Wishbone's posting perpetuates the medical fraternity's touching (but totally misguided) belief in the myth that blood is pumped round the systemic vasculature in 'waves' of blood, -which of course is demonstrably not the case
If it were, then the pulse would be audible simply by placing the stethoscope on the brachial artery
, and picking up the sounds of these "waves of blood". But irritatingly, (and most inconveniently for medics and other exponents of the "pulsatile arterial flow" theory), ..... the beat is essentially inaudible until cuff pressure induces constriction and disappears as flow becomes laminar again.
A stethoscope only registers turbulent flow and pulses where the turbulence converts pressure to force and force to sound, -typically at locations such as at ,or near to, the heart and relatively close to the aortic valve
So, -Wishbone is failing to distinguish between pulses in pressure, and pulses in FLOW. He's in very august company, of course; - all textbooks make the same mistake, and conflate the two.
While volumes of ventricular blood are indeed ejected at each stroke
into the aorta
, generating waves of pulse-pressure that flow down the arterial tree in the process, that's all they are......
They're only pressure waves, not waves of flowing blood.
The pressure waves travel at a much higher velocity THROUGH the blood than does the blood itself, (and tissue) and therefore do not ( -indeed CAN not)- 'drive blood' -any more than a ghost passing through a door can open it.
Why? - Well because the pulse pressure waves are not in phase with the flow.
Even at the aortic valve, at the instant the valve opens, hydrostatic pressure within the ventricle is maximum when flow is at first zero, and then as flow rises to its maximum, the intra-ventricular pressure
is falling towards minimum. They're out of phase, and pressures out of phase with flows aren't performing any work.
(It's exactly the same as volts and amps. If they're not in phase no watts result and no power is expended.)
But once the valve has closed and the pressure waves travel down the aorta and downstream arteries, they don't even have a (net) vectorial component that's in phase with the direction of flow. The waves pass through the blood; they don't drive it.
So what the pressure monitor registers is merely the instantaneous peak-to-peak values of a transient, traveling, longitudinal wave ...... - of pressure, not flow.
A flow-meter, however, would register smooth laminar flow, and an intra-arterial pressure transducer registers only fleeting, transient pressure pulses.
The audible pressure pulse heard during ausculatation has nothing whatever to do with what drives the blood round. What drives blood round is simply the diastolic pressure gradient. -Sorry.!