CLINICS 2012;67(6):615-621 RESULTS A total of 34 COPD patients were screened, 14 of whom were not admitted to the study due to the exclusion criteria. Twenty male patients were enrolled in the study (Table 1). According to the GOLD standards, nine (45%) patients were classified as having severe disease, seven (35%) were classified as having moderate disease, three (15%) were classified as having very severe disease, and one (5%) was classified as having mild disease. The mean plasma Mg level in the basal condition was within the normal range of the method for the whole group. However, when we analyzed the results considering the lower level of normal- ity (1.5 Meq/L) as a limit, seven (35%) of the patients may be classified as exhibiting an Mg deficiency. The mean time interval between the first and the second visit was 1.9 days, ranging from 1 to 5 days. Half of the volunteers received a placebo on day 1 and Mg on day 2. The statistical analysis showed no carryover effects, indicating that the order of the treatments and the variable washout period did not influence the final results. As expected, the infusion of 2 g of magnesium sulfate was associated with a significant increase in the mean plasma ion level compared with the placebo (Figure 1). The patients did not complain of serious side effects either during or immediately following the Mg infusion. Three (15%) patients noted a transitory hot wave sensation throughout their bodies. Another two (10%) patients described a short period of drowsiness. The administration of Mg was not associated with significant changes in FVC, FEV1, FEV1/FVC or FEF25–75% (Table 2). Magnesium infusion was associated with a non- significant decrease in TLC, but it was associated with significant reductions in the residual volume (RV) and functional residual capacity (FRC). The mean effects of the Mg treatment on the TLC, RV and FRC were, respectively, -0.30 l, -0.47 l, and -0.41 l. The inspiratory capacity (IC) improved to approximately 0.12 l, but this change did not reach statistical significance. Table 1 - Characteristics of the 20 studied male COPD patients*. Age (years) TLC (% predicted) FVC (% predicted) FEV1(% predicted) FEV1/FVC FEF25-75% (% predicted) RV (% predicted) FVC bd. response (% baseline) FEV1 bd. response (% baseline) FEF25-75% bd. response (% baseline) pH PaO2 (mmHg) PaCO2 (mmHg) P(A-a)O2 (mmHg) Plasma Mg level (mEq/l) 66.2¡8.3 121.4¡17.9 89.0¡22.7 49.3¡19.8 43.8¡11.4 17.0¡9.6 169.7¡52.6 7.7¡8.0 9.0¡7.3 13.9¡18.6 7.42¡0.03 76.3¡7.8 40.3¡3.9 21.9¡6.7 1.6¡0.4 *TLC: total lung capacity; FVC: forced vital capacity; FEV1: forced expiratory volume in the first second; FEF25-75%: middle curve forced expiratory flow; P(A-a)O2: alveolo-arterial oxygen gradient. Mg loading and exercise on COPD Amaral AF et al. 617 Figure 1 - Mg plasma levels after infusion of 2 g of magnesium sulfate or saline in 20 male COPD patients. Among the several cardiorespiratory parameters measured with the patients seated on the cycle ergometer at rest, administration of Mg led to significant decreases only in the diastolic and mean arterial blood pressures (Table 3). In addition, the cardiac double product was significantly reduced as a result of Mg administration (-734.8 bpm.mmHg), and the arterial oxygen saturation evaluated by the pulse oximeter improved slightly (0.8%). The use of Mg was associated with a significant increase in the duration of exercise (53 seconds) and of the maximal reached load (8.0 w) (Table 4). The respiratory exchange ratio (RER) showed a small but significant increase after Mg administration (0.06). Although Mg use led to a significant increase in the tidal volume at the peak of exercise (90.2 ml), there were no differences between the drug and the placebo treatments regarding the maximal ventilation. The anaerobic threshold could be determined in only 12 subjects due to technical questions. There were no sig- nificant differences between the treatment and the placebo days, except that the time required to reach the anaerobic threshold after the Mg administration was significantly longer than that observed after the placebo was adminis- tered (10923’’ ¡2914’’ 69943’’ ¡1951’’; p = 0.029). The mean load reached at the anaerobic threshold was higher after the Mg administration than after the saline was administered, but the difference did not reach statistical significance (52.9¡19.0 w646.6¡19.7 w; p = 0.083). To clarify the potential mechanisms related to the exercise improvements after Mg loading, we also analyzed the results with the patients divided in two subgroups based on changes in the maximal workloads that were lower than, or equal to or higher than 5 watts, respectively designated as Group I and Group II (Table 5). Ten patients were included in each group, and they did not differ in regard to age (64.9¡9.6667.5¡7.0 years; p = 0.499) or basal Mg plasma levels (1.6¡0.461.6¡0.3 mEq/l; p = 0.709). These groups did not significantly differ regarding the treatment’s effect on the Mg plasma levels or on the exercise hemodynamic parameters. However, the Group II patients showed a significantly better response of IC at rest and of the minute ventilation at the exercise peak. DISCUSSION This study detected low plasma Mg levels in 35% of a highly selective sample of COPD patients. This figure is consistent with the results of previous papers (10,11).