Swimming involves muscular activity and submersion creating a conflict of autonomic reflexes elicited by the trigeminal receptors and skeletal muscle afferents. We sought to determine the autonomic cardiovascular responses to separate and concurrent stimulation of the trigeminal cutaneous receptors and metabolically sensitive skeletal muscle afferents (muscle metaboreflex). In 8 healthy men (30±2 yr) muscle sympathetic nerve activity (MSNA; microneurography), mean arterial pressure (MAP; Finometer), femoral artery blood flow (duplex Doppler ultrasonography) and femoral vascular conductance (femoral artery blood flow / MAP) were assessed during three experimental conditions; 1) facial cooling [trigeminal nerve stimulation], 2) post-exercise ischemia [PEI; muscle metaboreflex activation] following isometric handgrip, and 3) trigeminal nerve stimulation with concurrent PEI. Trigeminal nerve stimulation produced significant increases in MSNA total activity (Δ347±167%) and MAP (Δ21±5%), and a reduction in femoral artery vascular conductance (Δ-17±9%). PEI also evoked significant increases in MSNA total activity (Δ234±83%) and MAP (Δ36±4%), and a slight non-significant reduction in femoral artery vascular conductance (Δ-9±12%). Trigeminal nerve stimulation with concurrent PEI evoked changes in MSNA total activity (Δ341±96%), MAP (Δ39±4%) and femoral artery vascular conductance (Δ-20±9%) that were similar to those evoked by either separate trigeminal nerve stimulation or separate PEI. Thus, excitatory inputs from the trigeminal nerve and metabolically sensitive skeletal muscle afferents do not summate algebraically in eliciting a MSNA and cardiovascular response, but rather exhibit synaptic occlusion suggesting a high degree of convergent inputs on output neurones.
|Journal||American Journal of Physiology. Heart and Circulatory Physiology|
|Early online date||19 Dec 2014|
|Publication status||Published - 1 Mar 2015|
- diving response