Transmission of slow waves in Masimo O₃ near infrared spectroscopy measures

Cerebral autoregulation (CA) dysfunction is a key complication following brain injury. CA assessment using near-infrared spectroscopy (NIRS) offers a promising alternative to the current non-invasive standard, cerebral blood flow velocity (CBFV) measured with transcranial Doppler.

Can autoregulatory slow waves (frequency range 0.005-0.05 Hz) associated with spontaneous and induced changes in ABP in healthy volunteers be detected by parameters measured with the Masimo O₃ NIRS device?

ABP, CBFV and Masimo O₃ parameters were measured in 10 healthy volunteers at baseline and during ABP oscillations induced by squat/stand manoeuvres. Transmission of slow waves was assessed with power spectral density and coherence analysis in NIRS signals and compared to that of CBFV.

At baseline, slow waves were detected with sufficient power that substantially exceeded the signals' measurement resolution in all parameters except cerebral oxygen saturation. During ABP oscillations in the 0.033 Hz range (induced by squat/stand), the power of slow waves increased in all parameters in a similar pattern, with total (cHb) and oxygenated (O₂Hb) haemoglobin concentrations most closely mirroring CBFV (median standardised power [first-third quartile], baseline vs squat/stand: CBFV 0.35 [0.28-0.42] vs 0.50 [0.45-0.62], O₂Hb 0.47 [0.33-0.68] vs 0.61 [0.59-0.69]). Coherence with ABP increased for both CBFV and NIRS measures from low at baseline (<0.4) to high during induced changes (>0.8).

Spontaneous fluctuations in ABP can be observed in analysed Masimo O₃ metrics to a varying degree. The clinical utility of Masimo O₃ signals in CA assessment requires further investigation in brain injury patients.