Effects of an auditory startle stimulus on blood pressure and heart rate in humans

Objective To describe the effects of an auditory startle stimulus on blood pressure (BP) and heart rate (HR) in humans. Design and methods Twenty-five volunteers, including nine untreated hyperte nsive subjects, were studied in the supine position. Polygraphic recordings were obtained for finger BP, R-R interval using ECG, respiratory movements using a thoracoabdominal belt and for electrooculomyogram using adhesive e lectrodes. Haemodynamic estimations were derived by modelling flow from the noninvasive BP signal. A background noise of 55 dB was administered throug h headphones and two acoustic startle stimuli (110 dB, 1-20 kHz, 0.15 s) we re generated at 5-min intervals during the tele-expiratory phase. The sham stimulation (0 dB, event marker) was compared with the effects of the noise stimulus (one-way ANOVA with repeated measures followed by a protected t t est for multiple comparisons). Results A biphasic cardiovascular profile was observed in response to noise stimulation. Blood pressure and HR increases were combined in the early re sponse (0-10 s) observed after the immediate motor contraction (blink), The average systolic BP rise was 18.7 +/- 2.7 mmHg (peak at 5.1 s) and the ave rage HR increase was 10.8 +/- 1.1 bpm (peak at 3.4 s) for the first stimulu s. These effects were highly significant compared with the sham response (P < 0.01). The second stimulus elicited BP and HR rises of a lesser amplitud e (P < 0.01). The delayed response (10-30 s) corresponded with a moderate B P decrease. The haemodynamic indexes suggest that the early rise in blood p ressure reflects a rise in total peripheral resistance. Conclusion This is the first description of the BP response to an acute lou d noise in humans. The early (within 10 s) BP and HR rises may depend upon the autonomic component of the startle reflex. One application of this test could be the discrimination of the different classes of antihypertensive d rugs according to their sites of action. (C) Lippincott Williams & Wilkins.