Use of the forced-oscillation technique to estimate spirometry values

Figures & data

Table 1 Characteristics of study subjects. Results reported as mean ± SD

Parameters	Development data	Validation data
Subjects, n	1,089	552
Sex, n, male/female	615/474	330/222
Age, years	63±15	58±18
Height (cm)	160.4±8.9	162.2±8
Body weight (kg)	58.9±11.9	60.5±11.7
Smoking (never/current/past/unknown)	420/153/449/67	216/83/180/73
Diagnosis, n
Normal	73	31
Malignant lung tumors	381	30
Asthma	202	202
COPD	170	79
ILD	156	38
Bronchitis (acute or chronic)	53	100
Mediastinal tumor	52	0
Sarcoidosis	36	2
Pleural or chest-wall disease	21	6
Mycosis	10	4
Tbc or old Tbc	13	5
NTM	11	3
Other	51	87
Pulmonary function tests
VC (L)	3.03±0.9	3.15±0.9
%VC (%)	90.2±18.3	88.9±17
FVC (L)	3.02±0.91	3.12±0.92
%FVC (%)	93.2±19.3	91.4±18.2
FEV1 (L)	2.24±0.75	2.35±0.85
%FEV1 (%)	87.6±21.6	85.4±22.2
FEV1/FVC	0.74±0.12	0.74±0.12
MostGraph-01 data
R5	3.58±1.42	3.09±1.22
R20	2.93±1.04	2.40±0.91
X5	−0.64±0.9	−1.05±1.18
Fres	8.31±3.75	10.63±4.28
ALX	3.56±7.36	6.31±9.61

Abbreviations: ALX, low-frequency reactance area; FEV₁, forced expiratory volume in 1 second; Fres, resonant frequency; FVC, forced vital capacity; ILD, interstitial lung disease; NTM, nontuberculous mycobacteriosis; R5, resistance at 5 Hz; R20, resistance at 20 Hz; Tbc, tuberculosis; VC, vital capacity; X5, reactance at 5 Hz.

Figure 1 Recruitment flowchart for study participants.

Table 2 Correlations between spirometry and MostGraph-01 data

Parameters	VC	%VC	FVC	%FVC	FEV1	%FEV1	FEV1/FVC
Development study
R5	−0.525*	−0.377*	−0.537*	−0.399*	−0.543*	−0.418*	−0.16*
R20	−0.478*	−0.28*	−0.488*	−0.303*	−0.465*	−0.31*	−0.089
X5	0.489*	0.565*	0.499*	0.577*	0.548*	0.594*	0.26*
Fres	−0.551*	−0.647*	−0.562*	−0.657*	−0.622*	−0.677*	−0.286*
ALX	−0.402*	−0.489*	−0.413*	−0.504*	−0.473*	−0.544*	−0.284*
Validation study
R5	−0.362*	−0.224*	−0.357*	−0.221*	−0.354*	−0.27*	−0.183*
R20	−0.337*	−0.186*	−0.33*	−0.178*	−0.329*	−0.23*	−0.176*
X5	0.544*	0.565*	0.557*	0.573*	0.602*	0.617*	0.423*
Fres	−0.633*	−0.682*	−0.648*	−0.689*	−0.716*	−0.746*	−0.509*
ALX	−0.497*	−0.525*	−0.511*	−0.535*	−0.565*	−0.591*	−0.435*

Note:

* P<0.001.

Abbreviations: ALX, low-frequency reactance area; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; Fres, resonant frequency; R5, resistance at 5 Hz; R20, resistance at 20 Hz; X5, reactance at 5 Hz; VC, vital capacity.

Table 3 Regression coefficients for parameters predictive of vital capacity

Parameters	Unstandardized coefficients		95% Cl		P-value
	β	SE	Low	High
Anthropometric parameters only
Age	−0.02	0.001	−0.023	−0.017	<0.001
Sex	0.382	0.056	0.273	0.491	<0.001
Height	0.047	0.003	0.040	0.053	<0.001
Body weight	0.004	0.002	0.00007	0.007	0.046
Anthropometric and FOT parameters
Age	−0.015	0.001	−0.017	−0.013	<0.001
Sex	0.539	0.044	0.453	0.624	<0.001
Height	0.026	0.003	0.021	0.031	<0.001
Body weight	0.007	0.001	0.004	0.01	<0.001
R5	0.268	0.047	0.175	0.361	<0.001
R20	−0.388	0.058	−0.502	−0.273	<0.001
X5	0.365	0.093	0.183	0.547	<0.001
Fres	−0.149	0.012	−0.172	−0.126	<0.001
ALX	0.062	0.008	0.045	0.078	<0.001

Abbreviations: ALX, low-frequency reactance area; FOT, forced-oscillation technique; Fres, resonant frequency; R5, resistance at 5 Hz; R20, resistance at 20 Hz; SE, standard error; X5, reactance at 5 Hz.

