Metabolic Acidosis during Exercise in Patients with Chronic Obstructive Pulmonary Disease: Results

Normal Subjects
The mean values for age, size, and pulmonary function of the 56 normal subjects are shown in Table 1. As described above, all had normal pulmonary function. Exercise capacity expressed as maximum oxygen uptake as percent predicted value and AT as determined by both the modified V-slope method and from changes in standard bicarbonate are shown for individual subjects in Table 2. In 43 normal subjects, the AT could be determined by both methods; in the other 13, an AT could be clearly selected only by the V-slope method in four, only from the log standard bicarbonate method in three, and by neither method in one subject There was a significant correlation between the two methods (r = 0.75; Fig 2) although the mean AT values for these 43 subjects differed between the two methods (mean AT by V-slope, 1.54 [SD 0.32] L/min, mean AT from log HC03~ vs log Vo2 plots, 1.45 [SD 0.33] L/min, n = 43, t = 2.71, p<0.05). The mean absolute difference was 11 percent (SD 9 percent), while in 28 of 43 subjects, the AT values differed by less than 15 percent.

Patients with COPD
Exercise Metabolic Acidosis in Patients with COPD: In Table 3 are shown the characteristics and pulmonary function of the 22 patients with COPD. They were divided into two groups for comparison on the basis of the maximum fall in standard bicarbonate from rest to 2 min into recovery. Group 1 contained eight patients in whom standard bicarbonate decreased by 2.0 mEq/L or less, and group 2 consisted of 14 whose standard bicarbonate fell by 2.5 mEq/L or more. Mean vital capacity, both absolute and expressed as percent predicted, was significantly greater, and FEV/VC was significantly smaller in group 2 patients; however, mean FEVi, MVY and Dsb were not different between the two groups. Thus, an important proportion of patients with the degree of obstructive lung disease shown in Table 3 had metabolic acidosis during exercise.
Maximum Exercise Capacity in COPD Patients: Table 4 summarizes the data from the incremental exercise tests of the COPD patients. Group 2 patients had a slightly higher mean tidal volume, and, although they did not reach statistical significance using a two-tail t test, mean Ve, and Ve/MW were higher in group 2. Thus, there was a trend towards use of a higher proportion of potential maximal ventilatory capacity (MW) during exercise in those who developed metabolic acidosis.
We were particularly interested in seeing whether resting pulmonary function could be used to predict exercise capacity and the severity of metabolic acidosis during exercise. Figure 3, A and B, shows the relationship between the severity of obstructive lung disease (FEV1? percent predicted) and maximum work capacity and severity of metabolic acidosis (decrease in standard HC03″ at 2 min of recovery). Neither maximum Vo2 (r = 0.25, NS) nor the decrease in standard HC03“ as a result of exercise (r = 0.11,NS) correlated strongly with the degree of airways obstruction.
In contrast to FEV^ percent predicted, there was a significant correlation between the maximum Vo2 during exercise and the Dsb in these patients (Fig 4A) (r = 0.72, p<0.05). However, the Dsb did not correlate with the degree of metabolic acidosis during exercise (Fig 4B). Thus, the Dsb measurement, regarded to be an index of abnormal lung gas exchange, was unable to identify which patients would be able to exercise to a level high enough to develop a metabolic acidosis. On the other hand, the maximum exercise heart rate, expressed as percent predicted, correlated significantly with the fall of standard bicarbonate between rest and 2 min of recovery (r=0.55, p<0.05). Thus, those COPD patients with more marked metabolic acidosis appeared to be closer to their predicted maximum cardiovascular (heart rate) capacity.
Table 1—Mean Size, Resting Pulmonary Function, and Exercise Performance during Maximum Incremental Exercise Test in 56 Normal Subjects

Age, yr 54±9
Height, cm 172 ±8
Wsight, kg 88± 18
VC, L 4.13 ± 0.6 (104 ± 14)
FEVi, L 3.26± 0.49 (104±15)
MVV L 133 ±22 (99 ±19)
Dsb, ml/min/mm Hg 30.1 ±5.0 (115±18)
Maximum Vo2, L/min 2.25±0.43 (101 ± 14)
Maximum heart rate, beats/min 156 ±18 (94 ±13)
Maximum Ve/MVY % 71 ±21

