Comparison of impedance measured by the forced oscillation technique and pulmonary functions, including static lung compliance, in obstructive and interstitial lung disease

Figures & data

Figure 1 Sigmoidal regression analysis fitted to the data and calculation of static lung compliance in one healthy subject.

Notes: The regression analysis was performed using a sigmoidal equation of the form, V = a + b [1+ e^–(P–c)/d]^–1, a corresponds to the volume of a lower asymptote, b to the volume difference between upper and lower asymptotes, c to the pressure at the inflection point of the sigmoidal curve, and d to the proportional to the pressure range within which most of the volume change takes place. The static lung compliance (Cst) was calculated as the slope between resting expiratory level (FRC level) and 500-mL inspiratory level.
Abbreviations: FRC, functional residual capacity; Ptp, transpulmonary pressure; Cst, static lung compliance.

Table 1 Characteristics and the results of pulmonary function test of healthy subjects and patients with obstructive lung disease and interstitial lung disease

	HS	OLD	ILD
Number	23	18	11
Age, years	61.5±2.9	75.9±1.9 **	68.3±3.2
Sex, male/female	23/0	18/0	10/1
Smoking history, pack·year	12.6±3.7	40.5±6.3 **	23.7±7.4
BMI, kg/m^2	23.4±0.5	21.0±0.5 **	22.3±2.2^†
VC, %	107.5±2.0	110.0±2.4	78.0±7.5**^††
FEV1, %	106.7±2.3	75.0±3.4 **	72.6±6.9 **
FEV1/FVC, %	81.3±1.4	55.0±2.8 **	76.7±2.9 ^††
FRC, %	102.1±2.9	103.1±3.6	80.0±5.1**^††
RV, %	126.8±5.1	158.3±10.0 *	108.6±5.7 *^††
TLC, %	120.3±3.5	131.7±4.6	87.9±5.5 **^††
RV/TLC, %	34.2±1.4	43.4±1.7 **	41.4±2.5 *
DLCO, %	99.5±3.2	65.4±6.2 **	53.8±4.9 **
DLCO/VA, %	118.5±4.3	76.1±7.0 **	93.1±7.3 **
ΔN2, %	1.03±0.11	3.80±0.48 **	7.12±3.19 **
Cst, L/cmH2O	0.24±0.02	0.27±0.03	0.09±0.02 **^††
Pes max, cmH2O	−22.8±1.5	−14.8±1.6 **	−24.2±5.1
Cdyn, L/cmH2O	0.14±0.01	0.15±0.01	0.07±0.01 **^††
RL, cmH2O/L/s	1.92±0.16	3.04±0.39 **	5.32±1.19 **
ΔRL, cmH2/L/s	1.29±0.29	1.63±0.28	3.94±1.15 **
C1/Cst,%	61.0±12.3	33.8±4.1 **	111.3±32.8^††

Notes: Values are means ± SEM. *P <0.05 and **P <0.01 vs HS, ^†<0.05 and ^††<0.01 vs OLD.

Abbreviations: HS, healthy subjects; OLD, obstructive lung diseases; ILD, interstitial lung disease; BMI, body mass index; VC, vital capacity; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; FRC, functional residual capacity; RV, residual volume; TLC, total lung capacity; DLCO, lung diffusion capacity of carbon monoxide; ΔN₂, N2 phase III slope of single-breath N2 washout; Cst, static compliance; Pes max, maximum difference between esophageal and oral pressure at the level of total lung capacity; Cdyn, dynamic compliance; R_L, lung resistance; ΔR_L, within-breath changes in R_L; C1, Cdyn during respiratory rate at 1 Hz; C1/Cst, an index of frequency dependency.

Figure 2 Percentage drop in Cdyn from Cst in accordance with the increased respiratory frequency in healthy subjects, patients with obstructive lung disease and interstitial lung disease.

Notes: In the HS group, the decreased of Cdyn was mild, but in OLD, the Cdyn was rapidly decreased from Cst. However, in patients with ILD, the Cdyn was decreased from Cst, withalmost no change even though the respiratory frequency was increased.
Abbreviations: Cdyn, dynamic lung compliance; Cst, static lung compliance; HS, healthy subjects; OLD, obstructive lung disease; ILD, interstitial lung disease.

Table 2 Results of respiratory impedance measured by the multifrequency forced oscillation technique in healthy subjects, patients with obstructive lung disease, and interstitial lung disease

	HS	OLD	ILD
Number	23	18	11
R5, cmH2O/L/s	1.72±0.18	2.22±0.19	3.08±0.51**
R20, cmH2O/L/s	1.50±0.14	1.71±0.11	2.22±0.29*
R5–R20, cmH2O/L/s	0.22±0.07	0.51±0.11 *	0.86±0.24**
X5, cmH2O/L/s	−0.30±0.04	−0.71±0.16 *	−1.52±0.48**
ƒres, Hz	7.37±0.42	10.37±1.00 **	14.17±1.89**
ΔR5, cmH2O/L/s	0.27±0.06	0.39±0.09	0.61±0.21
Δ(R5–R20), cmH2O/L/s	0.14±0.03	0.17±0.05	0.45±0.12**^†
ΔX5, cmH2O/L/s	0.06±0.03	−0.31±0.14 **	−0.11±0.10*

Notes: Values are means ± SEM. *P <0.05 and **P <0.01 vs HS, ^†<0.05 vs OLD.

Abbreviations: HS, healthy subjects; OLD, obstructive lung disease; ILD, interstitial lung disease; R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5–R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; ƒres, resonant frequency.

