Abstract
Heart disease ranks first in the ranking of the world’s causes of death. Our heart every second affects the quality of our health life. If people do not meet heart disease in adulthood, the heart muscle is weakened in old age. In this regard, it is important to understand how the heart behaves under certain loads and in shock situations. Disorders in the work of the heart can radically change the human way of life, make it dependent on medical stupefaction or drugs. A detailed study in this area will warn about the possible consequences of overload, stress and other negative (oxidative stress), also will show positive factors (moderate physical activity). In addition, it describes how an imbalance of vitamins and hormones can affect heart function and what dangerous diseases this can lead to. This work talks in detail about the work of the heart with examples of oxidative processes, acute exercise and exercise training.
Introduction
Our heart is in constant motion and in constant performance. It is always working hard to give our bodies the oxygen it needs to perform all our normal duties and all those duties that require extra energy. In response to our Sympathetic Nervous System, our heart knows exactly when to speed up and when to slow down. In its optimal state there is no need to worry about how it’s working or whether or not it is going to perform when needed. However, during different states of exertion or stress and with high levels of those stressful occurrences, it can cause the heart to give out or go into heart failure. These states of exertion or stress can be caused from chemical or physical reactions. Throughout life we are exposed to types of situations that have different causes and effects on the heart. How our body responds to these situations depends a lot on how we have conditioned our heart. The proper and constant exercise on the heart prepares it for whatever life will bring us. Everyone understands that the heart is a muscle and like all muscles when conditioned can work far and above optimal levels. Having a heart that is prepared can lead us into a better and healthier life. The following paragraphs explain different situations which can put the heart under stress and in a state of exertion. They also explain how the heart handles those types of situations and how we can better our lifestyle in order to make the heart more efficient. Let’s take a look, in detail, at how Oxidative Stress, Acute Exercise, and Exercise Training affect the heart.
Oxidative Stress
There is a constant battle within the body to maintain balance between oxidants and antioxidants. An excess production of Reactive Oxygen Species, which are highly reactive chemicals formed from oxygen, relative to the levels of antioxidants is known as Oxidative Stress. Oxidative Stress happens to represent the most common toxicity in the body. There are many different pathways that can affect oxidative stress from the broadest such as a physical pathway to the microscopic chemical pathway. The damage that takes place ranges from direct damage to your DNA, protein, and lipids which in turn implicates in cardiovascular and pulmonary diseases, diabetes, neurodegenerative diseases, and even some cancers (1). Regardless of the pathway, oxidative stress can lead to stress of all tissues and cells, including cardiac tissue. Oxidative Stress in the heart occurs in the myocardium which directly affects cardiac function and more specifically creates left ventricular dysfunction. Left Ventricular Dysfunction is an early stage of heart failure that occurs when the ventricle cannot pump enough blood. The myocardium is the middle layer of the heart wall, the thickest of all layers, and comprises all the muscle within the heart, becoming weak and stressed when in dysfunction. Once a person is in oxidative stress the body’s response is to produce reactive oxygen species (ROS) in order to counteract the stress and lead the body to a balance of oxidants and antioxidants. ROS maintains the oxidative balance. Low levels of ROS can have a protective role in improving the antioxidative capacity. However, high levels of ROS can result in negative effects. Once the ROS has been activated it directly affects the myocardial calcium handling. The high levels of ROS cause a remodeling of the cardiac function. one chemical change within the heart includes calcium. Calcium plays an important role in the firing off of cardiac cells within the electrocardiogram. If the firing off of these cells is interrupted or disturbed, cardiac arrhythmia can occur thus contributing to hypertrophic effects of the myocardium. Cardiac arrhythmia is the out of sync or lack of rhythm within the cardiac cycle or the electrical activity of the heart. Hypertrophy of the heart is the thickening of the cardiac wall compromising the cardiac function, which is what will occur if the heart is