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Blood Flow

Ok, so it’s weird flying and running (Blogs M01, M02) in null-momentum

What about inside your body?

Blood is pumped around by the heart. Would null-momentum mean higher, lower or no difference to blood pressure.

Basically the heart is a pump: the muscle contracts, squeezing the blood out through the appropriate valve, then relaxes/expands, sucking blood back in through the other valve. Null-momentum implies this process happens at immediate steady state flow speeds, which are the peak speeds of the normal pump cycle.

The normal pump pressure curve is relatively quickly rising but still with a relatively long rising and falling tail, as is common with most biological systems. Some of this is due to inertia of the muscle contraction, some to inertia in the blood flow, some due to muscle response time. Under null momentum all of these happen immediately, reaching normal steady state right at the beginning of the compression (or relaxation) time, i.e., the pump curve would become a step-function.

I am unsure of the precise shape of the normal pump pressure/flow rate curves, but let’s suppose it to be similar to most natural processes, and largely follow a normal curve out to three standard deviations before the heart muscle changes to relax (suck). Then a step-function shape over the same time frame, with the same peak flow rate would pump approx. 2.4 times as much blood in the same pulse.

If the heart didn’t alter its action from the biological feedback, then this would supply 2.4 times as much blood, and forced around at maximum pressure.

This would be a serious over-supply of blood/oxygen! Consider average resting heart rate of 70 beats/min. If we ignore the fall-off of volume as the heart tries to pump faster, then achieving this level of increased blood flow would imply at least 170 beats/min. And really, heart efficiency (any pump) goes inversely with the speed, so a conservative estimate to achieve this might be, say, 200+ beats/min. That’s adrenaline-level flight or fight stuff: maximum body-muscle outputs, achieved at resting heart rates. Imagine if you were actually exercising!

But of course the heart is controlled by a very complex feedback system that incorporates the oxygen state of various indicator cells, amongst a slew of other biological inputs. This feedback system would not be fundamentally altered by null-momentum, except possibly to react faster. Therefore, as the blood flow increased, the heart would slow and/or pump less forcefully, dropping the total blood flow back to the required range.

So, under null-momentum the heart would work less energetically, and since it’s a step-function flow rate, the peak pressure will be significantly reduced, at least by the area factor (2.4 times), probably considerably more, as lower pressure also means more efficient flow rate (consider the analogy of peak traffic vs off-peak).

So under null-momentum, your heart might beat at 20 or beats per minute (once every 3 seconds). That would be quite weird feeling!

Also, a perhaps surprising finding from the mechanical assist devices used no suitable donor heart or other repair is available, is that in a large number of cases the time spent beating less energetically seems to allow the heart to repair itself to some extent. Perhaps a null-momentum treatment could achieve this while allowing complete freedom of movement, and no surgical intervention!

What would it mean for normally healthy heart? Could null-momentum actually promote a significantly longer lifespan?

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