title: Cardiovascular System Response to Carbon Dioxide and Exercise in Oxygen-Enriched Environment at 3800 m.
abstract: BACKGROUND
  This study explores the responses of the cardiovascular system as humans exercise in an oxygen-enriched room at high altitude under various concentrations of CO₂.
  
  
  METHODS
  The study utilized a hypobaric chamber set to the following specifications: 3800 m altitude with 25% O₂ and different CO₂ concentrations of 0.5% (C1), 3.0% (C2) and 5.0% (C3). Subjects exercised for 3 min three times, separated by 30 min resting periods in the above-mentioned conditions, at sea level (SL) and at 3800 m altitude (HA). The changes of heart rate variability, heart rate and blood pressure were analyzed.
  
  
  RESULTS
  Total power (TP) and high frequency power (HF) decreased notably during post-exercise at HA. HF increased prominently earlier the post-exercise period at 3800 m altitude with 25% O₂ and 5.0% CO₂ (C3), while low frequency power (LF) changed barely in all tests. The ratios of LF/HF were significantly higher during post-exercise in HA, and lower after high intensity exercise in C3. Heart rate and systolic blood pressure increased significantly in HA and C3.
  
  
  CONCLUSIONS
  Parasympathetic activity dominated in cardiac autonomic modulation, and heart rate and blood pressure increased significantly after high intensity exercise in C3.
authors.affiliation: School of Aeronautic Science and Engineering, Beihang University, Beijing 100191, China. guohui_l@buaa.edu.cn.
authors.forename: Guohui
authors.initials: G
authors.lastname: Liu
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. liu_xiao_peng@hotmail.com.
authors.forename: Xiaopeng
authors.initials: X
authors.lastname: Liu
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. zhifeng_q@hotmail.com.
authors.forename: Zhifeng
authors.initials: Z
authors.lastname: Qin
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. guzhao_gz@hotmail.com.
authors.forename: Zhao
authors.initials: Z
authors.lastname: Gu
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. guiyouw@hotmail.com.
authors.forename: Guiyou
authors.initials: G
authors.lastname: Wang
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. swr7823@sohu.com.
authors.forename: Weiru
authors.initials: W
authors.lastname: Shi
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. wendongqing@gmail.com.
authors.forename: Dongqing
authors.initials: D
authors.lastname: Wen
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. lihua19780420@163.com.
authors.forename: Lihua
authors.initials: L
authors.lastname: Yu
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. yongchang_l@hotmail.com.
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Luo
authors.affiliation: High Altitude Physiology Laboratory, Institute of Aviation Medicine, Air Force, Beijing 100142, China. xiao-hj@263.net.
authors.forename: Huajun
authors.initials: H
authors.lastname: Xiao
mesh_terms: D000328:Adult; D000531:Altitude; D002245:Carbon Dioxide / Q000032:analysis*; D002320:Cardiovascular Physiological Phenomena; D015444:Exercise; D006801:Humans; D008297:Male; D010100:Oxygen / Q000378:metabolism*; D055815:Young Adult
chemical_list: D002245:Carbon Dioxide; D010100:Oxygen
keywords: blood pressure; cardiac autonomic  modulation; exercise; heart rate; heart rate variability