How would severe bleeding from a major veins affect heart rate and heart output?

Answer 1

Your cardiac output is equal to your stroke volume (amount of blood being pushed out every time your heart beats) multiplied by your heart rate. Your cardiac output equals the amount of circulating blood needed to function at a given time.

Your body will try to compensate for any changes in the amount of blood in your system, therefore your body will always try to maintian cardiac output. With any type of major bleeding, your stroke volume will decrease. In order to maintain your cardiac output, your heart rate will increase. For example:

(Stroke Volume of 50mL) x (Heart Rate of 60) = Cardiac Output of 300

With major bleeding, the decrease in stroke volume will require an increase in heart rate:

(Stroke Volume of 25mL) x (Heart Rate of 120) = Cardiac Output of 300

You can see that the amount of blood decreased in half for every heart beat (50mL to 25mL), so the heart has to beat twice as fast (60 beats per minute to 120 beats per minute) to make up for the blood loss.

Answer 2

It would decrease blood pressure due to a change in cardiac output.