Effects of acute hypoxic provocation on the autonomic nervous system in 'healthy' young smokers, measured by heart rate variability

Aim: The aim of this u was to compare the activity of the autonomic nervous system (ANS) using heart rate variability (HRV) in 'healthy' young smokers and non-smokers before, during and after exogenous hypoxic provocation. Methods: Twenty-one healthy non-smoking males aged 28.0 +/- 7.4 years imean +/- SD) and 14 'healthy' smoking males aged 28.1 +/- 4.3 years with 9.2 +/- 5.6 pack-years were subjected to one-hour hypoxic exposure (F-i,O-2, = 12.3 +/- 1 5%) via a hypoxicator. HRV data was derived via Kubios HRV. Finland software by analysing the pre-hypoxic, hypoxicnndpost-hypoxic periods. Results: Standard deviation of the intervals between normal beats (SDNN) was higher in the non-smokers in the prehypoxic period (62.0 +/- 32.1 vs 40.3 +/- 16.2 ms. p = 0.013) but not in the hypoxic period (75.7 +/- 34.8 vs 57.9 +/- 18.3 ms.p = 0.167). When comparing intra-group HRV changes. shifting from hypoxic to normoxic conditions, there was an increase in the mean square root of successive R-R interval differences (RMSSD) (65.9 +/- 40.2 vs 75.1 +/- 45.9 ms.p = 0.011), but these changes were observed in only the group of non-smokers. Conclusions: Smoking probably impairs autonomic regulation in healthy young males and may lead to decreased HRV, even before subjective clinical signs and symptoms appear.