Assessment of cardiovascular reactivity by fractal and recurrence quantification analysis of heart rate and pulse transit time.

Observed Findings

• ME/CFS patients showed markedly lower FRAS scores (median −24.2) compared to healthy controls (−1.85) and hypertensive patients (+0.52).
• Hypertensive patients had significantly higher FRAS scores than both healthy controls and ME/CFS patients (P=0.0036 and P<0.0001, respectively).
• Fractal and recurrence quantification variables of heart rate and pulse transit time differed significantly among the three groups.
• The multivariate analysis identified five key predictors of group membership related to heart rate and pulse transit time responses during tilt.
• Healthy controls showed intermediate cardiovascular reactivity patterns, distinct from both disease groups.

Inferred Conclusions

• Nonlinear dynamical analysis methods (fractal and recurrence quantification analysis) detect cardiovascular phenotypes that traditional linear methods may miss.
• ME/CFS patients exhibit a distinctive, severely abnormal cardiovascular reactivity pattern during postural challenge, consistent with known dysautonomia in this condition.
• The FRAS score may serve as an objective biomarker to distinguish ME/CFS from healthy controls and other cardiovascular conditions.
• Cardiovascular reactivity phenotypes exist along a spectrum and can be objectively quantified using these advanced mathematical approaches.

Remaining Questions