METHODS

Twenty non-smoking, healthy men and women, mean (SD) age 33 (7) years, with normal blood pressure, cholesterol, and blood glucose provided written informed consent to participate in this randomised and counterbalanced, crossover study approved by the institutional review board. After an overnight fast that included abstinence from alcohol, vitamins, herbs, and aerobic activity, volunteers had a baseline brachial artery reactivity test and were then randomly assigned to view a 15–30 minute segment of a movie designed to induce either mental stress or laughter. Each subject was instructed to watch as much of the movie as necessary until they felt they had been affected by viewing it. Volunteers watched the movie while lying in a recumbent position in a temperature controlled room (22 C). An example of a movie causing mental stress is the opening scene of Saving Private Ryan (DreamWorks, 1998). Laughter was readily elicited when observing selected scenes of a comedy such as the movie Kingpin (MGM, 1996) or There’s something about Mary (20th Century Fox, 1998). Because the time course of the effects of laughter or mental stress on endothelial function has not been established, a minimum of 48 hours elapsed between the two arms of the trial to minimise the possibility of an interphase effect. Baseline brachial artery reactivity was tested in each of the two phases and one ultrasonographer performed all studies. Brachial artery flow mediated (endothelial dependent) vasodilatation (FMD) was measured with an 11.5 MHz broadband linear array transducer and baseline images were acquired after a 15 minute supine equilibration period by well established methods. 5 Post-stimulus images were acquired one minute�15 seconds after the release of a five minute upper arm occlusion. A total of 160 arterial measurements were taken including measurements before and one minute after laughter and mental stress phases. FMD was quantified as the percentage diameter change of the post-occlusion arterial diameter measurement relative to baseline. An experienced investigator blinded to the subject’s identity and study phase analysed the end diastolic frames. The paired t test was used to compare brachial artery FMD before versus after the laughter phase, as well as before versus after the mental stress phase. The two baseline phases and the post-laughter/post-mental stress phases were also compared.

RESULTS

Brachial artery FMD was reduced in 14 of the 20 volunteers after watching the movie clips that caused mental stress. In contrast, brachial vasodilatation was increased in 19 of 20 volunteers after watching the movie segments that generated laughter (p< 0.0001). Significant changes in flow mediated reactivity were noted between baseline and the laughter phase (p< 0.0001) and between baseline and the mental stress phase (p= 0.017). Overall, mean (SD) upper arm FMD was increased 22 (15)% during laughter and reduced 35 (47)% during mental stress (p< 0.0001) with absolute changes of 2.6 (1.9)% and− 1.9 (3.2)%, respectively (p= 0.0007)(fig 1). The groups did not differ in baseline diameters or baseline flow mediated reactivity (9.6 (4.1)% and 8.8 (2.8)% in the mental stress and laughter phases, respectively) suggesting consistent image acquisition scan technique and internal consistency of measurements.