Cardiovascular and autonomic modulation during nighttime rest under real-world conditions in miners exposed to chronic intermittent hypoxia

Background: Chilean mine workers commuting between sea level (SL) and high altitude (HA) are repeatedly exposed to chronic intermittent hypoxia (CIH). However, cardiovascular responses during nighttime rest, particularly the combined behavior of blood pressure (BP) and heart rate variability (HRV), remain insufficiently characterized under real-world occupational field conditions.Methods: Nineteen male mine workers (35–55 years) with over 10 years of rotational work (7-on/7-off shifts) were evaluated at SL (<500 m) and HA (∼3,800 m). Participants were classified as normotensive (NT, n = 9) or hypertensive (HT, n = 10). Resting SpO2, continuous 1-lead ECG and ambulatory BP monitoring were recorded simultaneously during a standardized 4-h nocturnal window (00:30–04:30 h), selected based on sustained absence of movement assessed by accelerometry. HRV was analyzed using time-, frequency-, and non-linear indices.Results: SpO2 significantly decreased from SL to HA (97.6% ± 0.5% vs. 87.8% ± 3.0%; p < 0.001), with a greater decline in hypertensive workers (p < 0.001). HA exposure significantly increased systolic and diastolic BP during the analyzed nighttime window (p < 0.05) and mean heart rate (p < 0.05) in both groups, without a significant group × altitude interaction. Parasympathetic-related HRV indices (RMSSD and SampEn) decreased significantly at HA, while SDNN increased under CIH exposure. Correlations between HRV and nocturnal BP were weak and non-significant in the overall sample.Conclusion: CIH exposure is associated with reduced oxygen saturation, elevated BP, and decreased vagal modulation during a standardized nighttime rest period under real-world conditions. Although HRV and BP changed in parallel at the group level, their individual associations were weak, suggesting that short-term cardiac vagal modulation alone does not fully explain BP responses during this predefined rest window under hypoxic stress. These findings describe field-based autonomic–hemodynamic responses during nighttime rest in CIH-exposed male workers.