Evaluation of isokinetic muscle strength of upper limb and the relationship with pulmonary function and respiratory muscle strength in stable COPD patients

Figures & data

Table 1 The formula to calculate the predicted value of FEV1

Indicators	Gender	Formula
FEV1	Male	0.043*(height*100)-0.029*age-2.49
	Female	0.0395*(height*100)-0.025*age-2.6

Notes: Height was expressed as meter.

Abbreviation: FEV1, forced expiratory volume in 1 second.

Table 2 Patient demographics

Variables	Overall (n=88)
Age, years	65.5±8.7
Sex (M/F), n	64/24
BMI, kg/m^2	22.8 (20.3–25.3)
Duration of disease, years	11.5 (10–14)
Pulmonary function
FEV1%pred, %	57.18±17.51
FEV1/FVC, %	60.58 (51.24–67.39)
Respiratory muscle strength
MIP, kPa	4.15 (3.6–4.96)
MEP, kPa	4.92±1.47
Isokinetic muscle strength
Extensor PT, Nm	38.85±9.89
Flexor PT, Nm	38.43±8.45
Extensor PT/BW, Nm/kg	0.59 (0.52–0.7)
Flexor PT/BW, Nm/kg	0.59 (0.51–0.69)
Extensor TW, J	380.05 (304.78–436)
Flexor TW, J	347.5 (291.23–415.4)
Extensor ER	0.67 (0.61–0.74)
Flexor ER	0.7±0.12

Notes: Data are expressed in the form of mean±SD or median (IQR 25–75) or n as appropriate.

Abbreviations: BMI, body mass index; BW, body weight; ER, endurance ratio; F, female; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; M, male; MIP, maximal inspiratory pressure; MEP, maximal expiratory pressure; PT, peak torque; TW, total work.

Table 3 Relationship between pulmonary function and other variables

Variables	FEV1%pred, %		FEV1/FVC, %
	r	P-value	r	P-value
Age, years	−0.07	0.51	0.021	0.845
Sex, M/F	0.505	<0.001	0.35	0.001
BMI, kg/kg^2	0.188	0.079	0.224	0.036
Duration, years	−0.071	0.513	0.139	0.195
MIP, kPa	0.06	0.58	0.134	0.215
MEP, kPa	−0.175	0.102	0.02	0.854
Extensor PT, Nm	−0.153	0.155	−0.005	0.966
Flexor PT, Nm	−0.073	0.502	−0.176	0.101
Extensor PT/BW, Nm/kg^2	−0.24	0.024	−0.23	0.031
Flexor PT/BW, Nm/kg^2	−0.249	0.019	−0.435	<0.001
Extensor TW, J	−0.048	0.655	0.101	0.35
Flexor TW, J	−0.08	0.45	−0.051	0.635
Extensor ER	0.145	0.179	0.183	0.088
Flexor ER	0.107	0.321	0.232	0.029

Notes: Relationships were calculated by Pearson or Spearman coefficients analysis as appropriate. The degree of significance was set at P<0.05.

Abbreviations: BMI, body mass index; BW, body weight; ER, endurance ratio; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; MIP, maximal inspiratory pressure; MEP, maximal expiratory pressure; PT, peak torque; TW, total work.

Table 4 Results of multivariate stepwise regression analysis of the FEV1%pred and the independent determinants taking into account covariates

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	32.224 (22.451–41.997)
Sex	19.609 (12.361–26.857)	0.502	<0.001	1
Adjusted R^2=0.243

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT/BW, Flexor PT/BW. Covariates: sex.

Abbreviations: β, regression coefficient; BW, body weight; CI, confidence interval; FEV1, forced expiratory volume in the first second; PT, peak torque.

Table 5 Results of multivariate stepwise regression analysis of the FEV1/FVC and the independent determinants

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	57.443 (37.417–77.469)
Flexor PT/BW	−36.6 (−57.919–−15.281)	−0.336	0.001	1.007
Flexor ER	34.015 (10.891–57.14)	0.288	0.004	1.007
Adjusted R^2=0.161

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT/BW, Flexor PT/BW, Flexor ER.

Abbreviations: β, regression coefficient; BW, body weight; CI, confidence interval; ER, endurance ratio; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; PT, peak torque.

