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imginit

Development Team Member
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 #1 
Has there been any testing to rule out sources of error from the data collection?

1) Does skin blood flow or sweat or skin color affect the readings?

2) Does temperature affect readings?

3) Is there a test to rule out the detection of myoglobin? 

4) Do local metabolites affect the readings?

5) Calibration: Should there be a place that should give a reading near 100?  I tested the device by checking places where arterial blood flow should be maximal (fingers) with a maximum value of 90.  I tried placing the device over the carotid artery; however, the data did not stabilize.
Roger

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 #2 
Great Questions!!!  I'll answer as best I can.

Has there been any testing to rule out sources of error from the data collection?
The primary validation testing that we've done is what I call 0 and 100 testing.  We test to see if the device reads near zero when we expect it to and near 100 when we expect it to.  Here's a link to a post that discusses this further.  http://forum.moxymonitor.com/post/nirs-moxy-validation-6433145

1) Does skin blood flow or sweat or skin color affect the readings?

Skin blood flow and skin color (primarily melanin) have color in the near infrared regions which means that they absorb the 4 wavelengths of light that Moxy uses differently.  However both of them are very near to the surface.  The Moxy uses 2 emitter to detector distances to help remove the effects of skin blood and melanin.  Also, the use of 4 wavelengths helps to remove the effects of melanin compared to systems that only use 2 or 3 wavelengths.

The effect of sweat is to change how effectively the optodes couple to the tissue.  Wet optodes couple more effectively.  The Moxy algorithm is designed to be completely independent of the optical coupling.  For example, you could take a piece of black tape and block off 1/2 of one of the optodes and the Moxy would still measure the same SmO2.

2) Does temperature affect readings?

Temperature probably affect the athlete's SmO2 levels, but Moxy is designed to maintain accuracy over a wide temperature range.  LEDs change their center wavelength with temperature.  Moxy has a temperature sensor and is calibrated at the factory to adjust for this effect.

3) Is there a test to rule out the detection of myoglobin? 
In the wavelength range that Moxy uses, myoglobin and hemoglobin look alike.  The SmO2 reading is a combination of myoglobin and hemoglobin oxygenation.

4) Do local metabolites affect the readings?
They probably affect SmO2 levels in the athlete, but they have low concentrations and little color in the near infrared so they don't affect the accuracy of the measurement.

5) Calibration: Should there be a place that should give a reading near 100?  I tested the device by checking places where arterial blood flow should be maximal (fingers) with a maximum value of 90.  I tried placing the device over the carotid artery; however, the data did not stabilize.
It's difficult to get readings very close to 100.  Muscle is always consuming oxygen even at rest.  The best way I've found is to induce a hyperemic response by applying a tourniquet upstream from the measurement site for a long time (several minutes) so that the blood vessels dilate and then suddenly release the tourniquet.

The Moxy Algorithm is designed to measure over tissue that is in layers of skin, adipose and a thick layer of muscle (thick enough that whatever is behind the muscle doesn't affect the optical path).  When you try to measure over the carotid or on a finger, the optical properties are VERY different than skin-fat-muscle so the absolute value of the readings would be very questionable.
Juerg Feldmann

Fortiori Design LLC
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Posts: 1,530
 #3 
Thanks for  the questions .
 I will give you some answers  from a practical point of view  and then the  technical  inventors  can give  you a much smarter response.

1. Skin blood flow seems to clearly  make a difference when we compared  Portamon and  MOXY.
. When we increase  skin blood flow   than the SmO2  in MOXY  due to  possibly movement of Blood   to the surface and with it  O2Hb. As well we see a drop in tHb.
  In the portamon we see   interesting result   at this  same time   as TSI %  can go up  and tHb as well.
  We  have some tests  from the USA  9 Clint) where we comp[red this on pressure stockings.  When looking at Portamon data's and pressure stocking the  stockings  go a review, as if the result  would be  worse  as the  pressure pushed possibly the blood into the  deeper areas  . So n the Portamn TSI %  dropped  but in MOXY SmO2  increase.
 For us as coaches  the  MOXY  trend  was some what   more likable  as we  have test , where as harder the athletes   went  as  higher TSI %. In practical terms, If we  have to "cool " the system and we  move  blood to the surface we see  with MOXY a drop in SmO2   as a indication of less O2   and tHb  available  in the working  area.
There  are questions  how dark the skin  can be  to still have an okay reading. Experts  must tell us. Till now never  had a problem  but  black  platsic bag   will not gove a reading. Sweat  or water  per see seems to have no effect.
  If it is very cold  so we iced the skin  no  with MOXY. Main problem is the  batteries as  we tested it in Davos   in cold temperature  and we had ot cover  MOXY  at the start , till the body would keep the  equipment  warm enough  so below   pants  it works,  exposed to  air  we had batterie problems

Myoglobin.  No  NIRS   can not  make a difference   betwen O2  loaded on Hb   and or on Mb. That would be  really the next  optimal step  wouldn't it be ???.

