Heart rate variability at different thermal comfort levels.

Area of Science:

• Environmental Science
• Human Physiology
• Building Science

Background:

• Understanding human thermal comfort is crucial for designing healthy and comfortable indoor spaces.
• Human physiological responses to thermal conditions are complex and not fully understood.
• Heart rate variability (HRV) offers a potential non-invasive method to assess physiological responses to environmental factors.

Purpose of the Study:

• To investigate the relationship between human thermal comfort levels and heart rate variability (HRV).
• To explore the role of autonomic nervous system activity, specifically sympathetic activity, in thermal discomfort.
• To determine if the LF/HF ratio of HRV can serve as a reliable indicator of human thermal comfort.

Main Methods:

• Recruited 33 subjects divided into 3 groups.
• Recorded electrocardiograms (ECG) for 5 minutes at various air temperatures (21, 24, 26, 28, 29, 30°C).
• Analyzed heart rate variability (HRV), focusing on the low-frequency to high-frequency power ratio (LF/HF ratio).

Main Results:

• The LF/HF ratio was significantly higher (P < 0.05) during thermal discomfort compared to comfort levels, even when thermal sensation was similar.
• This finding suggests increased sympathetic nervous system activity during thermal discomfort.
• The LF/HF ratio demonstrated a notable difference between comfort and discomfort states.

Conclusions:

• Sympathetic activity plays a significant role in the human experience of thermal discomfort.
• The LF/HF ratio of heart rate variability (HRV) shows potential as an objective indicator for assessing human thermal comfort.
• This research provides insights into the physiological mechanisms underlying thermal comfort and discomfort in indoor environments.