Physiological Oscillations of Lateral Ventricular Volume Revealed by Fast fMRI: Effects of Aging and Vigilance

Abstract Background: Cyclic ventricular deformation may contribute to CSF displacement. However, the physiological mechanisms underlying ventricular motion remain poorly understood. This study characterized physiological oscillations of lateral ventricular volume (LVV) and examined their associations with aging and vigilance. Methods: We analyzed two fast resting-state fMRI scans from 99 adults aged 35-82 years. The first scan was acquired during eyes-open wakefulness, followed by 30 min of eyes-closed rest and a second scan during eyes-closed drowsiness. LVV was estimated for each image volume using automated ventricular segmentation, yielding time-resolved volume measurements. Temporal variability was quantified using the standard deviation and coefficient of variation, and spectral power was quantified for low-frequency, respiratory, and cardiac oscillations. Age-related associations were assessed using multiple linear regression adjusted for sex. Awake-drowsy differences were assessed using paired t-tests. False discovery rate correction was applied for multiple comparisons in all analyses. Results: After quality-control exclusions, 97 participants were analyzed. LVV exhibited distinct low-frequency, respiratory, and cardiac oscillatory components. Respiratory and cardiac oscillations accounted for 37.7% and 38.4% of total physiological spectral power, respectively, compared with 23.9% for low-frequency oscillations. Mean lateral ventricular volume increased with age (FDR-adjusted p = 0.010), while respiratory and cardiac power also showed positive associations with age, although neither survived FDR correction (both FDR-adjusted p = 0.067). The transition to eyes-closed drowsiness was associated with greater LVV fluctuation magnitude, reflected by increases in standard deviation (FDR-adjusted p < 0.001) and coefficient of variation (FDR-adjusted p = 0.028) and accompanied by increased low-frequency (FDR-adjusted p < 0.001) and respiratory power (FDR-adjusted p = 0.015). Mean LVV and cardiac power did not change significantly between conditions. Conclusions: LVV exhibits prominent respiratory and cardiac oscillations in addition to low-frequency fluctuations, suggesting that ventricular dynamics reflect multiple physiological influences rather than a single dominant physiological driver. Aging was primarily associated with ventricular enlargement, whereas reduced vigilance was accompanied by increased LVV fluctuation magnitude, primarily reflected in increased low-frequency and respiratory power, without a change in mean LVV. Time-resolved LVV provides a complementary approach for investigating the physiological regulation of ventricular dynamics in health and disease. Keywords: Cerebrospinal fluid; Lateral ventricular volume; Fast fMRI; Physiological oscillations; Cardiac pulsation; Respiration; Low-frequency oscillations; Aging; Vigilance