China
Africa
Explore chapters and articles related to this topic
Physical work and the Physiological consequences for the aging worker
Published in Jan Snel, Roel Cremer, H. C. G. Kemper, E. Zeef, M. J. Schabracq, P. T. Kempe, Work and Aging: A European Perspective, 2020
Data from cross-sectional studies suggest a decline in adulthood in ṾO2 max at a rate of 0.40-0.45 ml/kg min. per year in males and 0.30 ml/kg min. per year in females. The rate of loss tends to be larger in sedentary compared with active individuals. This age-related decline in ṾO2 max is inevitable and appears to be caused by the decline in maximal cardiac output. The maximal cardiac output, which is the product of two components, stroke volume and heart rate, declines by about 30 per cent between ages 30 and 70. The reduced maximal heart rate is a consistent finding, and is ascribed to decreased end-organ sensitivity to catecholamines. To offset the decline in maximal heart rate, maximal stroke volume may increase. As for the maximal arterio-venous oxygen difference, a decline in the elderly is found, but not always: a decline in muscle mass and a lower capillary/fibre ratio would contribute to lower a — vO2 differences, but a reduced cardiac output to a greater a — vO2 difference. Pulmonary function does not appear to limit ṾO2 max as in young adults, although in elderly people this function may be less efficient, while ventilating during strenuous exercise.
Chapter 19 Blood Flow Measurement
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
What are typical values for some blood flow measurements? Cardiac output is typically about 61 min-1 which corresponds to a stroke volume (the volume expelled by the left ventricle on cardiac systole) of 100 ml if the heart rate is 60 beats per minute. This 100 ml is distributed throughout the body with about 20 ml going to the kidneys, 17 ml to the muscles and 12 ml to the brain. If we know the sizes and numbers of the blood vessels then we can calculate the blood velocities. This is relatively easy for the main arteries, because there are only a few of them, and we conclude that the peak velocities might be of the order of 1 m s-1. As the blood vessels branch and get smaller the average velocities fall and in the capillary beds the red blood cells (erythrocytes) move through in single file and very slowly. In the major veins the velocities involved are a few centimetres per second.
C
Published in Splinter Robert, Illustrated Encyclopedia of Applied and Engineering Physics, 2017
[biomedical, fluid dynamics] Blood flow principle recognized by Adolf Eugen Fick (1829–1901) as the total volume ejected by the contracting heart per minute of time, expressed in liters per minute. The cardiac output (CO) is thus a function of both the volume of the ventricles and the heart rate (HR): heart rate multiplied by stroke volume (SV): CO = HR × SV. The heart ejects a volume of blood based on the muscular function of the cardiac muscle as well as the fluid dynamic constraints resulting from the vascular resistance and compliance in the whole body circulation. The circulation system comprises the aorta on the left ventricular side and the pulmonary artery on the right ventricular side, branching out into a web of arteries, arterioles, and capillaries, flowing under a combination of venules and veins, leading back to the left and right atrium by means of the pulmonary veins from the lungs (carrying oxygen-rich blood) and the hollow vein (superior vena cava), carrying oxygen-depleted blood, respectively. During exercise the cardiac output can increase by more than fivefold, depending on the training and general health of the individual.
Construction of lumped-parameter cardiovascular models using the CellML language
Published in Journal of Medical Engineering & Technology, 2018
Yubing Shi, Patricia Lawford, D. Rodney Hose
The CellML models described above are executed in the OpenCell software environment. For each of the cardiovascular system models illustrated in Figure 1, the main model file is opened in the OpenCell, and the OpenCell solver is invoked for calculation. The results can be plotted directly using the graph windows in the OpenCell programme. Figure 4 shows a snapshot of the computer screen for the OpenCell calculation of cardiovascular dynamics in a typical healthy human subject using the model presented in Figure 1(d). To facilitate further analysis, results of the calculation are exported in the standard CSV format for processing with other data plotting programmes like MS Excel, as shown in Figure 5. Consistent with the published cardiovascular changes in the textbooks such as in [18], the simulated left ventricular pressure varies from 0 to 120 mmHg, and the arterial pressure stays in the range of 80–120 mmHg. Aortic and mitral flows show an average flow-rate of about 5 L/min and peaks of about 1000 mL/s (60 L/min) and 800 mL/s (48 L/min). The left ventricular volume changes between 55 mL to 130 mL, producing a stroke volume of 75 mL. The results also agree with that presented in the original base model [5], in terms of both the shape and the range of the pressure, flow-rate and volume curves.
Low- to moderate-intensity blood flow restricted walking is not an acute equivalent for unrestricted jogging in young active adults
Published in European Journal of Sport Science, 2023
Thomas P. Walden, Olivier Girard, Brendan R. Scott, Andrew M. Jonson, Jeremiah J. Peiffer
A main effect of both exercise intensity and BFR was observed for LCWi (both p < 0.01) and cardiac output (both p < 0.01). During BFR sessions LCWi (+23.8%; p < 0.01, dz = 0.34) and cardiac output (+19.8%; p < 0.01, dz = 0.34) were higher compared with unrestricted sessions. Furthermore, LWCi (+27.8%; p < 0.01, dz = 0.44) and cardiac output (+36.5%; p < 0.01, dz = 0.44) were higher during moderate-intensity compared with low-intensity. Only a main effect of exercise intensity was observed for stroke volume (p < 0.01) with higher values recorded during moderate-intensity compared with low-intensity (+9.6%; p < 0.01, dz = 0.24) sessions.
Relationship between heat loss indexes and physiological indicators of turnout-related heat strain in mild and hot environments
Published in International Journal of Occupational Safety and Ergonomics, 2023
Huipu Gao, A. Shawn Deaton, Roger Barker, Xiaomeng Fang, Kyle Watson
Figures 8a–10a show the predicted effects that study turnout systems have on cardiac output in different environmental conditions. The cardiac output prediction was provided by our manikin physiological model. The cardiac output was predicted according to metabolic rate, skin temperature, hypothalamus temperature, vasodilatation, vasoconstriction, etc. More details can be found in Fiala et al. [18,19]. Cardiac output is the product of heart rate and stroke volume. Stroke volume can increase in heat stressful conditions; increased heart rate is the primary driving force behind increased cardiac output [20]. An increase in cardiac output is a physiological response to human heat stress [21].