overworked. Hypertrophy, untreated, will eventually lead to heart failure. With this occurring alongside the Sympathetic Nervous System and the increase in preload and afterload, which affect cardiac performance, will in turn further deposit extra oxidative stress on the heart. All of these in combination with each other create multiple negative effects of the heart to include arrhythmia, hypertrophy, and ultimately heart failure. Heart failure is the gradual decrease in heart function to the point where the heart functions at the bare minimum supplying the body extremely low levels of oxygen and creating extreme fatigue on the heart and on the body. If an individual does have heart failure, engaging in regular physical exercise can help. Regular physical exercise has been shown to promote adaptations to ROS that are beneficial to people with heart failure (9). Heart failure can also lead to fluid retention which will result in peripheral edema or the swelling of the legs. This will increase total peripheral resistance. Chronic heart failure results in low ejection fractions in patients. Ejection Fraction is the percentage of blood that was ejected from the left ventricle in one cardiac cycle. A normal ejection fraction is 55-80%. Anything lower than 55% can be classified as heat failure. With Oxidative Stress continuing on within the patient the ejection fraction can eventually decrease to as low as 30% resulting in the need for intervention consisting of medications or even internal defibrillators. Not only does oxidative stress specifically affect cardiac tissue it also affects endothelial tissue and all vasculature. The effect on endothelial tissue will eventually cause atherosclerosis and an increase in total peripheral resistance causing hypertension. When in a hypertensive condition, there is nitric oxide impairment that is attributed to high oxidative stress in the vascular endothelium. This causes reduced vasorelaxation and elevation in blood pressure (5). Exercise improves cardiorespiratory capacity, which in turn, improves endothelial function (9). Even though all these reactions occur, the body still constantly fights to be in balance with oxidants and antioxidants. One simple way we can help the body is to start an easy aerobic exercise program. One study suggests that participation in a 12 month aerobic exercise program improves oxidative stress levels, compared to a stretching program, due to the adaptations of the antioxidant defense system in older women. More specifically, it improved their F2-isoprostane levels, which are a general marker of oxidative stress. The F2-isoprostane decreased among women in the exercise group and increased among the control group (1). This maintains a steady balance of oxidants and antioxidants without overpowering other systems. The F2-isoprostane decreased among women in the exercise group and increased among the control group. F2-isoprostane is a general marker of oxidative stress. This is just another reason to add an exercise program into your daily routine. Oxidative stress even takes a toll on head and neck cancer patients. Chemotherapy can cause dysfunction of the left ventricle and systemic oxidative stress is a side effect of chemotherapy. Constant evaluation of the cardiac function needs to be done with chemotherapy in order to make sure that the chemo is not decreasing cardiac function. With elevated oxidative stress being a promoter for increasing inflammation, this can be extremely harmful for the patients. It can be reduced with exercise though. As shown in this study, the systemic oxidative stress was mitigated when these patients were placed on an exercise program consisting of 8 weeks of moderate intensity aerobic and resistance training 3 days a week with their maximum heart rate ranging between 60 to 70%. This oxidative stress reduction can be attributed to the lowering of plasma levels of carbonyl content and 8-OHdg (12). In individuals with type 2 diabetes mellitus, an aerobic exercise program helps with oxidative stress as well. With the production of ROS and lipid peroxidation being increased in this population, it is important to implement and utilize a method to combat this circumstance. In this study, type 2 diabetes mellitus individuals were grouped into three groups: aerobic training combined with the use of a fitness center (group A), aerobic training only (Group B), and controls (group C). Participants in groups A and B were asked to perform aerobic exercise at 50% of VO2 max, 3 times a week for over a 12 month period. It was found to decrease urinary 8-OHdg levels at the 12 month mark in groups A and B, but not in C, and shown to improve glycemic control. Both of these factors have a role in reducing oxidative stress (7). These findings illustrate the importance of a chronic aerobic exercise program in this population to enhance antioxidant defense mechanisms to reduce oxidative stress.
