CLINICS 2012;67(6):615-621 Mg loading and exercise on COPD Amaral AF et al. Table 4 - Effects of Mg loading on the cardiorespiratory parameters of 20 COPD patients at maximal exercise*. Saline 133.3¡12.7 86.9¡9.0 194.0¡33.2 103.0¡18.7 133.3¡22.7 91.1¡3.0 25,900¡5,375.7 30.4¡6.7 1,318.4¡314.8 41.1¡15.1 85.4¡19.1 12942’’ ¡ 3943’’ 73.4¡37.8 1,110.6¡342.5 1,216.8¡433.2 1.09¡0.13 98.1¡10.0 39.2¡8.3 6.2¡2.6 5.1¡2.8 Mg 135.6¡13.0 88.4¡9.0 191.0¡25.4 99.5¡16.1 130.2¡17.9 91.6¡3.4 25,876¡3641.9 30.9¡7.5 1,408.5¡286.8 43.6¡15.5 88.9¡21.6 13936’’ ¡3919’’ 81.4¡33.7 1,110.3¡319.8 1,288.0¡410.6 1.15¡0.19 98.6¡10.6 38.9¡8.7 6.0¡2.6 5.1¡3.0 Treatment Effect (CI 95%) (Mg-Saline) 2.3 (-2.8 – 7.4) 1.5 (-1.8 – 4.8) -2.5 (-9.3 – 4.3) -3.5 (-8.8 – 1.8) -3.2 (-8.2 – 1.9) 0.5 (-1.0 – 2.0) (-734.8 – 1,341.5) 0.5 (-1,4 – 2,4) 90.2 (20.3 – 160.0) 2.5 (-0.3 – 5.3) 3.5 (-5.1 – 12.0) 53’’ (14’’ – 1933’’) 8.0 (1.5 – 14.4) 8.7 (-54.6 – 72.0) 71.3 (-27.0 – 169.5) 0.06 (0.01 – 0.11) 0.5 (-0.9 – 1.9) -0.4 (-1.6 – 0.9) -0.2 (-0.91 – 0.51) 0.03 (-0.63 – 0.68) p-value 0.355 0.353 0.449 0.185 0.205 0.480 0.982 0.593 0.014 0.078 0.405 0.011 0.018 0.777 0.146 0.023 0.468 0.548 0.560 0.937 HR peak (bpm) HR peak/HR maxpred. SBP peak (mmHg) DBP peak (mmHg) MBP peak (mmHg) SaO2 peak (%) Double product (bpm.mmHg) RR peak (bpm) TV peak (ml) MV peak (l) MV peak /MVV (%) Duration (min, sec) Maximal load (w) VO2 peak (ml/min) VCO2 peak (ml/min) RER peak PETO2 peak (mmHg) PETCO2 peak (mmHg) Borg peak dyspnea Borg peak leg effort Plasmatic Mg (mEq/L) TLC (L) FVC (L) FEV1 (L) FRC (L) RV (L) ERV (L) IC (L) HRpeak (bpm) MBPpeak (mmHg) SaO2 peak (%) MV peak (l) Duration (min, sec) Maximal load (w) VO2 peak (ml/min) VCO2 peak (ml/min) RER peak Borg peak dyspnea Borg peak leg effort 619 same amount of VO2 and corresponding levels of limiting symptoms. The cardiovascular measurements evaluated at the maximal exercise load also did not show significant changes with Mg treatment. Although the tidal volume measured at the peak of exercise was significantly higher after Mg administration, the observed elevation in peak ventilation did not reach statistical significance (p = 0.078). To further explore the potential mechanisms related to the improvement of exercise performance, we have compared the effects of the Mg treatment on the measurements of two sub-sets of patients, classified according to the level of work load responses. Neither basal Mg plasma levels, nor the degree of Mg plasma elevations after loading, differed between the groups. Additionally, there were no significant differences in the hemodynamic parameters during exer- cise. Both groups also exhibited decreases of similar proportions in TLC, RV, and FRC after treatment. The group with a positive exercise response, however, showed a substantial increase in IC after the Mg infusion. This finding strongly suggests that improvements in the respiratory mechanics played an important role in the genesis of improved exercise performance. This latter result is also compatible with the concept that progressive respiratory constraints are central limiting factors for maximal exercise capacity in COPD, and it highlights the importance of IC measurements in this setting (33-35). It is worth noting that the minute ventilation at the peak of exercise in Group II was significantly higher than that in Group I. Although this finding might only reflect the higher level of work load reached, it may also be interpreted as the true mechanism responsible for an improved exercise performance. The use of Mg, most likely, was associated with reductions in dynamic hyperinflation during exercise in the responders. Unfortunately, measurements of IC during exercise, which is considered to be a proxy for dynamic hyperinflation, were not available to completely confirm this possibility (26). *HR: heart rate; SBP: systolic blood pressure; DBP: diastolic blood pressure; MBP: mean arterial blood pressure; SaO2: peripheral arterial oxygen saturation; RR: respiratory rate; TV: tidal volume; MV: minute ventilation; VO2: oxygen consumption; VCO2: carbon dioxide production; RER: respiratory exchange rate; PETO2: end tidal expiratory oxygen; PETCO2: end tidal expiratory carbon dioxide. the maximal achieved load associated with Mg treatment. This occurred although there were no significant differences in the peak oxygen consumption, or in Borg dyspnea and the leg fatigue scores, between treatment days. These results indicate that the overall exercise performance improved after Mg loading, as more work was performed with the Table 5 - Comparisons between Mg treatment effects with COPD patients classified according to the level of work load response *. Group I (n = 10) 1.5¡0.5 -0.46¡1.02 -0.03¡0.21 -0.01¡0.17 -0.43¡1.04 -0.57¡1.10 -0.07¡0.70 -0.06¡0.29 -0.4¡9.7 0.0¡10.5 1,3¡3.2 -0.8¡4.5 -21.8¡20.9 -2.6¡5.8 -85.4¡89.7 -48.5¡91.5 0.1¡0.1 0.3¡1.2 0.4¡1.0 Group II (n = 10) 1.5¡0.4 -0.14¡0.82 0.10¡0.26 0.09¡0.12 -0.40¡0.72 -0.37¡0.85 -0.03¡0.26 0.29¡0.32 5.0¡11.7 -6.3 10.6 -0.3¡3.2 5.8¡5.6 128.1¡45.4 18.5¡11.0 102.8¡104.3 191.0¡229.8 0.1¡0.1 -0.7¡1.7 -0.3 1.7 p-value 1 0.447 0.209 0.158 0.947 0.647 0.894 0.020 0.278 0.197 0.260 0.009 ,0.0001 ,0.0001 0.0004 0.007 0.785 0.142 0.312 *Group I: Changes in work load ,5 w; Group II; Changes in work load $5 w. TLC: total lung capacity; FVC: forced vital capacity; FEV1: forced expiratory volume in the first second; FRC: functional respiratory capacity; RV: residual volume; ERV: expiratory reserve volume; IC: inspiratory capacity; HR: heart rate; MBP: mean blood pressure; SaO2: peripheral arterial oxygen saturation; MV: minute ventilation; VO2: oxygen consumption; VCO2: carbon dioxide production; RER: respiratory exchange rate.