Noninvasive cardiac output estimation using a novel photoplethysmogram index

Area of Science:

• Biomedical Engineering
• Cardiovascular Physiology
• Wearable Technology

Background:

• Cardiac output (CO) monitoring is crucial for assessing cardiovascular health.
• Current CO monitoring methods are invasive or require specialized equipment and trained personnel, limiting their use to clinical settings.

Purpose of the Study:

• To develop a novel, noninvasive indicator for continuous cardiac output monitoring.
• To integrate this indicator into existing wearable devices for widespread use.

Main Methods:

• Proposed the inflection and harmonic area ratio (IHAR) index derived from photoplethysmographic (PPG) signals.
• Validated the IHAR index against bio-impedance CO measurements (CO(imp)) in sixteen healthy subjects.
• Assessed IHAR performance before and after controlled exercise.

Main Results:

• Demonstrated a strong intra-subject correlation (mean r = 0.82, p<0.01) between IHAR and CO(imp) in 15 subjects.
• Achieved a precision of 1.40 L/min between CO(imp) and CO estimated from IHAR (CO(IHAR)).
• Reported a total percentage error of 16.2%, significantly below the clinical acceptance limit of 30%.

Conclusions:

• The IHAR index is a viable and promising method for noninvasive, continuous cardiac output monitoring.
• This approach facilitates the development of wearable devices for accessible CO tracking.
• The findings support the potential of IHAR for remote and at-home cardiovascular assessment.