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

Table 2 Partial regression coefficients for spirometric parameters of adipotic subjects (cohort A)

Spirometric parameter	a0	a1	a2	a3	a4	ΔLLN
Ln (FVC)
M	-7.158	0	1.669	-0.001•A	-0.1	0.375
F	-7.752	0	1.793	-0.001•A	0	0.279
Ln (FEV1)
M	-5.593	-0.001•A	1.321	0	-0.124	0.379
F	-6.439	-0.001•A	1.495	0	0	0.287
Ln (FEV1/FVC)
M	5.509	0	-0.2	0	0	0.11
F	5.661	0	-0.272	0.044	0	0.111
Ln (PEF)
M	-2.597	0	0.936	-0.001•A	-0.001•A	0.484
F	-1.859	-0.010•A	0.649 + 0.009•A	0	0	0.391
Ln (FEF50)
M	0.665	0	0	0.002•A	-0.855 + 0.014•A	0.566
F	0.779	-0.015•A	0.014•A	0	0	0.557
Ln (FEF75)
M	-1.217	0	0	0.216	-0.914 + 0.013•A	0.739
F	-2.927	-0.003•A	0.676	0	0	0.701

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).