The individual values for b are shown in Figure 1. Parameter b was considerably greater in COPD patients compared with normal subjects (4.49±1.72 versus 2.66±0.47, respectively, P<0.005). As indicated by the dotted line, in 30 of 46 patients, parameter b was greater than the upper value obtained in the normal group.
La/VO2 relationship and the functional class: Peak exercise data obtained for normal subjects and each class of patients are reported in Table 2. In normal subjects, peak VO2 amounted to 32±6 mL/min/kg. In patients the response to exercise was characterized by a rapid increase in symptom scores, a reduced or absent ventilatory reserve, oxygen desaturation and carbon dioxide retention. These abnormalities occurred at a gradually lower exercise work rate with the deterioration in functional status.
Table 2. Peak exercise data in relation to the functional class
| Class D (n=8) | Class C (n=31) | Class B (n=15) | Normal subjects (n=10) | |
| VO2 (L/min) | 0.62±0.14* | 0.89±0.18* | 1.31±0.30t | 2.18±0.40t |
| VO2 (mL/min/kg) | 8.7±0.9t | 13.0±1.5t | 18.0±1.5t | 31.7±6.4t |
| VCO2 (L/min) | 0.51±0.11* | 0.80±0.19* | 1.30±0.37t | 2.39±0.48t |
| Heart rate (beats/min) | 119±16* | 128±15* | 138±10§ | 158±8t |
| Heart rate (% maximum) | 72±11* | 76±9* | 83±5§ | 95±5t |
| VE (L/min) | 22±5* | 33±8* | 45±15§ | 93±26t |
| VE/MVV (%) | 94±15 | 107±21 | 106±24 | 91±25 |
| Borg score | ||||
| Dyspnea | 7.2±2.0T | 8.3±1.6t | 7.9±2.2t | 5.5±2.0§ |
| Leg fatigue | 4.2±4.3 | 7.1±2.6 | 6.3±3.0 | 5.6±2.8 |
| PaO2 (mmHg) | 61±14* | 65±10t | 72±13** | 100±12t |
| Oxygen saturation (%) | 88±7t | 90±6t | 92±5t | 98±1§ |
| pH | 7.32±0.01 | 7.34±0.04 | 7.32±0.04 | 7.35±0.04 |
| PCO2 (mmHg) | 56±5§ | 49±7** | 49±6** | 36±5t |
All values mean ±SD. *P<0.01 versus any other group; TP<0.001 versus any other group; fP< 0.05 versus class Band normal subjects; §P<0.05 versus any other group; *P<0.05 versus normal subjects; **P<0.05 versus class D and normal subjects. MVV Maximum voluntary ventilation; VO2 Oxygen uptake; VCO2 Carbon dioxide output; Ve Minute ventilation
/td
Category: Pulmonary disease
Tags: Chronic obstructive pulmonary disease, Exercise, Lactate
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