Question

1) Cardiac output increases during exercise due to an increase in both heart rate and stroke volume. Which of the following contribute to this increase in stroke volume? (Select all that apply).

a) Constriction of veins by the sympathetic nervous system

b) The increase in heart rate directly increases filling time

c) Increased stretching of the cardiac myocytes due to increased EDV

d) Increased sympathetic stimulation of the ventricles

e) Withdrawn (decreased) parasympathetic stimulation of the ventricles

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2) Which parameter is primarily responsible for the differences in MAP observed between dynamic and static exercise?

Answer 1

1. Stroke volume is the blood that is ejected from each ventricle.This happens due to the contraction of muscles in heart compressing the ventricles.This is calculated by the diffrence between the end diastolic volume and end systolic volume.End diastolic volume is volume of blood prior to contraction of muscles in heart and end systolic volume is volume of blood remaining in ventricle after the ejection of blood due to contraction.Increase in End diastolic volume increases stoke volume.During exercise,there is an increase in the rate of blood returning to the heart. When heart rate increases, less time is spent in diastole and thus less time needed for the ventricles to fill with blood. SV will initially remain high. As heart rate continues to increase, SV gradually decreases due to decreased filling time.During exercise increase in stretching of Myocyte increases the length of sarcomere , which increases force to enable heart to eject the additional venous return, thus increasing stroke volume. increaseSympathetic nerves also innervate the myocardium; increases in sympathetic activity increase myocardial contractility and, therefore, increase stroke volume.Also sympathetic stimulation of the ventricles increases myocardial contractility and, therefore, increase stroke volume.So options b,c and d are correct.

2)Static exercises are exercises involves no movements of joints.For example a squat position,push up position.This improves strength.Dynamic exercise are exercises that invoves slow movements to keep joints and muscles moving.Eg:step ups,push ups.During static exercise the mean arterial pressure increases due to an increase in heart rate and so cardiac output with no significant change in stroke volume. During dynamic exercises cardiac output increase is more than resistance decrease, that in turn increases mean arterial pressure slightly. The increase in mean arterial pressure would be much greater if resistance did not decrease.So the parameter for diffrence in MAP observed between dynamic and static exercise is cardiac output.