Study on circadian changes in autonomic function in heart failure and central hypercapnic chemosensitivity

This study was designed to determine abnormal circadian variations in autonomic function in rats with heart failure. We developed an experimental system that enables continuous 24-48 hour sampling of blood pressure and heart rate in conscious, unrestrained rats. Low frequency components of diastolic blood pressure variability, an index of sympathetic tone, were higher during the awakening period than during the sleeping period. The enhanced sympathetic tone during the awakening period was related to an augmentation of central chemosensitiviy evaluated by hourly intermittent hypercapnic conditions.