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

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.

Use of inertial sensors for ambulatory assessment of center-of-mass displacements during walking.

Current methods for center-of-mass (CoM) estimation are restricted to gait laboratories. The aim of this study was to estimate CoM displacement under ambulatory conditions with inertial sensors. A sacral inertial sensor (SIS method) was used to estimate the CoM displacement by double integration of the acceleration. Overestimation of the displacement caused by pelvic rotations was compensated (CSIS method). The CoM displacement estimations using the (C)SIS method were compared to the conventional methods of the segmental analysis (SA) method and the sacral marker (SM) method by the intraclass correlations and the root-mean-square (RMS) differences between the CoM curves. Accurate ambulatory measurement of the CoM displacement using inertial sensors was possible. Estimations of the sacrum position using the SIS method and the SM method were similar with mean (SD) RMS differences of 3.23 (0.87), 2.96 (0.42), and 3.22 (0.78) mm for, respectively, the x-, y- and z-directions. The CoM estimation of the SIS method has RMS differences of 5.67 (1.20), 7.16 (3.28), and 3.49 (1.29) mm compared the SA method. The CSIS method shows a clear improvement in these estimations of the CoM with RMS differences of 5.52 (1.29), 4.44 (1.89), and 3.17 (1.41) mm and is generally applicable for healthy subjects.