Acute Exercise
The definition of acute is something characterized by a sudden onset of severity. When referring to acute exercise on the heart, this could mean sudden physical stress such as a burst of extreme exercise or sudden emergency action bringing on stress. Regardless of the cause the sympathetic nervous system will react the same. The fight or flight response activates and a multitude of chemical reactions in the body take place. Heart rate increases in order to rapidly supply the body with extra oxygen. Respirations increase for the same reason, to increase oxygen consumption and to expel carbon dioxide as fast as possible. The vascular system will dilate in order to supply a greater amount of oxygenated blood to the body. All of these reactions and many more affect the cardiac function. One example of being impacted with acute exercise is running from a dog, where the dog’s sole purpose is to attack you. All the previous reactions stated above will take place and an extreme rush of adrenaline takes over. Once the dog has caught up with you and you realize that all it wanted was to lick you and be loved, all the physical responses will soon go back to normal. But, what if another situation such as the dog occurs again the following day. Now we have stressed out the heart with acute exercise again. With more of the same occurrences the patient may start to feel shortness of breath that can’t be controlled. They could also be feeling chest pain that was brought on with the amount of anxiety that took place during those incidences. Activating the sympathetic nervous system multiple times begins to take a toll on the patient’s heart health. Let us examine a unique condition dealing with acute emotional stress/exercise on the heart. A patient is rushed into the ER complaining of shortness of breath and chest pain with the pain radiating down his left arm and back. A normal cardiac workup is done along with a trip to the cath lab for an emergency left heart catheterization. During the procedure the physician realizes that the patient has coronary arteries that are only about 25-35% blocked including the Left Anterior Descending coronary artery, which is the primary artery that feeds oxygen to the left ventricle, the main pumping chamber of the heart. Even though the patient’s coronary arteries look well the patient’s heart is showing extreme decrease in function with about a 30% ejection fraction. After speaking to the family of the patient the physician learns that the patient just buried her husband of 50 years yesterday. With that news, the physician came to the diagnosis that the patient has Takotsubo, which is an acute stress-induced cardiomyopathy. Cardiomyopathy is a disease of the heart that attacks the heart wall, specifically the myocardium, which is the middle layer of the heart wall with the most muscle. Generally, patients who have cardiomyopathy also have coronary artery disease (CAD). With CAD, patients have severe blockage in the coronary arteries causing myocardial infarctions (MI), which is a lack of oxygen to the heart muscle. This would then cause damage to the heart muscle leading to depressed heart function and causing some of the heart wall to die and decrease in function. Symptoms include shortness of breath and chest pain, which are the exact same symptoms that Takotsubo portrays. Both diagnoses have the same symptoms and the same results but the root causes are completely different. The patient that was explained earlier suffered from severe acute stress from traumatic emotions brought on by the death of her husband. These symptoms can be the same as the experience of suddenly having to run for your life from a dog on the attack. The female ER patient was suffering from Takotsubo Syndrome, also known as “Broken Heart Syndrome”. It is an emotional induced cardiomyopathy brought on by acute stress in a person’s life. The patient’s emotions were so strong that the stress brought on to the heart caused damage and the heart could no longer work at its full capacity. Treatment also is the same as normal cardiomyopathy with medications such as beta blockers and ACE inhibitors. With this specific disease, most of the abnormalities with the heart wall and function dissipate within a few weeks.
With the two examples given, we can see that the effects on the body, more specifically the heart, are the same. There are ways of training our heart, so to speak, to be ready for such occasions. Even though we would never be emotionally ready for either of the situations, our body can still be conditioned to withstand the negative effects that acute exercise/stress puts on the heart. This conditioning again would be to add an exercise program into your lifestyle. The activity would provide the heart with aerobic conditioning and better prepare the heart for extreme stress, physical or emotional.
Exercise Training
Exercise training has been proven to have remodeling effects on the heart. These remodeling effects occur gradually over time with exercise that allow the heart to be more efficient. The remodeling effects include effects on the cardiac cycle as well as the effects on the cardiac structure and function. The cardiac cycle or the electrical activity of the heart, is our heart rhythm. Our cardiac cycle increases or decreases based on the need of oxygen to the body. Normal resting heart rate ranges between 60-80 beats per minute. This gives the body enough oxygen to do normal everyday functions. During exercise the body needs more oxygen than normal so in order to supply the body with more oxygen the heart would need to increase its heart rate. This would increase the heart rate to over 80 bpm. For a person who is just starting an exercise program, their heart rate would increase to more than 140 bpm in order to maintain enough oxygen for the exercise they are doing. Once this person becomes acclimated to exercise and is no longer new to that lifestyle their heart rate will come down. This not only includes their exercise heart rate but their resting heart rate as well. The athletes resting heart rate will fall below 60 bpm putting the athlete into sinus bradycardia. Exercise training that is consistent and steady changes the composition of the body. The body no longer needs as much oxygen for daily tasks or exercise training as it did prior to having an exercise program or the beginning of the exercise program. Chronic endurance exercise training creates left ventricular adaptations. These adaptations include Left Ventricular modifications of cardiac muscle. The left ventricle dimensions will increase in size to include wall thickness and volume. The need for less oxygen after prolonged exercise training is the enhancement of the cardio-respiratory capacity.