Table 2—Maximum Vot and Anaerobic Threshold of 56 Normal Subjects

Subject MaximumVo.,L/min MaximumVo.,% pred Astd HCOr Rest-Recovery AT by Modified V-slope, L/mint AT from log HCOr vs log Vo2t
1 1.57 102 1.3 1.40 1.05
2 3.16 104 1.6 2.35 2.24
3 2.34 91 1.8 1.05
4 1.99 111 2.9 1.32
5 2.09 91 3.0 2.00 2.00
6 2.55 116 3.6 1.38 1.00
7 2.20 100 4.0 1.85 1.41
8 2.00 101 4.1 1.50
9 2.72 115 4.4 1.60 1.51
10 2.80 100 4.5 1.28 1.58
11 2.41 120 4.5 1.30 1.35
12 3.40 152 4.8 1.80 1.66
13 2.28 87 4.8 1.25 1.55
14 2.14 87 4.8 1.50 1.38
15 1.81 87 4.9 0.56
16 2.23 95 4.9 1.26 1.26
17 1.66 82 4.9 0.90 0.85
18 2.48 94 5.3 1.07
19 2.49 97 5.4 1.58
20 1.47 95 5.4 1.25 1.00
21 3.42 135 5.4 1.12
22 2.45 106 6.0 1.40 1.55
23 2.06 92 6.2 1.70 1.86
24 1.98 94 6.3 1.70 1.55
25 1.61 95 6.4 1.40 1.38
26 3.17 103 6.4 0.93
27 1.95 115 6.6 1.75 1.86
28 2.24 92 6.8 1.50 1.38
29 2.24 112 6.8 1.40 1.48
30 2.22 119 7.1 1.20 1.07
31 2.31 91 7.2 1.25 1.10
32 2.30 84 7.2 1.63 1.66
33 1.99 87 7.5 1.75 1.78
34 2.21 98 7.7 1.50
35 1.81 92 7.7 1.10 1.23
36 1.86 94 7.8 1.80 1.66
37 1.96 90 8.1 1.51 1.51
38 2.30 99 8.1 1.60 1.48
39 2.40 101 8.2 1.35 1.02
40 2.18 90 8.2 1.50
41 2.11 91 8.2 1.55 1.58
42 1.91 83 8.2 1.90 2.24
43 2.74 105 8.2 1.38
44 2.37 106 8.3
45 1.61 82 8.4 1.40 1.41
46 2.67 98 8.6 1.60 1.35
47 2.22 122 8.7 1.65 1.48
48 1.96 102 8.7 1.30
49 2.32 119 8.7 1.05 1.35
50 2.76 88 9.2 1.75 1.38
51 2.73 125 9.2 1.50 1.12
52 2.07 98 9.4 2.20 2.00
53 1.84 93 9.7 1.75 1.20
54 2.11 92 10.2 1.13 1.00
55 1.70 108 11.3 1.38 1.15
56 2.66 106 13.4 2.25 1.78
Mean 2.25 101 6.6 1.51 1.41
SD 0.43 14 2.4 0.31 0.35
N 56 56 56 51 47

Table 3—Resting Pulmonary Function of 22 Patients with Chronic Obstructive Pulmonary Disease

Subject Astd HCOr, mEq/L Age,yr Height,cm VC, L VC,% pred FEVX, L FEVb% pred FEV/VC,% MvyL/min Mvy% pred Dsb, ml/min/mm Hg Dsb, % pred
Group 1* 1 1.0 71 166 2.37 72.4 1.40 55.7 59.1 56 50.9 14.td 5 64.7
2 1.0 70 165 1.63 50.4 0.62 28.3 38.0 25 27.0 9.6 31.5
3 1.1 59 182 3.38 72.5 0.91 24.3 26.9 37 25.3 12.8 43.8
4 1.5 58 159 1.37 42.9 0.84 36.8 61.3 26 26.8 17.5 80.6
5 1.8 45 158 2.51 71.6 1.58 62.5 62.9 76 71.1 24.7 100.8
6 1.9 61 173 1.67 41.6 0.53 16.8 31.7 36 27.3 18.5 59.9
7 1.9 59 166 2.93 80.9 1.73 61.0 59.0 59 47.2 20.2 91.4
8 2.0 51 154 2.42 87.5 1.69 81.9 69.8 65 73.5 23.3 105.4
Mean 1.5 59 165 2.29 65.0 1.16 46.0 51.1 48 43.6 17.6 72.3
SD 0.4 9 9 0.69 17.6 0.49 22.6 16.3 19 20.3 5.2 26.8
Group 2* 9 2.5 63 164 2.76 81.8 0.77 29.3 27.9 37 31.5 18.2 75.8
10 2.6 66 175 2.87 71.7 1.10 35.3 38.3 39 30.4 13.4 51.9
11 2.8 55 168 4.07 105.3 1.43 46.9 35.1 64 48.2 22.3 105.2
12 3.6 68 157 3.00 108.1 1.29 60.7 43.0 45 44.2 10.0 49.3
13 3.8 64 157 2.85 98.6 1.11 49.7 38.9 42 39.3 16.9 84.9
14 4.0 58 174 2.64 63.3 0.90 27.4 34.1 48 35.1 18.4 63.4
15 4.1 68 164 3.34 103.4 1.80 81.6 53.9 73 78.1 20.8 98.1
16 4.5 64 175 2.17 53.4 0.73 23.0 33.6 39 29.8 27.5 110.9
17 4.7 66 180 3.14 72.6 1.00 29.6 31.8 42 31.1 10.6 38.5
18 4.8 71 173 3.16 94.2 1.86 71.9 58.9 87 81.1 13.1 60.1
19 5.0 50 179 3.00 70.5 0.96 28.4 32.0 42 30.4 19.0 70.6
20 6.4 62 173 4.60 115.3 1.47 47.1 32.0 67 51.3 15.6 46.7
21 7.0 64 179 2.71 62.7 1.27 37.6 46.9 74 54.4 25.0 78.4
22 9.8 63 170 3.41 90.6 1.57 53.5 46.0 67 53.5 32.2 120.1
Mean 4.7 63 171 3.12 85.1 1.23 44.4 39.5 55 45.6 18.8 75.3
SD 2.0 6 8 0.61 19.7 0.36 17.8 9.1 17 17.0 6.4 25.7
Pt <0.05 NS NS <0.05 <0.05 NS NS <0.05 NS NS NS NS

