Reference Equations for Assessing the Physical Activity of Japanese Patients with Chronic Obstructive Pulmonary Disease

Figures & data

Figure 1 Flow diagram.

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

Table 1 Characteristics

Age (years)	73.1 ± 6.7
Gender [M/F]	213/14
Height (cm)	163.6 ± 6.7
Weight (kg)	60.2 ± 10.2
BMI (kg/m^2)	22.5 ± 3.4
Smoking
[non/ex/curr]	5/187/35
(Pack·Year)	64.2 ± 66.5
COPD stage [I/II/III/IV]	54/110/48/15
Treatment [yes/no]	207/21
[LAMA/LABA/ICS/Theo/Muco/Other]	175/154/63/3/22/62
Pulmonary Rehabilitation [yes/no]	15/212
Comorbidity [yes/no]	168/59
Pulmonary function
IC (L)	2.22 ± 0.56
FVC (L)	3.28 ± 0.78
FVC % pred (%)	99.6 ± 19.5
FEV1 (L)	1.64 ± 0.60
FEV1/FVC (%)	49.7 ± 13.2
FEV1% pred (%)	62.7 ± 20.9
mMRC	1.2 ± 0.9
6-minute walk test
Distance (m)	390.0 ± 102.6
Lowest SpO2 (%)	89.2 ± 5.1
Grip strength (kgf)	31.8 ± 7.4
Blood tests
Fasting plasma glucose (mg/dL)	109.1 ± 25.9
Hemoglobin A1c (%)	6.0 ± 0.6
Red blood cells (×10^4/μL)	473.1 ± 55.0
Hemoglobin (g/dL)	14.7 ± 1.5
Brain Natriuretic Peptide (pg/mL)	36.0 ± 46.1
Albumin (g/dL)	4.2 ± 0.3
Nutrition
Upper arm circumference (cm)	26.8 ± 3.2
Subcutaneous fat thickness of triceps brachii (cm)	1.34 ± 0.76
Anxiety score of HADS	3.3 ± 2.6
Depression score of HADS	4.3 ± 3.1
Physical activity
Duration at ≥3.0 METs (min)	60.3 ± 36.4
Duration at ≥2.0 METs (min)	223.8 ± 93.1
Total activity at ≥3.0 METs (METs∙h)	3.31 ± 2.12
Step count (steps)	4350.2 ± 2845.8

Abbreviations: BMI, body mass index; LAMA, long-acting muscarinic antagonist; LABA, long-acting beta 2 adrenergic agonist; ICS, inhaled corticosteroid; Theo, theophylline; Muco, mucolytic agent; IC, inspiratory capacity; FVC, forced vital capacity; FEV1, forced expiratory volume in one second; %pred, % of predicted value; mMRC, modified Medical Research Council; HADS, Hospital Anxiety and Depression Scale, METs, metabolic equivalents.

Table 2 Simple Regression Analysis Results

	Duration at ≥2.0 METs		Duration at ≥3.0 METs		Total Activity at ≥3.0 METs		Step Count
	r	p	r	p	r	p	r	p
Age (years)	−0.131	0.049	−0.194	0.003	−0.197	0.003	−0.208	0.002
Gender [M/F]	−0.157	0.018	−0.073	0.275	−0.064	0.336	−0.002	0.976
Height (cm)	−0.149	0.025	−0.039	0.561	−0.031	0.639	0.086	0.195
Weight (kg)	0.010	0.876	0.094	0.160	0.094	0.156	0.056	0.403
BMI (kg/m^2)	0.102	0.126	0.134	0.044	0.131	0.049	0.029	0.668
Smoking [non/ex/curr]	0.002	0.980	0.022	0.739	0.029	0.662	−0.039	0.559
Smoking (Pack·Year)	−0.085	0.208	−0.006	0.927	−0.004	0.956	0.069	0.308
IC (L)	0.122	0.066	0.210	0.002	0.212	0.001	0.195	0.003
FVC %pred (%)	0.193	0.219	0.248	<0.001	0.245	<0.001	0.247	<0.001
FEV1/FVC	0.303	<0.001	0.311	<0.001	0.306	<0.001	0.236	<0.001
FEV1 %pred (%)	0.335	<0.001	0.370	<0.001	0.365	<0.001	0.315	<0.001
6MWD (m)	0.278	<0.001	0.411	<0.001	0.407	<0.001	0.393	<0.001
Lowest SpO2 during 6-minute walk test (%)	0.154	0.021	0.196	0.003	0.198	0.003	0.176	0.008
Upper arm circumference (cm)	0.134	0.044	0.155	0.019	0.157	0.018	0.104	0.117
Subcutaneous fat thickness of triceps brachii (cm)	−0.017	0.796	−0.058	0.381	−0.057	0.390	−0.130	0.051
Grip strength (kgf)	0.116	0.081	0.136	0.041	0.128	0.054	0.150	0.024
Fasting plasma glucose (mg/dL)	−0.037	0.575	0.058	0.385	0.076	0.253	0.004	0.958
Hemoglobin A1c (%)	−0.042	0.531	0.016	0.806	0.037	0.579	−0.014	0.839
Red blood cells (×10^4/mL)	−0.048	0.474	−0.059	0.377	−0.054	0.420	−0.059	0.379
Hemoglobin (g/dL)	−0.097	0.146	−0.063	0.343	−0.060	0.371	−0.051	0.443
Brain Natriuretic Peptide (pg/mL)	−0.065	0.330	−0.148	0.026	−0.152	0.022	−0.049	0.467
Albumin (g/dL)	0.117	0.078	0.122	0.066	0.124	0.062	0.112	0.094
Anxiety score of HADS	0.163	0.014	0.142	0.033	0.148	0.026	0.156	0.019
Depression score of HADS	−0.039	0.563	−0.042	0.533	−0.039	0.557	−0.017	0.796
mMRC	−0.314	<0.001	−0.392	<0.001	−0.377	<0.001	−0.323	<0.001
Treatment [yes/no]	−0.164	0.014	−0.212	0.001	−0.205	0.002	−0.216	0.001
Rehabilitation [yes/no]	−0.125	0.060	−0.091	0.173	−0.096	0.150	0.031	0.647
Comorbidity [yes/no]	−0.002	0.980	0.022	0.739	0.029	0.662	−0.003	0.967