Table 3 Correlations between parameters of respiratory impedance and pulmonary function tests among healthy subjects and patients with obstructive lung disease and interstitial lung disease (total 53 subjects)

	R5	R5–R20	X5	ƒres	ΔR5	ΔX5
VC,%	−0.32*	−0.30*	0.51**	−0.51**	−0.15	−0.15
%FEV1, %	−0.50**	−0.53**	0.65**	−0.75**	−0.17	0.40**
FEV1/FVC, %	−0.28	−0.33*	0.25	−0.40**	−0.08	0.56**
DLCO, %	−0.37**	−0.48**	0.48**	−0.61**	−0.19	0.33*
FRC, %	−0.31*	−0.30*	0.28*	−0.32*	−0.22	0.03
ΔN2, %	0.59**	0.63**	−0.89**	0.77**	0.34*	−0.33*
Cst, L/cmH2O	−0.16	−0.16	0.27	−0.31*	0.03	−0.27
C1/Cst, %	0.18	0.11	−0.03	0.09	−0.02	0.20
RL, cmH2O/L/s	0.57**	0.59**	−0.80**	0.73**	0.22	−0.35*

Notes: *P <0.05 and **P <0.01.

Abbreviations: HS, healthy subjects; OLD, obstructive lung disease; ILD, interstitial lung disease; R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5 – R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; ƒres, resonant frequency; ΔR5 and ΔX5, within-breath changes in R5 and X5; VC, vital capacity; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; DLCO, lung diffusion capacity of carbon monoxide; ΔN₂, N2 phase III slope of single-breath N2 washout; Cst, static compliance; C1, Cdyn during respiratory rate at 1 Hz; C1/Cst, an index of frequency dependency; R_L, lung resistance.

Table 4 Correlations between parameters of respiratory impedance and pulmonary function tests in 18 patients with obstructive lung disease

	R5	R5–R20	X5	ƒres	ΔR5	ΔX5
VC, %	0.33	0.43	−0.42	0.29	−0.03	−0.47*
%FEV1, %	−0.42	−0.55*	0.66**	−0.80**	0.13	0.40
FEV1/FVC, %	−0.45	−0.61**	0.75**	−0.87**	0.14	0.55*
DLCO, %	−0.18	−0.44	0.38	−0.62**	−0.12	0.31
FRC, %	0.15	0.18	0.06	−0.24	−0.04	0.09
ΔN2, %	0.29	0.55*	−0.67**	0.82**	−0.27	−0.42
Cst, L/cmH2O	0.13	0.11	−0.15	−0.02	0.13	−0.35
C1/Cst, %	−0.17	−0.23	0.38	−0.24	0.12	0.46
RL, cmH2O/L/s	0.49*	0.60**	−0.65**	0.57*	0.06	−0.62**

Notes: *P <0.05 and **P <0.01.

Abbreviations: OLD, obstructive lung disease; R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5–R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; ƒres, resonant frequency; ΔR5 and ΔX5, within-breath changes in R5 and X5; VC, vital capacity; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; DLCO, lung diffusion capacity of carbon monoxide; FRC, functional residual capacity; ΔN₂, N2 phase III slope of single-breath N2 washout; Cst, static compliance; C1, Cdyn during respiratory rate at 1 Hz; C1/Cst, an index of frequency dependency; R_L, lung resistance.

Table 5 Correlations between parameters of respiratory impedance and pulmonary function tests in 11 patients with interstitial lung disease

	R5	R5–R20	X5	ƒres	ΔR5	ΔX5
VC,%	−0.19	−0.29	0.61*	−0.66**	0.10	−0.10
%FEV1, %	−0.40	−0.48	0.69*	−0.78**	0.06	0.00
FEV1/FVC, %	−0.50	−0.52	0.13	−0.26	−0.25	0.46
DLCO, %	−0.09	−0.20	0.38	−0.38	0.29	−0.27
FRC, %	−0.04	−0.18	0.06	−0.24	−0.10	0.20
ΔN2, %	0.64*	0.67*	−0.93**	0.84**	0.39	−0.53
Cst, L/cmH2O	−0.15	−0.18	0.30	−0.39	0.35	−0.17
C1/Cst, %	0.14	0.13	0.14	−0.00	−0.16	−0.05
RL, cmH2O/L/s	0.47	0.47	−0.77**	0.71*	0.10	−0.20

Notes: *P <0.05 and **P <0.01.

Abbreviations: ILD, interstitial lung disease; R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5–R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; ƒres, resonant frequency; ΔR5 and ΔX5, within-breath changes in R5 and X5; VC, vital capacity; FEV₁, forced expiratory volume in 1 second; FVC, forced vital capacity; DLCO, lung diffusion capacity of carbon monoxide; FRC, functional residual capacity; ΔN₂, N2 phase III slope of single-breath N2 washout; Cst, static compliance; C1, Cdyn during respiratory rate at 1 Hz; C1/Cst, an index of frequency dependency; R_L, lung resistance.

Figure 3 Relationships between lung resistance and R5–R20 (A) or X5 (C), and between static lung compliance and X5 (B) in obstructive lung disease. Hz.Abbreviations: R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5–R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; R_L, lung resistance; Cst, static lung compliance.

Figure 4 Relationships between static lung compliance and R5–R20 (A) or X5 (B), and between lung resistance and X5 (C) in interstitial lung disease. R5–R20: difference in resistance at oscillation of 5 Hz and 20 Hz; X5, reactance at oscillation of 5 Hz.

Abbreviations: R5, respiratory resistance at 5 Hz; R20, respiratory resistance at 20 Hz; R5 – R20, difference from R20 to R5; X5, respiratory reactance at 5 Hz; Cst, static compliance; R_L, lung resistance.