned above. (Kumar 2006) II. Organ Failure and the disruption to other organ systems Cardiac organ failure cannot be described as one solitary event, because if so the entire person dies. Therefore, we must address minor to major anomalies which cause injury to the heart itself (ischemia), long term processes like congestive heart failure, hypertension and others. These events can damage the heart itself and not affect other organ systems, or it can, in consort with the vascular system, lead to peripheral problems to be discussed briefly later in this section. First, let us address problems within the heart itself and potential complications with the remainder of the body if there is any. Valvular problems such as aortic stenosis and regurgitation, along with several others interfere with the flow of blood to the organs. They can cause problems with the heart itself or lead to clot formation which can lead to stroke. Aortic Stenosis is a narrowing of the aortic valve and slows the rate at which blood is ejected. The volume of blood then builds up in the left ventricle leading to hypertrophy of the muscle and eventually failure. Regurgitation events in all the valves can lead to a back flow of the blood into the prior area from whence it came. The amount of blood regurgitated may be as much as 60-70% of the amount ejected during systole (aortic valve) (Harrisons 2008). The valvular problems may also be heard during normal auscultation by a trained healthcare professional and the appendix lists the types and where they are heard. Cardiac arrhythmia’s can be divided into two basic types: tachycardiass and bradycardias. These are abnormal rhythmic contractions which are usually symptomatic changes (Zipes 2006). Tachycardias present far more problems than do bradycardias clinically as they can present with a variety of problems including dyspnea, dizziness, syncope, chest pain, fatigue, weakness, sudden death and other consequences of the arrhythmia. With most types of arrhythmia, the main consequences of the problem lies in heart failure or arrest. Inflammation of the myocardial tissue, myocarditis, can also cause problems and arrythmias and usually follow an infection and should be investigated. Heart failure (HF) is not the sudden arrest of the heart beat, rather it is the inability of the heart and peripheral circulation to meet homeostatic metabolic demands while maintaining normal blood pressures and rate (HFSA 1999). Systolic failure indicates an inability to empty the ventricle of blood completely or within normal variant limits. There will be a reduced ejection fraction and ventricular dilatation as a result. The heart enlarges and eventually fails to contract normally leading to elevated end diastolic pressures. Subsequently, there is a decrease in blood pressure and declining CO which triggers both the sympathetic system and the renin-angiotensin system as a compensatory response. However, due to these elements of compensation there is increased after load and worsening HF. The use of diuretics will alleviate the volume loading problem decreasing vascular volume and lessening the work of the cardiac muscle. (HFSA 1999) (Kumar 2006) The effects of poor dietary intake and other problems also lead to cardiac function decline, namely atherosclerosis, which when affecting the coronary arteries leads to a myocardial infarction (MI). In this process, a segment or large portion of the heart muscle may denied adequate blood flow, which will cause a lack of oxygen and nutrients to it, effectively causing the cells in that area to die. The patient presentation in an MI can include, diaphoresis, dyspnea, nausea, vomiting, fear, palpitations, radiating pain to the left arm, chest discomfort and in some cases, rapid onset of coma and death if the MI is bad enough. Rapid administration of nitroglycerin can alleviate the symptoms if available quickly enough as it opens the veins and lowers the preload work on the heart. However, in many cases, the administration of drugs is not available and the long term damage is significant and permanent. While rare, tumors affecting the performance of the heart do occur. The best known of this is the myxoma which usually occurs on the left side of the heart (Harrisons 2008). They take place on the valve flaps and can be hard to detect early on as they may cause no murmur effect to be heard on normal auscultation. Echocardiogram is the best diagnostic test to find one if suspected and surgical resection is usually curative (Kumar 2006)). No effect on subsequent organ systems is known and unlikely. III. Diagnostic Tests and Treatment Strategies Diagnosis of heart problems begins clinically with a simple auscultation. Listening to the heart is critical to finding causes to common presentations. Secondly, a thorough and complete exam will include an EKG and in some cases, more advanced diagnostic procedures such as echocardiogram, trans-esophageal U/S, invasive catheterization, and MRI/CT imaging.