Running head: CASE STUDY 1
Case Study Question 2: Aerobic Capacity
Kanani Jackson
Liberty University
EXSC 510 Advanced Exercise Physiology
Dr. Kilian
CASE STUDY 2
Case Study Question 2: Aerobic Capacity
Autoregulation refers to the intrinsic ability of an organ to maintain blood flow at a nearly
constant rate despite changes in arterial perfusion pressure. It is the intrinsic capacity of
resistance vessels in end organs, such as the heart, kidney, and brain, to dilate and constrict in
response to dynamic perfusion pressure changes, maintaining blood flow relatively constant
renal blood flow (RBF) (Powers et al., 2021). Autoregulation is a vital homeostatic mechanism
that protects the kidney from elevations in arterial pressure that would be transmitted to the
glomerular capillaries and cause possible injury. In addition to that, it can refer to the ability of a
tissue to automatically adjust blood flow to match its metabolic demands. Meaning walls of
blood vessels in the systemic circulation can dilate in response to low oxygen (Powers et al.,
2021). In pulmonary circulation, the blood vessels constrict in response to the low oxygen levels.
These resistance vessels dilate in response to reduced pressure and blood flow. This
autoregulation in particular is very important in organs such as the brain and heart. These partial
occlusions of large arteries can lead to significant reductions in oxygen delivery, resulting in
leading to tissue hypoxia and organ dysfunction.
The three aspects of autoregulation are myogenic, shear-dependent, and metabolic
responses. The myogenic response is the contraction of a blood vessel that occurs when
intravascular pressure is elevated and, conversely, the vasodilation that follows a reduction in
pressure (Powers et al., 2021). Continuing, the myogenic mechanism appears to play a role in
basal vascular tone and the regulation of transmural pressure in resistance vessels. On the other
hand, the metabolic mechanism serves to maintain tissue oxygenation by regulating oxygen
delivery to meet changes in oxygen demand. The metabolic mechanism chiefly contributes to
autoregulation in the microvasculature, where changes in the microenvironment such as PC02
CASE STUDY 3
and H+ will lead to vasodilation (Powers et al., 2021). Additionally, endothelial factors, such as
nitric oxide, may also contribute to autoregulation. Autoregulation only works within certain
limits of pressure. The points at which blood vessels dilate or constrict to their maximum
capacity. Various mechanisms contribute to changes in vascular tone, including responses to
intraluminal pressure (myogenic response), shear stress on the endothelial lining of vessels
(shear-dependent response), metabolite concentrations in vessels and/or tissue (metabolic
response), and neural stimuli (Powers et al., 2021). To top it off the cerebral and renal
vasculature show the most stable flow over a wide range of arterial pressures whereas, in other
beds, such as those in the mesentery, autoregulation is less effective.
Finally, a person will physiologically improve their aerobic capacity after several months
of cardiovascular training in many ways, one of the main ways being an adaptation. The
functionally most important adaptation is the improvement in maximal cardiac output which is
the result of an enlargement in cardiac dimension, improved contractility, and an increase in
blood volume. This allows for greater filling of the ventricles and a consequent larger stroke
volume. Speaking of stroke volume and cardiac output, stroke volume increases due to a stronger
heart which can pump more blood with each beat (Powers et al., 2021). Whereas the cardiac
output increases during exercise as the heart can pump more blood each beat and can therefore
deliver more blood if required. The cardiovascular adaptations supporting this include an
increase in total body water, plasma volume expansion, better sustainment and/or elevation of
stroke volume, reduction in heart rate, improvement in ventricular filling and myocardial
efficiency enhanced skin blood flow, and sweating responses (Powers et al., 2021). After long-
term aerobic training, the body adapts to become more efficient at meeting metabolic demands.
The changes to the cardiovascular system include increased maximal cardiac output (Qmax),
CASE STUDY 4
increased stroke volume (SV), and reduced heart rate (HR) at rest and during sub-maximal
exercise.
Overall, the autoregulation of blood flow, the maintenance of almost constant blood flow
in the face of variations in arterial pressure, is characteristic of many tissue types. Here,
contributions to the autoregulation of pressure-dependent, shear stress-dependent, and metabolic
vasoactive responses are analyzed using a theoretical model. Seven segments, connected in
series, represent classes of vessels: arteries, large arterioles, small arterioles, capillaries, small
venules, large venules, and veins. The large and small arterioles respond actively to local
changes in pressure and wall shear stress and the downstream metabolic state is communicated
via conducted responses (Powers et al., 2021). All other segments are considered fixed
resistances. The myogenic, shear-dependent, and metabolic responses of the arteriolar segments
are represented by a theoretical model based on experimental data from isolated vessels. To
assess autoregulation, the predicted flow at an arterial pressure of 130 mmHg is compared with
that at 80 mmHg (Powers et al., 2021). If the degree of vascular smooth muscle activation is held
constant at 0.5, there is a fivefold increase in blood flow. When myogenic variation of tone is
included, flow increases by a factor of 1.66 over the same pressure range, indicating weak
autoregulation. The inclusion of both myogenic and shear-dependent responses results in an
increase in flow by a factor of 2.43. Further addition of the metabolic response produces strong
autoregulation with flow increasing by a factor of 1.18 and gives results consistent with
experimental observation (Powers et al., 2021). The model results indicate that the combined
effects of myogenic and metabolic regulation overcome the vasodilatory effect of the shear
response and lead to the autoregulation of blood flow.
Kanani Jackson
