Eighty-eight patients and forty controls had complete data (Figure 1). Five patients and two controls were removed from the analysis. Two patients and two controls did not wear the monitor for seven days and therefore were excluded. Three patients returned the monitor after 14 days and the batteries of the monitors were dead and we could not retrieve the data after charging the monitors. The patients and controls were similar in age, gender proportion and BMI. The patients had poorer lung function (FEV1, FVC and their ratio), lower resting oxygen saturations and greater tobacco exposure than the control group (all p<0.001) (Table 1). The severity of airflow obstruction by GOLD stratification (Table 2). The distribution of the modified MRC breathlessness score was: mMRC 0 n=11, mMRC 1 n= 34, mMRC 2= 17, mMRC 3 n=18 and mMRC 4 n=8. The patients were also classified according to GOLD quadrants based on CAT score (Table 2).
Measures of daily physical activity
The DPA was lower in the patients, mean (SD), 4095 (2720) steps than controls 6734 (3491) steps, p<0.001, however, there was no difference in DPA for males and females in either group, p>0.05. The DPA was not related to age in either patients or controls. Using the minimum recommended level of DPA of 5000 steps/day, only 31% of the patients had reached the recommended amount of physical activity; while in contrast, 73% of the controls met the minimum amount of the DPA.
[Figure 1]
Table 1: Physical and Clinical Characteristics of patients with COPD and Controls.
|
COPD
(n= 88)
|
Comparator
(n= 40)
|
p
|
Gender Male: female
|
46:42
|
19:21
|
0.117
|
Age (years)
|
66 (8)
|
66 (7)
|
0.923
|
Smoking (pack years)
|
42.2 (24.8)
|
22.9 (20.8)
|
0.001
|
FEV1 (L)
|
1.5 (0.8)
|
2.6 (0.6)
|
0.001
|
FVC (L)
|
2.4 (0.9)
|
3.4 (0.9)
|
0.001
|
FEV1/FVC
|
0.52 (0.1)
|
0.78 (0.05)
|
0.001
|
FEV1 (%)
|
56 (17)
|
106 (17)
|
0.001
|
FVC (%)
|
84 (19)
|
112 (17)
|
0.001
|
Resting O2 saturation (%)
|
96 (2)
|
98 (1)
|
0.001
|
BMI (kg/m2)
|
27.5 (5.2)
|
28.6 (4.9)
|
0.297
|
Waist:Hip ratio
|
0.95 (0.09)
|
0.89 (0.06)
|
0.002
|
FFM (kg)
|
49.5 (10.5)
|
50.9 (9.1)
|
0.486
|
FM (kg)
|
24.8 (9.9)
|
27.2 (10.3)
|
0.243
|
FFM/FM
|
2.3 (1.1)
|
2.2 (1.1)
|
0.556
|
FFMI (kg/m2)
|
18.2 (2.4)
|
18.5 (2.1)
|
0.589
|
FMI (kg/m2)
|
9.3 (3.9)
|
10.1 (4.3)
|
0.3
|
6MWD (m)
|
336 (107)
|
515 (88)
|
0.001
|
Mean handgrip (kg)
|
27.2 (9.6)
|
29.7 (10.2)
|
0.209
|
Fibrinogen (g/l) #
|
3.8 (1.3)
|
3.2 (0.6)
|
0.012
|
HsCRP (mg/l)#
|
3.3 (3.1)
|
1.6 (3.2)
|
0.023
|
No. Steps
|
4095 (2720)
|
6734 (3491)
|
0.001
|
Time spent on moderate activity (hr)*
|
1.3 (0.5-2.2)
|
1.3 (0.7-2.1)
|
0.662
|
No. Comorbidity
|
1.3 (1.2)
|
0.8 (0.8)
|
0.027
|
All data mean (SD) unless otherwise indicated *Median (range) # Geometric mean. Abbreviations: 6MWD= six minute walk distance; BMI = body mass index; FEV1 = forced expiratory volume in 1 second; FVC = forced vital capacity; FFM= fat free mass; FFMI= fat free mass index; FM= fat mass; FMI= fat mass index; HsCRP= high sensitivity C- reactive protein.