Table 4 Regression coefficients for parameters predictive of forced vital capacity

Parameters	Unstandardized coefficients		95% Cl		P-value
	β	SE	Low	High
Anthropometric parameters only
Age	−0.021	0.001	−0.024	−0.018	<0.001
Sex	0.371	0.057	0.26	0.482	<0.001
Height	0.048	0.003	0.041	0.054	<0.001
Body weight	0.003	0.002	−0.001	0.007	0.148
Anthropometric and FOT parameters
Age	−0.016	0.001	−0.018	−0.014	<0.001
Sex	0.526	0.044	0.44	0.613	<0.001
Height	0.026	0.003	0.021	0.032	<0.001
Body weight	0.006	0.001	0.003	0.009	<0.001
R5	0.269	0.048	0.175	0.363	<0.001
R20	−0.403	0.059	−0.518	−0.287	<0.001
X5	0.325	0.094	0.141	0.508	<0.05
Fres	−0.154	0.012	−0.178	−0.131	<0.001
ALX	0.058	0.008	0.042	0.075	<0.001

Abbreviations: ALX, low-frequency reactance area; FOT, forced-oscillation technique; Fres, resonant frequency; R5, resistance at 5 Hz; R20, resistance at 20 Hz; SE, standard error; X5, reactance at 5 Hz.

Table 5 Regression coefficients for parameters predictive of forced expiratory volume in 1 second

Parameters	Unstandardized coefficients		95% Cl		P-value
	β	SE	Low	High
Anthropometric parameters only
Age	−0.026	0.001	−0.028	−0.023	<0.001
Sex	0.207	0.049	0.111	0.303	<0.001
Height	0.03	0.003	0.024	0.036	<0.001
Body weight	0.001	0.002	−0.002	0.005	0.382
Anthropometric and FOT parameters
Age	−0.021	0.001	−0.023	−0.019	<0.001
Sex	0.318	0.038	0.244	0.392	<0.001
Height	0.011	0.002	0.007	0.016	<0.001
Body weight	0.004	0.001	0.002	0.007	<0.05
R5	0.157	0.041	0.077	0.237	<0.001
R20	−0.306	0.05	−0.405	−0.208	<0.001
X5	0.012	0.08	−0.145	0.169	0.88
Fres	−0.135	0.01	−0.155	−0.115	<0.001
ALX	0.022	0.007	0.008	0.036	<0.05

Abbreviations: ALX, low-frequency reactance area; FOT, forced-oscillation technique; Fres, resonant frequency; R5, resistance at 5 Hz; R20, resistance at 20 Hz; SE, standard error; X5, reactance at 5 Hz.

Table 6 Correlations between actual and estimated data, and performance of estimation equations

