Mg loading and exercise on COPD Amaral AF et al. Table 2 - Effects of Mg loading on the pulmonary function parameters of 20 COPD patients*. CLINICS 2012;67(6):615-621 TLC (l) FVC (l) FEV1 (l) FEV1/FVC (%) FEF25-75% (l) FRC (l) RV (l) ERV (l) IC (l) Before 6.35¡1.16 2.85¡0.80 1.27¡0.56 43.4¡10.4 0.44¡0.27 4.34¡1.07 3.40¡1.03 0.94¡0.58 1.98¡0.49 Saline After 6.47¡0.95 2.88¡0.88 1.26¡0.61 42.4¡11.1 0.40¡0.22 4.38¡0.83 3.54¡0.99 0.85¡0.56 2.07¡0.56 Before - After 0.12¡0.80 0.03¡0.24 -0.01¡0.10 -0.95¡3.21 -0.03¡0.11 0.04¡0.84 0.13¡0.83 -0.09¡0.23 0.09¡0.31 Before 6.19¡0.85 3.11¡0.72 1.28¡0.53 42.4¡10.5 0.43¡0.24 4.12¡0.83 3.21¡0.69 1.02¡0.72 2.05¡0.43 Mg After 6.01¡1.04 3.18¡0.80 1.31¡0.56 42.7¡9.9 0.43¡0.24 3.75¡1.01 2.87¡0.92 0.87¡0.50 2.25¡0.48 Before - After -0.18¡0.90 0.07¡0.19 0.03¡0.13 0.29¡3.41 -0.01¡0.10 -0.37¡0.93 -0.34¡0.97 -0.14¡0.51 0.20¡0.27 Treatment effect (CI 95%) (Mg-Saline) p-value -0.30 (-0.73 – 0.13) 0.03 (-0.08 – 0.14) 0.04 (-0.03 – 0.11) 1.24 (-0.88 – 3.36) 0.03 (-0.04 – 0.09) -0.41 (-0.82 – -0.01) -0.47 (-0.92 – -0.02) -0.05 (-0.29 – 0.19) 0.12 (-0.05 – 0.28) 0.161 0.542 0.227 0.235 0.370 0.048 0.042 0.677 0.148 *TLC: total lung capacity; FVC: forced vital capacity; FEV1: forced expiratory volume in the first second; FEF25-75%: middle curve forced expiratory flow; FRC: functional residual capacity; ERV: expiratory reserve volume; IC: inspiratory capacity. Most important, this study also demonstrated that acute IV loading with 2 g of Mg sulfate attenuates static hyperinflation and positively affects the maximal exercise performance in stable COPD patients. We chose to investigate the effects of Mg on exercise performance following acute IV loading to guarantee similar stable clinical conditions for the COPD patients on both study days. Although the experimental conditions do not neces- sarily replicate results that would be obtained with the dietary supplementation of Mg for longer periods, they suggest that elevations in the body’s Mg levels may be associated with meaningful physiological effects for COPD. Static hyperinflation in COPD results mainly from the decreased elasticity of the lung parenchyma associated with emphysematous changes (26). In this study, treatment with Mg was associated with significant changes in the FRC and RV, indicating its substantial effect on lung hyperinflation approximately 45 minutes after the end of infusion. The decreases in the FRC and the RV are, most likely, secondary to the reductions in the expiratory airflow resistance because there is evidence that Mg antagonizes the action of calcium at the bronchial smooth muscle level, promoting relaxation and bronchodilatation (27). Other potential mechanisms leading to bronchodilatation may also include the inhibition of the release of acetylcholine at the nerve endings, stimulation of prostacyclin generation, and increases in the local synthesis of nitric oxide (28-30). The Mg loading also led to significant changes in the cardiovascular parameters at rest. The mean blood pressure dropped approximately 5.6 mmHg, and this effect was secondary to a significant decrease of the diastolic measure- ment. The latter finding suggests that Mg-promoted peripheral arteriolar dilatation and the reduction of the systemic peripheral resistance are the most important mechanisms responsible for the decrease in the mean arterial blood pressure (31). The significant effect on the group’s mean double product following Mg use indicates that the treatment was responsible for a reduction in the heart’s work and in the level of myocardial oxygen consumption at rest. A small but significant increase in SaO2 has also been found at rest following Mg administration. Although this finding could actually represent an improvement in gas exchange, an alternative explanation may be found in the vasodilatory effect of Mg itself. Because pulse oximeters evaluate SaO2 based on changes in skin color, improve- ments in peripheral perfusion associated with vasodilata- tion may lead to overestimated readings (32). The most striking finding observed in the incremental maximal exercise test was the significant improvement in Table 3 - Effects of Mg loading on the cardiorespiratory parameters of 20 COPD patients at rest*. HR (bpm) SBP (mmHg) DBP (mmHg) MBP (mmHg) SaO2 (%) Double product (bpm.mmHg) RR (bpm) TV (ml) MV (l/min) VO2 (ml/min) VCO2 (ml/min) RER PETO2 (mmHg) PETCO2 (mmHg) Saline 74.6¡11.2 137.8¡25.5 87.5¡13.3 104.3¡15.6 95.2¡2.3 10,261.3¡2,291.9 19.0¡5.4 517.0¡150.7 9.7¡3.6 204.2¡82.5 167.6¡66.4 0.83¡0.14 101.9¡5.4 30.1¡4.2 *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. Mg 72.8¡9.8 131.0¡17.1 82.5¡8.7 98.7¡10.5 95.9¡2.0 9,526.5¡1,638.5 19.3¡3.7 575.4¡222.4 9.3¡2.4 202.2¡78 167.5¡67.2 0.83¡0.10 100.9¡4.9 30.2¡3.1 618 Treatment Effect (CI 95%) (Mg-Saline) -1.8 (-5.4 – 1.8) -6.8 (-15.6 – 2.1) -5.0 (-9.2 – -0.8) -5.6 (-10.2 – -1.0) 0.8 (0.01 – 1.49) -734.8 (-1,362.6 – -106.2) 0.3 (-2.1 – 2.7) 58.4 (-62.8 – 179.5) -0.4 (-2.0 – 1.2) -2.0 (-46.9 – 43.0) -0.1 (-39.5 – 39.3) -0.01 (-0.072 – 0.062) -1.0 (-2.73 – 0.73) 0.05 (-1.14 – 1.24) p-value 0.308 0.127 0.023 0.019 0.048 0.024 0.794 0.326 0.608 0.929 0.996 0.877 0.240 0.931