Classical regression equations of spirometric parameters are not applicable for diagnosing spirometric abnormalities in adipotic adults

Table 1 Partial regression coefficients for spirometric parameters of non-adipotic subjects[13]

Spirometric parameter	a0	a1	a2	a3	a4	ΔLLN
Ln (FVC)
M	-10.269	0.358	1.989	0.164 - 0.003•A	-0.001•A	0.146
F	-5.659	-0.009•A	0.909 + 0.013•A	0.497 - 0.007•A	-0.067	0.178
Ln (FEV1)
M	-7.823	0.116 - 0.002• A	1.74	0	-0.001•A	0.136
F	-5.784	-0.003 •A	1.291	0.082 + 0.002 × A	-0.002•A	0.17
Ln (FEV1/FVC)
M	6.041	-0.11	-0.238	0	0	0.075
F	6.313	-0.178	-0.289	0.001×A	-0.171 + 0.003•A	0.079
Ln (PEF)
M	-1.185	-0.011•A	0.573 + 0.010•A	0	0	0.246
F	0.078	-0.012•A	0.011•A	0.293	-0.002•A	0.284
Ln (FEF50)
M	-1.194	-0.002•A	0.462	0.14	0	0.314
F	1.238	-0.004•A	-0.005•A	0.009•A	-0.15	0.37
Ln (FEF75)
M	-6.334	-0.003•A	1.498	-0.171	-0.282 + 0.004•A	0.4
F	-0.057	-0.88	0.381	0.167 + 0.002•A	-0.869 + 0.012•A	0.576

a₀ is invariable constant, while a₁, a₂, a₃, and a₄ are, respectively, age-dependent and/or age-independent partial regression coefficient for describing the effect of age (A), height (H), body weight (BW), and fat fraction of body mass (F) on a specific spirometric parameter (SP). Using a_i (i = 0 to 4), reference mean of each Ln (SP) is estimated (see eq. (1)); ΔLLN: The 5^th percentile of the residual’s distribution of each Ln (SP), from which lower limit of normal (LLN) of each SP is determined [see eq. (3)]. M: Male; F: Female; A: Age; FVC: Forced vital capacity (L); FEV₁: Forced expiratory volume after one second (L); PEF: Peak expiratory flow rate (L/s); FEF₅₀: Forced expiratory flow rate at 50% expiration of FVC (L/s); FEF₇₅: Forced expiratory flow rate at 75% expiration of FVC (L/s).