		r (95% Cl)	P-value	Bias (95% Cl)	RMSE
Development study
Equation 1$\begin{array}{l}\text{Estimated VC}=- 4.003-\text{age}\times 0.020+\text{sex}\times 0.382+\text{height}\times 0.047+\text{weight}\times 0.004\\ \text{Estimated FVC}=- 4.060-\text{age}\times 0.021+\text{sex}\times 0.371+\text{height}\times 0.048+\text{weight}\times 0.003\\ {\text{Estimated FEV}}_1=- 1.413-\text{age}\times 0.026+\text{sex}\times 0.207+\text{height}\times 0.030+\text{weight}\times 0.001\end{array}$Equation 1
VC	0.745 (0.717–0.77)		<0.001	0.075 (0.039–0.111)	0.606
FVC	0.741 (0.713–0.767)		<0.001	0.058 (0.021–0.094)	0.614
FEV1	0.711 (0.68–0.739)		<0.001	−0.095 (−0.126, −0.063)	0.537
Equation 2$\begin{array}{c}\text{Estimated VC}=- 0.011-\text{age}\times 0.015+\text{sex}\times 0.539\\ +\text{height}\times 0.026+\text{weight}\times 0.007\\ +\mathrm{R}5\times 0.268-\mathrm{R}20\times 0.388+\mathrm{X}5\\ \times 0.365-\text{Fres}\times 0.149+\text{ALX}\times 0.062\\ \text{Estimated FVC}=0.112-\text{age}\times 0.016+\text{sex}\times 0.526\\ +\text{height}\times 0.026+\text{weight}\times 0.006\\ +\mathrm{R}5\times 0.269-\mathrm{R}20\times 0.403+\mathrm{X}5\\ \times 0.325-\text{Fres}\times 0.154+\text{ALX}\times 0.058\\ {\text{Estimated FEV}}_1=2.410-\text{age}\times 0.021+\text{sex}\times 0.318\\ +\text{height}\times 0.011+\text{weight}\times 0.004\\ +\mathrm{R}5\times 0.157-\mathrm{R}20\times 0.306+\mathrm{X}5\\ \times 0.012-\text{Fres}\times 0.135+\text{ALX}\times 0.022\end{array}$Equation 2
VC	0.867 (0.851–0.881)		<0.001	0.007 (−0.02–0.034)	0.45
FVC	0.867 (0.851–0.881)		<0.001	−0.064 (−0.091, −0.037)	0.458
FEV1	0.857 (0.84–0.872)		<0.001	−0.039 (−0.062, −0.016)	0.389
Validation study
VC	0.891 (0.872–0.907)		<0.001	−0.201 (−0.236, −0.167)	0.457
FVC	0.889 (0.87–0.905)		<0.001	−0.262 (−0.3, −0.227)	0.5
FEV1	0.897 (0.879–0.912)		<0.001	−0.174 (−0.205, −0.142)	0.411

Note: Bias (estimated data – actual data) expressed as means and 95% CIs.

Abbreviations: FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; RMSE, root-mean-square error; VC, vital capacity.

Figure 2 Correlations between actual and estimated VC, FVC, and FEV₁ in the development and validation study.

Notes: Estimated data obtained using equation 1$\begin{array}{l}\text{Estimated VC}=- 4.003-\text{age}\times 0.020+\text{sex}\times 0.382+\text{height}\times 0.047+\text{weight}\times 0.004\\ \text{Estimated FVC}=- 4.060-\text{age}\times 0.021+\text{sex}\times 0.371+\text{height}\times 0.048+\text{weight}\times 0.003\\ {\text{Estimated FEV}}_1=- 1.413-\text{age}\times 0.026+\text{sex}\times 0.207+\text{height}\times 0.030+\text{weight}\times 0.001\end{array}$Equation 1 (A–C) and equation 2$\begin{array}{c}\text{Estimated VC}=- 0.011-\text{age}\times 0.015+\text{sex}\times 0.539\\ +\text{height}\times 0.026+\text{weight}\times 0.007\\ +\mathrm{R}5\times 0.268-\mathrm{R}20\times 0.388+\mathrm{X}5\\ \times 0.365-\text{Fres}\times 0.149+\text{ALX}\times 0.062\\ \text{Estimated FVC}=0.112-\text{age}\times 0.016+\text{sex}\times 0.526\\ +\text{height}\times 0.026+\text{weight}\times 0.006\\ +\mathrm{R}5\times 0.269-\mathrm{R}20\times 0.403+\mathrm{X}5\\ \times 0.325-\text{Fres}\times 0.154+\text{ALX}\times 0.058\\ {\text{Estimated FEV}}_1=2.410-\text{age}\times 0.021+\text{sex}\times 0.318\\ +\text{height}\times 0.011+\text{weight}\times 0.004\\ +\mathrm{R}5\times 0.157-\mathrm{R}20\times 0.306+\mathrm{X}5\\ \times 0.012-\text{Fres}\times 0.135+\text{ALX}\times 0.022\end{array}$Equation 2 (D–F) in the development study. Using equation 2$\begin{array}{c}\text{Estimated VC}=- 0.011-\text{age}\times 0.015+\text{sex}\times 0.539\\ +\text{height}\times 0.026+\text{weight}\times 0.007\\ +\mathrm{R}5\times 0.268-\mathrm{R}20\times 0.388+\mathrm{X}5\\ \times 0.365-\text{Fres}\times 0.149+\text{ALX}\times 0.062\\ \text{Estimated FVC}=0.112-\text{age}\times 0.016+\text{sex}\times 0.526\\ +\text{height}\times 0.026+\text{weight}\times 0.006\\ +\mathrm{R}5\times 0.269-\mathrm{R}20\times 0.403+\mathrm{X}5\\ \times 0.325-\text{Fres}\times 0.154+\text{ALX}\times 0.058\\ {\text{Estimated FEV}}_1=2.410-\text{age}\times 0.021+\text{sex}\times 0.318\\ +\text{height}\times 0.011+\text{weight}\times 0.004\\ +\mathrm{R}5\times 0.157-\mathrm{R}20\times 0.306+\mathrm{X}5\\ \times 0.012-\text{Fres}\times 0.135+\text{ALX}\times 0.022\end{array}$Equation 2 , we calculated estimated data in the validation data set (G–I).

