Spectral analysis of blood pressure and heart rate variability in response to stress from air-jet in the Lyon rat.

1. Power spectral analysis of the frequency of wave-forms of blood pressure and heart rate was used to characterize short-term fluctuations of these parameters in three strains of conscious Lyon rat, normotensive (LL and LN) and hypertensive LH. 2. A mild stress produced by means of a jet of air elicited blood pressure rises, associated with tachycardia. This response was of similar magnitude in the three strains. The stressor amplified the medium frequency (195-605 mHz) Mayer waves of blood pressure and heart rate which are under autonomic control. 3. Clonidine (10 micrograms kg-1 i.v.) lowered blood pressure and heart rate and dramatically reduced the amplitude of blood pressure and heart rate oscillations in the frequency region of 195-605 mHz. 4. A jet of air applied after clonidine administration led to blood pressure rise associated with tachycardia and enhanced oscillations in the 195-605 mHz region. 5. These results indicate that in Lyon normotensive and hypertensive rats, a mild emotional stressor elicits blood pressure and heart rate rises associated with spectral modifications reflecting sympathetic hyperactivity. Clonidine lowers blood pressure and heart rate and reduces their related variabilities. This effect is more pronounced in LH rats than in their normotensive controls. Clonidine appears to reduce the autonomic response to stress as indicated by the medium frequency oscillations.