Failure in evoking the trigeminal cardiac reflex by mandibular stretching in healthy volunteers

Stimulation of trigeminal sensory afferences has been reported to evoke hypotension and bradycardia, a phenomenon known as the trigeminal cardiac reflex. We attempted to evoke such a reflex through cycles of alternate mandibular stretching in healthy volunteers, as previously reported, for its possible therapeutic exploitation. In Phase 1 of the study, 10 healthy volunteers [5 male, 5 female, age (mean ± SD) 27±2 years)] underwent 2 randomized sessions of automated monitoring, every 6 minutes, of systolic blood pressure (SBP), diastolic (D) BP, and heart rate (HR), with a one-week interval, either with mandibular stretching (12 minutes with a spring device fitted in the mouth), or nothing (control). Observation was prolonged for 180 minute after the end of the stretching. In Phase 2, 7 other volunteers (4 male and 3 female, age 24±1.3 years) repeated the protocol with a sampling interval of 2 minutes until the end of stretching. Baseline levels of SBP, DBP and HR were similar in the test and control sessions. There was a progressive fall of BP and HR as a function of time during the test session. With stretching: SBP changed from 119.2±10.1 to 118.1±10.1 to 115.8±10.5 mmHg, at baseline, end of stretching and 180 minutes after, respectively, p<0.001 at ANOVA for time effect). However, similar changes occurred in the control group: from 120.7±12.0 to 120.8±12.0 to 115.4±3.6 mmHg at the same times, P=0.822 for group effect). In Phase 2, again we observed no significant changes for any of the parameters investigated as a function of treatment. Despite attempts at maximum standardization of study condition and the use of operator-independent BP and HR measurements, we could not detect significant BP or HR effects of repeated mandibular stretching.