Abstract
Orthostatic lightheadedness in healthy young adults often leads to syncope in severe cases. One suggested underlying mechanism of orthostatic lightheadedness is a drop in transient blood pressure (BP); however, a decrease in BP does not always lead to a drop in cerebral blood flow (CBF) due to cerebral autoregulation (CA). We present a direct assessment method of CA using a multichannel continuous-wave near-infrared spectroscopy (CW-NIRS) device that measures the temporal changes in oxy- and deoxy-hemoglobin concentrations in the prefrontal cortex. Twenty healthy young adults were recruited. During the experiment, continuous beat-to-beat BP and heart rate were simultaneously measured during repetitive squat-stand maneuvers. We introduce a new metric termed ‘time-derivative hemodynamic model (DHbT)’, which is the time-derivative of total-hemoglobin concentration change that reflects the changes of cerebral blood volume and CBF. Although the absolute levels and the variations of systolic and diastolic BPs and mean arterial pressure showed no significant difference between the two groups, the proposed model showed a distinct difference in slope variation and response time of DHbT between the subjects with frequent symptom of orthostatic intolerance and the healthy control subjects. Thus, these results clearly demonstrate the feasibility of using CW-NIRS devices as a CA performance assessment tool.
Highlights
Orthostatic lightheadedness, which occurs upon abrupt standing from supine or squatting positions, is common even in healthy young adults[1]
Several reports have shown that near-infrared spectroscopy (NIRS) can be used as a tool for non-invasive continuous monitoring of cerebral circulation[7,8,9]
The block-averaged response was divided into four distinct time intervals to derive a single representative value; one averaged 30-second epoch from the squatting-rest position and three averaged 5-second epochs from the standing-rest position (T1, T2, and T3) representing for each of the recovery phases after standing at 60, 120, and 180 seconds
Summary
Orthostatic lightheadedness, which occurs upon abrupt standing from supine or squatting positions, is common even in healthy young adults[1]. It may appear as a mild transient orthostatic dizziness, but it can lead to syncope in severe cases. Physiologic monitoring studies using continuous assessment of beat-to-beat blood pressure (BP) and heart rate (HR) have suggested that the underlying mechanism behind orthostatic lightheadedness is a transient BP drop[2,3,4]. We explored the possibility of using NIRS for the assessment of the arterial-cardiac baroreflex function during repeated squat-stand maneuvers. The NIRS measurements were compared with conventional prognostic indicators such as systematic BP and HR measured using beat-to-beat photoplethysmography
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