Abbreviations: BMI, body mass index; LAMA, long-acting muscarinic antagonist; LABA, long-acting beta 2 adrenergic agonist; ICS, inhaled corticosteroid; Theo, theophylline; Muco, mucolytic agent; IC, inspiratory capacity; FVC, forced vital capacity; FEV1, forced expiratory volume in 1 second; %pred, % of predicted value; 6MWD, 6-minute walk distance; HADS, Hospital Anxiety and Depression Scale; mMRC, modified Medical Research Council, METs, metabolic equivalents.

Table 3 Multiple Regression Analysis Results

	Duration at ≥2.0 METs		Duration at ≥3.0 METs		Total Activity at ≥3.0 METs		Step Count
	β	p	β	p	β	p	β	p
6MWD	0.187	0.010	0.241	0.001	0.250	0.001	0.299	<0.001
mMRC	−0.210	0.005	−0.239	0.001	−0.211	0.005	−0.153	0.043
HADS-A	0.148	0.019	0.119	0.047	0.142	0.020	0.156	0.012
FEV1 %pred	0.171	0.028	0.766	0.047	–	–	–	–
Age	–	–	−0.190	0.008	–	–	–	–
BNP	–	–	–	–	−0.142	0.018	–	–

Abbreviations: METs, metabolic equivalents; 6MWD, 6-minute walking distance; mMRC, modified Medical Research Council; HADS-A, anxiety score of Hospital Anxiety and Depression Scale; FEV1 %pred, forced expiratory volume in 1 second % of predicted value; BNP, brain natriuretic peptide.

Table 4 Factors Detected by the Stepwise Method

	Duration at ≥2.0 METs		Duration at ≥3.0 METs		Total Activity at ≥3.0 METs		Step Count
	β	p	β	p	β	p	β	p
6MWD	0.139	0.044	0.221	0.001	0.240	<0.001	0.295	<0.001
mMRC	−0.199	0.007	−0.256	<0.001	−0.240	<0.001	−0.180	0.011
HADS-A	0.178	0.004	0.127	0.026	0.141	0.013	0.119	0.047
FEV1 %pred	0.213	0.002	0.245	<0.001	0.242	<0.001	0.175	0.008
Age	–	–	−0.132	0.020	–	–	–	–
BNP	–	–	–	–	−0.127	0.022	–	–

Abbreviations: METs, metabolic equivalents; 6MWD, 6-minute walking distance; mMRC, modified Medical Research Council; HADS-A, anxiety score of Hospital Anxiety and Depression Scale; FEV1 %pred, forced expiratory volume in 1 second % of predicted value; BNP, brain natriuretic peptide.

Figure 2 Reference equations of physical activity. METs, metabolic equivalents. Units: Duration at ≥2.0 METs (min), Duration at ≥3.0 METs (min), Total activity at ≥3.0 METs (METs∙h), Step count (steps), 6MWD (m), mMRC (point), HADS-A (point), FEV1 %pred (%), age (years old), BNP (pg/mL).

Figure 3 Relationships between the measured and predictive values. (A) duration at ≥2.0 METs; r=0.462, P<0.0001, (B) duration at ≥3.0 METs; r=0.598, P<0.0001, (C) total activity at ≥3.0 METs; r=0.614, P<0.0001, (D) Step count; r=0.539, P<0.0001.

Abbreviation: METs, metabolic equivalents.

Figure 4 Bland-Altman Plots. (A) duration at ≥2.0 METs, (B) duration at ≥3.0 METs, (C) total activity at ≥3.0 METs, (D) Step count.

Abbreviation: METs, metabolic equivalents.

Figure 5 Bland-Altman Plots after excluding highly active patients. (A) duration at ≥2.0 METs (patients with <231 minutes of measured value), (B) duration at ≥3.0 METs (patients with <87 minutes of measured value), (C) total activity at ≥3.0 METs (patients with <4.4 METs∙h of measured value), (D) Step count (patients with <5108 steps of measured value).

Abbreviation: METs, metabolic equivalents.