(Harrisons 2008) The principles of diagnostic imaging are approached with an idea of getting a thorough and complete image of the heart and chambers to detect abnormalities in the size, contractility, and blood flow. Table 1 shown here gives a comparison of the types of imaging from echocardiogram: Clinical Uses of Echocardiogram Two-Dimensional Echocardiography Cardiac chambers Chamber size Left ventricular Hypertrophy Regional wall motion abnormalities Valve Morphology and motion Pericardium Effusion Tamponade Masses Great vessels Stress Echocardiography Two-dimensional Myocardial ischemia Viable myocardium Doppler Valve disease Doppler Echocardiography Valve stenosis Gradient Valve area Valve regurgitation Semiquantitation Intracardiac pressures Volumetric flow Diastolic filling Intracardiac shunts Transesophageal Echocardiography Inadequate transthoracic images Aortic disease Infective endocarditis Source of embolism Valve prosthesis Intraoperative (taken from Harrisons Principles of Internal Medicine, Section 222, 17th Edition) EKG is likely the most used diagnostic device in cardiology, family practice, and emergency medicine for determining the electrical potential of the heart and what activity is being impaired and what is not being affected. (The appendix contains illustrations of the most common electrical events). The EKG is highly popular due to its lack of invasion of the person, its accuracy, low cost, and versatility in diagnostics. Because the primary electrolytes involved in myocardial functioning cause certain variances in cardiac contractility, the EKG can be useful in determining metabolic disturbances such as hypokalemia and the like. The EKGs efficacy also helps detect enlargements of the heart in all areas of it, helping diagnostic evaluation immensely. For example, Right Ventricular Hypertrophy can be seen as a relatively tall R wave in lead V1 with right axis deviation (Harrisons 2008). There may also be ST depression and T-wave inversion in the right to midprecordial leads. Treatment modalities for cardiac disease are fairly specific to the degree of pathology present. Table 2 will show the types of treatments available for the most common medically treatable problems not needing surgical intervention. Heart Failure Valvular HD Cardiomyopathy Pericardial Dz ACE Inhibitors Same Anti-arrhythmic Bacterial Agents ARBs Nitroglycerin Verapamil, diltiazem Globulins Diuretics HMG CoA reductase “-” disopyramide NSAIDs β blockers Same Same Glucocorticoids Digoxin Warfarin, Heparin Amiodarone ---- OUTCOMES Moderate: >5 Life Exp Surgical: 98% recovery. Dep on severity: transplant possible Dependent on severity of infection: mortality 5-10% Severe: Death < 1yr Medical: LT good if asympt Death within 4 yrs Operational need dependent (LT- long term) IV. Conclusions and Discovery The heart is the beginning and ending of human life. Embryologically, the heart starts beating before the brain is fully formed. It is that important. Therefore, many factors that can impede the organs ability to pump blood through the body affect the whole host, not just itself or one other organ system. The heart is the center of the thorax and midiastinum, being protected by the rib cage and sternum. Any minor elevation of pressure can activate the parasympathetic nerves to slow the heart and conversely, any drop in vascular pressures increases it. While the hearts beating is not in a perfect mechanical synchronous action (in other words, its not pumping identically in all 4 chambers all at once), its action forces blood throughout many feet of vessel tubing carrying the oxygen and nutrients all organs need. Without the blood flowing, the kidneys do not manufacture urine for expulsion and elimination of the toxin urea. The liver does not store fat and the body eliminates sugars which are needed for energy. The pancreas fails to get the signal for an increase in blood sugar content and fails to make insulin via its β-cells or pull stored fats from the body via the action of glucagon. When negatively affected by atherosclerosis, the heart can have areas killed off, as it were, and affect the fluid action of the pump, making blood flow to the brain, liver and kidneys difficult and cause liver congestion, kidney failure, and strokes in the brain. These events lead us to the conclusion that the heart is the beginning and end of all actions in the body, for without it, the body dies completely. Resources used: Heart Failure Society of America (HFSA) practice guidelines, HFSA guidelines for management of patients with heart failure caused by left ventricular systolic dysfunction – pharmaceutical approaches. J Cardiac Failure. 1999;5 :357-382 Kasper DL, Braunwald E, Fauci AS, Hauser SL, Longo DL, Jameson JL, Loscalzo J. (2008). Harrisons principles of internal medicine (17th ed.). New York: McGraw-Hill Medical Publishing Division. Kumar, P. and Clark, M., eds. (2005). Kumar & Clark Clinical Medicine.(6th ed.) Edinburgh : Elsevier Saunders. Runge, Marschall Stevens,, Greganti, M. Andrew.Netter, Frank H. (Eds.) (2009) Netters internal medicine /Philadelphia : Saunders/Elsevier Kaushansky, K., & Williams, W. J. (2010).Williams hematology. New York: McGraw-Hill Medical. Zipes DP et al: ACC/AHA/ESC 2006 Guidelines for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Circulation 114:e385 Appendix Mediastinum Afib and AV blocks Read More