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The Effects of a Respiratory Acidosis on Human Heart Rate Variability

  • S. J. Brown
  • R. Howden
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 605)

Human heart rate variability (HRV) was examined during a mild respiratory acidosis induced by inhalation of a normoxic hypercapnic gas mixture. On two separate occasions, separated by 72 but not more than 120 hr, ECG was recorded from 9 normotensive subjects during supine rest. ECG was recorded for 20 min breathing room air or a 5% CO2 in normoxic air mixture. Expired V'E, O2 and CO2 were measured with breath-by-breath mass spectrometry. HRV spectra were calculated using a Welch averaged periodogram method and banded as Very Low Frequency (VLF: 0 – 0.04 Hz), Low Frequency (LF: 0.04 – 0.15 Hz), and High Frequency (HF: 0.15 – 0.4 Hz). Student paired samples t-tests were used to compare room air (RA) versus inhaled 5% CO2 in air (5% CO2) data. All results reported as mean +/− SD. In the HRV time domain, hypercapnic normoxia reduced mean r-r intervals (5% CO2: 956.1 ± 149.2 vs. RA: 1035 ± 146.8 ms, p = 0.022) and median r-r intervals (5% CO2: 942.6 ± 153.1 vs. RA: 1047.8 ± 157.3 ms, p = 0.010), and increased heart rates (5% CO2: 64.4 ± 12 vs. RA: 59.3 ± 10.1 bpm, p = 0.019). In the HRV frequency domain, hypercapnic normoxia increased the high frequency component of HRV (5% CO2: 9799 ± 7649 vs. RA: 4399 ± 3857 ms4) and reduced the LF/HF ratio (5% CO2: 0.243 ± 0.145 vs. RA: 0.906 ± 0.672, p = 0.017). An incomplete ventilatory compensation probably accounts for the increased HF contribution.

Keywords

Heart Rate Variability Respiratory Sinus Arrhythmia High Frequency Component Muscle Sympathetic Nerve Activity Respiratory Acidosis 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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Copyright information

© Springer 2008

Authors and Affiliations

  • S. J. Brown
    • 1
  • R. Howden
    • 2
  1. 1.Massey UniversityAucklandNZ
  2. 2.National Institute of Environmental Health SciencesLaboratory of Respiratory BiologyNorth CarolinaUSA

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