The Physical Rules

of the Heart, Blood Flow, and Cardiac Output

Week 14: The Heart, Cardiac Output, and Blood Flow Physics

by | Lessons

The physics of blood flow:

<u>4D MRI Heart Blood Flow </u>
1. Physics of Blood Flow: 4DMRI



1. How can a ‘strong contraction’ of the left ventricle improve flow, reduce friction, and reduce ‘clogs’?

  • vortical flow or spinning blood reduces friction, charges the vessel wall, which in turn repels calcium away from the wall.

see: Fred Kummerick, Riddick, and Steiner

  • A strong contraction and a fuller volume of blood go together. Starling’s Law.


2. How does fat(ty acid) figure into the 3 phases of ‘oxidative stress’ or ‘free radical chain reaction’?:


– Initiation



  • Oil painters,wood deck varnish, gummed carb, ethane pentane gas, more


Q. What makes a strong muscle weaken?

overuse. Heart stats:

6Kg ATP/day (20-30 x its own weight)

10 tons of blood/day

100,000 beats/day


Feed cells specifically for their particular energy need (Heart, Nerves (Brain), Skeletal Muscle, Gut cells, etc

Energy Starvation Model:

The failing heart is an engine out of fuel

2. Demonstration: Directly measuring O2 removed from blood

Props needed

1 Mason jar

20 marbles or beads

100ml Water

1 Spoon.


Illustrated here


Calculation of (a-v) O2 difference:

Assume we extract a wad of freshly oxygenated arterial blood (100ml) the moment it leaves your heart.

  • This blood holds 20ml of dissolved O2.

Oxygen is removed as blood circulates.

Now we measure the O2 remaining in blood just before it returns to the heart.

At rest: 8ml O2 is removed during aerobic metabolism.

  • a-v O2 diff = 12. (20-8 = 12)

At max intensity: 16ml O2 removed

  • a-v O2 diff = 4. (20-16 = 8)


3. Stroke Volume, Cardiac Output, and Calculating VO2 Consumed per Minute

Illustrated here


How to calculate cardiac output.

  • Cardiac output is the volume of blood pumped per minute

Cardiac Output = Stroke Volume x Heart Rate

  • An untrained person’s heart pumps out approximately 60ml blood per beat. This is stroke volume.
  • Assume we measure resting heart rate in an untrained person at 70 bpm (beats per minute)
  • Thus, 60ml blood is pumped out 70 times in one minute.

Cardiac output is 60 ml x 70 BPM = 4,200ml/min.

How to Calculate Oxygen Uptake at Rest

  • Assume we use the same untrained person from above:

Total blood ejected per minute:
70BPM x 60ml = 4,200 ml/min

We know by directly measuring blood that 8ml/O2 is removed from a wad of blood returning to the heart. (Calculated in previous section)

  • The ‘truck load’ or wad of blood is = 100ml of liquid (recall O2 gas dissolves in liquid)

Blood is flowing continuously into the heart – and in 1 minute, 4200ml blood actually returned to the heart – which is 42x greater than 100ml.

  • A proportional amount of oxygen  (42x more) is also removed in 1 min.

42 x 8ml = 336ml/min.  –> 1 MET