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Instantaneous beat-to-beat variability reflects vagal tone during hyperbaric hyperoxia
1Department on Anesthesiology and Intensive Care, Turku University Hospital, Turku, Finland.
Summary
Hyperbaric hyperoxia increases vagal tone, measurable by beat-to-beat variability (SD1). Heart rate dynamics become more random (decreased alpha1) under these conditions, impacting divers.
Area of Science:
- Cardiovascular physiology
- Diving medicine
- Autonomic nervous system function
Background:
- Hyperbaric hyperoxia is known to influence heart rate variability (HRV).
- Parasympathetic activity, indicative of vagal tone, is a key factor affected by hyperbaric conditions.
Purpose of the Study:
- To assess if instantaneous beat-to-beat variability (SD1) can detect changes in vagal tone during hyperbaric hyperoxia.
- To investigate alterations in heart rate dynamics fractality (alpha1) under hyperbaric hyperoxia.
Main Methods:
- Ten divers underwent continuous ECG monitoring at 2.5 ATA with air and oxygen (PO2 235 kPa) for 60 minutes.
- Analysis included power spectral analysis, Poincaré plot analysis (SD1), and detrended fluctuation analysis (alpha1) at various time points.
- Correlations between HRV parameters were calculated post-exposure.
Main Results:
- Significant increases in SD1 and high-frequency (HF) power were observed, indicating heightened vagal activity.
- A significant decrease in alpha1 suggested a shift towards more random heart rate dynamics.
- HF power and SD1 showed a significant positive correlation, but inversely correlated with alpha1.
Conclusions:
- SD1 is a viable alternative to HF power for assessing vagal activity in hyperbaric hyperoxia, especially when stationarity is compromised.
- The observed decrease in alpha1 signifies increased randomness in heart rate dynamics during hyperbaric hyperoxia, relevant for diving safety.