Dr Gawad Physiology Course Online Exam - CVS – Course Lecture 4 – Cop & Cardiac Reserve

The cardiac index is a measure that takes into account the body surface area to normalize the cardiac output. It is calculated by dividing the cardiac output by the body surface area. This is important because it allows for a more accurate comparison of cardiac function between individuals of different sizes. The other options, such as body weight, work of the heart, and body height, do not take into account the body surface area and therefore do not accurately reflect the cardiac function.

When the heart rate increases, the cardiac output also increases. This is because the cardiac output is the amount of blood pumped by the heart per minute, and it is determined by the heart rate and stroke volume. When the heart rate increases, the heart pumps more blood in a given amount of time, thus increasing the cardiac output.

The cardiac output is the total volume of blood pumped by the heart per minute, while the heart rate is the number of times the heart beats per minute. Dividing the cardiac output by the heart rate gives us the stroke volume, which is the volume of blood pumped by the heart with each beat. Therefore, the correct answer is stroke volume.

During deep inspiration, the COP (chest wall compliance) usually increases in volume. This is because during deep inspiration, the diaphragm and intercostal muscles contract, causing the chest cavity to expand. As a result, the lungs are able to expand more and fill with more air, leading to an increase in volume.

Increased end-diastolic volume does not decrease cardiac output. End-diastolic volume refers to the amount of blood in the ventricles at the end of diastole, before contraction. An increase in end-diastolic volume actually leads to an increase in stroke volume and cardiac output, as it allows for more blood to be ejected with each contraction. In contrast, increased vagal activity, beta-adrenergic receptor blockers, and standing up from the recumbent position all decrease cardiac output by reducing heart rate or contractility.

Skeletal muscle contraction plays a crucial role in counteracting the effects of gravity on venous return. When muscles contract, they squeeze the veins, helping to push the blood back towards the heart against the force of gravity. This contraction increases the pressure within the veins, aiding in the return of blood to the heart. The pressure gradient, arteriolar vasodilation, and increased heart and respiratory rates also contribute to venous return, but skeletal muscle contraction is the primary mechanism for counteracting the effects of gravity.

The cardiac output refers to the volume of blood pumped by the heart in one minute. It is determined by multiplying the stroke volume (the volume of blood pumped by the ventricle in one beat) by the heart rate (the number of beats per minute). In a normal heart, the cardiac output matches the venous return, which is the volume of blood returning to the heart from the veins. This is because the heart pumps out the same amount of blood that is being returned to it, ensuring a balance in the circulatory system.