Table 6 Results of multivariate stepwise regression analysis of the FEV1/FVC and the independent determinants taking into account covariates

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	12.184 (−20.67–45.038)
Flexor PT/BW	−19.19 (−41.514–3.134)	−0.176	0.091	1.243
Flexor ER	35.988 (14.128–57.847)	0.305	0.002	1.013
Sex	8.946 (2.924–14.968)	0.292	0.004	1.14
BMI	0.951 (0.142–1.76)	0.228	0.022	1.109
Adjusted R^2=0.255

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT/BW, Flexor PT/BW, Flexor ER. Covariates: sex, BMI.

Abbreviations: β, regression coefficient; BMI, body mass index; BW, body weight; CI, confidence interval; ER, endurance ratio; FEV1, forced expiratory volume in the first second; FVC, forced vital capacity; PT, peak torque.

Table 7 Relationship between respiratory muscle strength and other variables

Variables	MIP, kPa		MEP, kPa
	r	P-value	r	P-value
Age, years	0.297	0.005	−0.13	0.224
Sex, M/F	−0.173	0.05	−0.389	<0.001
BMI, kg/kg^2	0.099	0.358	0.338	0.001
Duration, years	−0.107	0.32	−0.028	0.793
Extensor PT, Nm	0.427	<0.001	0.558	<0.001
Flexor PT, Nm	0.361	0.001	0.421	<0.001
Extensor PT/BW, Nm/kg^2	0.301	0.004	0.225	0.035
Flexor PT/BW, Nm/kg^2	0.217	0.042	0.07	0.517
Extensor TW, J	0.427	<0.001	0.352	0.001
Flexor TW, J	0.471	<0.001	0.285	0.007
Extensor ER	0.198	0.065	−0.158	0.141
Flexor ER	0.26	0.014	0.039	0.716

Notes: Relationships were calculated by Pearson or Spearman or Kendall’s tau-b coefficients analysis as appropriate. The degree of significance was set at P<0.05.

Abbreviations: BMI, body mass index; BW, body weight; ER, endurance ratio; MIP, maximal inspiratory pressure; MEP, maximal expiratory pressure; PT, peak torque; TW, total work.

Table 8 Results of multivariate stepwise regression analysis of the MIP and the independent determinants taking into account covariates

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	2.852 (1.938–3.766)
Flexor TW, J	0.004 (0.002–0.007)	0.349	0.001	1
Adjusted R^2=0.112

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT, Flexor PT, Extensor PT/BW, Flexor PT/BW, Extensor TW, Flexor TW, Flexor ER. Covariates: age.

Abbreviations: β, regression coefficient; BW, body weight; CI, confidence interval; ER, endurance ratio; MIP, maximal inspiratory pressure; PT, peak torque; TW, total work.

Table 9 Results of multivariate stepwise regression analysis of the MEP and the independent determinants

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	2.324 (1.137–3.511)
Extensor PT, Nm	0.117 (0.077–0.156)	0.782	<0.001	2.352
Extensor PT/BW, Nm/kg^2	−3.163 (−6.015–−0.312)	−0.296	0.033	2.352
Adjusted R^2=0.333

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT, Flexor PT, Extensor PT/BW, Extensor TW, Flexor TW.

Abbreviations: β, regression coefficient; BW, body weight; CI, confidence interval; MEP, maximal expiratory pressure; PT, peak torque; TW, total work.

Table 10 Results of multivariate stepwise regression analysis of the MEP and the independent determinants taking into account covariates

Variables	Coefficient (95% CI)	Standardized β	P-value	VIF
Intercept	4.183 (2.463–5.902)
Extensor PT, Nm	0.095 (0.054–0.136)	0.64	<0.001	2.699
Extensor PT/BW, Nm/kg^2	−2.981 (−5.722–−0.24)	−0.279	0.033	2.357
Sex	−0.902 (−1.526–−0.277)	−0.274	0.005	1.289
Adjusted R^2=0.385

Notes: The degree of significance was set at P<0.05. Independent determinants: Extensor PT, Flexor PT, Extensor PT/BW, Extensor TW, Flexor TW. Covariates: sex, BMI.

Abbreviations: β, regression coefficient; BMI, body mass index; BW, body weight; CI, confidence interval; MEP, maximal expiratory pressure; PT, peak torque; TW, total work.