Dynamic hyperinflation and dyspnea during the 6-minute walk test in stable chronic obstructive pulmonary disease patients

Figures & data

Table 1 Demographic and pulmonary function data of the subjects with COPD

	Mean ± SD
Age (y)	75.5±6.4
Height (cm)	160.8±4.1
Weight (kg)	57.0±10.2
BMI (kg/m^2)	22.0±3.8
Brinkman index	1,398±484
GOLD (I/II/III/IV)	(7/11/5/0)
MMRC dyspnea score (0–4)	1.9±0.5
FVC (L)	3.38±0.67
FEV1 (L)	1.67±0.56
FEV1/FVC (%)	48.9±12.9
FEV1 % predicted (%)	68.0±24.9
TLC (L)	6.25±1.06
TLC % predicted (%)	122.8±21.8
FRC (L)	3.95±0.87
FRC % predicted (%)	113.8±29.8
RV (L)	2.58±0.83
RV % predicted (%)	157.5±50.7

Note: n=23, all male.

Abbreviations: COPD, chronic obstructive pulmonary disease; SD, standard deviation; BMI, body mass index; MMRC, modified Medical Research Council dyspnea scale (0–4); FVC, forced vital capacity; FEV₁, forced expiratory volume in 1 second; TLC, total lung capacity; FRC, functional residual capacity; RV, residual volume; GOLD, Global initiative for chronic Obstructive Lung Disease.

Table 2 Results of the 6-minute walk test

	Resting	Peak value
6-minute walk distance (m)	–	505.7±100.4
Oxygen uptake (mL/min/kg)	3.04±0.55	12.92±2.47
Carbon dioxide production (mL/min/kg)	2.83±0.56	12.53±3.24
Minute ventilation (L/min)	8.74±2.35	28.24±9.21
Respiratory rate (breaths/min)	18.5±4.4	26.7±5.1
Heart rate (bpm)	83.6±12.8	113.8±18.3
Percutaneous oxygen saturation (%)	96.4±0.8	89.3±2.9

Notes: n=23, mean ± SD.

Abbreviations: bpm, beats per minute; SD, standard deviation; min, minutes.

Table 3 Change over time in the 6-minute walk test

	0 min	2 min	4 min	6 min
Inspiratory capacity* (L)	1.34±0.41	1.17±0.35	1.13±0.32	1.08±0.29
Tidal volume* (L)	0.43±0.10	0.96±0.28	1.00±0.30	1.04±0.28
Borg CR-10 scale*	0.0±0.0	1.7±1.4	3.0±1.5	4.6±2.2

Notes: n=23, mean ± SD,

* P<0.01 (analysis of variance).

Abbreviations: SD, standard deviation; CR, category-ratio; min, minutes.

Figure 1 Relationship between the Borg CR-10 scale and IC in the 6-minute walk test.

Abbreviations: CR, category-ratio; IC, inspiratory capacity.

Figure 2 Relationship between the changes in the Borg CR-10 scale and IC in the 6-minute walk test.

Abbreviations: CR, category-ratio; IC, inspiratory capacity.

Figure 3 Changes over time of the VT, IRV, and Borg CR-10 scale in the 6-minute walk test.

Notes: The sum of VT and IRV shows IC. IC and IRV decrease significantly over time (P<0.01).
Abbreviations: VT, tidal volume; IRV, inspiratory reserve volume; CR, category-ratio; IC, inspiratory capacity; min, minutes.

Figure 4 Relationship between the Borg CR-10 scale and the IRV in 6-minute walk test.

Abbreviations: CR, category-ratio; IRV, inspiratory reserve volume.