Table 4—Values at Maximum Cycle Incremental Exercise for 22 Patients with Chronic Obstructive Pulmonary Disease

Subject Astd HC03“, mEq/L Ve, L/min Ve/MVY % f, min Vt, L Vo2, L/min pH Po* mm Hg Pcoa, mm Hg HR, min”
Group 1* 1 1.0 43.2 77 31 1.39 1.01 7.37 73 44 140
2 1.0 16.7 67 21 0.80 0.56 7.33 83 60 122
3 1.1 34.6 94 33 1.05 0.88 7.37 62 42 145
4 1.5 25.0 96 29 0.86 0.82 7.37 75 43 132
5 1.8 50.5 66 58 0.87 1.29 7.39 90 38 127
6 1.9 34.1 95 36 0.95 1.17 7.32 53 49 125
7 1.9 55.2 94 39 1.42 1.18 7.31 102 31 134
8 2.0 50.7 78 55 0.92 1.20 7.39 74 39 128
Mean 1.5 38.8 83 38 1.03 1.01 7.36 77 43 132
SD 0.4 13.6 13 13 0.24 0.25 0.03 15 9 8
Group 2* 9 2.5 30.4 82 36 0.84 0.96 7.36 51 51 132
10 2.6 45.1 116 35 1.29 1.11 7.39 60 42 132
11 2.8 62.7 98 44 1.43 1.49 7.37 90 38 104
12 3.6 38.7 86 42 0.92 0.80 7.37 51 45 127
13 3.8 36.3 86 41 0.89 0.82 7.31 77 46 148
14 4.0 54.8 114 38 1.44 1.41 7.27 67 45 174
15 4.1 42.7 58 26 1.64 1.11 7.34 89 39 133
16 4.5 46.2 118 44 1.05 1.67 7.32 61 52 117
17 4.7 44.4 106 33 1.35 0.90 7.32 56 38 168
18 4.8 78.9 91 55 1.43 0.94 7.40 53 34 134
19 5.0 43.3 103 38 1.14 1.32 7.30 58 55 123
20 6.4 48.5 72 41 1.18 1.42 7.35 59 38 124
21 7.0 72.8 98 41 1.78 1.80 7.38 83 37 171
22 9.8 77.9 116 44 1.77 2.11 7.30 98 36 192
Mean 4.7 51.6 96 40 1.30 1.28 7.34 68 43 141
SD 2.0 15.6 18 7 0.31 0.40 0.04 16 7 25
pt <0.05 NS NS NS <0.05 NS NS NS NS NS

 

Figure 2. Comparison of anaerobic threshold (AT) during cycle ergometer exercise determined by the change in log standard HC03" and the AT determined by the modified V-slope method for 43 normal subjects, r=0.75. Line drawn is line of identity.

Figure 2. Comparison of anaerobic threshold (AT) during cycle ergometer exercise determined by the change in log standard HC03″ and the AT determined by the modified V-slope method for 43 normal subjects, r=0.75. Line drawn is line of identity.

Figure 3. Relationship between FEVj, percent predicted, and (A) maximum Vo2, percent predicted and (fi) degree of metabolic acidosis (fall in standard HC03~).

Figure 3. Relationship between FEVj, percent predicted, and (A) maximum Vo2, percent predicted and (fi) degree of metabolic acidosis (fall in standard HC03~).

Figure 4. Relationship between single-breath diffusing capacity for carbon monoxide (Dsb) and (A) maximum Voj, percent predicted, and (B) degree of metabolic acidosis during exercise.

Figure 4. Relationship between single-breath diffusing capacity for carbon monoxide (Dsb) and (A) maximum Voj, percent predicted, and (B) degree of metabolic acidosis during exercise.

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Category: Pulmonary Disease

Tags: lung disease, metabolic acidosis, Pulmonary function