Sex differences in central and peripheral cardiovascular response with trigeminal nerve stimulation during dynamic exercise
Authors: Prodel Eliza , Barbosa Thales Coelho , Galdino Iuri , Alexandria Gabrielly , ClaudioNobrega Antonio , Vianna Lauro Casqueiro 
Published: November 2023

The trigeminal nerve stimulation (TGS) partially evokes the mammalian diving reflex, which stimulates both branches of the autonomic nervous system. This reflex causes profound cardiovascular changes characterized by pressor response and bradycardia. In turn, dynamic exercise evokes sympathetic activation and vagal withdraw increasing cardiac output (CO) that matches metabolic demand. Therefore, TGS during dynamic exercise might evoke complex autonomic interactions, and the net effect on the cardiovascular system is not completely understood. Furthermore, it is known that sympathetic mediated cardiovascular responses are different between men and women. Hence, we sought to determined central and peripheral cardiovascular response with TGS during dynamic exercise in men and women. Nine men (age 28±3 yr; BMI 24±1 kg/cm2; mean±SD) and thirteen women (age 26±5yr; BMI 23±2 kg/cm2; mean±SD) were tested. We measured, heart rate (HR), blood pressure (BP), CO, total vascular resistance (TVR) and estimated the augmentation index (AIx), augmented pressure (AG), transient time of the reflected wave (TR) and the energy wasted by the myocardium (EW) by applanation tonometry. Values are reported as means±SE. At rest, TGS decreased HR (men Δ−10±4 bpm; women Δ −3±2 bpm; p>0.05), increased mean BP (men Δ24±2 mmHg; women Δ22±3 mmHg; p>0.05 sex), TVR(men Δ2.2±0.4 mmHg.min.L−1; women Δ2.0±0.5 mmHg.min.L−1; p>0.05 sex) and CO (men Δ0.2±0.2 L.min−1; women Δ0.7±0.2 L.min−1; p>0.05 sex)), in the same magnitude in men and women. The AIx at 75bpm and EW increased (men Δ22±3%; women Δ25±3%; p>0.05 sex; men Δ1100±257 dynes.cm2.s−1; women Δ1189±173 dynes.cm2.s−1; p>0.05 sex) during TGS. TR decreased more in women during the TGS (men Δ −7±2 ms; women Δ −15±2 ms; p<0.05 sex). There was no correlation between AIx and blood pressure in men or women at rest. However, the increase of the AIx positively correlated with the increase of mean PB only in women (men r=0.15, p=0.7 and women r=0.61, p=0.02). During exercise TGS evoked bradycardia only in men (men Δ −8±3 bpm; women Δ0±1 bpm; p<0.05 sex). Mean BP increased in both groups, but the magnitude was higher in women (men Δ14±3 mmHg; women Δ24±2; p<0.05 sex). The AG was higher in women and did not change with TGS; AIx was higher in women and increased in the same magnitude during the TGS (men Δ16±3 %; women Δ10±1; p<0.05 ANCOVA). EW increased in both groups during TGS, but with a higher increase in men (men Δ912±209 dynes.cm2.s−1; women Δ 348±109 dynes.cm2.s−1; p<0.05 sex). Men had higher CO and TGS did not change it; although women had higher TVR, TGS evoked the same magnitude of increase in both groups (men Δ1.5±0.3 mmHg.min.L−1; women Δ1.8±0.4 mmHg.min.L−1; p>0.05 sex). In conclusion, the cardiovascular control during the TGS is sex specific. Additionally, exercise blunted the cardiovascular response to diving reflex, but further investigations are needed to fully understand the underlying mechanism.Support or Funding InformationCAPESCNPqFAPERJ