Abbreviations: VC, vital capacity; FVC, forced VC; FEV₁, forced expiratory volume in 1 second.

Figure 3 Bland–Altman plot comparing actual and estimated VC, FVC, and FEV₁.

Notes: Estimated data obtained using equation 1$\begin{array}{l}\text{Estimated VC}=- 4.003-\text{age}\times 0.020+\text{sex}\times 0.382+\text{height}\times 0.047+\text{weight}\times 0.004\\ \text{Estimated FVC}=- 4.060-\text{age}\times 0.021+\text{sex}\times 0.371+\text{height}\times 0.048+\text{weight}\times 0.003\\ {\text{Estimated FEV}}_1=- 1.413-\text{age}\times 0.026+\text{sex}\times 0.207+\text{height}\times 0.030+\text{weight}\times 0.001\end{array}$Equation 1 (A–C) and equation 2$\begin{array}{c}\text{Estimated VC}=- 0.011-\text{age}\times 0.015+\text{sex}\times 0.539\\ +\text{height}\times 0.026+\text{weight}\times 0.007\\ +\mathrm{R}5\times 0.268-\mathrm{R}20\times 0.388+\mathrm{X}5\\ \times 0.365-\text{Fres}\times 0.149+\text{ALX}\times 0.062\\ \text{Estimated FVC}=0.112-\text{age}\times 0.016+\text{sex}\times 0.526\\ +\text{height}\times 0.026+\text{weight}\times 0.006\\ +\mathrm{R}5\times 0.269-\mathrm{R}20\times 0.403+\mathrm{X}5\\ \times 0.325-\text{Fres}\times 0.154+\text{ALX}\times 0.058\\ {\text{Estimated FEV}}_1=2.410-\text{age}\times 0.021+\text{sex}\times 0.318\\ +\text{height}\times 0.011+\text{weight}\times 0.004\\ +\mathrm{R}5\times 0.157-\mathrm{R}20\times 0.306+\mathrm{X}5\\ \times 0.012-\text{Fres}\times 0.135+\text{ALX}\times 0.022\end{array}$Equation 2 (D–F) in the development study. Using equation 2$\begin{array}{c}\text{Estimated VC}=- 0.011-\text{age}\times 0.015+\text{sex}\times 0.539\\ +\text{height}\times 0.026+\text{weight}\times 0.007\\ +\mathrm{R}5\times 0.268-\mathrm{R}20\times 0.388+\mathrm{X}5\\ \times 0.365-\text{Fres}\times 0.149+\text{ALX}\times 0.062\\ \text{Estimated FVC}=0.112-\text{age}\times 0.016+\text{sex}\times 0.526\\ +\text{height}\times 0.026+\text{weight}\times 0.006\\ +\mathrm{R}5\times 0.269-\mathrm{R}20\times 0.403+\mathrm{X}5\\ \times 0.325-\text{Fres}\times 0.154+\text{ALX}\times 0.058\\ {\text{Estimated FEV}}_1=2.410-\text{age}\times 0.021+\text{sex}\times 0.318\\ +\text{height}\times 0.011+\text{weight}\times 0.004\\ +\mathrm{R}5\times 0.157-\mathrm{R}20\times 0.306+\mathrm{X}5\\ \times 0.012-\text{Fres}\times 0.135+\text{ALX}\times 0.022\end{array}$Equation 2 , we calculated estimated data in the validation data set (G–I). Bias of equations expressed as mean difference between estimated data and actual data (estimated data – actual data).
Abbreviations: VC, vital capacity; FVC, forced VC; FEV₁, forced expiratory volume in 1 second.