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Factors Effecting Cardiac Output

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The Factors that effect cardiac output The Cardiovascular system is responsible for the transport of blood, oxygen and nutrients, to the tissues in the body. There are two components that are important to the system the heart, which pumps the blood, and arteries and veins that transport the blood to and from the tissues. The function of the system is crucial during exercise. Studies involving cardiovascular system focuses on the responses and adaptions of the cardiovascular system to exercise, such as the effects of the structure and function of the blood vessels and the relationship between exercise and neurological control of the heart i.e. cardiac output. Cardiac output is the amount of blood pumped out of the heart in a minute. Cardiac output is determined by the equation Q = HR x SV, the amount of blood expelled with each beat (stroke volume) in combination with the number of beats per minute (heart rate), the amount of blood return, and the resistance to blood flow through vessels. During exercise the heart rate usually increases causing an increase of cardiac output and bringing more blood to the muscles. However, heart rate alone doesn’t improve cardiac output, but along with muscle demand of oxygen. The demand for more oxygen causes vasodilation, allowing an increase in blood flow and the return of blood back to the heart. Some factors that facilitate improvement in cardiac output for performance are intensity, duration, and aerobic/anaerobic exercises. Different levels of exercise intensity require specific needs from the body. For example, the physical activity of taking a brisk walk through a park requires less expenditure and overall cardiac output compared to activities like hill sprinting or soccer. Sprinters and soccer players are trained athletes that can demonstrate and maintain higher levels of cardiac output. When an individual participates in high intensity activities regularly, the heart becomes stronger and adapts to more strenuous circumstances. Cardiac output is directly related to heart rate and stroke volume. Under more intense circumstances, heart rate and the amount of needed oxygen for aerobic respiration increases. As a result, blood pressure also increases in order to transport hormones and glucose to fuel the body’s metabolic processes. With repeated practice, the cardiovascular system learns to meet the bodies’ demands more efficiently and becomes acclimated to higher intensities. Stroke volume will also improve in order to pump more blood to various areas of the body when performing at more intense levels. The muscles of the body are contracting at higher rates and need sustained sources of energy to do so. Stroke volume allots for the increased demands by pumping a higher volume of blood faster due to increased heart rate. Cardiac output will improve when the heart and circulatory system adapt to these heavier loads of performance. Exercise duration plays a significant role in cardiac output. The duration of exercise along with the intensity of exercise are a perfect formula for increasing cardiac output. Some feel that the longer you exercise the more you will benefit from it however, that is not always true. In a single exercise session, exercise duration does not have to be long. If the intensity of the exercise session is moderate to high intensity, the exercise duration can be low. Exercising for a long period at low intensity will not increase stroke volume or heart rate significantly enough to train the heart muscles to adapt to such stress. On the other hand exercising at high intensities for very long durations can also be detrimental to the cardiovascular system. In order to maintain a comfortable homeostasis for the heart during cardiac output there must be a happy medium of intensity and duration during exercise. In a study done to investigate the effects of intensity and duration on cardiac biomarkers, the results explained this theory. The study examined 21 trained marathon runners as subjects over a 6-day period. The subjects were tested for increase or decrease in cardiac troponin (cTnI) and N-terminal pro-branin natiuretic peptide (NT-proBNP) from blood samples taken before, 30 minutes in, and after an exercise session. The authors of this study tested these cardiac biomarkers because the levels of cTnI and NT-proBNP signify that there is too much stress on the heart. These factors show signs of cardiac injury; the heart is working too fast and too hard. The subjects ran for 45, 90, and 180 minutes at randomized times. The study revealed that the post exercise blood samples had higher levels of NT-proBNP that were linked to duration during the exercise session that lasted 180 minutes. cTnI also had high levels which were linked to both duration and intensity during 90 and 180 minute exercise sessions. This data suggest that exercise duration along with intensity will significantly alter cardiac biomarkers, which will affect cardiac output during exercise. Another study compared the heart muscles of long-term marathon runners and health non-marathon runners after a long period. The authors of the study noted results of the marathon runners having fibrosis, cardiac scarring. This is detrimental to the heart in that scarring of the heart muscle can lead to thickening and stiffening of the heart muscles which will further cause contractility to decrease in the heart. Low contractility during any form of exercise can make it hard for the heart to function prosperously. The systems we use during exercise depend on the duration and intensity of the exercise. The anaerobic systems glycolysis and the ATP-CP system produce ATP quickly. The fiber types recruited are type IIa to type IIx. Actives where tremendous amounts of energy are required in short amounts of time, such as shot put and 100 meter sprints. Energy has to be produced in a short amount of time recruiting type II fibers. (Powers 2015) These fiber types fire quickly and produce lots of force, but lactic acid builds up very quickly and is not readily transported away by the blood. Glycogen stores are also used up quickly. Although if trained solely for powerful bursts; overall endurance would decrease. A lack of type I aerobic fibers would make that an athlete a terrible distance runner. On the other hand, they would be very powerful short distance sprinter or long jumper. Aerobic athletes go long and slow and resist fatigue. They aerobically train for longer times like 45 minutes to hours. For example normal everyday activities like running to class, your body would adapt and get more efficient at running. Although the running would get easier you would not necessarily remain dynamically powerful. Cross training these systems would provide the perfect athlete. A powerful light, fast athlete that does not get tired is an example of the ideal elite athlete.
Pushing subjects to work in the higher ranges of their VO2max the cardiac range of 60% or higher have several benefits. Such as increasing time to exhaustion, and prolonging time before hitting the lactate threshold. High intensity training (HIT) has greater overall results in untrained people. (M. Siahkouhian 2012) Most people are born with more of one type of muscle fiber than the other. Excluding the human aspect of motivation stress, and compliance; the body is a machine. In a theoretical sense the more trials you put a person’s body though it has no option but to adapt or fail. Our bodies constantly are in a state of unbalanced equilibrium. The ability for coaches and doctors to measure and test the maximal power output, lactate threshold and VO2 max of an athlete. Help them determine the muscle predisposition, strengths and weakness of said athlete. The athletic review board process protects subjects from the researchers. Not running the subject, like a machine and making the best ethical decisions about subjects’ well being. Not the fastest product possible regardless of the negative results to human test subject. The duration of many studies are not long enough to observe modification happening in subjects. Several studies HIT only last 2 weeks, little to no effect observed on non-active or active subjects. (David 2014) A physiological shift of type IIa fibers to type I fibers receive a larger blood supply and move lactate out of the muscles and send it to the liver for gluconeogenesis to occur returning more glucose to active tissues. Aerobic and anaerobic training are the best factors to improve cardiac output. Cardiac output respond and adapt to intensity, duration, and aerobic/anaerobic exercise due to their interrelated relationship. When exercising at a moderate to high intensity, the duration of the activity is best performed at shorter intervals for optimal results. Where as, aerobic and anaerobic depend upon intensity and duration to facilitate which metabolic response would be best to used to produce ATP quickly. In turn, heart rate and stroke volume increases and cardiac output is improved.