Table 2: Distribution of Patients with COPD according to GOLD classifications and Quadrants
GOLD Classification
|
Patients Number
|
GOLD Quadrants
|
Patients Number
|
GOLD I
|
9
|
GOLD A
|
8
|
GOLD II
|
50
|
GOLD B
|
24
|
GOLD III
|
25
|
GOLD C
|
10
|
GOLD IV
|
4
|
GOLD D
|
46
|
The DPA related to FEV1% predicted (r= 0.39, p<0.001), oxygen saturation (rs= 0.29, p=0.012) and mMRC dyspnoea score (r= -0.45, p< 0.001), in the patients. Only was FEV1% predicted related to DPA in the controls, r=0.39, p=0.017.
Daily physical activity and Disease severity
Level of DPA differed across the GOLD categories, between GOLD 1 and GOLD 4, p=0.004 (Figure 2). Patients with an FEV1>50% had greater level of DPA, lower exacerbation rate, breathlessness score and CAT score than patients with an FEV1<50%, p<0.001. There was an association between level of DPA and BODE index, p<0.001. Patients with BODE score of ≥6 walked less significantly than patients with a lower score, p<0.001 (Figure 3).
[Figure 2]
Daily physical activity and body composition and physical function
There was no relationship between body composition parameters and DPA in the patients or control group. However, in the patients, the time spent undertaking moderate activity was related to BMI, r=-0.39, FM, r=-0.37, FFM:FM, r=0.50, all p<0.001. Similar relationships were evident in the control group, all p<0.05.
The 6MWD and HGS were less in patients than controls, both p<0.001 (Table 1). In the patients, the level of daily of daily physical activity was related to the 6MWD, r=0.45, p=0.001, and controls, r=0.49, p=0.002, but it was not related to HGS, p>0.05. The 6MWD and HGS were all related to each other in the patients, p<0.01.
[Figure 3]
Daily physical activity and aortic stiffness
In the patients, the time spent undertaking moderate activity was related to aortic stiffness (rs=-0.28, p<0.01), resting oxygen saturation (rs=-0.38, p<0.002). This was not evident in controls. Aortic stiffness was greater in patients, 9.5 (2.2), than controls, 8.2 (1.4),p<0.01.
Patient reported outcomes
The level of DPA and the SGRQ total score were related (r=-0.38, p<0.001), as was the SGRQ activity domain (r=-0.40, p<0.001). The CAT score was also related to the level DPA (r=-0.34, p=0.003). The 6MWD also related to the total SGRQ score, r=-0.63, and the CAT score r=-0.54, (all p<0.001).
Of the patients, 41 reported 0-1 exacerbations/ year and 47 reported two or more exacerbations/ year. The level of DPA was related to the frequency of exacerbations r=-0.34, p<0.001, and frequent exacerbators, 3348 (2221) steps, had lower physical activity of daily living than infrequent exacerbators, 5094 (3027) steps.
Systemic inflammation
Circulating CRP and fibrinogen were greater in patients than controls (p<0.001) and both were related to the level of DPA, CRP, rs =-0.29, p=0.013, and fibrinogen, r=-0.30, p=0.009, but were unrelated to the level of DPA in the control group.
Predictive factors for the daily physical activity.
In the patients, a stepwise multivariate regression analysis including DPA as a dependent variable and FEV1%, mMRC and the number of exacerbations as the independent variables showed that mMRC and number of exacerbations explained 28% of the variability in the DPA with FEV1% predicted excluded from the analysis, adjusted R2=0.28,p<0.001. The mMRC and the number of exacerbations explained 34% and 25% of the reduction in the DPA, respectively.