Heart Rate Flashcards
(6 cards)
Cardiac output
CardiacOutput
Cardiac Output is how much blood gets pumped out of the heart every minute.
It’s calculated by:
HeartRate
×
StrokeVolume
CardiacOutput=HeartRate×StrokeVolume
Heart Rate = how many times the heart beats each minute
Stroke Volume = how much blood is pumped with each beat
🩸 So Stroke Volume is NOT the amount in a whole minute — just per beat.
💡 Put Together:
If your heart beats 70 times in one minute (HR = 70 bpm)
And each beat pumps 70 mL of blood (SV = 70 mL)
Then:
70
×
70
=
4900
mL/min
=
4.9
liters/min
70×70=4900mL/min=4.9liters/min
That means your heart pumps 4.9 liters of blood per minute — that’s your cardiac output!
Let me know if you want a memory trick or want to go over how this changes during exercise or disease!
when one changescardiac output changes
The normal adult blood volume is about 6,000 ml, so nearly the entire blood supply passes through the body once each minute. Cardiac output varies with the demands of the body. It rises when the stroke volume is increased, or the heart beats faster, or both; it drops when either or both of these factors decrease. Let’s take a look at how stroke volume and heart rate are regulated.
stroke voulme
A healthy heart pumps out about 60 percent of the blood present in its ventricles. As noted previously, this is approximately 70 ml (about 2 ounces) with each heartbeat. Three factors influence stroke volume: preload, contractility, and afterload.
70 ml — Stroke Volume (SV)
This is the amount of blood ejected by the heart in one beat.
It’s usually about 60% of the total blood in the ventricles (called the ejection fraction).
So, one heartbeat pumps out approximately 70 ml of blood.
🔹 6,000 ml — Total Blood Volume / Cardiac Output
There are two things this number could be referring to:
Total Blood Volume in an Adult:
The average adult has about 5,000–6,000 ml (5–6 liters) of blood in their entire circulatory system.
Cardiac Output (CO):
If the heart pumps 70 ml per beat and beats about 70–75 times per minute, you get:
𝐶
𝑂
=
𝑆
𝑉
×
𝐻
𝑅
=
70
ml
×
75
bpm
=
5
,
250
ml/min
≈
5
–
6
𝑙
𝑖
𝑡
𝑒
𝑟
𝑠
𝑝
𝑒
𝑟
𝑚
𝑖
𝑛
𝑢
𝑡
𝑒
CO=SV×HR=70ml×75bpm=5,250ml/min≈5–6litersperminute
So in one minute, your heart pumps roughly all your blood volume once—that’s the cardiac output.
✅ In Short:
70 ml = per beat (stroke volume)
6,000 ml = total volume of blood in the body or amount pumped per minute (cardiac output)
Let me know if you want a visual to tie it together—it helps clarify this really well.
Ask ChatGPT
preload
Breakdown of the paragraph:
Frank-Starling law:
The more the heart muscle stretches before contraction (preload), the stronger the squeeze and the bigger the stroke volume.
Preload is influenced by:
Venous return: how much blood comes back to the heart.
Time ventricles spend relaxed and filling, which depends on heart rate.
How heart rate affects preload:
A slow heart rate gives the ventricles more time to fill → more preload → bigger stroke volume.
A fast heart rate gives less filling time → less preload → smaller stroke volume.
How exercise affects venous return:
Exercise → muscles contract more → they squeeze veins → more blood pushed back to heart → venous return increases → preload increases → stroke volume increases.
At the same time, exercise increases heart rate, which reduces filling time.
So where’s the confusion?
Exercise makes venous return increase (good for preload and stroke volume) and heart rate increase (which shortens filling time, bad for preload).
These two effects oppose each other in terms of how they influence preload and stroke volume.
But the net effect of exercise is usually an increase in cardiac output because:
Venous return goes up a lot (from muscle pump action)
Heart rate goes up (though filling time is shorter)
The heart compensates by squeezing stronger (contractility)
Summary in simple terms:
Effect During Exercise Result on Preload/Stroke Volume
Increased venous return ↑ Preload → ↑ Stroke Volume
Increased heart rate ↓ Filling time → ↓ Preload (if too fast)
But since venous return increases so much, stroke volume usually still goes up during exercise — unless the heart rate is extremely fast, then stroke volume can decrease.
contractibiliy
Contractility — Key Points:
It’s the ability of cardiac muscle to generate tension and contract forcefully.
It doesn’t depend on how much the muscle is stretched (that’s preload).
Instead, it’s influenced by:
Calcium ions (Ca²⁺) inside heart muscle cells (more calcium → stronger contraction)
Sympathetic nervous system stimulation (the “fight or flight” response)
Hormones like epinephrine (adrenaline) and thyroxine
Why does contractility matter?
Higher contractility → stronger heart squeeze → more blood pumped out per beat → increased stroke volume.
This is especially important during exercise or stress when your body needs more blood flow.
If something is wrong with contractibility we take digitals pills which slows down heart contractibility but makes the contractibility more stronger
afterload
Afterload is the pressure in the arteries (like the aorta and pulmonary artery) that the heart’s ventricles must overcome to push blood out during contraction.
To open the semilunar valves and eject blood, the ventricles have to generate a pressure higher than the pressure already in the arteries.
So, if arterial pressure (afterload) is high (like in high blood pressure), the heart must work harder to pump blood out.
Quick summary:
Term Meaning
Afterload Pressure in arteries opposing ventricular ejection
Ventricular pressure Must be higher than afterload to open valves and pump blood out
This is why high blood pressure increases afterload and can strain the heart over time.
Want me to explain how the heart adapts to increased afterload or what happens in diseases like hypertension?
You said:
Wait high blood pressure could increase afterloaf
ChatGPT said:
Yes, exactly! High blood pressure increases afterload.
Here’s why:
Afterload is basically the pressure in the arteries that the heart has to push against to get blood out.
When someone has high blood pressure (hypertension), the pressure inside the arteries is higher than normal.
That means the heart’s ventricles must generate even more force to overcome this higher pressure and open the semilunar valves to eject blood.
This extra work can strain the heart over time and may lead to problems like ventricular hypertrophy (thickening of the heart muscle) or heart failure.
So:
High blood pressure → higher afterload → heart works harder → risk of heart problems
Want me to explain how the heart compensates for increased afterload or what treatments help reduce afterload?
You said:
Does the high blood pressure increase the afterload because the blood keeps increasing in the arteries as we pump blood
ChatGPT said:
You’re thinking along the right lines! Let me clarify how high blood pressure increases afterload:
How High Blood Pressure Increases Afterload:
Blood pressure in the arteries is mainly the force exerted by blood against the artery walls.
When arteries are narrowed, stiff, or less elastic (due to factors like plaque buildup, aging, or chronic high blood pressure), the blood pushes harder against the artery walls.
This higher pressure inside the arteries means the ventricles have to push against a stronger force (the afterload) to open the semilunar valves and eject blood.
So it’s not just the volume of blood increasing, but the pressure in the arteries being elevated because of resistance in the blood vessels.
Simple analogy:
Imagine trying to push water through a narrow, stiff hose — it takes more effort (pressure) compared to a wide, flexible hose.
Summary:
High blood pressure = high arterial pressure
High arterial pressure = increased afterload
Increased afterload = heart has to work harder