References David Hauton et al. (2014) “Changes to both cardiac metabolism and performance accompanyacute reductions in functional capillary supply” Biophysica Acta (681-690) Djordje G. Jakovljevic, PhD et al. (2010) “Comparison of Cardiac Power Output and ExercisePerformance with Left Ventricular Assist Devices, Explained (recovered) patients, andthose with moderate to severe heart failure” The American Journal of Cardiology(1780-1785) Charles A. Boucher MD (1983) “Exercise Testing in Aortic Regurgitation: Comparison of radionuclide Left ventricular ejection fraction with exercise performance at the anaerobic threshold and peak exercise.” American Journal of Cardiology 52 (801-808) M. Siahkouhian, D. khodadadi, K. Shahmoradi (2012) “Effects of high-intensity training on aerobic an anaerobic indices: Comparison of physically active and inactive men” Science &Sports 28 (119-125) Scott K. Powers, Edward T. Howley (2015) “Theory and application to fitness and performance”Exercise Physiology 9 (26,185-212) Serrano-Ostáriz, E., Terreros-Blanco, J. L., Legaz-Arrese, A., George, K., Shave, R., Bocos-Terraz, P., & Carranza-García, L. E. (2011). The impact of exercise duration and intensity on the release of cardiac biomarkers. M. Wilson, R. O'Hanlon, S. Prasad, A. Deighan, P. MacMillan, D. Oxborough, R. Godfrey, G. Smith, A. Maceira, S. Sharma, K. George, G. Whyte.J Appl Physiology (1985) 2011 June; 110(6): 1622–1626. Published online 2011 February 17. doi: 10.1152/japplphysiol.01280.2010

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