Capturing postural blood pressure dynamics with near-infrared spectroscopy-measured cerebral oxygenation

Abstract

Orthostatic hypotension (OH) is highly prevalent in older adults and associated with dizziness, falls, lower physical and cognitive function, cardiovascular disease, and mortality. OH is currently diagnosed in a clinical setting with single-time point cuff measurements. Continuous blood pressure (BP) devices can measure OH dynamics but cannot be used for daily life monitoring. Near-infrared spectroscopy (NIRS) has potential diagnostic value in measuring cerebral oxygenation continuously over a longer time period, but this needs further validation. This study aimed to compare NIRS-measured (cerebral) oxygenation with continuous BP and transcranial Doppler-measured cerebral blood velocity (CBv) during postural changes. This cross-sectional study included 41 participants between 20 and 88 years old. BP, CBv, and cerebral (long channels) and superficial (short channels) oxygenated hemoglobin (O₂Hb) were measured continuously during various postural changes. Pearson correlations between BP, CBv, and O₂Hb were calculated over curves and specific characteristics (maximum drop amplitude and recovery). BP and O₂Hb only showed good curve-based correlations (0.58-0.75) in the initial 30 s after standing up. Early (30-40 s) and 1-min BP recovery associated significantly with O₂Hb, but no consistent associations were found for maximum drop amplitude and late (60-175 s) recovery values. Associations between CBv and O₂Hb were poor, but stronger for long-channel than short-channel measurements. BP associated well with NIRS-measured O₂Hb in the first 30 s after postural change. Stronger associations for CBv with long-channel O₂Hb suggest that long-channel NIRS specifically reflects cerebral blood flow during postural transitions, necessary to better understand the consequences of OH such as intolerance symptoms.

Keywords: Aging; Blood pressure; Cerebral oxygenation; Near-infrared spectroscopy; Orthostatic hypotension.

Fig. 1

Example of A blood pressure response during standing and B oxygenation response during standing. Different phases (indicated by 1, 2) and characteristics (indicated by a, b, c, d, e) are shown in blue. 1, early recovery phase (0–30 s after standing up); 2, late recovery phase (30–175 s after standing up); and a, baseline, calculated as the average value between 60 and 30 s before standing up; b, initial drop within 30 s, calculated by minimum value minus baseline; c, early recovery, calculated as average value between 30 and 40 s after standing up; d, 1-min recovery, calculated as average value between 50 and 60 s after standing up; e, late recovery, calculated as average value between 60 and 175 s after standing up

Fig. 2

Responses of A + E blood pressure (BP), systolic in red (solid line), diastolic in blue (dashed line), and heart rate (HR) in green (dashed-dotted line); B + F cerebral blood velocity (MCAv), systolic in red (solid line), and diastolic in blue (dashed line); C + G cerebral oxygenation measured with long channels, oxygenated hemoglobin in red and deoxygenated hemoglobin in blue (dashed line); and D + H cerebral oxygenation measured with short channels, oxygenated hemoglobin in red and deoxygenated hemoglobin in blue (dashed line). All signals are shown from 1 min before standing up to 175 s after standing up, during a supine-stand transition (A–D) or sit-stand transition (E–H). These responses were averaged over all supine-stand or sit-stand transitions and all participants. Standing up is indicated by a vertical black dashed line. Shaded areas show standard deviations for all signals