Exercise mode, intensity, prescription, volume, type, frequency and duration all play an important role in the health of individuals with cardiovascular risk factors. Engaging in regular physical activity and exercise programs reduce the risk of developing a cardiovascular disease. It also reduces the severity of the disease in individuals who have already acquired one. For example, glycemic control and lipid profiles can be improved with the correct exercise program. Glycemic control is improved when conducting a combination of an aerobic and resistance exercise program. Lipid profiles, such as improvements in triglycerides and HDL cholesterol, are improved by moderate intense aerobic exercise. Regular exercise also improves the anti-inflammatory response and displays antithrombotic effects (11). In general, exercise should be performed at a minimum of 30 minutes a day for most, if not all, days of the week at a moderate intensity. When comparing resistance trained individuals, those who trained intensively for 4 days out of the week for a year, and endurance trained individuals, those who train intensively 5 days out of the week for a year, to untrained men, those individuals that are trained show lower cardiovascular stress and lower heart rate when put under psychosocial stress. The lowest heart rate occurred in the endurance trained men, followed by the resistance trained men, and lastly the untrained men. The stress included public speaking and mental arithmetic tasks. This shows that when performing endurance and resistance exercise over a long period of time, it can increase cardiac performance and reduce cardiovascular reactivity to acute stress (4).
Regular physical exercise can also help individuals with pulmonary arterial hypertension. Pulmonary arterial hypertension causes vasoconstriction and progressive remodeling of the pulmonary arterial wall. This can then lead to increased pulmonary vascular resistance and right heart failure. Most of these patients will have a continuous shortness of breath and an increase in right side heart pressure. Also, these patients have a heart rate that is higher and their heart rate variability is lower, which can cause a higher possibility of arrhythmias. A 16 week endurance and resistance training program consisting of children and adolescents with pulmonary arterial hypertension was conducted. This program consisted of exercising 2 days a week for 20 to 25 minutes a day while achieving between 50 to 69% maximum heart rate. Duration increased as the participants became accustomed to the regime, but it did not exceed 80 minutes a week. This program was shown to lower heart rate and improve heart rate variability, especially during intense training (8).
Routine aerobic exercise also has benefits in postmenopausal hypertensive women. Hypertension in postmenopausal women has its risk factors such as dyslipidemia, oxidative stress, endothelial dysfunction, and cardiac remodeling. All these factors can be improved with aerobic exercise. When engaging in an 8 week aerobic fitness program, systolic blood pressure, diastolic blood pressure, heart rate, nitric oxide levels, and baroreflex sensitivity all showed greater improvement in postmeopasual hypertensive women compared to a resistance program. Although most benefits and improvements come from an aerobic program alone, when combining a resistance and aerobic program, it shows reduced arterial stiffness (5).
Test Questions
- 1. What is the name of the cardiomyopathy also known as “ Broken Heart Syndrome”?
- Takotsubo Syndrome.
- 2. What is the most common toxicity in the body?
- Oxidative Stress.
Conclusion
Chemical processes in the body, such as oxidative stress, can harm the functioning of the heart. Oxidative stress leads to heart failure, affects cardiac tissue and the entire vascular network, and causes atherosclerosis by affecting endothelial tissue. Acute exercise instantly overloads the heart and causes an abrupt array of chemical reactions. In life, they are usually associated with fear, anxiety, and severe stress. They cause an extreme adrenaline rush, and the person becomes short of breath. The multiple activations of the sympathetic nervous system begin to take their toll on the patient’s health. Takotsubo syndrome, emotional cardiomyopathy caused by life stress, can occur. It is necessary to resort to moderate and combined physical activity for heart training, ready for various pressures. They will reduce shortness of breath, lower cholesterol levels, increase physical endurance, reduce the risk of cardiovascular disease, and reduce the severity of acquired diseases.
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