Diastolic blood pressure?

At work yesterday I got caught in a discussion about systolic and diastolic blood pressure. Simple as it may sound, we couldn’t agree on the physics determinating the diastolic blood pressure when measuring with a sphygmomanometer.

Applying a lateral pressure on the brachial artery above, say, 200 mm Hg, makes the artery close and no blood can flow past the occlusion. Thus, according to Beroulli, the energy that is produced by the heart and transferred through the artery will exercise a pressure towards the occlusion, i. e. a ‘wedge pressure’ (?), which equals the lateral pressure, since no energy is used to produce movement of the blood. If we lower the pressure in the spygmomanometer we will eventually reach a point where the pressure in the sphygmomanometer equals or is just below the wedge pressure in the artery, forcing the artery open. Blood will flow through the artery and produce the Korotkoff sound; and thus we can determine the systolic blood pressure. The systolic blood pressure could therefore be considered to equal the maximum energy per unit of blood volume produced by the heart at any given moment? ((N/m2) x m3 = Nm).

But the fact that the once closed artery now is open means that some of the energy produced by the heart will be used to move blood through the artery, lowering the lateral pressure again. So once the pressure is high enough to open the artery, that same pressure will be transformed into motion energy, making the lateral pressure fall and since the pressure of the spygmomanometer is just below the maximum wedge pressure, the artery will once again close..? And once it closes, the pressure will build up again and once more force the artery open; and if I am correct the walls of the artery would start to oscillate. At the same time the pulsatile energy produced by the heart will cause the total amount of energy in the closed artery to rise and fall, making the artery oscillate in systole and close in diastole.

If the continue to release the pressure in the sphygmomanometer, the ‘wedge pressure’ in the closed artery during diastole will eventually force the artery open, and the pressure in the sphygmomanometer at this moment would, according to me, represent the diastolic pressure. But at that point, why does the sound in the distal artery change? We would still have the oscillation, which I think now would be present during both systole and diastole.  Rather than the Korotkoff sound disappearing at this point, I would have guessed the sound would change to a  more constant murmur due to turbulence after the oscillating part of the artery. The oscillation would, if I am correct, continue until the point where the pressure in the sphygmomanometer no longer causes a deformation of the artery wall making the area of that section of the artery smaller than the surrounding vessel area. So the pressure we have reached where the turbulence completely disappears in the artery would rather represent the resistance to compressive stress of the vessel wall; maybe this pressure would correlate better to vessel wall changes and atheromatosis?

Where do I go wrong?

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