Clinical Significance of Cerebral Oxygenation During Exercise in Patients With Coronary Artery Disease

Abstract

n resting conditions, complex compensatory mechanisms are believed to adequately regulate blood flow to vital organs, especially to the brain. During exercise, however, the O2 demand of exercising muscles surges to levels 10-15 times higher than that in the resting condition. The blood flow to the exercising muscles increases tremendously to meet this sudden surge in O2 demand, thereby leading to a relative hypoperfusion of other organs. Our group recently studied cerebral oxygenation during exercise using near-infrared spectroscopy (NIRS) in patients with left ventricular dysfunction. 1 We found, as a result, that nearly half of the patients exhibited decreases in the cerebral oxyhemoglobin (O2Hb) during exercise, and that the decrease was more prominent in patients with a lower left ventricular ejection fraction (LVEF). 1 In these patients, cerebral O2Hb, a parameter that initially remained constant at lower work rates during incremental exercise, began to decrease at higher work rates. 1,2 The decrease in cerebral O2Hb presumably reflected a cerebral hypoxia during exercise resulting from impaired O2 transport to the brain.While risk stratification of chronic heart disease had been primarily based on resting hemodynamic measurements, cardiopulmonary exercise testing (CPX) has now become indispensable in singling out those patients with a poor prognosis. Among the parameters obtained from CPX, the peak O2 uptake (V • O2) is considered a gold standard for identifying patients with a poor prognosis and selecting candidates for cardiac transplantation. 3 The ratio of the increase in ventilation (V • E) to the increase in CO2 output (V • CO2) during exercise (V • E/V • CO2 slope) and the ratio of the increase in V• O2 to the increase in work rate (ΔV • O2/ΔWR) are also independent prognostic markers in cardiac patients. 4 In 1999, Lee et al reported that cerebral metabolism measured by magnetic resonance spectroscopy is abnormally deranged in patients with heart failure. 5 They also found that this abnormality is an independent predictor of mortality in these patients. 6 The cerebral metabolic abnormality is assumed to be due to overall and/or local disturbances of cerebral blood flow, that is, impaired cerebral oxygenation. 5 The impaired cerebral oxygenation can be detected by the non-invasive measurement of cerebral O2Hb using NIRS, and the detection might be more sensitive during exercise in which the O2 demand by exercising muscles increases tremendously, rather than measurements taken at rest. If the cerebral metabolic abnormality resulting from decreased cerebral O2 transport is related to prognosis, the decrease in cerebral O2Hb during exercise must also influence the prognosis.In the present study, we sought to establish a prognostic value of decreased cerebral O2Hb during exercise in cardiac patients. We selected patients with coronary artery disease, and compared the prognostic power of cerebral O2Hb during exercise with those of established respiratory gas indexes obtained from CPX, as cerebral oxygena...

Preoperative Cerebral Oxygen Saturation and Clinical Outcomes in Cardiac Surgery

“…24 Koike et al showed that the decrease in ScO 2 during exercise in patients with coronary artery disease had prognostic effect and was associated with an unfavorable outcome in these patients. 25 Paquet et al observed that baseline ScO 2 was related to LVEF in patients undergoing cardiac surgery and that ScO 2 had an acceptable accuracy to identify left ventricular dysfunction in these patients. 26 The findings of the current study, showing significant correlations between NTproBNP, hsTNT, LVEF, and ScO 2 in a large patient sample, support the concept that ScO 2 is influenced by myocardial function and the performance of the cardiopulmonary system.…”

Oxygen Uptake Kinetics During and After Exercise are Useful Markers of Coronary Artery Disease in Patients With Exercise Electrocardiography Suggesting Myocardial Ischemia

“…• O2 decay in recovery is not affected by the exercise duration in an increasing work rate test 12,17 and is easily determined when patients perform at least 50% of maximum exercise. Another advantage for use of T1/2 in recovery as a marker for myocardial ischemia is its sensitivity and specificity.…”

Letter to the Editor, "Clinical Significance of Cerebral Oxygenation During Exercise in Patients With Coronary Artery Disease"

“…Therefore, speculations on the forehead oxygenation changes based only on the increase and decrease of O2Hb during the exercise are not fully reliable. Considering the potential clinical relevance of their findings, 1 we would suggest they expand the results to include the TOI data as correctly done in their other recent interesting clinical studies. 10,11 …”

“…With great pleasure we read the article by Koike et al 1 This is an interesting study investigating, by non-invasive near infrared spectroscopy, 2 the forehead cortical oxy-hemoglobin changes (∆O2Hb) during an incremental symptomlimited cycling exercise test in 344 cardiac patients, and comparing the data with indexes obtained from cardiopulmonary exercise testing. The ∆O2Hb measured from rest to peak exercise was significantly lower in non-survivors than in survivors, suggesting that a decrease in cerebral O2Hb during exercise predicts future cardiovascular events in patients with coronary artery disease.…”