High frequency heart rate variability was increased by addition of 5% CO2 to breathing air in healthy, young humans

Oscillations in cardiovascular variables may be part of the cardiovascular control mechanisms. Heart rate variability in the high frequency interval is part of the cardiorespiratory interactions. Main part of high frequency heart rate variability is called respiratory sinus arrhythmia, which is influenced by ventilation pattern. We investigated how addition of 5 % CO2 to the air affected the high frequency heart rate variability. CO2 breathing increased heart rate variability, and this was linearly related to increases in both tidal volume and end-tidal CO2. CO2 breathing also increased heart rate, which did not affect heart rate variability.