NDD easyone pro, Operator'S Manual, Page: 148 / 188

Appendix
148 EasyOne Pro™ / EasyOne Pro™ LAB
12.5 How to interpret TLC from a single breath maneuver
Instruments for lung volume measurement (Body Plethysmography, Multi-
breath Nitrogen Washout or Helium equilibration methods) today require
well trained personnel, stable conditions and significant maintenance to
provide reliable results. Therefore, these tests are normally performed in
larger, hospital based lung function laboratories.
It has been shown that a total lung capacity (TLC) measured from a single
breath maneuver (TLCsb) systematically underestimates the TLC when com-
pared to Body Plethysmography (TLCpleth) or Multibreath washout (TLC-
wash) methods. The degree of underestimation has been shown to increase
as airflow obstruction worsens.
A study by Punjabi, et al [1] shows that an approximation of the TLCpleth
and TLCwash is possible by applying a simple correction formula to the sin-
gle breath TLCsb:
Without correction Punjabi showed:

there is a very good correlation between TLCsb and TLCpleth (r=0.97-
0.99) in patients with FEV1/FVC >70%. Therefore, no correction of the
TLCsb was necessary in patients without obstructive patterns.

in patients with FEV1/FVC <70%, TLCsb is a systematically underesti-
mated and showed poor correlation to TLCwash (r = 0.67-0.94)
After using the simple correction equation:

they showed that in patients with FEV1/FVC <70% (range: 40-70%) had
an acceptable correlation between TLCsb and TLCwash (r = 0.83-0.94,
p<0.05). The software labels of all Punjabi-corrected values (if any) with
“Cor”, e.g., “TLC Cor.”.
This means that in patients with FEV1/FVC ratios > 70%, the TLCsb is reliable
and can be used directly in the ATS/ERS interpretative strategies diagnostic
algorithm. When the TLCsb is measured in the presence of an obstructive
pattern (FEV1/FVC < 70%), it needs adjustment by the equation of Punjabi
and then applied to the ATS/ERS diagnostic algorithm. The only possibility
of an difference in diagnosis between using a corrected TLCsb and a TLC
measured with plethysmography or N2-wahout is when the corrected TLCsb
falls below the lower limit of normal.
The decision Tree according to the ATS/ERS Task force
In the decision tree published by the ATS ERS Task Force(2) “Standardiza-
tion of Lung Function Testing” some yes/no decisions are based on the TLC.
The value being above or below the lower limit of normal (LLN) determines
the diagnostic path:

For the case that TLCsb from the single breath maneuver is above LLN, it
is always correct to use the measured result in the ATS/ERS algorithm for