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).

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).

Table 3 Incidence of obese subjects (cohort B) who are judged to have impaired lung function

	Measured values < LLNs of adipotic equations	Measured values < LLNs of non-adipotic equations
FVC
M	0.40%	24.8%b
F	6.20%	24.1%b
FEV1
M	0.40%	26.1%b
F	8.40%	47.8%b
FEV1/FVC
M	3.10%	16.8%b
F	2.20%	6.6%d
PEF
M	1.30%	26.5%b
F	3.60%	19.3%b
FEF50
M	0.90%	27.9%b
F	11.70%	16.40%
FEF75
M	1.30%	11.5%b
F	5.50%	6.60%

^bP < 0.0001.

^dP < 0.02 between the two conditions (the χ² test). LLNs of respective SPs are estimated from the 5^th percentiles of the residual’s distributions applying eq. (3) to adipotic and non-adipotic regression equations. 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).