ATS Pulmonary Function Laboratory Manual

CHAPTER  12

APPENDIX 12.4  Calculation of the Provocative Dose (PD) 1. Responsiveness is expressed as the dose of inhaled methacholine that causes a threshold response. 2. The term PD 20 FEV 1 is defined as the dose that causes a 20% fall in FEV 1 . The term PD 40 sGaw is defined as the dose that causes a 40% fall in sGaw. 3. The PD 20 is obtained by linear interpolation between the final two doses. The formula is as follows:

[ log D1 + ( 20 − R1 ) ( logD2 − logD1 ) ( R2 − R1 ) ]

= antilog

PD 20

FEV 1

where: D1 = next-to-last dose of methacholine D2 = final dose of methacholine R1 = percent fall in FEV 1 after D1 R2 = percent fall in FEV 1 after D2

FEV 1

, using the highest FEV 1

value from the two FVC tests at 150 and 210 seconds.

Example calculation of PD 20

150 s

210 s

Baseline FEV 1

3.24 3.24 3.24. 2.98 2.53

3.30 3.29 3.29

Post-diluent FEV 1

Post 0.03 mg/ml FEV1 (Cum Dose = 1.275 μg)

(Cum Dose = 3.825 μg) (Cum Dose = 9.138 μg)

3.03* 2.55**

Post 0.06 mg/ml FEV 1 Post 0.125 mg/ml FEV 1

*percent fall in FEV 1 **percent fall in FEV 1

from diluent = 7.9% from diluent = 22.5%

[ log D1 + ( 20 − R1 ) ( logD2 − logD1 ) ( R2 − R1 ) ]

= antilog

PD 20

FEV 1

[ log 3 . 825 + ( 20 − 7 . 9 ) ( log 9 . 138 − log 3 . 825 ) ( 22 . 5 − 7 . 9 ) ]

= antilog

PD 20

FEV 1

[ 0 . 5826 + ( 12 . 1 ) ( 0 . 9609 − 0 . 5826 ) ( 14 . 6 ) ]

= antilog

PD 20

FEV 1

= antilog 0 . 8961

PD 20

FEV 1

= 7 . 872 μ g

PD 20

FEV 1

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