Cardiovascular and respiratory profiles during the sleep-wake cycle of rats previously submitted to chronic intermittent hypoxia.

Chronic intermittent hypoxia (CIH) increases arterial pressure (AP) and changes sympathetic-respiratory coupling. However, the alterations in the sleep-wake cycle after CIH and their potential impact on cardiorespiratory parameters remain unknown. Here, we evaluated whether CIH-exposed rats present changes in their short-term sleep-wake cycle pattern and in cardiorespiratory parameters. Male Wistar rats (∼250 g) were divided into CIH and control groups. The CIH rats were exposed to 8 h day-1 of cycles of normoxia (fraction of inspired O2  = 0.208, 5 min) followed by hypoxia (fraction of inspired O2  = 0.06, 30-40 s) for 10 days. One day after CIH, electrocorticographic activity, cervical EMG, AP and heart rate were recorded for 3 h. Plethysmographic recordings were collected for 2 h. A subgroup of control and CIH rats also had the diaphragm and oblique abdominal muscle activities recorded. Chronic intermittent hypoxia did not alter the time for sleep onset, total time awake, durations of rapid eye movement (REM) and non-REM (NREM) sleep and number of REM episodes in the 3 h recordings. However, a significant increase in the duration of REM episodes was observed. The AP and heart rate were increased in all phases of the cycle in rats exposed to CIH. Respiratory frequency and ventilation were similar between groups in all phases, but tidal volume was increased during NREM and REM sleep in rats exposed to CIH. An increase in the incidence of active expiration during wakefulness was observed in rats exposed to CIH. The data show that CIH-related hypertension is not caused by changes in the sleep-wake cycle and suggest that active expiration is not required for the increase in AP in freely moving rats exposed to CIH.