Alzheimer’s disease (AD) is the leading cause of dementia in both industrialized and developing countries, accounting for most of all dementia cases [
It is well known that amyloid-
In normal subjects, the neurovascular unit (NVU), which is a functional unit consisting of neuronal, glial, and vascular cells, is responsible for maintaining an adequate cerebral blood flow (CBF) in response to internal and external stimuli. The NVU (and CBF in consequence) can respond to changes in blood CO2 concentration, which is the termed cerebral vascular motor reactivity or cerebral vasomotor reactivity (CVMR) [
The aim of this study was to measure and compare CVMR response with TCD in AD participants versus control subjects matched for age and sex and to associate these changes with their cognitive scores in a Latin-American AD sample.
A case-control study was conducted, and participants were consecutively recruited from the Neurology Outpatient Clinic of the Universidad Autonoma of Nuevo Leon, Monterrey, Mexico, from July 2009 to July 2010. Inclusion criteria were subjects with a diagnosis of AD according to the DSM IV and NINCDS-ADRA Criteria [
To evaluate for possible confounding factors, an MRI study was made to assess for white matter damage (leukoaraiosis) and a carotid ultrasound study to assess for carotid plaques and an intima-media thickness (IMT). In addition, blood samples were obtained for every participant and processed for common vascular risk biomarkers: cholesterol, low-density lipoprotein, high-density lipoprotein, triglycerides, C-reactive protein, and homocysteine.
Demographic and vascular risk factors data were obtained through a structured clinical interview, and participants were classified as having diabetes mellitus (DM) if they were using antidiabetic drugs or with self-reported history; also hypertension and dyslipidemia status were assessed similarly. Cognitive function was evaluated with Mini-Mental State Examination test (MMSE) Spanish version [
CBFVs and Pulsatility Indices (PIs) were evaluated with a 2 MHz Probe TCD (Rimed; Smart-Lite SL-1 TCD System) with the participant in a supine position; measurements were taken in the left MCA by the same examiner at an insonation deep of 55 millimeters through the temporal window. After baseline CBFVs and PIs measurement, a CVMR test was made asking the patient to inhale a 7% CO2-air mixture for 5 minutes according to Deplanque et al. [
Comparisons of continuous variables were analyzed with a Mann–Whitney U test and a chi-square test was used for categorical variables. A multivariate analysis was made to adjust for age and sex. Finally, a Spearman correlation test between MMSE results, CBFVs difference, and %CVMRs was performed. Results were considered significant if p=<0.05. All statistical analysis was made using SPSS v22.0.
A total of 51 subjects, 26 participants with AD and 25 healthy, were initially included; however, 6 controls who did not attend the initial carotid ultrasound and MRI study appointment were excluded. General demographic, cognitive, and depression test results are shown in Table
Demographic, clinical, imaging, and blood sample characteristics of Alzheimer’s disease and healthy control participants.
Characteristic | Alzheimer’s disease (n=26) | Healthy controls (n=19) |
---|---|---|
| ||
| ||
Age, median (range) | 78(67-93) | 78 (59-90) |
| ||
Gender, fem (%) | 21 (81%) | 15 (79%) |
| ||
Education years, median (range) | 3(0-15) | 6 (0-16) |
| ||
Diabetes mellitus, n (%) | 9(35%) | 4(21%) |
| ||
Hypertension, n (%) | 13(50%) | 8(42%) |
| ||
Dyslipidemia, n (%) | 5(19%) | 9(47%) |
| ||
Active smoking, n (%) | 6(23%) | 7(37%) |
| ||
MMSE, media (±SD) | 14.08(±5.80) | 27±(3.20) |
| ||
GDS, median (range) | 4 (0-9) | 3 (0-7) |
| ||
| ||
| ||
Leukoaraiosis >5mm | 6 (23%) | 2 (11%) |
| ||
Carotid plaques >30% | 11 (42%) | 6 (32%) |
| ||
Intima-media thickness | 0.902 (0.60 -2.0) | 0.826 (0.6-1.10) |
| ||
| ||
| ||
Total cholesterol | 182.2 ± 36.4 | 197.6 ± 33.5 |
| ||
LDL | 111.6 ± 31.5 | 129.8 ± 32.3 |
| ||
HDL | 36.7 ± 11.5 | 38.2 ± 9.6 |
| ||
Triglycerides | 164.7 ± 100.4 | 147.5 ± 56.9 |
| ||
CRP | 3.7 ± 5.0 | 6.6 ± 9.1 |
| ||
Homocysteine | 10.3 ± 2.9 | 8.9 ± 3.6 |
MMSE: Mini-Mental State Examination; BMI: body mass index; GDS: Geriatric Depression Scale 15 item version; MRI: magnetic resonance imaging; LDL: low-density lipoprotein; HDL: high-density lipoprotein; CRP: C-reactive protein.
