多段階運動負荷時の二重積の屈曲点と乳酸閾値の関係

Relation between Lactate Threshold and Double Product Break Point during Graded Exercise Test

　多段階運動負荷時の二重積が乳酸閾値近辺を境にして急増し，屈曲点（double-productbreak point；DPBP）が存在するとの仮説を検証することを本研究の目的とした．①健常者36名を対象に自転車エルゴメーターで多段階運動負荷テストを行い，心拍数，収縮期血圧，DP,DPBP，乳酸閾値（LT），換気閾値（VT）を同時測定した．②心筋梗塞患者15名と高血圧患者15名を対象に，自転車エルゴメーターで多段階負荷テストを施行し，DPと血中乳酸濃度を測定し，DPBPとLTを測定した．その結果①DPBPはLTと有意な相関を示し（r＝0.84,p＜0.01），両者間の相関係数はLTとVTの相関係数（r＝0.74,p＜0.01）よりも高かった．②全ての患者にDPBPが存在し，DPBPはLTと高い相関（r＝0.90）が認められた．極めて簡便に測定可能なDPBPは，有酸素的運動能の評価法ならびに運動療法のための運動強度決定法として有用であると考えられた．

The purpose of this study was to verify the possibility to estimate LT from the breaking points of the hemodynamic parameters during graded exercise test-ing. Thirty-six students performed a stepwise in-cremental test on cycle ergometer. The slopes of the two regression lines below and above LT as the func-tion of heart rate (HR), systolic blood pressure (SBP), and double product (DP) against VO₂, were compared respectively. In all three parameters, the slope of the regression line above the LT was significantly higher than that below the LT. Although higher slope in DP above LT was found to exist in all the subjects, 8 subjects in HR, and 4 subjects in SBP showed same or lower slope above the LT as compared to that below the LT. Objectively determined DP break-point (DPBP) was significantly correlated with the LT (r= 0.84, p＜0.001) and the ventilatory threshold (r=0.74, p＜0.01). The correlation between DPBP and LT was higher than that between the ventilatory threshold and LT (r=0.74, p＜0.001). Fifteen cardiac patients and 15 hypertensive patients also performed a similar exercise test. DPBP was detected in all of the subjects, that was also significantly correlated to LT (cardiac patients; r=0.86 p＜0.001, hypertensive patients; r=0.95 p＜0.001). The regression line to estimate LT from DPBP, calculated from the both data of healthy students and cardiac patients, was nearly coincident with the identity line. These results suggest that DPBP, which is easily measured, may become useful and practical for estimat-ing LT.