A Simplified Approach to Select Exercise Endurance Intensity for Interventional Studies in COPD

Figures & data

Figure 1. Study protocol. CPET: cardiopulmonary exercise test; CWR: constant work rate; Tlim: time to exercise intolerance; BD: bronchodilator.

Table 1. Resting and exercise characteristics of the whole sample and subgroups based on tolerance to the initial endurance test (CWR_75%).

Variable	All (N = 59)	Low endurance (N = 6)	Mid-endurance (N = 27)	High endurance (N = 26)
Demographic/anthropometric
Age (yrs)	62 ± 1	64 ± 2	63 ± 2	60 ± 2
Gender (M:F)	35: 24	1: 5	13: 14^†	21: 5^*
BMI (kg/m^2)	27.4 ± 0.8	23.6 ± 1.7	26.1 ± 1.0	29.7 ± 1.3^*
Pack-years	47 ± 3	52 ± 14	50 ± 4	43 ± 4^*
Lung function
FEV1 (L)	1.3 ± 0.1	0.8 ± 0.1^‡	1.3 ± 0.1^†	1.6 ± 0.1^*
FEV1 (% pred)	49 ± 2	38 ± 3	49 ± 2	52 ± 3
GOLD spirometric stage
II	34 (57.6%)	1 (16.7%)	16 (59.3%)	17 (65.4%)
III – IV	25 (42.4%)	5 (83.4%)	11 (40.7%)	9 (34.6%)^*
FVC (L)	3.0 ± 0.1	2.1 ± 0.2	2.9 ± 0.1	3.4 ± 0.2^*
FVC (% pred)	81 ± 2	75 ± 5	82 ± 3	81 ± 3
FEV1/FVC	0.46 ± 0.02	0.37 ± 0.04	0.46 ± 0.02	0.47 ± 0.02
IC (% pred)	80 ± 2	74 ± 6	77 ± 3	85 ± 3
RV (% pred)	172 ± 7	187 ± 18	175 ± 12	165 ± 8
TLC (% pred)	109 ± 2	104 ± 7	107 ± 3	106 ± 3
RV/TLC	0.52 ± 0.13	0.60 ± 0.02	0.53 ± 0.19	0.50 ± 0.19
TLCO (% pred)	67 ± 4	45 ± 7	63 ± 4	77 ± 6^*
Peak exercise
Work rate (W)	80 ± 4	43 ± 9	71 ± 5^†	99 ± 6^*
Work rate (% pred)	57 ± 3	55 ± 11	56 ± 3	58 ± 2
O2 (ml/min/kg)	16.8 ± 0.8	12.3 ± 1.8	16.3 ± 0.8	18.5 ± 1.3^*
O2 (% pred)	73 ± 3	65 ± 10	75 ± 4	72 ± 4
E /MVV	0.84 ± 0.03	0.80 ± 0.08	0.85 ± 0.03	0.84 ± 0.04
SpO2 (%)	93.1 ± 0.7	91.2 ± 2.1	92.9 ± 1.1	93.2 ± 0.8
Borg dyspnoea	6.0 ± 0.3	4 ± 1	6.2 ± 0.5	6.3 ± 0.4
Borg leg discomfort	6.5 ± 0.3	4 ± 1^‡	6.5 ± 0.5	7.0 ± 0.4^*

Values are presented as mean ± SE or n (%).

^* p < 0.05 low vs. high endurance.

^† p < 0.05 mid vs. high endurance.

^‡ p < 0.05 low vs. mid endurance.

Definitions and abbreviations: BMI: Body mass index; FEV1: forced expiratory volume in 1 second; GOLD: Global Initiative for Chronic Obstructive Lung Disease; FVC: forced vital capacity; RV: residual volume; TLC: total lung capacity; T_LCO: transfer factor for carbon monoxide; ̇VO₂: total oxygen consumption; ̇V_E: ventilation; MVV: maximum voluntary ventilation; SpO₂: peripheral oxygen saturation.

Figure 2. Individual time to limitation (Tlim) in response to constant work rate testing at 75% peak (CWR_75%) and after intensity adjustment (CWR_{50%⇐75%⇒90%}) in patients whom CWR_75% did not provide Tlim between 3 and 8 min (Tlim_3′–8′) (N = 32, panel A). Tlim distribution in response to CWR_75% and CWR_{50%⇐75%⇒90%} is shown in panel B. Note that a fraction of “high-endurance” patients were told to stop exercising at the 8th minute during CWR_75% (N = 8): this explains higher Tlim frequency near this time point. Tlim: time to intolerance; Tlim_3′–8′: time to intolerance within 3 to 8 minutes; CWR: constant work rate.

