A number of stressors (e.g. cold pressor, mental arithmetic, breath holding) have been used to investigate the cardiovascular response to stress (Herd, 1991). Blood pressure (BP) has been found to increase but heart rate (HR) responses have been found to vary with the stressor type (commonly a decrease).

Voluntary breath-holding (VBH) has been used as a stressor but the effect of involuntary breath-holding (IBH), requiring a mechanical shutter to occlude breathing, has not been reported.

The aim of this study was to investigate the effect of normal inspiratory VBH and IBH on BP and HR. We expected that IBH would produce a bigger stress response than VBH.

With local ethics committee approval, twenty-four healthy Caucasian student volunteers (12 males, 12 females), mean ± S.D. age 21 ± 2.57 years, height 1.68 ± 0.08 m, weight 69 ± 0.03 kg were tested wearing a noseclip in the seated position. Each completed three VBH and three IBH testings, with a minute’s rest after each breath hold. Basal measurements of BP using an automatic sphygmomanometer and HR using an electrocardiograph were taken before each breath hold. Measurements were taken in the first 30 s of breath holding.

Differences in mean data (basal versus VBH or IBH ) were analysed at the 95 % significance level using a Student’s paired t test where *P < 0.05, **P < 0.01, ***P < 0.001.

Basal measurements (mean ± S.E.M.) of systolic blood pressure (SBP), diastolic blood pressure (DBP) and HR were 112.2 ± 2.7 mmHg, 73.8 ± 1.4 mmHg and 71.7 ± 2.6 beats min^-1, respectively, and these increased during VBH to 119.6 ± 3.2 mmHg***, 78.4 ± 2.3 mmHg** and 74.0 ± 2.9 beats min^-1, respectively.

Basal measurements of SBP, DBP and HR were 112.1 ± 2.5 mmHg, 73.2 ± 1.4 mmHg and 72.0 ± 2.7 beats min^-1, respectively, and these increased during IBH to 115.9 ± 3.2 mmHg*, 78.4 ± 1.9 mmHg*** and 72.9 ± 2.7 beats min^-1, respectively.

Both VBH and IBH increased blood pressure but not heart rate. The change in SBP and DBP between VBH and IBH did not significantly differ (P = 0.07 and 0.68, respectively).

Our findings suggest that blood pressure and heart rate responses were not affected by stressor type.

All procedures accord with current local guidelines.