Nitrous Oxide Inhalation Attenuates an Increase in Muscle Sympathetic Nerve Activity during Cold Stress

Abstract

Nitrous oxide inhalation was reported to suppress pressor response to pain stimulation, while an increase in heart rate (HR) remained unchanged. We evaluated whether nitrous oxide inhalation attenuates an increase in muscle sympathetic nerve activity (MSNA) during cold stress. MSNA (microneurography), arm cuff and beat‐to‐beat blood pressure (BP), and HR were measured during 5‐min baseline, 2‐min cold pressor test (CPT) in 12 young men [30±1 (SE) yrs] after they receive room air, 100% oxygen, 30%, and 40% nitrous oxide for 20 min through a mask, respectively. BP increased during CPT in all conditions, while the increase of systolic BP tended to be smaller during inhalation of 40% nitrous oxide than room air (26±5 vs 15±4 mmHg, P=0.081). HR also increased during CPT without any difference the increase between the conditions. MSNA burst frequency increased during CPT, while the increase was smaller during the inhalation of 40% nitrous oxide than room air (21±4 vs 12±3 burst/min, P=0.045). Change (Δ) in systolic BP during CPT was correlated with ΔMSNA burst frequency (r=0.40), but not ΔHR (r=0.06) in all conditions. These results suggest that suppressed pressor response to pain stimuli by inhalation of nitrous oxide is attributable to the attenuation of increase in muscle sympathetic nerve activity.Supported by JSPSKAKENHI70566661.