Author(s): MAST, I., BAAS, K.P.A., JØRSTAD, H.T., WOOD, J.C., NEDERVEEN, A.J., BAKERMANS, A.J., Institution: AMSTERDAM UMC, Country: NETHERLANDS, Abstract-ID: 1880

INTRODUCTION:
The brain is primarily supplied by the common carotid arteries (CCAs) and receives up to 20% of the total cardiac output at rest. Hemodynamic changes in the CCAs due to anatomical asymmetries or vascular abnormalities can increase susceptibility to atherosclerotic plaque formation and may become apparent during physiological stress, such as physical exercise. This study aimed to characterize hemodynamics in both carotid arteries before, during, and after in-magnet exercise in healthy subjects using 2D phase-contrast (PC) MRI.
METHODS:
After resting-state measurements, subjects performed supine exercise using an MR-compatible bicycle ergometer (Lode) inside a 3 Tesla MRI scanner (Philips). The protocol consisted of two 5-minute stages of steady-state moderate (60% of supine maximal heart rate; HRmax) and vigorous (80% of supine HRmax) exercise, and passive recovery (1). During each stage, transversal 2D PC-MRI series of the CCAs were acquired. CCA flow patterns were evaluated using feature points within the cardiac cycle, and pulsatility (PI) and resistance indices (RI) were calculated (2). Bilateral differences and changes from rest were assessed using mixed model analyses.
RESULTS:
Healthy subjects (n = 12; 6/6, m/f; 25 ± 6 y) completed the in-magnet exercise protocol. Relative timing of peak systole with respect to the cardiac cycle increased progressively with exercise from 5.3 ± 1.7% (HR, 62 ± 9 beats/min) at rest, to 6.6 ± 1.5% (p ≤ 0.001; HR, 101 ± 7 beats/min) with moderate exercise, and 7.0 ± 1.0%, (p ≤ 0.001; HR, 131 ± 7 beats/min) with vigorous exercise. Larger delays were observed for the secondary systolic peak (rest, 20.9 ± 4.3%; moderate, 27.8 ± 5.6%; vigorous, 32.0 ± 6.3%; p ≤ 0.001) and for onset of diastole (rest, 30.7 ± 3.8%; moderate, 44.2 ± 5.1%; vigorous, 48.8 ± 3.2%; p ≤ 0.001). Consequently, the systolic fraction of total CCA flow increased from 55.7 ± 6.2% at rest to 75.8 ± 10.0% (p ≤ 0.001) during moderate and to 88.9 ± 4.9% (p ≤ 0.001) during vigorous exercise, decreasing to 65.2 ± 7.2% during recovery (p ≤ 0.001). PI and RI increased from rest (PI, 2.3 ± 0.7; RI, 0.8 ± 0.1) to moderate (PI, 2.9 ± 0.8; RI, 0.9 ± 0.1; p ≤ 0.001) and vigorous exercise (PI, 4.0 ± 0.8; RI, 0.9 ± 0.04; p ≤ 0.001), decreasing again during recovery (PI, 2.8 ± 0.6; RI, 0.9 ± 0.1; p ≤ 0.01). No differences were observed between the left and right CCA.
CONCLUSION:
This study provided quantitative MRI measurements of the hemodynamic response in the CCAs during exercise. Elevated pulsatility and resistance indices suggest that arterial stiffness and cerebrovascular resistance increase during exercise. No asymmetries in any of the parameters were observed in these healthy subjects. Our findings provide insight into the blood flow adaptations through the CCAs in response to exercise that may be relevant for investigating atherosclerosis and neurodegenerative diseases.

1. Mast et al. NeuroImage 2022;250:118961
2. Hoi et al. Physiol Meas 2011;31:3