Experimental study on the effects of low pressure and acoustic characteristics on heart rate and acoustic comfort.

While extensive research exists on acoustic comfort and heart rate under normal atmospheric pressure conditions, studies examining low-pressure environments (e.g., aircraft cabins at 75-85 kPa and high-altitude trains) remain limited. Focusing on the asymptomatic pressure range (80-101 kPa, equivalent to altitudes below 3000 m), this study addresses two fundamental research questions: (1) whether atmospheric pressure and acoustic characteristics significantly affect heart rate, and (2) whether systematic variations in acoustic comfort occur with these environmental factors. Through controlled experiments combining pressure variations (80-101 kPa) with acoustic characteristics (white noise: 65/85 dB; speech/music: 70 dB), we obtained three principal findings: First, neither pressure nor acoustic characteristics (sound pressure level and sound frequency) significantly alter heart rate within this range-a finding that contrasts with known hypoxic effects observed at altitudes above 3650 m. Second, acoustic comfort decreased with reduced pressure exclusively in white noise environments (65-85 dB), while it remained stable for speech and music at 70 dB. Third, we established both an acoustic comfort evaluation function and frequency-band-specific comfort zones, which enable differentiated noise control standards across frequency bands and identify 75 dB as a critical threshold and low-frequency noise as key design parameters. These results yield the first piecewise comfort evaluation function specifically developed for low-pressure transportation environments. The findings provide immediate applications for noise control strategies in both aviation and high-altitude rail systems, offering scientifically grounded standards for environmental design.