Background: Mind/body practices that elicit the relaxation response (RR)are currently practiced by over 30% of American adults. RR elicitation reduces volumetric oxygen consumption(VO[sub]2[/sub]) from rest and counteracts the effects of stress, although the mechanisms mediating the RR remainunknown. This study was designed to investigate whether RR elicitation is mediated by nitric oxide (NO).We developed a method to quantify depth of RR using change in VO[sub]2[/sub] (slope) during RR elicitation. Weevaluated whether depth of RR elicitation was correlated with changes in NO, as measured by percentagechanges in fractional exhaled nitric oxide (F[sub]E[/sub]NO). Material/Methods: We conducted a randomized, controlledtrial, in which 46 subjects were randomized to either 8-weeks of RR training using audiotapes (n=34)or 8-weeks of exposure to a control condition - receiving health-education by audiotapes (n=12). Priorto randomization, VO[sub]2[/sub]and F[sub]E[/sub]NO were measured while subjects listened to a control audiotape. Eightweeks later, VO[sub]2[/sub]and F[sub]E[/sub]NO were measured while the RR group listened to a RR-eliciting audiotape andthe control group listened to a control audiotape. Results: Prior to receiving any training, there wasno association between VO[sub]2[/sub]slope and F[sub]E[/sub]NO. After training, there was an inverse correlation betweenVO[sub]2[/sub] slope and F[sub]E[/sub]NO in the RR group (r=-0.41, P=0.037, n=26), but not in the control group (r=0.12,P=0.78, n=8). Conclusions: Depth of RR elicitation was associated with increased concentrations of F[sub]E[/sub]NOafter RR training. The RR may be mediated by NO helping to explain its clinical effects in stress-relateddisorders.

Keywords: Nitric Oxide - biosynthesis, Relaxation - physiology, Relaxation Therapy, Statistics as Topic, Tape Recording