Cerebral Haemodynamic Changes During Cognitive Testing: A fTCD Study

Dementia is the most common neurodegenerative disorder in the United Kingdom (UK); 850,000 people currently live with dementia in the UK, and that number is expected to rise to more than 1 million within the next 5 years. The annual cost to the UK of dementia is £23.6 billion. The most common type of dementia in the population (55%) is Alzheimer's dementia (AlzD). AlzD typically has a gradual onset and a slow progression. Vascular dementia (VascD) is the second commonest form of dementia (15%), and is suggested by the presence of vascular risk factors such as high blood pressure, high cholesterol, smoking and heart disease. The onset of vascular dementia is often abrupt, and the progression stepwise and irregular; cognitive deficits are often less uniform than those of Alzheimer's dementia. Mild cognitive impairment (MCI) affects up to 20% of older adults and describes a set of symptoms rather than a specific medical condition or disease. A person with MCI has subtle problems with one or more of the following: day-to-day memory, planning, language, attention and visuospatial skills. Although MCI significantly increases the risk of developing dementia at present it is not possible to accurately predict which patients with MCI will progress to dementia.

In recent times, our knowledge regarding the mechanisms of dementia development has changed considerably. In contrast to previous thoughts, there is now a growing understanding that problems with blood vessels (vascular dysfunction) and brain blood flow (cerebral haemodynamics) are present in AlzD as well as in VascD. Research studies investigating the vascular contributions to dementia generally report low blood flow (cerebral hypoperfusion). It is thought that this hypoperfusion affects cellular health which in turn triggers neurodegenerative pathways.

Brain blood flow is directly linked to brain activity, a concept known as 'neurovascular coupling'. Brain activation can be achieved through various cognitive and visual tasks (e.g reading and writing), and also by sensorimotor tasks (e.g. movement or touch). Cognitive assessments are routinely used in the diagnosis of dementia. Brain blood flow can be studied using techniques such as functional magnetic resonance imaging (fMRI), positron emission tomography (PET) or single-photon emission computed tomography (SPECT). However, these techniques are expensive, in the case of SPECT involve radiation, and there are feasibility issues which are particularly problematic for older populations, including the need to lie still for prolonged periods and have no metal implants. Transcranial Doppler (TCD) ultrasound is a simple, non-invasive imaging technique which allows for the continuous and bilateral recording of brain blood flow velocity through the major arteries in the brain.

Cognitive testing with standardised assessment tools such as the Mini Mental State Examination, Montreal Cognitive Assessment and Addenbrooke's-III Cognitive Examination (ACE-III) is a key component of the formal diagnosis of dementia, yet the effects of these tests on brain blood flow and haemodynamics is unknown. The ACE-III is a widely used, validated, cognitive screening tool recommended for use by health practitioners and researchers in patients over 50 years old with suspected dementia. The ACE-III is available for free. The copyright is held by Professor John Hodges, ARC Federation Fellow and Professor of Cognitive Neurology at Neuroscience Research Australia, who is happy for the test to be used in clinical practice and research projects.

This protocol has been used successfully by this group to examine changes in CBFv in 40 healthy volunteers from the University of Leicester. The data from this analysis has been presented at an international conference and is currently undergoing peer review for publication. Therefore, this protocol has demonstrated feasibility in a healthy population and warrants further investigation for the utility in a patient population.

This research will therefore use transcranial Doppler ultrasound to study the brain blood flow responses of healthy controls, patients with AlzD, patients with VascD, and patients with MCI, in response to performance of the ACE-III cognitive examination.

Inclusion criteria

• Informed volunteer consent, patient consent
• Male or female, aged between 18 and 100 years of age
• Able (in the Investigator's opinion) and willing to comply with all study requirements
• Willing to allow his or her General Practitioner (GP) to be notified of participation in the study
• Good understanding of written and verbal English

Healthy Controls-specific Inclusion Criteria

• No evidence of subjective or objective memory impairment on cognitive testing
• No major medical co-morbidity (outlined in detail in the exclusion criteria) or medication use that could adversely affect cognition

MCI Patient-specific Inclusion Criteria

Clinical diagnosis of MCI made by a specialist* in a patient who fulfils the established clinical consensus criteria for MCI [NIA/AA 2011] specifically:

• Concern regarding a change in cognition compared to the person's previous level, by the patient and/or informant
• Objective evidence of impairment of one or more cognitive domains, greater than expected for age, and educational background, over time if repeated measures are available.
• Preserved independence of functional abilities and minimal to no impairment on complex instrumental functions
• Not demented

Vascular Dementia Specific Inclusion Criteria

Clinical diagnosis of VascD made by a specialist* in a patient who fulfils the NINDS-AIREN criteria for VascD, specifically:

• Cerebrovascular disease defined by the presence of focal signs on neurological examination consistent with stroke and evidence of cerebrovascular disease on brain imaging.
• One or more of:

• Onset of dementia within 3 months of a diagnosed stroke
• Abrupt deterioration in cognitive function
• Fluctuating, stepwise progression of cognitive deficits

Alzheimer's Dementia Specific Inclusion Criteria

Clinical Diagnosis of AlzD made by a specialist* in a patient who fulfils the NIA/AA criteria for Probable AlzD, specifically:

• Meets the criteria for dementia

• The memory impairment and cognitive deficits cause significant impairment in social or occupational functioning, and represent a significant decline from a previous level of functioning, not explained by a delirium or a major psychiatric disorder
• Impairment of at least two cognitive domains
• Insidious or gradual onset
• Clear history of worsening cognition by report or observation
• The initial and most prominent cognitive deficits are evident on history and examination in one of the following domains:

• Amnestic: impaired learning and recall of recently learned information
• Non amnestic: language/visuospatial/executive dysfunction
• No evidence of substantial cerebrovascular disease, core features of dementia with lewy bodies, features of frontotemporal dementia, prominent features of semantic variant primary progressive aphasia, evidence of active neurological disease, a non-neurological co-morbidity or medication that could affect cognition

• A specialist being defined as a psychiatrist or a geriatrician, or a specialist mental health nurse with a specific interest or expertise in cognitive disorders.

Exclusion criteria

Exclusion criteria

• Male or Female, aged under 18 years
• Unable (in the Investigator's opinion) or unwilling to comply with any study requirements
• Female participants who are pregnant, lactating or planning pregnancy during the course of the study
• Major co-morbidity likely to affect cerebral autoregulation; severe respiratory disease, carotid artery stenosis, atrial fibrillation, severe cardiac failure (left ventricular ejection fraction <20%), extreme frailty or multi-morbidity.