Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Nov 23:9:697.
doi: 10.3389/fendo.2018.00697. eCollection 2018.

Sex Differences in Autonomic Cardiac Control and Oxygen Saturation Response to Short-Term Normobaric Hypoxia and Following Recovery: Effect of Aerobic Fitness

Michal Botek  1 , Jakub Krejčí  1 , Andrew McKune  2   3
Affiliations

Sex Differences in Autonomic Cardiac Control and Oxygen Saturation Response to Short-Term Normobaric Hypoxia and Following Recovery: Effect of Aerobic Fitness

Michal Botek et al. Front Endocrinol (Lausanne). .

Abstract

Introduction: The main aims of this study were to investigate autonomic nervous system (ANS) and arterial oxygen saturation (SpO2) responses to simulated altitude in males and females, and to determine the association between maximal oxygen uptake (VO2max) and these responses. Materials and Methods: Heart rate variability (HRV) and SpO2 were monitored in a resting supine position during Preliminary (6 min normoxia), Hypoxia (10 min, fraction of inspired oxygen (FiO2) of 9.6%, simulated altitude ~6,200 m) and Recovery (6 min normoxia) phases in 28 males (age 23.7 ± 1.7 years, normoxic VO2max 59.0 ± 7.8 ml.kg-1.min-1, body mass index (BMI) 24.2 ± 2.1 kg.m-2) and 30 females (age 23.8 ± 1.8 years, VO2max 45.1 ± 8.7 ml.kg-1.min-1, BMI 21.8 ± 3.0 kg.m-2). Spectral analysis of HRV quantified the ANS activity by means of low frequency (LF, 0.05-0.15 Hz) and high frequency (HF, 0.15-0.50 Hz) power, transformed by natural logarithm (Ln). Time domain analysis incorporated the square root of the mean of the squares of the successive differences (rMSSD). Results: There were no significant differences in SpO2 level during hypoxia between the males (71.9 ± 7.5%) and females (70.8 ± 7.1%). Vagally-related HRV variables (Ln HF and Ln rMSSD) exhibited no significant differences between sexes across each phase. However, while the sexes demonstrated similar Ln LF/HF values during the Preliminary phase, the males (0.5 ± 1.3) had a relatively higher (p = 0.001) sympathetic activity compared to females (-0.6 ± 1.4) during the Hypoxia phase. Oxygen desaturation during resting hypoxia was significantly correlated with VO2max in males (r = -0.45, p = 0.017) but not in females (r = 0.01, p = 0.952) and difference between regression lines were significant (p = 0.024). Conclusions: Despite similar oxygen desaturation levels, males exhibited a relatively higher sympathetic responses to hypoxia exposure compared with females. In addition, the SpO2 response to resting hypoxia exposure was related to maximal aerobic capacity in males but not females.

Keywords: autonomic nervous system; gender; heart rate variability; maximal oxygen uptake; simulated altitude; sympathovagal balance; vagal activity.

PubMed Disclaimer

Figures

Figure 1
Figure 1
Course of experimental protocol. Gray colored phases were intended for oxygen saturation and ECG recording. Pauses were used to skip the transitory phase and to be able to assume stationarity of the data. This is a reprint of the figure entitled “Course of hypoxic experimental protocol” by Macoun et al. (9) and licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/).
Figure 2
Figure 2
Differences between sexes in the oxygen saturation (A), heart rate (B), natural logarithm of low frequency power (C), natural logarithm of standard deviation of RR intervals (D), natural logarithm of high-frequency power (E), natural logarithm of square root of the mean of the squares of the successive differences (F), natural logarithm of ratio of low-frequency to high-frequency power (G), natural logarithm of ratio of SDNN to rMSSD (H). Values of females are denoted by filled circles and solid line. Values of males are denoted by open circles and dashed line. Values are presented as the mean ± standard deviation. Comparisons were performed by means of Fisher's LSD post-hoc test and only significant differences are displayed: *p < 0.05.
Figure 3
Figure 3
Regression analysis between oxygen desaturation (ΔSpO2 = SpO2 Hypoxia-SpO2 Preliminary) and the maximal oxygen uptake (VO2max) measured in normoxia. Values of females are denoted by filled circles and solid line. Values of males are denoted by open circles and dashed line.
Figure 4
Figure 4
Differences in the oxygen desaturation (ΔSpO2 = SpO2 Hypoxia - SpO2 Preliminary) between females with low aerobic capacity (FL, n = 7), males with low aerobic capacity (ML, n = 7), females with high aerobic capacity (FH, n = 7), and males with high aerobic capacity (MH, n = 7). Values are presented as the mean ± standard deviation. Comparisons were performed by means of Fisher's LSD post-hoc test and only significant differences are displayed: *p < 0.05.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Álvarez-Herms J, Julià-Sánchez S, Hamlin MJ, Corbi F, Pagès T, Viscor G. Popularity of hypoxic training methods for endurance-based professional and amateur athletes. Physiol Behav. (2015) 143:35–8. 10.1016/j.physbeh.2015.02.020 - DOI - PubMed
    1. Bonetti D, Hopkins W. Se-level exercise performance following adaptation to hypoxia: a meta analysis. Sports Med. (2009) 39:107–27. 10.2165/00007256-200939020-00002 - DOI - PubMed
    1. Wilber RL. Application of altitude/hypoxic training by elite athletes. Med Sci Sport Exerc. (2007) 39:1610–24. 10.1249/mss.0b013e3180de49e6 - DOI - PubMed
    1. Chen YC, Lin FC, Shiao GM, Chang SC. Effect of rapid ascent to high altitude on autonomic cardiovascular modulation. Am J Med Sci. (2008) 336:248–53. 10.1097/MAJ.0b013e3181629a32 - DOI - PubMed
    1. Sutherland A, Freer J, Evans L, Dolci A, Crotti M, Macdonald JH. MEDEX 2015: heart rate variability predicts development of acute mountain sickness. High Alt Med Biol. (2017) 18:199–208. 10.1089/ham.2016.0145 - DOI - PubMed