Blood pressure gradients in cerebral arteries: a clue to pathogenesis of cerebral small vessel disease

Abstract

Rationale: The role of hypertension in cerebral small vessel disease is poorly understood. At the base of the brain (the 'vascular centrencephalon'), short straight arteries transmit blood pressure directly to small resistance vessels; the cerebral convexity is supplied by long arteries with many branches, resulting in a drop in blood pressure. Hypertensive small vessel disease (lipohyalinosis) causes the classically described lacunar infarctions at the base of the brain; however, periventricular white matter intensities (WMIs) seen on MRI and WMI in subcortical areas over the convexity, which are often also called 'lacunes', probably have different aetiologies.

Objectives: We studied pressure gradients from proximal to distal regions of the cerebral vasculature by mathematical modelling.

Methods and results: Blood flow/pressure equations were solved in an Anatomically Detailed Arterial Network (ADAN) model, considering a normotensive and a hypertensive case. Model parameters were suitably modified to account for structural changes in arterial vessels in the hypertensive scenario. Computations predict a marked drop in blood pressure from large and medium-sized cerebral vessels to cerebral peripheral beds. When blood pressure in the brachial artery is 192/113 mm Hg, the pressure in the small arterioles of the posterior parietal artery bed would be only 117/68 mm Hg. In the normotensive case, with blood pressure in the brachial artery of 117/75 mm Hg, the pressure in small parietal arterioles would be only 59/38 mm Hg.

Conclusion: These findings have important implications for understanding small vessel disease. The marked pressure gradient across cerebral arteries should be taken into account when evaluating the pathogenesis of small WMIs on MRI. Hypertensive small vessel disease, affecting the arterioles at the base of the brain should be distinguished from small vessel disease in subcortical regions of the convexity and venous disease in the periventricular white matter.

Keywords: Small vessel disease; amyloid; blood pressure; lacunar; lobar; mathematicalmodelling.

Figure 1

Anatomically Detailed Arterial Network (ADAN) model with detail of the vasculature in the head. Computational haemodynamics model containing over 2000 arterial vessels to simulate pulsatile pressure and blood flow rate using mass and momentum conservation principles. For the intracranial vasculature, 162 cerebral vessels are considered.

Figure 2

Results of the simulations for the two considered scenarios: normotensive (N) and hypertensive (H). Pulsatile arterial pressure (mean between brackets) is displayed at selected arterial vessels covering medium-sized arteries and small-sized arteries. Vessels have been picked up in both centrencephalic and cortical areas. The MAP, SBP and DBP at the same arterial vessels are also reported in table 1 for the normotensive (N) and hypertensive (H) cases. BA, basilar artery; BrA, brachial artery; DBP, diastolic pressure; DMSA, distal medial striate artery; ICA, internal carotid artery; LsA, lenticulostriate artery; MAP,  mean arterial pressure; MCA, middle cerebral artery; PCA, posterior cerebral artery; PfA, prefrontal artery; PPB, posterior parietal branch; SBP, systolic blood pressure; TB, terminal branch.

Figure 3

Detail of the peripheral beds corresponding to the lenticulostriate artery and to the posterior parietal branch of the middle cerebral artery. Pressure waveforms are shown for the normotensive (N, dashed line) and hypertensive (H, solid line) cases. Right panels (top and bottom) display the pressure waveform in the feeding artery to the corresponding arteriolar networks. Middle and left panels show the pressure level in arterioles with diameter ranges between D ∈ (190 μm, 210 μm) and D ∈ (30 μm, 50 μm), respectively; n indicates the number of vessels taken to calculate the average and SD pressure waveforms (grey-shaded area). In brackets, the mean arterial pressure is reported. LsA, lenticulostriate artery; MCA, middle cerebral artery; PPB, posterior parietal branch.

Figure 4

Mean arterial pressure throughout the peripheral beds under analysis. Arteriolar regional pressure drop for the peripheral arterioles of the lenticulostriate artery (top row) and of the posterior parietal branch of the middle cerebral artery (bottom row), for the normotensive case (left column) and the hypertensive case (right column).