The relationship between cerebral oxygenation detected by near-infrared spectroscopy and exercise intensity in patients with cardiac diseases

Abstract

Studies using near-infrared spectroscopy (NIRS) have clearly shown an inverted U-shape relationship between cerebral oxygenation and exercise intensity in healthy adults. However, the pattern of cerebral oxygenation in patients during exercise has not been adequately established. The aim of this study was to investigate the correlation between cerebral oxygenation and exercise intensity in patients with cardiac diseases in order to find the optimal exercise intensity while prescribing cardiac rehabilitation. This observational study included 18 patients with coronary artery disease (CAD) ( n = 9), mitral valve regurgitation (MVR) ( n = 4), congestive heart failure (CHF) ( n = 4) and atrial septal defect(ASD) ( n = 1). They performed incremental cardiopulmonary exercise test (CPET) using a cycle ergometer by the ramp 10 W/min. The concentration of oxyhemoglobin (HbO 2 ), total hemoglobin (HbT) and tissue hemoglobin saturation (STO 2 ) were measured by two bands of non-invasive NIRS positioned on bilateral frontal area during the CPET. The exercise intensity related to highest STO 2 of the two hemispheres were determined. The mean ± standard deviation (SD) age of the study cohort was 58.22 ± 10.12 years and was comprised predominantly of men (77.8%). Five patients reached highest STO 2 during warm-up, 3 after anaerobic threshold, 4 after respiratory compensation point, 6 during recovery stage. The 5 patients with downsloping STO 2 were patients with MR ( n = 3), with ASD ( n = 1), and with CHF ( n = 1). Excluding the 5 patients of downsloping pattern, the mean highest STO 2 of right hemisphere was 49.6622 ± 1.8046 (mM) and left hemisphere was 50.5095 ± 1.7310 (mM). The mean percentage to peak oxygen consumption during highest STO 2 of right hemisphere was 76.27 ± 14.02 (%), left hemisphere was 72.14 ± 17.94 (%). The relationship between cerebral oxygenation and exercise intensity in patients with cardiac diseases such as CAD and CHF revealed a trend as inverted U-shape, with the peak STO 2 located at moderate to high exercise intensity.