Table 2. Physiological and sensory responses to constant work rate (CWR) test at different percentage of peak WR in COPD patients separated by tolerance to the initial endurance test (CWR_75%).

	Low endurance			High-endurance
			Mid-endurance
	CWR75%	CWR50%	CWR75%	CWR75%	CWR90%
At Tlim
Time (s)	125 ± 13	225 ± 17	307 ± 17	778 ± 80	325 ± 21
̇VO2 (mL/min)	620 ± 76 ^†	586 ± 64	1100 ± 68	1458 ± 89	1536 ± 68 ^*
̇VO2(% peak)	101 ± 5	97 ± 5	97 ± 2	100 ± 2	106 ± 3 ^*
HR (% pred)	69 ± 4	65 ± 4	78 ± 3	78 ± 2	78 ± 2
̇VE/MVV	0.87 ± 0.08	0.87 ± 0.08	0.82 ± 0.03	0.83 ± 0.04	0.88 ± 0.04 ^*
VT/IC (%)	76 ± 7	70 ± 6	74 ± 2	75 ± 3	77 ± 2
IRV (L)	0.30 ± 0.06	0.42 ± 0.10	0.47 ± 0.04	0.58 ± 0.07	0.52 ± 0.06
EILV/TLC	0.92 ± 0.05	0.93 ± 0.07	0.92 ± 0.07	0.92 ± 0.06	0.92 ± 0.05
Borg dyspnea	5.8 ± 1	6.3 ± 0.5	6.4 ± 0.4	6.9 ± 0.5	6.9 ± 0.5
Time course
̇VO2 t^1/2 (s)	28 ± 4 ^†	38 ± 5	49 ± 3 ^‡	86 ± 6	43 ± 5^*
̇VE t^1/2 (s)	34 ± 5 ^†	46 ± 7	58 ± 9 ^‡	93 ± 7	51 ± 7^*
Time at VT/IC 70%	58 ± 6 ^†	188 ± 12^*	173 ± 44	201 ± 10	121 ± 9^*
Time at dyspnea “5”	118 ± 10 ^†	237 ± 12^*	243 ± 16 ^‡	431 ± 21	251 ± 14^*

Values are presented as mean ± SE.

^* p < 0.05 for intragroup comparisons.

^† p < 0.05 low vs. mid and high endurance at CWR_75%.

^‡ p < 0.05 mid vs. high endurance at CWR_75%. ̇VO₂: oxygen consumption; HR: heart rate; ̇V_E: ventilation; MVV: maximum voluntary ventilation; V_T: tidal volume; IC: inspiratory capacity; IRV: inspiratory reserve volume.

Figure 3. Metabolic, cardiovascular, mechanical-ventilatory and sensory responses in patients whom initial CWR_75% was shorter than 3 min (“low-endurance”) or longer than 8 min (“high-endurance”) and the effect of repeating the test at lower (CWR_50%) or higher (CWR_90%) intensities, respectively. ̇VO₂: oxygen consumption; HR: heart rate; IRV: inspiratory reserve volume; V_T: tidal volume; IC: inspiratory capacity; ̇V_E: ventilation; MVV: maximum voluntary ventilation. ^*p < 0.05 for CWR_90% vs. CWR_75% at isotime. ^ǂp < 0.05 for CWR_50% vs. CWR_75% at isotime.

Figure 4. Metabolic, cardiovascular, mechanical-ventilatory, and sensory responses patients whom initial CWR_75% was within the desired time range (Tlim_3′–8′) and those who reached Tlim_3′–8′ after repeating the test at CWR_50% (“low-endurance”) or CWR_90%(“high-endurance”).̇VO₂: oxygen consumption; HR: heart rate; IRV: inspiratory reserve volume; V_T: tidal volume; IC: inspiratory capacity; ̇V_E: ventilation; MVV: maximum voluntary ventilation. ^*p < 0.05 for low-endurance at CWR_50% vs. mid-endurance at CWR_75% and high-endurance at CWR_90%.

Figure 5. Mechanical-ventilatory and sensory responses in the subgroup of patients (N = 12) who exercised at the work rate associated with Tlim_3′–8′ after placebo and bronchodilator. IRV: inspiratory reserve volume; ̇V_E: ventilation; MVV: maximum voluntary ventilation; V_T: tidal volume; IC: inspiratory capacity. ^*p < 0.05 for postbronchodilator vs. initial/postplacebo tests at isotime.