Interference No. 103,197
(f) Insufficient tissue thickness
Falkowksi offers both a theoretical explanation and an
experiment which allegedly prove that a needle tip spacing of
1-2 mm of tissue is too small to yield provide a detectable
modulation signal. The theoretical explanation is that a112
finger sensor used on a tissue layer 10 mm to 15 mm thick
results in a modulation depth of about 1% to 5%, that
decreasing the thickness by a factor of 5 decreases the
modulation depth by a factor of 5 or even more, and that
decreasing the tissue thickness to 1 mm will result in a
modulation depth below the 0.05% to 0.07% minimum modulation
depth accepted by commercial pulse oximeters. This argument
is unconvincing for the following reason. Taking the worst
case of a 1% modulation depth for 15 mm of tissue, the
modulation depth for 1 mm of tissue (the lower end of the 1-2
mm range given by Dr. Morrison) would be 1% divided by 15, or
0.067%, which is within the minimum acceptable modulation
range of 0.05% to 0.07%. For 1.5 mm of tissue, the modulation
would be 1% divided by ten, or 0.1%, which is above the
minimum acceptable modulation range. The experiment on which
BR 27, ¶ 6.112
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