Cardiovascular coupling during graded postural challenge: comparison between linear tools and joint symbolic analysis

Area of Science:

• Cardiovascular Physiology
• Systems Biology
• Biomedical Engineering

Background:

• Assessing cardiovascular coupling strength between heart period (HP) and systolic arterial pressure (SAP) is crucial for understanding autonomic control.
• Orthostatic challenges, like head-up tilt, induce baroreflex unloading and alter cardiovascular variability.

Purpose of the Study:

• To evaluate the efficacy of Joint Symbolic Analysis (JSA) in quantifying cardiovascular coupling during graded baroreflex unloading.
• To compare JSA's performance against traditional linear methods (squared correlation, squared coherence, baroreflex sequences).

Main Methods:

• Application of Joint Symbolic Analysis (JSA) to beat-to-beat HP and SAP variability.
• Experimental protocol involving graded head-up tilt to induce baroreflex unloading.
• Calculation of traditional linear coupling indices for comparative analysis.

Main Results:

• JSA demonstrated that cardiovascular coupling strength increased at slow time scales and decreased at fast time scales with increasing orthostatic challenge.
• Traditional methods like squared correlation coefficient and percentage of baroreflex sequences failed to detect these dynamic coupling changes.
• Squared coherence function showed some time-scale dependency but was less powerful than JSA due to higher index dispersion.

Conclusions:

• JSA offers a powerful and sensitive tool for analyzing cardiovascular coupling dynamics across different time scales.
• JSA's ability to detect subtle changes in HP-SAP variability makes it suitable for studying pathological conditions affecting cardiovascular control.