The evaluation of heart functioning and circulation introduces a common topic for analysis. Heart rate and stroke volume are the two measures of cardiac output, which, in its turn, shows the volume of blood “ejected by each ventricle in 1 minute” (Saladin, 2020, p. 714). To change cardiac output, it is important to change heart rate or stroke volume, which are interdependent in opposite directions. It means that the factors that raise the heart rate reduce the stroke volume. The main nervous and chemical factors affecting heart rate and stroke volume and leading to changes in cardiac output are chronotropic and inotropic agents.
Chronotropic agents provoke positive and negative outcomes in the heart. For example, the combination of norepinephrine and epinephrine, known as catecholamines, has a positive effect (Saladin, 2020). Cyclic adenosine monophosphate stimulation also raises the heart rate and cardiac output at the same time. Such steps as parasympathetic vagus nerve stimulation acetylcholine secretion reduce the heart rate (Capilupi, Kerath, & Becker, 2020). A chemical factor like thyroid hormone acceleration makes the heart more sensitive (Saladin, 2020). Glucagon, nicotine, and caffeine are responsible for an increased heartbeat and elevated blood pressure. Beta-blockers and calcium may be used to treat hypertension and manage cardiac outcomes by slowing down the heartbeat.
Inotropic agents, like preload, contractility, and afterload, are related to stroke volume. Preload-related tensions activate muscles and lead to increased venous return and stroke volume, respectively (Berger & Takala, 2018). Contractility is associated with the calcium inotropic effect, increasing contraction strength in the heart (Saladin, 2020). Thus, hypercalcemia positively affects stroke volume and heart rate, meaning the same effect on the cardiac outcome. However, the same hypocalcemia may weaken the heartbeat because the cardiomyocytes lose calcium and damage skeletal muscles (Saladin, 2020). Finally, afterload forces change blood pressure and provoke new cardiac outcomes. Hypertension, as well as hyperkalemia, increases the afterload and reduces stroke volume. All these factors have to be properly recognized and examined to help people contribute to the correct condition of the heart and predict its disorders.
(W/C 340)
Critical Thinking
Understanding nervous and chemical factors in cardiac output is important for me and society for several purposes. First, people need to control their heart rates and predict the progress of severe heart complications. Second, if caffeine and nicotine effects are commonly known, calcium and training outcomes remain poorly investigated. Finally, the heart affects other systems, and its condition has to be constantly monitored and improved.
(W/C 65)
References
Berger, D., & Takala, J. (2018). Determinants of systemic venous return and the impact of positive pressure ventilation. Annals of Translational Medicine, 6(18).
Capilupi, M. J., Kerath, S. M., & Becker, L. B. (2020). Vagus nerve stimulation and the cardiovascular system. Cold Spring Harbor Perspectives in Medicine, 10(2).
Saladin, K. (2020). Anatomy & physiology: The unit of form and function (9th ed.). McGraw Hill Education.