ver the past 2 decades, many studies have shown that a number of factors contribute to the exercise intolerance of patients with chronic heart failure (CHF). Factors suggested include skeletal muscle underperfusion caused by central hemodynamic alterations such as diminished cardiac output, as well as left ventricular (LV) 1-3 and right ventricular dysfunction, 4 and abnormalities in peripheral mechanisms such as skeletal muscle vasodilation, 5-7 skeletal muscle histology, 8,9 metabolism, 10-14 and muscle oxygen uptake. 15,16 Blunt vasodilation during exercise is also reported in apparently healthy, coronary highrisk subjects. 17 Among these factors, cardiac output and skeletal muscle vasodilation are the important determinants of skeletal muscle blood flow during exercise. Particularly in patients with CHF, impaired skeletal muscle vasodilation plays a key role in their exercise intolerance by reducing muscle blood flow. Therefore, the evaluation of muscle vasodilation during exercise is an important issue; however, until recently, no non-invasive method by which to assess muscle vasodilation during dynamic exercise had been available.Near-infrared spectroscopy (NIRS) is a non-invasive method suitable for the measurement of tissue oxygenated and deoxygenated hemoglobin (Hb) and myoglobin (Mb) content. This technique utilizes the principal that the absorbance of light by oxygenated Hb and Mb (oxy-Hb + Mb) and deoxygenated Hb and Mb (deoxy-Hb + Mb) differs at different near-infrared wavelengths. 18 By using NIRS, oxyHb + Mb, deoxy-Hb + Mb and total-Hb + Mb can be measured. As the amount of Mb does not change over a short period of time, the changes in total-Hb + Mb represent the changes in total Hb, that is, the blood volume, and because blood exists in blood vessels, we hypothesized that changes in working muscle total-Hb + Mb indicate muscle vasodilation, that is, the conductance of the vessel.The present study was designed to investigate whether the changes in total-Hb + Mb obtained by non-invasive measurement using NIRS reflect blood vessel conductance of working muscle during exercise.
Methods
SubjectsTen male patients without LV systolic dysfunction (normal LV systolic function group) and 6 male patients with cardiac dysfunction (cardiac dysfunction group) participated in this study. The clinical characteristics of the participants are shown in Table 1.The mean age of the normal LV systolic function group was 64±10 years. Clinical diagnoses were angina pectoris in 6 patients, arrhythmia (paroxysmal atrial fibrillation or Background In patients with chronic heart failure, an inadequate increase in muscle blood flow resulting from impaired vasodilation plays a key role in their exercise intolerance. However, no non-invasive methods to assess muscle vasodilation during dynamic exercise were available. We investigated whether the changes in tissue hemoglobin and myoglobin content (total-Hb + Mb) determined by non-invasive measurement using near-infrared spectroscopy (NIRS) reflect vessel conductance of working ...
