以動物模式探討阻力呼吸訓練對降低放射照射引起之橫膈肌收縮功能異常之成效

Abstract

研究背景：過去動物實驗證實，放射照射會造成急性橫膈肌收縮功能異常。吸氣肌訓練在臨床與動物實驗均已被證實可以增進吸氣肌收縮功能，然而前置性吸氣肌訓練是否可以降低因放射照射所引起的橫膈肌收縮功能異常則需進一步探討。研究目的：以動物模式探討：1）大鼠橫膈肌收縮功能、抗氧化能力及氧化傷害在1週阻力呼吸訓練後之改變；及2）此前置性訓練是否可降低放射照射引起的橫膈肌收縮功能異常及其相關機制之初探。研究方法：本研究分兩階段進行。第一階段將Sprague-Dawley（SD）大鼠隨機分配至阻力呼吸訓練（TG, n=7）與假訓練組（SG, n=6），TG以氣道限制方式進行為期1週之阻力呼吸訓練，SG則接受假手術。兩組大鼠在訓練1週後犧牲並取下橫膈肌進行收縮功能測試、抗氧化能力與氧化傷害分析。第二階段將大鼠隨機分配至訓練後+放射（TR, n=6）與假訓練後+放射組（SR, n=6）。訓練同第一階段。訓練後，兩組大鼠之橫膈肌均接受5 Gy單次放射照射，並於照射後24小時犧牲取下橫膈肌進行收縮功能測試、抗氧化能力與氧化傷害分析。抗氧化能力以總SOD活性、CuZnSOD與MnSOD mRNA表現量分析，而氧化傷害則以蛋白質羰基及8-OHdG濃度來分析。以廣義估計或線性廣義方程式分析相關測試參數在組間與組內之差異，統計顯著水平為0.05。結果：氣道限制法提供平均1.6倍之呼吸阻力。第一階段結果顯示，1週的阻力呼吸訓練可增加大鼠橫膈肌之收縮力（p<0.05）、總SOD活性（p=0.004）、及MnSOD mRNA表現量（p=0.03），但蛋白質羰基濃度也會顯著上升（p<0.001）。第二階段結果顯示，先訓練再接受放射照射後，TR大鼠橫膈肌之收縮力顯著大於SR（p<0.05），疲勞指數（p=0.002）與蛋白質羰基濃度（p<0.001）則顯著小於SR。TR之相對張力-頻率曲線相較於SR在30-50 Hz間有顯著向下偏移之情形。TR之CuZnSOD與MnSOD mRNA表現皆顯著大於SR（p均<0.05）。結論：本研究結果顯示1週之阻力呼吸訓練可增加橫膈肌之收縮功能，並藉由正調控其抗氧化能力來減少放射照射引起之橫膈肌功能異常。

Background: Radiotherapy (RT) had shown to induce acute diaphragm contractile dysfunction. Inspiratory muscle training (IMT) have proven to be effective in enhancing contractile function of the muscle; however, whether IMT prior to RT could ameliorate RT-related contractile dysfunction remains to be determined. Purposes: The purposes of this study were to investigate: 1) the effect of 1-week resistive breathing training on contractile function, antioxidant capacity and oxidative injury of the diaphragm; and 2) the effect of this training on RT-induced diaphragm contractile dysfunction and exploring the potential underlying mechanism in animal model. Methods: This study included two phases. In phase I, Sprague-Dawley (SD) rats were randomized into training (TG, n=7) or sham training (SG, n=6) group. TG received resistive breathing training using tracheal banding method for 1-week and SG received sham operation. Upon the completion of training, rats in both groups were sacrificed and the diaphragms were removed en bloc for contractile function assessment, antioxidant capacity and oxidative injury analysis. Antioxidant capacity analysis included total SOD activity, CuZnSOD and MnSOD mRNA expression. Oxidative injury was analyzed using protein carbonyl and 8-OHdG. In phase II, SD rats were randomized into training then RT (TR, n=6) or sham training then RT (SR, n=6) group. Training method was identical to that of phase I. After the completion of training, rats in both groups received one-shot 5 Gy RT to the diaphragm region. Twenty-four hours following RT, all rats were sacrificed and the diaphragms were removed for all the analyses as described in phase I. Generalized Estimated Equation and Generalized Linear Model were used to detect differences of variables between and within groups when suitable. Significant α level was set at 0.05. Results: Tracheal banding provided an average of 1.6 times increases in airway resistance. After 1-week of training, contractility (p<0.05), total SOD activity (p=0.004), and MnSOD mRNA expression (p=0.03) of the diaphragm were significantly higher in TG than those of SG. However, protein carbonyl level of the diaphragm were also increased after training (p<0.001). In phase II, contractility of the diaphragm were significantly higher (p<0.05), while fatigue index (p=0.002) and protein carbonyl level (p<0.001) were lower in TR than those of SR. Compared to SR, relative force-frequency curve showed significant downward shift between 30-50 Hz in TR. mRNA expression of CuZnSOD and MnSOD were significant higher in TR than those of SR (both p<0.05). Conclusions: This study showed that 1-week resistive breathing training could enhance diaphragm contractile function and thus reducing RT-induced its dysfunction through training related upregulation of antioxidant capacity of the diaphragm.