Investigating the Relationship between Cerebral Blood Flow and Cognitive Function in Hemodialysis Patients

Abstract

Background: The immediate and longer-term effects of hemodialysis on cerebral circulation, cerebral structure, and cognitive function are poorly understood.

Methods: In a prospective observational cohort study of 97 adults (median age 59 years) receiving chronic hemodialysis, we used transcranial Doppler ultrasound to measure cerebral arterial mean flow velocity (MFV) throughout dialysis. Using a well validated neuropsychological protocol, we assessed cognitive function during and off dialysis and after 12 months of treatment. We also used brain magnetic resonance imaging (MRI) to assess atrophy, white matter hyperintensities (WMHs), and diffusion parameters, and tested correlations between MFV, cognitive scores, and changes on MRI.

Results: MFV declined significantly during dialysis, correlating with ultrafiltrate volumes. Percentage of decline in MFV correlated with intradialytic decline in cognitive function, including global function, executive function, and verbal fluency. At follow-up, 73 patients were available for repeat testing, 34 of whom underwent repeat MRI. In a subgroup of patients followed for 12 months of continued dialysis, percentage of decline in MFV correlated significantly with lower global and executive function and with progression of WMH burden (a marker of small vessel disease). Twelve of 15 patients who received renal transplants during follow-up had both early and follow-up off-dialysis assessments. After transplant, patients' memory (on a delayed recall test) improved significantly; increased fractional anisotropy of white matter (a measure of cerebral diffusion) in these patients correlated with improving executive function.

Conclusions: Patients undergoing hemodialysis experience transient decline in cerebral blood flow, correlating with intradialytic cognitive dysfunction. Progressive cerebrovascular disease occurred in those continuing dialysis, but not in transplanted patients. Cognitive function and cerebral diffusion improved after transplant.

Keywords: cardiovascular disease; cerebrovascular disease; cognition; hemodialysis.

Graphical abstract

Figure 1.

Haemodialysis related decline in cerebral mean flow velocity The change in MFV during dialysis session (n=82), is presented as a median value and IQR (error bars). TCD recordings were taken prior, during, and after completion of dialysis, demonstrating a significant decline in MFV after dialysis; weighted GEE P<0.001.

Figure 2.

White matter hyperintensities progress in those on continued haemodialysis. The images on the left represent baseline MR images and on the right MR imaged at follow-up following 12 months of treatment. Additionally, a loss of cerebral volume can be appreciated as enlargement of lateral ventricles. This figure demonstrates visible progression of WMH on standard T2 fluid-attenuated inversion recovery sequences (top row) and after application of volumetric analyses software (bottom row).