 Local metabolites  ?


 I am not sure  but  when we look at  the idea  I do not think  , that they  will interfer, but lets' see what other people think about that.

 Check on  what  is different between SpO2  and  SmO2   as a technology.
  On the arteria  you may have a problem to  test  for the SmO2   changes as there is no  exchange of  O2.  You have a pulsatile effect there  and SmO2  will steady  change. But  again  let's the  specialist  in the technology talk about that.
.  Calibration and validation see what we   know for now.
 in that section  and  again hopefully some  otehr feedbacks   here from NIRS users. 

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Juerg Feldmann

Fortiori Design LLC
Registered:
Posts: 1,530
 #4 
Well here you go  nearly telephatic  ( Smile ) and Rogers answer  are even in  English . Thanks Roger  for jumping in from the techno side. Very very help full for all of us.
imginit

Development Team Member
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Posts: 7
 #5 
Your responses are really helpful.  Thank you.  
Juerg Feldmann

Fortiori Design LLC
Registered:
Posts: 1,530
 #6 
Your  welcome  and  I am always amazed  . that  people   can  at least partially understand  my Swenglish  , Thanks so much   to all readers  for you acceptance. Will  most likely not improve anymore  and I know that since  my English teacher   40 years back  warned  me, if I do not  care  and look at the skiers  outside  I will always think on his words  later in my live.
 How  right he  was and is  . Smile

imginit

Development Team Member
Registered:
Posts: 7
 #7 
Regarding skin blood flow, I understand that the device is supposed to rule out the skin blood flow in it's measurements; however, what applied work has been done to show it is in fact doing so.  And if it is, what is the correction?

Thanks, Shawn
Roger

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Posts: 266
 #8 
The Moxy algorithm is created from a Monte Carlo model of light traveling through layered tissue consisting of epidermis, dermis, adipose and muscle.  Monte Carlo modeling traces individual "Rays" of light as they bounce on a random (but statistically based on the optical properties) path through the tissue.  The algorithm and optical layout is designed for high sensitivity to the muscle layer and low sensitivity to everything else.

The algorithm is created entirely from published values for the optical properties of tissue.  There are no fudge factors to make it read what we want.  It's based entirely on the model.

Since we get reasonable numbers out of the algorithm (it goes to 0 when it should and it gets close to 100 when it should and it goes up and down when it should) we assume the Monte Carlo model is pretty good.  We then also assume that the other aspects of the model like minimizing skin flow sensitivity are also reasonable.

Beyond that, we just look for special cases that act like we would expect.  The following discussion is a good example based on a compression clothing test that highlights the difference between a device that does not used a layered tissue model and the Moxy.  The results indicate that the Moxy is on the right track for isolating data from the muscle layer.

http://forum.moxymonitor.com/post/compression-tsi-vs-smo2-6294044
Juerg Feldmann

Fortiori Design LLC
Registered:
Posts: 1,530
 #9 
I like to add  an example here as well but I will keep the discussion on  the other topic  on " what do we do with it.
 If yo go there you see a  great workout  done  by Carson  and his team.
 It was as mentioned  2  x 10 min   with  high and low wattage.
 It is  a great example how "wattage " believer " could extremely enhance their    training ideas by adding MOXY  so they can see, what a workout like this   stimulates , when ever they do it as it may be the same  some days  and it may be very different  on other days  despite the same physical wattage  but a very different physiological   situation.
 Here the 2  x  10 min MOXY only  information by Carson  and look for  critics on   whether we can repeat this , the wattage  overlap is actually much less accurate than the MOXY overlap.
 What yous see are  the load  and deload   repetitions   every time  including the trend in SmO2  . we will go much further   to show  how   and what we learned over the last 15 years  working with physiological parameter  and combining it with  if possible performance. In sports where performance as wattage is not available  SmO2  is their performance parameter.
 Here to enjoy
 Thanks  Carson for that great  feedback  of data's.

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