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Bioenergetics
Published in Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan, Strength and Conditioning in Sports, 2023
Michael H. Stone, Timothy J. Suchomel, W. Guy Hornsby, John P. Wagle, Aaron J. Cunanan
How energy systems are used in a practical setting is quite important for sport scientists, coaches, and athletes. Bioenergetic systems supply energy at different rates for various intensities and durations of exercise (Table 2.4). Conley et al. (57) using cycle ergometry, and Harman (personal communication) using a treadmill, have shown that power (intensity) at VO2max is approximately 25% to 35% of peak power capabilities. Therefore, aerobic exercise even at 100% of VO2max should not be classified as high-intensity exercise. It should be noted that a maximum-intensity of exercise requires a maximum rate of energy production in order to reach and sustain the intensity. High-intensity exercise can be supported by fast (anaerobic) glycolysis; however, long-term aerobic exercise must be supported by the oxidative system because of its high capacity for ATP production. Because of the time required to fully activate other energy systems, the ATP-PCr system is also used to a small extent at the initiation of most exercises (35).
Integrated Cardiovascular Responses
Published in Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal, Principles of Physiology for the Anaesthetist, 2020
Peter Kam, Ian Power, Michael J. Cousins, Philip J. Siddal
When the blood loss is greater than 20%, both arterial blood pressure and cardiac output decrease rapidly, because the compensatory mechanisms become inadequate. Various mechanisms that are important for returning the blood pressure to normal may be activated. When the arterial blood pressure falls below 50 mmHg, a central nervous system ischaemic response is elicited, causing a powerful sympathetic stimulation throughout the body (Figure 32.2). Sympathetic stimulation is maximal within 30 s after a haemorrhage. Irreversible hypotension can occur with a blood loss greater than 30% of the blood volume. Inadequate tissue perfusion leads to increased anaerobic glycolysis, with the production of large amounts of lactic acid. The resulting lactic acidosis depresses the myocardium and reduces the peripheral vascular responses to catecholamines.
Major obstetric haemorrhage
Published in Jennifer Duguid, Lawrence Tim Goodnough, Michael J. Desmond, Transfusion Medicine in Practice, 2020
Shock is a potent stimulus to respiration, and so respiratory rate and minute ventilation increase, mediated partly by metabolic changes as carotid chemoreceptors respond to alterations in arterial partial pressures of oxygen and carbon dioxide (PaO2 and PaCO2) and hydrogen ion. Haemorrhage may cause substantial metabolic derangements: with decreased tissue perfusion, there is a progressive decline in aerobic metabolism, which is accompanied by a compensatory increase in anaerobic metabolism as tissue ischaemia progresses. The shift to anaerobic metabolism results in a decrease in energy production and the development of a metabolic acidosis. In the aerobic (tricarboxylic acid, TCA) cycle, the hydrogen ions produced are carried by NADH and NADH2 to the electron transport chain, in which the final acceptor is molecular oxygen, which is then converted to water. In the absence of molecular oxygen, the final acceptor (oxygen) is lacking, and so NADH accumulates. The lack of NAD+ effectively blocks the TCA cycle, and so pyruvate accumulates (at the ‘entrance’ to the cycle). NADH and pyruvate react to form lactate and NAD+. The lactate then diffuses out of the cell and accumulates as lactic acid; NAD+ meanwhile allows anaerobic glycolysis to proceed. This process is important because severe metabolic acidosis is deleterious to tissue and organ function, particularly that of the myocardium.
St. Thomas and del Nido cardioplegia are superior to Custodiol cardioplegia in a rat model of donor heart
Published in Scandinavian Cardiovascular Journal, 2021
Gulsum Karduz, Muhittin Onur Yaman, Mehmet Altan, Gulderen Sahin, Fevzi Toraman, Ugur Aksu
In our study, low contractile strength also followed low ATP levels in Custodiol cardioplegia. Accordingly, glycolysis and ATP production are suppressed by both weak aerobic metabolism and the accumulation of hydrogen ions in the cell. Therefore, to maintain intracellular and extracellular ion balance and continue energy production, anaerobic glycolysis should be supported. St. Thomas and del Nido cardioplegia solutions contain sodium bicarbonate as a buffer solution to maintain intracellular pH and ion balance [23]. The reason for the poor protective effect of Custodiol cardioplegia solution may be due to the lack of bicarbonate ion in it. Therefore, our findings suggest that Custodiol cardioplegia solution may have caused mitochondrial damage in the tissue. As a limitation, mitochondrial enzyme systems should be evaluated to support this result.
Physiological factors which influence the performance potential of athletes: analysis of sports medicine performance testing in Nordic combined
Published in The Physician and Sportsmedicine, 2021
Rupert Schupfner, Stefan Pecher, Eva Pfeifer, Christian Stumpf
Energy production within the cell is achieved on the one hand by anaerobic glycolysis (breaking down carbohydrates to produce lactic acid) and on the other by the citric acid cycle, the oxidation of triglycerides, proteins and lactate and/or pyruvate to acetyl-CoA or adenosine triphosphate. The metabolization of triglycerides and glycogen at rest forms the physiological basis for part of the performance diagnostics. When intensity increases, the metabolization of glycogen increases. Lactate and pyruvate are produced as by-products of this anaerobic glycolysis. Lactate production is countered by lactate elimination via oxidation and gluconeogenesis, thus establishing a steady state under physical stress. When maximum endurance capacity is reached, this steady state becomes turbulent, meaning that there is a sudden accumulation of lactate in the blood [2,3].
Etiology of posterior subcapsular cataracts based on a review of risk factors including aging, diabetes, and ionizing radiation
Published in International Journal of Radiation Biology, 2020
Richard B. Richardson, Elizabeth A. Ainsbury, Christina R. Prescott, Frank J. Lovicu
An in-vitro study of whole clear lenses from albino rabbits in 53 mmHg or 7% oxygen, which measured the anaerobic-to-aerobic glycolytic rate of lactate production, found half of LEC ATP was of anaerobic origin, compared with ∼70% in lenses composed of lens fibers with fewer mitochondria than found in LECs (Winkler and Riley 1991). Nevertheless, most of the lenticular ATP was produced in lens fiber cells (∼99%), with no transfer of ATP to the LECs (these LECs have a small mass <1% of the lens). Anaerobic glycolysis provides energy at low nutrient efficiency (2 moles of ATP per mole of glucose), transforming glucose to lactate when oxygen is in short supply. If the ocular oxygen concentration is elevated by cataractogenic risk factors (see section 3), this presents a potential advantage by promoting more aerobic respiration in mitochondria, since aerobic respiration produces up to 15-fold greater ATP production than by anaerobic metabolism. However, this additional deployment of aerobic metabolism has the considerable disadvantage of increasing mitochondrial ROS generated by electron leak from the respiratory chain, hence elevating the risk of cataractogenesis (Richardson and Harper 2016).