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xercise intolerance and left ventricular dysfunction are both significant predictors of prognosis in patients with heart failure. 1 In these patients, exercise capacity is limited by abnormalities of cardiac function, ventilation, skeletal muscle blood flow, skeletal muscle oxygen extraction, or skeletal muscle metabolism. 2 Methods to assess blood flow and oxygen kinetics in the lower limbs have utilized femoral vein catheter techniques (including thermodilution, dye-dilution and determination of the difference between arterial and venous oxygen), 3 venous plethsmography 4 and the 133 Xe technique. 5 However, all these methods are difficult to apply to working muscles during exercise. Since the application of near-infrared (NIR) spectroscopy in vivo by Jöbsis, 6 it has been used as a non-invasive method to assess the oxygen kinetics in tissues, mainly through monitoring the oxygenation and deoxygenation of hemoglobin, 7 although this method cannot measure myoglobin and hemoglobin separately. In animal and human skeletal muscles during exercise, the changes in oxygenated hemoglobin (oxy-Hb) content measured by NIR spectroscopy bears a high correlation with the changes in venous hemoglobin oxygen saturation, and could be used to determine the oxygen kinetics in working muscles during exercise. 8,9 Wilson et al reported greater oxy-Hb decrease in the vastus lateralis muscles in heart failure patients than in sedentary normal subjects at the same work rate, and demonstrated the possible clinical applications of the method. 8 Matsui et al reported an earlier occurrence of oxy-Hb decrease in femoral muscles in patients with heart failure compared to normal subjects. 10 However, NIR spectroscopy measures the relative changes of oxy-Hb, deoxygenated hemoglobin (deoxy-Hb) and total hemoglobin volume (total-Hb) using NIR light absorption changes, and quantification of these parameters in human is difficult to achieve.Belardinelli et al performed constant load exercise tests in normal subjects, and reported that oxy-Hb reached a constant state at a workload lower than the anaerobic threshold (AT; obtained from expired gas analysis) but decreased at a workload higher than the AT. 11 Another study that used a ramp load in normal subjects, identified the inflection point of oxy-Hb decrease in the femoral quadriceps muscle and reported a high correlation with the AT. 12 Takahashi et al performed ramp load exercise tests in athletes, normal subjects and patients with heart failure, and reported an inflection point of oxy-Hb decrease in the femoral quadriceps muscle and a high correlation with the AT. 13 If an inflection point can be identified from the NIR spectroscopy measurements of oxy-Hb changes in working muscles, then quantification may be possible by simultaneously analyzing the expired gas which provides the oxygen uptake (V • O2) at specific points of oxy-Hb and deoxy-Hb changes. Although the AT and the respiratory compensation point (RCP), which is the starting point of respiratory compensation against metabolic acid...

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Exercise testing (EX) and Holter ECG (DCG) were performed consecutively in 52 patients with ischemic heart disease. A total of 100 episodes of myocardial ischemia (IE) were recorded during DCG in 30 patients, who constituted 94% of the patients with myocardial ischemia under 6 metabolic equivalents (METs) during EX. A significant increase in heart rate (HR) was observed before the development of IE. The duration of this increase in HR was longer in IE than in periods in which the HR increased above the ischemic threshold, but without ischemia. The incidence of IE showed two peaks at 8-10 am and 4-6 pm. The frequency of IE among all of the periods with increased HR was highest at 8-10 am (51%). IE in the morning was associated with a lower HR than that in the afternoon, and LF/HF, which reflects sympathetic activity, evaluated using power spectral analysis, increased before IE in the morning. The early appearance of myocardial ischemia in EX can predict its appearance in daily life. The increase in HR and its duration appear to be associated with the development of IE. The increases in sympathetic activity in the morning and the increase in myocardial oxygen demand accompanied by physical activity in the afternoon most likely contributed to the circadian variation in the incidence of ischemic episodes.