No-one has answered the criticism that they didn't control for hydration (did they? I don't usually get these papers for free...), when that could have been another reason for cognitive improvement. Older people are often dehydrated, and that would be even easier to improve their NVC and cognition (and no dairy or sugar, which might also be a factor). Assuming they all have an adequate water supply...
Another fine application of Doppler ultrasound in human circulation:NVC assessment. They don't seem to have any problem with velocity (AKA blood flow rate) in the brain vessels. I wonder how hard it would be to convert that to a volumetric measurement.
Speaking of measurement, it would be great if someone could come up with a non-invasive localized pressure measurement.
From another thread:
drsclafani wrote:The inherent pressures in veins is pretty low. trying to measure a gradient with conventional instruments is unsatisfactory.
I agree. The tools I have seen mention of in ads, etc. sound like they are only for arterial cathether-based measurement. I'm afraid the narrowing caused by the presence of a catheter, or the hole for insertion, would affect the pressure. It should be possible, though, somehow if the viscosity of blood can be measured:
Poisselle's Law in fluid mechanics has direct analogy with Ohm's Law in electricity, which was formerly considered a fluid. That law says P=FR. That means Pressure=Resistance x Flow Rate. This is not news to anyone familiar with fluid dynamics, nor is Ohms Law unfamiliar to those familiar with electricity.
Electricity was originally understood to be a kind of fluid. This “Hydrolic Analogy” is still conceptually useful for understanding circuits. This analogy is also used to study the frequency response of fluid mechanical networks using circuit tools, in which case the fluid network is termed a Hydraulic Circuit.
Poiseuille's law corresponds to Ohm’s law for electrical circuits (V = I * R), voltage = current * resistance, where the pressure drop P is analogous to the voltage V and volumetric flow rate F is analogous to the current I. So the analogous equation is (P = F * R). In one case R is resistance to electrical current flow, in the other it is resistance to fluid flow.
The resistance to fluid flow R is defined as
R = (8 * Viscosity * pipe length) / ((PI) * (radius)^4)
For Pressure drop, see http://en.wikipedia.org/wiki/Hagen%E2%80%93Poiseuille_equation
ΔP = 128 * η * L
/ ((PI) * d^4)
The viscosity is η, ΔP is the pressure drop, L
is the length of the pipe, Q
is the volumetric flow rate, and d is the pipe’s diameter.
Viscosity of blood should not be hard to measure from a sample.