Poor Work Efficiency is Associated with Poor Exercise Capacity and Health-Related Quality of Life in Patients with Chronic Obstructive Pulmonary Disease

Figures & data

Figure 1 Study flow chart.

Table 1 Baseline Characteristics

	All (n = 78)	Group I (n = 31)	Group II (n = 47)	p-value
Age (years)	69.9 ± 8.9	67.6 ± 9.9	71.5.9 ± 7.9	0.054
BH (cm)	162.5 ± 7.4	161.8 ± 8.1	163.1 ± 7.0	0.452
BW (kg)	60.5 ± 11.6	60.8 ± 11.3	60.4 ± 12.0	0.878
BMI (kg/m^2)	22.8 ± 3.7	23.1 ± 3.2	22.6 ± 4.0	0.559
FEV1/FVC (%)	47.5 ± 10.9	49.6 ± 11.0	46.1 ± 10.7	0.172
FEV1 (%)	48.4 ± 16.1	49.4 ± 14.2	47.8 ± 17.4	0.678
FVC (%)	80.3 ± 18.9	79.7 ± 18.1	80.7 ± 19.6	0.824
COPD stages				0.381
I	2	0	2
II	31	15	16
III	37	14	23
IV	8	2	6
Smoking				0.002*
Non-smoking	10	7	3
Current smoking	33	6	27
Ex-smoking	35	18	17

Note: *p < 0.05 statistical significance as comparison between group I and II.

Abbreviations: BH, body height; BW, body weight; BMI, body mass index; COPD, chronic obstructive pulmonary disease; FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity.

Figure 2 Respiratory parameters. There was no significant difference in respiratory parameters such as FEV1/FVC% (A), FEV1% (B), FVC% (C), MIP (D), MEP (E), RR at rest (F), and V_T at rest (H) or during exercise (I) between group I and group II (p > 0.05). However, the RR during exercise (G) was higher in group II than in group I (p < 0.05). *p < 0.05 as comparison between groups I and II.

Abbreviations: MIP, maximal inspiratory pressure; MEP, maximal expiratory pressure; FVC, forced vital capacity; FEV1, forced expiratory volume in 1 second; RR, respiratory rate; V_T, tidal volume.

Figure 3 Circulatory parameters. WE (A), VO₂ at maximal exercise (B) or AT (C), and O₂P (D) were higher in group I than in group II (p < 0.05). There was no significant difference in HR at rest (E) or during exercise (F) and in MBP at rest (G) or during exercise (H) between the two groups (p > 0.05). *p<0.05 as comparison between group I and II.

Abbreviations: AT, anaerobic threshold; O₂P, oxygen pulse; MBP, mean blood pressure; HR, heart rate; WE, work efficiency; VO₂, oxygen uptake.

Figure 4 Gas exchanges. There was no difference in SpO₂ at rest (A) or exercise (B) and PETCO₂ at rest (C) or exercise (D) were between the two groups (p > 0.05).

Abbreviations: SpO₂, blood oxygen saturation by pulse oximeter; PETCO₂, end tidal carbon dioxide.

Figure 5 Exercise capacity. Maximal VO₂% (A) and maximal VO₂ (B) were higher in group I than in group II (p < 0.05). However, there was no significant difference in the maximal workload% (C) and maximal workload (D) between the two groups (p > 0.05). *p<0.05 as comparison between group I and II.

Abbreviation: VO₂, oxygen uptake.

Figure 6 Dyspnea score and health-related quality of life. Dyspnea scores at rest (A) were similar between the two groups (p > 0.05), but dyspnea scores at maximal exercise (B) were significantly higher in group II than that in group I (p < 0.05). The SGRQ-total (C), -activity (D), -impact (E), and -symptom (F) scores were significantly poorer in group II than that in group I (p<0.05). *p<0.05 as comparison between group I and II.

Abbreviation: SGRQ, St. George’s Respiratory Questionnaire.

Table 2 Difference and Correlation Between WE and Variables

Variables	Group I	Group II	p-value
FEV1 (%)	49.4 ± 14.2	47.8 ± 17.4	0.6777
FVC (%)	79.7 ± 18.1	80.7 ± 19.6	0.8239
VO2max (mL/min)	1050±53	845 ±34	0.0011
Workload (watt)	69.6 ± 29.7	60.2 ± 23.7	0.1278
O2P (mL/beats)	8.2 ± 2.1	7.0 ± 1.9	0.0088
VO2 at AT (mL/min)	672±27	583 ±18	0.0052
Dyspnea score at exercise	5.1±0.2	6.1±0.2	0.0034
SGRQ-total	41.1±3.0	55±2.2	0.0002
Variables	Pearson correlation (r)	p-value (two-tailed)	Strength of correlation
FEV1 (%)	0.0299	0.7947	Not significant
FVC (%)	−0.0678	0.5552	Not significant
VO2max (mL/min)	0.4199	0.0001*	Moderate
Workload (watt)	0.1495	0.1914	Not significant
O2P (mL/beats)	0.3462	0.0019*	Weak
VO2 at AT (mL/min)	0.2818	0.0124*	Weak
Dyspnea score at exercise	−0.3918	0.0004*	Weak
SGRQ-total	−0.2722	0.0159*	Weak

Note: *p < 0.05 as statistical significance.

Abbreviations: FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; VO₂max, oxygen consumption at maximal exercise; O₂P, oxygen pulse; AT, anaerobic threshold; SGRQ, St. George’s Respiratory Questionnaire.

Figure 7 Correlation between WE and lung function, VO₂ at maximal exercise and AT, O₂P, dyspnea score, and HRQL. There was no significant correlation between WE and FEV1% (A) or FVC% (B) (both p > 0.05) between the two groups. A significant correlation was found between WE and VO₂ (r = 0.4199, p = 0.001) (C), but not between WE and workload at maximal exercise (p > 0.05) (D). There were significant correlations between WE and O₂P (r= 0.3462, p= 0.0019) (E), VO₂ at the AT (r = 0.2818, p = 0.0124) (F), dyspnea score during exercise (r= 0.3918, p= 0.0004) (G), and SGRQ-total score (r = 0.2722, p = 0.0159) (H).

Abbreviations: FEV1, forced expiratory volume in 1 second; FVC, forced vital capacity; VO₂, oxygen uptake; O₂P, oxygen pulse; AT, anaerobic threshold; SGRQ, St. George’s Respiratory Questionnaire; WE, work efficiency.