Changes in blood pressure, blood flow toward head and heart rate during 90 deg head-up tilting for 30 min in anaesthetized male rats

Abstract

Changes in cardiovascular parameters during long-term 90 deg head-up tilting (HUT) in animals have been not elucidated in detail. We clarified changes in systemic blood pressure (BP), blood flow toward the head (BF), and heart rate (HR) and the role of the baroreceptor reflex after transition from the supine posture to 90 deg HUT for 30 min in anaesthetized rats (n = 13). Mean BP and BF after the onset of 90 deg HUT significantly decreased by –15.4% ± 5.9% and –26.2% ± 11.5% at 2.9 ± 1.1 s (mean ± SD, n = 12), respectively, from 90 deg HUT control values in nerve-intact of baroreceptor reflex afferents, and then immediately increased and steadied at 30.7 ± 13.1 s (plateau; by –2.8% ± 8.5% in BP and by –17.5% ± 17.4% in BF compared with control values; BP was maintained during 90 deg HUT). After acute sinoaortic denervation (SAD) in seven rats, initial decreases in BP and BF after 90 deg HUT were observed at 3.9 ± 1.0 s, similar to decreases in the nerve-intact rat; the percentage changes from control were –19.2% ± 3.7% and –32.3% ± 8.4%, respectively, the each of them at 22.4 ± 5.8 s as plateau were –8.6% ± 7.7% and –29.5% ± 15.0%, respectively, and then BP decreased gradually throughout 90 deg HUT. HR slightly increased after 90 deg HUT in nerve-intact rats, but after SAD this increase disappeared and HR decreased gradually during 90 deg HUT. These results suggest that the baroreceptor reflex contributes to maintaining adequate BP during long-term 90 deg HUT.

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