Arterial and venous flow dynamics are modified by age in the non-human primate

Figures

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  Fig. 1.. TOF and PC-MRI acquisitions in marmoset monkey brain. TOF images were used to select two scanning planes perpendicular to the flow direction for PC-MRI acquisitions (insets in A and C). (A) A TOF image acquired in the coronal plane was selected to determine the orientation of the slice used for measuring blood velocity in arteries by PC-MRI (inset in A), simultaneously capturing the basilar trunk artery (BT), the left internal carotid artery (LC), and the right internal carotid artery (RC). (B) A 3D reconstruction of TOF images. (C) The sagittal plane, determined from the 3D reconstruction of TOF images, was used to position an oblique slice, perpendicular to the sinuses, for measuring blood velocity in the sinuses by PC-MRI (inset in C), simultaneously capturing the superior sagittal sinus (SS) and the straight sinus (StS). Scale bar = 5 mm. L: left, R: right.

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  Fig. 2.. Blood velocity acquisition and blood flow time course as a function of cardiac activity. (A) Representative velocity curve acquired from a carotid. PC-MRI acquisition (top) was synchronised with the ECG signal R-peaks (bottom). Velocity was acquired at regular intervals (every 25 ms) over 80% of the cardiac cycle. The blood velocity profile thus corresponds to the sequence of the whole ventricular systole and a large part of the ventricular diastole. (B) Blood flow was calculated as the product of blood velocity and vessel cross-sectional area obtained from PC-MRIs (black dots). To normalise the different acquisitions across all marmosets, blood flow values were linearly interpolated and extrapolated (orange dots) over the entire cardiac cycle (CC) with 32 steps (one step = 3.125% CC). The maximum blood flow value (M) was specified along with the corresponding % CC. This was determined for all arterial and venous blood flow profiles. The dicrotic notch (D) is commonly used to indicate the break between the steep and slow decrease in the arterial flow, marking the systole end.

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  Fig. 3.. Comparative arrival times of the blood flow peak (M) in the different arteries and sinuses. Lower part, right: comparison between the different inflow or outflow timings in either YA or OA. In YA, no significant difference can be found in the arrival times of the maximal flow, either between BT, RC, and LC or between StS and SS. In contrast, in OA, BT maximal flow input significantly precedes the RC input (p = 0.017, n = 7) and the LC input (p = 0.017, n = 7), and the StS maximal outflow is earlier than the SS one (p = 0.040, n = 7) (non-parametric paired-test with Bonferroni correction for multiple comparisons). Lower part, left: The maximal value of blood flow in OA precedes that in YA in the arterial (BT) as in the venous system (StS, SS). Mann–Whitney tests (p = 0.038 for BT, 0.043 for SS, 0.018 for StS). Upper part: Comparison of arterial input and venous output time course between YA and OA. The time intervals are calculated as the means of the difference in arrival times (expressed in %CC) of maximal blood flow in the different vessels or sinuses. During the cardiac cycle, the time interval between the arterial (BT or LC) and the venous (SS) maximal blood flow is…

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  Fig. 4.. Time course of arterial and venous blood flows along the cardiac cycle (CC). (A) Arterial flow is the sum of the blood flows measured in the basilar trunk artery and the two carotids. The venous flow is the sum of blood flow measured in the straight and superior sagittal sinus. The maximal value of arterial blood flow occurs at different steps of the CC: at step 10 for young (YA) and at step 8 for old (OA) marmosets. Step 3 represents the start of the large arterial inflow to the brain, and step 17 marks the dicrotic notch, which defines the transition between the systole and diastole cardiac phases. Data are presented as mean ± SEM; n = 7 per age group. Each marmoset provided both arterial and venous flow data. Error bars are shown on one side to improve legibility. *Indicates a significant difference in the flow values (p < 0.05). (B) The relationship between arterial and venous blood flows was established with 32 measurement steps over the CC (synchronised with the R-wave of the EEG, point 1) in young and old adult marmosets. This relationship exhibits a hysteresis phenomenon consisting of three successive periods. The first period involves nonlinear growth, with an increase…

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  Fig. 5.. Relationship between heart rate (HR) and cerebral blood flow (CBF) (individual analysis). Data for females and males may segregate based on heart rate (HR) and cerebral blood flow (CBF) values. The data distribution indicates a sex effect on both HR and CBF, while an age effect differentiates young from old males, suggesting an age–sex interaction.

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  Fig. 6.. Combined time courses of blood volume in the marmoset brain during the cardiac cycle. (A) Inflow (Art) and outflow (Ven) of blood during the cardiac cycle (CC) (Art = sum of BT, RC, and LC) and venous (Ven = sum of StS and SS) in young (YA) and old (OA) adult marmosets. Data are presented as mean ± SEM (n = 7 for each age group). (B) Evolution of the balance between arterial and venous blood volumes, that is, arterial blood volume minus corrected venous blood volume, along the CC. The excess of blood (Art-Ven > 0) within the brain vascular compartment (positive values) is greater and occurs earlier in OA than in YA marmosets, which is consistent with the earlier peak of arterial blood flow (systolic phase of the CC) observed in aged marmosets.