[Cardiovascular responses to a acoustic startle stimulus in man]

To describe the effects of an auditory startle stimulus on blood pressure (BP) and heart rate (HR) in man. Three sound levels were tested.

Twelve normotensive volunteers were studied in supine position. Polygraphic recordings were obtained for finger BP, R-R interval using an electrocardiograph, respiratory movements using a thoracoabdominal belt and for electrooculomyogram using adhesive electrodes. A background noise of 55 dB was administered through headphones and the acoustic startle was generated using 3 synthetized white noises of 95, 110 or 120 dB administered at 5-min intervals during the tele-expiratory phase in a randomized order. Noise duration was fixed to 150 msec. The sham stimulation (0 dB, event marker) was compared to the 3 levels of noise (one way ANOVA with repeated measures followed by multiple comparisons). Confidence intervals (95%) were calculated for BP and HR using the 30 sec period preceding each stimulation to obtain individual significance of the responses for the 30 sec following each stimulation.

A biphasic cardiovascular profile was observed following noise stimulation. The early response (0-10 sec) observed after the immediate motor contraction (blink) combined BP and HR increases. The average systolic BP rise was 15.9 +/- 2.6 mmHg (peak at 4.8 sec) and the average HR increase was 11.9 +/- 1.6 bpm (peak at 2.8 sec) for the 110 dB noise. These effects were highly significant compared to the sham response (P < 0.001). This 110 dB intensity determined 44% of significant systolic BP values and 25% significant HR values during this early period. Similar profiles were obtained with 95 and 120 dB with a lesser amplitude. The delayed response (10-30 sec) combined moderate BP and HR decreases.

This is the first description of the BP response to an acute loud noise in man. The early (within 10 sec) BP and HR rises may depend upon the autonomic component of the startle reflex. The reproducibility of this cardiovascular profile obtained with a 110 dB white noise makes this test applicable to the clinical trials of antihypertensive drugs.