Distal Leg Muscle Function in Patients with COPD

Figures & data

Figure 1.  Custom-made ankle foot orthosis designed to measure dorsi and plantar flexors muscle force.

Table 1.  Subject characteristics.

	Controls (n = 15)	COPD (n = 15)
Age, yr	64 ± 4	65 ± 3
Gender (M/F)	(10/5)	(9/6)
Height, cm	167 ± 9	166 ± 8
Weight, kg	69 ± 8	70 ± 12
Body mass index, kg/m^2	25 ± 2	26 ± 4
Pack-years	16 ± 20	48 ± 37*
FEV1, L	3.19 ± 0.78	1.38 ± 0.49**
% predicted	118 ± 17	54 ± 19**
FVC, L	4.19 ± 0.90	3.11 ± 1.02*
% predicted	125 ± 15	96 ± 21**
FEV1/FVC,%	76 ± 5	45 ± 12**
IC, L	2.93 ± 0.76	2.31 ± 0.66*
% predicted	107 ± 16	90 ± 16*
TLC, L	6.23 ± 1.14	6.42 ± 1.52
% predicted	105 ± 13	109 ± 12
FRC, L	3.31 ± 0.76	4.04 ± 1.16
% predicted	104 ± 23	126 ± 26*
RV, L	1.98 ± 0.54	3.13 ± 0.88*
% predicted	89 ± 25	141 ± 33**
DLCO,% predicted	84 ± 12	51 ± 15**
O2peak, mL•kg^1•min^−1	28.1 ± 4.9	18.7 ± 2.8**
Daily physical activity
Steps per day	8949 ± 3217	5081 ± 2758*
Energy expenditure > 3 METs, Kcal	582 ± 342	229 ± 211*

Definitions of abbreviations: FEV₁ = forced expiratory volume in 1 second; FVC = forced vital capacity; IC = inspiratory capacity; TLC = total lung capacity; FRC = functional residual capacity; RV = residual volume; DL_CO = diffusion capacity; O₂^peak = peak oxygen uptake during incremental walking; METs = metabolic equivalent. Values are mean ± SD. *p < 0.05 vs. healthy controls; ** p < 0.0001 vs. healthy controls.

Figure 2.  Baseline strength of i) dorsiflexors, ii) plantar flexors and iii) quadriceps for maximal voluntary contraction (MVC –panel A) and potentiated twitch force (Tw_pot –panel B) in patients with COPD (filled bars) and healthy control subjects (open bars). Values are mean ± SD. * p < 0.05 vs. controls.

Table 2.  End-exercise cardiorespiratory response to standardized endurance walking test.

	Controls (n = 15)	COPD (n = 15)	p-value
O2, L/min	0.811 ± 0.188	0.858 ± 0.163	0.48
O2,% O2peak during IWT	42 ± 12	70 ± 25*	0.001
CO2, L/min	0.749 ± 0.183	0.787 ± 0.133	0.53
E, L/min	23.2 ± 6.1	27.6 ± 5.1*	0.04
E/MVV,%	22 ± 8	64 ± 30*	< 0.001
E/CO2	31.0 ± 3.7	35.3 ± 3.5*	0.004
VT, L	1.04 ± 0.24	1.16 ± 0.22	0.19
Bƒ, breath/min	24 ± 6	24 ± 6	0.81
RER	0.92 ± 0.04	0.92 ± 0.04	0.89
HR, beat/min	86 ± 9	95 ± 9*	0.02
O2 pulse, mL O2/beat	9.4 ± 2.0	9.1 ± 1.8	0.66
SpO2,%	97 ± 1	95 ± 4	0.07
Dyspnea, Borg score	1 ± 1	4 ± 2*	< 0.001
Leg fatigue, Borg score	1 ± 1	4 ± 2*	0.001

Definitions of abbreviations: O₂ = oxygen uptake; IWT: incremental walking test; CO₂ = CO₂ output; _E = minute ventilation; MVV = maximal voluntary ventilation obtained by multiplying FEV₁ by 35; V_T = tidal volume; Bƒ = breathing frequency; RER = respiratory exchange ratio; HR = heart rate; SpO₂ = pulse oxygen saturation. Values are mean ± SD. * p < 0.05 vs. healthy controls.

Figure 3.  Post-exercise loss in strength for the i) dorsiflexors, ii) plantar flexors and iii) quadriceps for maximal voluntary contraction (MVC –panel A) and potentiated twitch force (Tw_pot –panel B) in patients with COPD (filled bars) and healthy control subjects (open bars). Values are mean ± SD and expressed as the% fall from resting values. * p < 0.05 vs. controls.

Figure 4.  Post-exercise loss in strength for the i) dorsiflexors and ii) plantar flexors for maximal voluntary contraction (MVC –panel A and C) and potentiated twitch force (Tw_pot –panel B and D) in patients with COPD (filled circles) and healthy control subjects (open circles) at 15 minutes and 40 minutes post-exercise. Values are mean ± SD. The values at 40 minutes post-exercise are only available for 8 patients with COPD (n = 8) and 6 healthy controls (n = 6). * p < 0.05 vs. baseline force values within groups.

Table

	COPD (n = 10)
Age, yr	63 ± 5
Gender (M/F)	(6/4)
BMI, kg/m^2	26 ± 4
Pack-years	47 ± 24
FEV1, L	1.41 ± 0.34
% predicted	54 ± 14
FVC, L	2.88 ± 0.68
% predicted	83 ± 18
FEV1/FVC,%	51 ± 15