Real-time heart rate variability analysis as a means of hypercapnia detection.

We hypothesized that heart rate variability (HRV) can be used as a physiological monitor of exposures to hypercapnia. HRV was analyzed in 15 male subjects breathing air and then air plus 4%, 5% or 6% carbon dioxide (CO2). A progressive elevation in randomness of HRV best depicted as a divergence of data on Poincar é plots of self-similarity occurred as CO2 increased, and resolved when returning sd to ambient conditions. Results indicate that HRV may be useful as a prompt (⟨ 2 minute) early warning of hypercapnia that occurs prior to overt symptomatology.