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

Metabolic Acidosis during Exercise in Patients with Chronic Obstructive Pulmonary Disease: Patients with COPDAnaerobic Threshold in Patients with COPD: Table 5 compares the AT determined by the two methods in the COPD patients. In 10/14 patients with a fall in standard bicarbonate ^2.5 mEq/L, the V-slope method indicated the presence of metabolic acidosis; the log standard bicarbonate method was successful in identifying all 14 of them. One patient with a fall in standard bicarbonate of 2.0 mEq/L had an AT value selected by both methods, and we identified a point consistent with metabolic acidosis using the V-slope method in one patient whose standard bicarbonate decreased 1.8 mEq/L. The AT determined by the modified V-slope method was compared with the AT determined by the standard bicarbonate method for 11 patients who had AT values chosen using both methods (Fig 5). The two methods closely correlated (r = 0.98); the V-slope method gave slightly higher values in seven of the 11 patients and higher mean value 0.97 [SD 0.34] L/min vs 0.89 [SD 0.34] L/min, p<0.05). avandia online

Discussion
During an incremental exercise test, about two thirds of our patients with chronic airflow obstruction developed metabolic acidosis. This finding may be surprising in view of the understanding that many of these patients with COPD are limited in their exercise capacity by exertional dyspnea, presumably due to reduced ventilatory capacity. In fact, it may have been thought that these patients would have such low exercise capacity that they would be unable to develop metabolic acidosis during exercise. Of particular note, while mean VC and FEVj/VC were different between those who did and did not develop metabolic acidosis during exercise, pulmonary function at rest did not distinguish individual patients who would or would not have metabolic acidosis.
The frequent occurrence of exercise metabolic acidosis in these patients is of considerable clinical interest The generation of hydrogen ion should predictably increase exercise minute ventilation in two ways: (1) the reaction of hydrogen ion with blood bicarbonate produces an additional amount of C02 (22.4 ml for each mEq of hydrogen ion reacting with HC03”) that results in a proportional increase in Ve requirement; and (2) the acidemia serves as a direct stimulus to ventilation via the carotid bodies to increase Ve.
Table 5—Comparison of Anaerobic Threshold (AT) Determined By V-Slope Method and from Change in Standard Bicarbonate

SubjectNo. Astd HCO3-, mEq/L Voj max, L/min AT from Alog std HCO3-, L/min AT by V-Slope, L/min
1 1.0 1.01 * *
2 1.1 0.56 * *
3 1.2 0.88 * *
4 1.5 0.82 * *
5 1.8 1.29 t 0.90
6 1.9 1.17 * *
7 1.9 1.18 t *
8 2.0 1.20 0.82 0.80
9 2.5 0.96 0.71 *
10 2.6 1.11 1.00 1.00
11 2.8 1.49 1.35 *
12 3.6 0.80 0.50 0.65
13 3.8 0.82 0.65 0.75
14 4.0 1.41 1.23 1.30
15 4.1 1.11 0.63 0.65
16 4.5 1.67 1.58 t
17 4.7 0.90 0.66 0.85
18 4.8 0.94 0.60 0.60
19 5.0 1.32 0.79 0.95
20 6.4 1.42 0.90 t
21 7.0 1.80 1.35 1.45
22 9.8 2.11 1.58 1.70

 

Figure 5. Comparison of anaerobic threshold (AT) during cycle ergometer exercise determined by the change in log standard HCOa~ and the AT determined by the modified V-slope method for 11 patients with COPD, r=0.98. The line of identity is drawn.

Figure 5. Comparison of anaerobic threshold (AT) during cycle ergometer exercise determined by the change in log standard HCOa~ and the AT determined by the modified V-slope method for 11 patients with COPD, r=0.98. The line of identity is drawn.


Category: Pulmonary Disease

Tags: lung disease, metabolic acidosis, Pulmonary function