Cardiac Output and Blood Pressure

Second lecture of seven! (Wow, can't believe we did the heart for so long... 0_o)

List the compartments of the cardiovascular system.

Heart, blood vessels, blood. Have I missed anything?

Define Heart Rate, Stroke Volume, Cardiac Output and Venous Return.
Know typical values for Heart Rate, Stroke Volume and Cardiac Output.

• Heart Rate: The number of times the heart pumps every minute. Usually around 70bpm at rest.
• Stroke Volume: The volume of blood pumped per beat. Usually measured in millilitres, and is usually around 70mL.
• Cardiac Output: The amount of blood pumped around the body in one minute. This is equal to the heart rate multiplied by the stroke volume, and is usually around 5L/min.
• Venous Return: This is the same as cardiac output, because you don't want more or less blood coming in as compared to what leaves the heart (or you'd have blood accumulating somewhere). Hence, this is usually around 5L/min as well.

List the variables which alter cardiac output and make calculations from CO = HR x SV.

As I just mentioned, the cardiac output is simply the heart rate multiplied by the stroke volume. Hence, anything that affects the heart rate and stroke volume (stimulation by the autonomic nervous system etc.) will likewise affect cardiac output. Venous return is one way in which cardiac output can be affected, as we shall see...

Explain the interaction among venous return and cardiac output for the left and right heart.
Describe the Frank-Starling law of the heart and sketch the cardiac function curve.

According to the Frank-Starling law of the heart, "within physiological limits the heart pumps out all of the blood that it receives." Hence, the more blood that returns to the blood via the veins, the larger the stroke volume. This is because the extra blood stretches the ventricles, allowing them to generate more force. This is kinda like an elastic band: if you stretch an elastic band a little bit, it won't really snap back. If you stretch an elastic band a lot though, it'll snap back hard.

This relationship can be displayed in the Cardiac Function Curve (which is probably the blandest graph I've ever drawn, and that's saying something):

Define Systolic, Diastolic, Mean and Pulse Pressure for the systemic arterial system.
Know typical values for systemic arterial systolic, diastolic, mean and pulse pressure.
Calculate mean and pulse pressure from systolic and diastolic pressure.

• Systolic Pressure: The highest systemic arterial pressure, attained when the heart contracts. This is usually around 120 mmHg.
• Diastolic Pressure: The lowest systemic arterial pressure, attained when the heart relaxes. This is usually around 80mmHg.
• Mean Pressure: The average pressure across the cardiac cycle. This is usually around 90-95mmHg. This is because the heart spends 2/3 of its time in diastole and only 1/3 of its time in systole, so to measure mean arterial pressure you'll need to take 1/3 of the systolic pressure and 2/3 of the diastolic pressure and add these values together.
• Pulse Pressure: The difference between systolic and diastolic pressures. Usually around 40mmHg.

Describe the systemic and pulmonary circulations and explain the difference between them.

The systemic circulation pumps blood from the left side of the heart to the whole body (except for the lungs). The blood in the systemic circulation is oxygenated when it leaves the heart, and loses oxygen to the tissues as it travels. Blood is deoxygenated by the time it comes back to the heart. This system is relatively high pressure, with a pressure of around 120/80 mmHg, as mentioned earlier.

The pulmonary circulation pumps blood from the right side of the heart to the lungs. This blood starts off deoxygenated, but becomes oxygenated as it passes through the lungs. This system is relatively low pressure (shorter vessels = less resistance due to less overall SA... I think), with a pulmonary artery blood pressure of around 25/8 mmHg.