Non-invasive monitoring of dynamic cerebrovascular autoregulation using near infrared spectroscopy and the Finometer photoplethysmograph

Background: Near infrared spectroscopy (NIRS) enables continuous monitoring of dynamic cerebrovascular autoregulation, but this methodology relies on invasive blood pressure monitoring (iABP). We evaluated the agreement between a NIRS based autoregulation index calculated from invasive blood pressure monitoring, and an entirely non-invasively derived autoregulation index from continuous non-invasive blood pressure monitoring (nABP) using the Finometer photoplethysmograph. Methods: Autoregulation was calculated as the moving correlation coefficient between iABP and rSO₂ (iTOx) or nABP and rSO₂ (nTOx). The blood pressure range where autoregulation is optimal was also determined for invasive (iABP_OPT) and non-invasive blood pressure measurements (nABP_OPT). Results: 102 simultaneous bilateral measurements of iTOx and nTOx were performed in 19 patients (median 2 per patient, range 1–9) with different acute pathologies (sepsis, cardiac arrest, head injury, stroke). Average iTOx was 0.01 ± 0.13 and nTOx was 0.01 ± 0.11. The correlation between iTOx and nTOx was r = 0.87, p < 0.001, 95 % agreement ± 0.12, bias = 0.005. The interhemispheric asymmetry of autoregulation was similarly assessed with iTOx and nTOx (r = 0.81, p < 0.001). Correlation between iABP_OPT and nABP_OPT was r = 0.47, p = 0.003, 95 % agreement ± 32.1 mmHg, bias = 5.8 mmHg. Coherence in the low frequency spectrum between iABP and nABP was 0.86 ± 0.08 and gain was 1.32 ± 0.77. Conclusions: The results suggest that dynamic cerebrovascular autoregulation can be continuously assessed entirely non-invasively using nTOx. This allows for autoregulation assessment using spontaneous blood pressure fluctuations in conditions where iABP is not routinely monitored. The nABP_OPT might deviate from iABP_OPT, likely because of discordance between absolute nABP and iABP readings.