Slowing and attenuation of baroreflex heart rate control with nitrous oxide in exercising men

• Published in: Journal of applied physiology (1985) Vol. 87; no. 2; pp. 830 - 834
• Main Authors: Ostlund, A, Linnarsson, D
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Am Physiological Soc 01.08.1999; American Physiological Society
• Subjects: Adult; Air; Anatomy & physiology; Baroreflex - drug effects; Biological and medical sciences; Blood pressure; Blood Pressure - drug effects; Bradycardia - physiopathology; Cardiovascular System - drug effects; Computer Simulation; Electrocardiography; Exercise; Exercise - physiology; Fundamental and applied biological sciences. Psychology; Gases; Heart; Heart Rate - drug effects; Humans; Male; Medicin och hälsovetenskap; Nitrous Oxide - pharmacology; Posture; Space life sciences; Vertebrates: cardiovascular system; Human; Heart; Physical exercise; Cardiovascular control; Inert gas; Heart rate; Partial pressure; Narcosis; Baroreflex; Blood pressure; Circulatory system; Hemodynamics; Nitrogen protoxide
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1999.87.2.830

Section of Environmental Physiology, Department of Physiology and Pharmacology, Karolinska Institutet, SE-171 77 Stockholm, Sweden The objective of the present study was to determine whether mild inert-gas narcosis impairs cardiovascular control mechanisms and contributes to the relative bradycardia that occurs in humans exercising in a hyperbaric environment. Eight healthy subjects were exposed to a normoxic 30% nitrous oxide (N 2 O) mixture and an air control during dynamic exercise of 100-W intensity. Beat-by-beat heart rate (HR) and invasive arterial blood pressure measurements were made. The sensitivity and the response latency of the arterial-cardiac-chronotropic baroreflex were determined from repeated blood pressure and HR transients induced by rapid tilts between the upright and supine posture. A significant increase (37%, P    0.02) of latency in baroreflex responses was found with 30% N 2 O, as well as a significant depression (16%, P    0.05) in baroreflex sensitivity. There were no differences between air and N 2 O in steady-state HR or arterial pressure. We conclude that mild inert-gas narcosis increases the latency and decreases the gain of HR responses to arterial baroreflex stimuli, but this cannot in itself account for the modest, relative bradycardia observed during moderately heavy exercise in a normoxic, hyperbaric environment. inert-gas narcosis; sedation; orthostatis; blood pressure; chronotropic control