Aim: 

Spontaneous fluctuations of heart period (HP) do not buffer the low-frequency variability of blood pressure (LF-BPV) in supine humans in wakefulness. It is unclear whether this conclusion is valid in sleep, which impacts deeply on cardiovascular control.

Methods: 

To clarify this issue, we performed pilot studies on an outbred Sprague Dawley (r1) and an inbred Wistar-Kyoto (r2) rat. Rats were implanted with an arterial catheter and with electrodes for discriminating sleep states and for cardiac pacing. LF-BPV (standard deviation of mean blood pressure values due to fluctuations <0.8 Hz) was estimated in episodes of rapid-eye-movement sleep (REMS) and non-rapid-eye-movement sleep (NREMS) longer than 60 s and compared between sinus rhythm and fixed-rate atrial pacing. Data are reported as mean±SEM (number of episodes).

Results: 

During NREMS, LF-BPV (mmHg) in r1 was 1.6±0.1 (296) in sinus rhythm and 1.6±0.1 (23) during pacing. In r2, corresponding values were 2.0±0.1 (294) and 1.9±0.1 (39). During REMS, LF-BPV (mmHg) in r1 was 3.9±0.3 (22) in sinus rhythm and 3.3±0.2 (18) during pacing. In r2, corresponding values were 5.1±0.4 (19) and 4.3±0.4 (5).

Conclusion: 

These data suggest that HP fluctuations do not buffer LF-BPV in sleep. In rats, baroreflex control of HP is known to be strongest in NREMS and overridden by central autonomic commands in REMS. Our data thus suggest that baroreflex control of HP is ineffective in buffering LF-BPV in NREMS, whereas central commands on HP may enhance LF-BPV in REMS.