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Time course analysis of baroreflex sensitivity during postural stress
Berend E Westerhof1, Janneke Gisolf, John M Karemaker
1BMEYE, Academic Medical Centre, University of Amsterdam, NL-1105 AZ Amsterdam, The Netherlands. berend.westerhof@bmeye.com
Summary
Cardiac baroreflex sensitivity (BRS) decreases with increasing postural stress. This adaptation to changes in body position occurs rapidly, indicating efficient autonomic nervous system regulation.
Area of Science:
- Physiology
- Autonomic Nervous System
- Cardiovascular Regulation
Background:
- Maintaining blood pressure during postural changes relies on rapid autonomic nervous system responses.
- Cardiac baroreflex sensitivity (BRS) is a key indicator of the body's ability to regulate blood pressure.
- Understanding how BRS changes with varying degrees of postural stress is crucial for assessing cardiovascular health.
Purpose of the Study:
- To quantify the relationship between postural stress and cardiac baroreflex sensitivity (BRS) using time-domain analysis.
- To investigate the time delay (tau) between blood pressure and heart rate variations during postural changes.
- To determine the speed of baroreflex adaptation to acute postural perturbations.
Main Methods:
- Utilized stepwise changes in body axis angle (alpha) from -20 to 90 degrees in 10 healthy volunteers.
- Measured noninvasive blood pressure over 6-minute intervals to analyze systolic blood pressure and interbeat interval variations.
- Employed frequency-domain analysis and a cross-correlation time-domain method (xBRS) to determine BRS and time delay (tau).
Main Results:
- Cardiac baroreflex sensitivity (BRS) demonstrated a linear decrease with increasing postural stress, described by the equation BRS = -10.1.sin(alpha) + 18.7.
- A strong correlation (r(2) ≈ 0.97) was observed between time-domain xBRS and frequency-domain cross-spectral gain.
- The time delay (tau) between blood pressure and heart rate variations shifted towards higher values as postural stress increased.
- Baroreflex adaptation to postural changes reached a new mean level within the first minute in 78% of cases and within 6 minutes in 93%.
Conclusions:
- Cardiac baroreflex sensitivity (BRS) in healthy individuals decreases linearly with the sine of the body axis angle (alpha).
- The baroreflex system adapts rapidly to physiological challenges like postural stress.
- Reduced vagal activity with increasing postural stress may explain the observed decrease in BRS and shortening of tau.