There were no differences in the severity of white matter damage between the groups. In addition, there were no significant differences in the presence of carotid plaques or intima-media thickness estimate. There were no statistically significant differences between AD participants and HC in cholesterol, LDL, HDL, triglycerides, C-reactive protein, and homocysteine levels. Full results of MRI, carotid doppler, and blood samples are shown in Table
Baseline CBFVs in MCA were obtained from all participants. Table
Baseline, post-CO2 test cerebral blood flow velocities, and calculated CVMR.
Healthy Controls | Alzheimer’s disease | |||||
| ||||||
Velocities | Baseline | Post-CO2 | Mean CVMR % (±SD) | Baseline | Post-CO2 | Mean CVMR % |
| ||||||
CBFV-S | 69.90 (18.44) | 82.64 (14.47) | 21.17(17.03) | 62.3619.83) | 68.30(20.50) | 10.88(15.26) |
| ||||||
CBFV-D | 26.36 (7.26) | 31.86 (7.42) | 23.29(17.48) | 25.348.21) | 27.09(9.78) | 7.45(18.25) |
| ||||||
CBFV-M | 49.00 (15.52) | 57.70 (14.08) | 20.88(14.97) | 38.8814.95) | 43.69(16.87) | 15.02(27.69) |
CBFV-S: cerebral blood flow velocity-systolic; CBFV-D: cerebral blood flow velocity-diastolic; CBFV-M: cerebral blood flow velocity-mean; CVMR %: cerebral vasomotor reactivity as a percentage of change between baseline CBFV and post-CO2 test CBFV.
All recruited participants were able to perform the entire CVMR test. There were significant absolute differences in CBFVs between AD and HC groups after the CO2 test, and calculated %CVMR for changes in diastolic, systolic, and mean CBFVs were statistically significant between both groups; however after adjusting for age, sex, hypertension, and DM, only changes in diastolic CVMR remained statistically significant (7.45±18.25 versus 23.29±17.48, p<0.05). Full results are shown in Table
There was a positive correlation between MMSE results and changes in CBFV-S (
This study shows that participants with AD have smaller changes in CBFVs than healthy controls matched for age, gender, and common vascular risk factors in response to an inhaled CO2 CVMR test, particularly in diastolic phase CBFV. Also, this decreased response may not be related to differences in common vascular risk biomarkers such as white matter damage, atherosclerotic disease, cholesterol, C-reactive protein, or homocysteine levels. As far as we know, these are the first results published from a Latin-American AD sample.
This study showed no baseline alteration in CBFVs or PIs. Similar results have been previously published; a study by Lee et al. [
CVMR attenuation in AD has also been shown in other studies; Abeelen et al. [
Vascular pathology plays a central role in the development and progression of Alzheimer’s disease. These changes may appear before the clinical manifestation [
This study showed a weak positive correlation between MMSE results and CBFVs change before and after CVMR test, although a study by Lee et al. [
This study had several limitations: first, we did not perform a measurement of end-tidal CO2 because of limited resources and we did not assess CVMR in hypocapnia condition. Also, AD diagnosis was clinical criteria-based, and severity of dementia was not directly assessed. Only MCA measurements were taken for feasibility purposes. DM as a cardiovascular risk factor was considered with only clinical history without considering blood sugar or HbA1c readings; thus there was not a distinction between those with controlled or uncontrolled DM and neither for hypertension or dyslipidemia. Weight/BMI and PAD were not assessed. Also, subjects with a GDS-15 score compatible with probable depression in the study appointment were not excluded. Moreover, 6 healthy control participants who did not attend the MRI appointment were excluded; however, baseline results showed no differences. Despite this, these results should be confirmed in a larger sample size.
Despite being an indirect measurement of overall vascular function, measurement of baseline CBFVs and CVMR responses in AD subjects with TCD is easy, safe, and cost-effective. Therefore, these virtues make this technique ideal for its use in the clinical setting of developing countries. This study adds strength to the general reproducibility of these results for the use of CVMR test in the clinical setting of AD with Latin-American samples.
The data used for this study are not publicly available due to local ethic regulation and patient privacy consent.
The authors declare that there are no conflicts of interest regarding the publication of this paper.
This research was done with internal resources from the Department of Neurology of the Universidad Autonoma of Nuevo Leon.