Does the coefficient of variation of the R-R intervals in diabetic patients and healthyu subjects reflect the cardiovascular response during exercise?

糖尿病患者と健常者のR-R間隔変動係数(CVR-R)と運動時における循環応答との関連を検討した。対象は2型糖尿病患者8名と,年齢をマッチさせた健常男性8名とした。対象者に自転車エルゴメータを用いた漸増負荷を行い,最大酸素摂取量(・VO2max)と換気性作業閾値(VT)を算出した。次に日を改めて,80%VTに相当する負荷強度で一定負荷運動を行わせた。その後,安静時におけるCVR-Rと,一定負荷運動における酸素摂取と心拍数の時定数を算出した。その結果,1)CVR-Rと・VO2maxはDM群で健常群と比較して低下していた。また,tau HRとtau・VO2はDM群で延長していた。2)tau・VO2とtau HRは二群共に正の相関を,CVR-Rとtau ・VO2は二群共に負の相関を認めた。2・VO2maxとtau HR,・VO2maxとtau・VO2は健常群のみ負の相関を認めた。以上の結果から,CVR-Rは運動に対する循環応答を反映する指標になる可能性が示唆された。また,先行研究において,健常者では運動開始時における循環応答特性は全身持久力を反映するものであることが示唆されているが,本研究では糖尿病患者においては関連を認めないことが明らかとなった。

OBJECTIVE: We investigated the relation of the coefficient of variation of the R-R intervals in diabetic patients and healthy subjects, and the cardiovascular responses during exercise. RESEARCH DESIGN AND METHOD: The subjects were 8 males with type 2 diabetes mellitus, and 8 age-matched healthy nondiabetic males (healthy controls). All subjects performed an incremental test on a bicycle ergometer at a work rate of 15 Watt・min-1 to determine the maximum oxygen uptake and to calculate ventilatory threshold. Subsequently, on another day, they all performed a constant-load exercise at a work rate chosen to elicit an oxygen uptake equivalent to 800f their individual the ventilatory threshold. The coefficient of variation of the R-R intervals (CVR-R) was calculated from the electrocardiogram at rest and used as an index of autonomic nerve function. The time constant (tau) and steady state level of the kinetic response for oxygen uptake (VO2) and heart rate (HR) were calculated using a mono-exponential model under constant- load exercise. RESULTS: 1) CVR-R andVO2max were significantly lower in the diabetic patients than in the healthy controls. Tau HR and tauVO2 were significantly longer in the diabetic patients than in the healthy controls. 2) TauVO2 and tau HR were significantly positively correlated in both groups, whereas CVR-R and tau HR, and tauVO2 were significantly negatively correlated in both groups. 3)VO2max and tau HR, and tauVO2 were significantly negatively correlated only in the healthy controls. CONCLUSIONS: These results suggest that CVR-R may reflect the characteristics of cardiovascular responses to exercise. However, though some previous studies have postulated that these characteristics of cardiovascular responses to exercise reflect cardiorespiratory endurance in healthy controls, our study confirmed no such correlation in diabetic patients.