BMC Pulmonary Medicine

Table 4 The relationships between the change in the curve parameters¹ and explanatory variables (CPET2 minus CPET1)

From: Peak oxygen uptake and breathing pattern in COPD patients – a four-year longitudinal study

	Unadjusted			Adjusted
Variable	B	p-value	B	St.B*	95 % CI	p-value
Intercept¹ (Curve parameter a)
Age	0.002	0.803	−0.0003	−0.004	−0.015–0.014	0.966
Sex	−0.089	0.468	−0.126	−0.138	−0.312–0.060	0.180
Height	0.145	0.844
a_baseline	−0.545	<0.001	−0.573	−0.588	−0.769–−0.376	<0.001
Δweight	−0.002	0.881
ΔFEV₁	0.601	0.005	0.762	0.461	0.376–1.149	<0.001
ΔFVC	0.427	0.001
ΔIC_rest (L)	0.116	0.374	−0.052	−0.053	−0.365–0.262	0.743
ΔIC_dynamic (L)	−0.025	0.882	−0.203	−0.166	−0.561–0.156	0.262
ΔIRV	−0.147	0.416
						R² = 0.507
Slope¹ (Curve parameter b)
Age	−0.0003	0.725	0.00003	0.006	−0.001–0.001	0.959
Sex	0.002	0.860	0.012	0.159	−0.005–0.029	0.177
Height	−0.059	0.311
b_baseline	−0.568	<0.001	−0.588	−0.510	−0.854–−0.322	<0.001
Δweight	0.002	0.862
ΔFEV₁	−0.046	0.009	−0.050	−0.373	−0.085–−0.015	0.006
ΔFVC	−0.032	0.003
ΔIC_rest (L)	−0.008	0.429	−0.001	−0.008	−0.029–0.028	0.963
ΔIC_dynamic (L)	0.005	0.734	0.018	0.183	−0.014–0.050	0.265
ΔIRV	−0.023	0.119				R² = 0.393
Curvature¹ (Curve parameter c)
Age	−4.8x10⁻⁶	0.774	−7.2x10⁻⁶	−0.061	−0.00004–0.00002	0.643
Sex	−7.3x10⁻⁵	0.746	−2.5x10⁻⁵	−0.016	−0.0004–0.0004	0.901
Height	0.001	0.586
c_baseline	−0.406	0.033	−0.345	−0.254	−0.695–0.006	0.054
Δweight	7.5x10⁻⁶	0.762	B
ΔFEV₁	0.001	0.001	0.001	0.372	0.0002–0.002	0.013
ΔFVC	0.001	<0.001
ΔIC_rest (L)	0.0005	0.025	0.0004	0.268	−0.00002–0.001	0.192
ΔIC_dynamic (L)	0.0001	0.651	−0.001	−0.249	−0.001–0.0002	0.179
ΔIRV	−0.0003	0.280
						R² = 0.315

95 % confidence interval (CI) examined by linear regression in bivariate and multivariate analyses
CPET: cardio pulmonary exercise test; Δweight: weight at CPET2 minus weight at CPET1; FEV₁: forced expired volume in one second, ΔFEV₁: FEV₁ at CPET2 minus FEV₁ at CPET1; FVC: forced vital capacity; ΔFVC: FVC at CPET2 minus FVC at CPET1; IC: inspiratory capacity; ΔIC_rest was calculated as IC at rest at CPET2 minus IC at rest at CPET 1; ΔIC was calculated as IC at start of the test minus IC at the end of the test; ΔIC_dynamic was calculated as ΔIC at CPET2 minus ΔIC at CPET1; IRV: inspiratory reserve volume; ΔIRV was calculated as IRV at CPET2 minus IRV at CPET1; a_baseline: curve parameter a at baseline; b_baseline: curve parameter b at baseline; c_baseline: curve parameter c at baseline; R²: The coefficient of determination
¹ The relationship between ventilation (V̇_E) and tidal volume (V_T) was described by a quadratic model (V_T = a + b·V̇_E + c·V̇_E²), and the a, b, and c were calculated as the difference between CPET2 minus CPET1
*St.B: Standardised beta

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ISSN: 1471-2466

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