Cardiac Output
Terms
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- The amount of blood pumped out by EACH ventricle per min. It is directly related to Heart rate and Stroke Volume.
- cardiac output
- What two factors does cardiac output depend on?
-
H.R.
S.V. - What is the mathematical relationship between cardiac output, heart rate, and stroke volume.
- CO = HR X SV
- The number of times the heart beats per min (bpm)
- heart rate
- What is the average heart rate in an adult at rest?
- 70 bpm
- The amount of blood pumped by each ventricle w/each heartbeat.
- stroke volume
- What is the average stroke volume in an adult at rest?
- 70mL per/beat
- The amount of blood in each ventricle at the end of diastole (relaxation).
- end diastolic volume
- The amount of blood remaining in each ventricle at the end of systole (contraction).
- end systolic volume
- What is the mathematical relationship between end diastolic volume, end systolic volume, and stroke volume?
- SV= EDV - ESV
- If the ESV is 50 ml and the EDV is 120 ml, what is the stroke volume?
- 70
- If the heart rate is 75 beats per minute and the stroke volume is 70 ml per beat, then what is the cardiac output?
- 5250 mL/min
- What's the relationship between cardiac muscle stretch and force of contraction? What effect does this have on stroke volume?
- The more cardiac muscle stretched, the more forcefully it contracts. Stronger contraction increase SV.
- What's the relationship between venous return and stroke volume?
- Cardiac muscle fibers are stretched by increased blood volume returning to the heart (increased venous return and EDV). Increased stretch results in greater force of contraction, which increases stroke volume.
- What is the effect of increased sympathetic activity on heart rate and stroke volume? How does this effect cardiac output?
- Increased sympathetic stimulation (due to fright, anger, etc.) increases the heart rate. It also increases stroke volume by increasing contractility, which results in more complete ejection of blood from the heart (lower ESV).
- What is the effect of increased parasympathetic activity on heart rate and stroke volume?
- Parasympathetic activity increases after a crisis has passed. This reduces heart rate and stroke volume from their high levels, bringing cardiac output back to normal.
- What is the effect of increased venous return on heart rate and stroke volume? How does this effect cardiac output?
- Cardiac muscle fibers are stretched by increased blood volume returning to the heart (increased venous return and EDV). Increased stretch results in greater force of contraction, which increases stroke volume.
- What effect does a slow heart rate have on stroke volume?
- Slow heart rate allows for more time for ventricular filling, increasing EDV and therefore stroke volume.
- What effect does a fast heart rate have on stroke volume
- Extremely rapid heart rate results in low venous return and therefore decreased stroke volume.
- What is the effect of exercise on heart rate and stroke volume? How does this effect cardiac output?
- Exercise activates the sympathetic nervous system, increasing heart rate, contractility, and stroke volume. Both the higher heart rate and squeezing action of skeletal muscles on veins increase venous return, contributing to increased stroke volume.
- What is the relationship between blood pressure and sympathetic activity? What effect does this have on heart rate?
- Rising blood pressure reduces sympathetic activity, decreasing heart rate.
- What is the effect of a sudden decrease in blood pressure on heart rate and stroke volume?
- A sudden drop in blood pressure results in low venous return and therefore decreased stroke volume. However heart rate increased due to sympathetic activity, and normal cardiac output is maintained.
- What is the effect of a sudden increase in blood pressure on heart rate
- It decreases heart rate
- What is the effect of a sudden increase in blood pressure on stroke volume
- It decreases SV
- What is the effect of a sudden drop in blood volume on heart rate and stroke volume?
- A sudden drop in blood volume (eg. due to severe blood loss) results in low venous return and therefore decreased stroke volume. Sympathetic activity increases heart rate, maintaining cardiac output.
- What is the effect of an increase in calcium on heart rate and stroke volume?
- Excess calcium can lead to spastic heart contractions, an undesirable condition. Calcium also increases stroke volume by enhancing contractility.