Cardiorespiratory: The Increase in Alzheimer’s Disease

 Cardiorespiratory: The Increase in Alzheimer’s Disease

 

Alzheimer’s is a type of dementia that affects memory, thinking and behavior. Symptoms start off small but eventually grow severe enough to interfere with daily tasks1. It accounts for approximately 60-80% of dementia cases1. It is known to have no current cure, but treatments for symptoms are available and so is research. Many changes begin in the brain before the first signs of memory loss. The brain is composed of more than 100 million nerve cells known as neurons in which each nerve cell connects to others composing communication networks. Each neuron has specialty ranging from thinking to remembering or even to our senses. To keep our brain functioning it requires oxygen which is crucial for many organs such as the heart and lungs.

With that being said, cardiorespiratory plays a large role in Alzheimer’s due to the increase in brain signal during an fMRI. An fMRI (functional magnetic resonance imaging) is a technique for measuring and mapping brain activity that is noninvasive and safe2. This approach was taken because the clinical diagnosis of Alzheimer’s is based on many extensive examinations neurologically and neuropsychological. Realistically, those whom have Alzheimer’s always wonder why and it is not part of the aging process. The diagnostic portion of Alzheimer’s is not fully accurate which then in turn causes unsatisfactory outcomes. With so much unsatisfied patients, in 2018, the National Institute of Aging and Alzheimer’s Association of the United States proposed a shift of the diagnostic paradigm away from clinical symptoms or post mortem findings, towards criteria based on some combination of biomarkers in living persons3. 

This experiment was performed to better understand how the brain works and mainly to understand the physiological brain pulsations are altered in Alzheimer’s disease then causing increased variability in the brain BOLD signal. During this study, the possibility is tested by measuring the variability of blood oxygen level-dependent signal in individuals from three data sets, 80 Alzheimer Disease patients with 90 controls2. Many objectives came about including; 1. Analyzing previous findings of BOLD brain signal variability in Alzheimer’s disease, 2. Developing noninvasive MR- biomarker for Alzheimer’s disease without contrast agents and lastly 3. Study the physiological origin of the signal alteration3. The data sets determined the rSDBOLD  for Alzheimer’s detection. The increase of BOLD signal variability was shown to be related to physiological mechanisms driving the network of vessels that clear waste from the Central Nervous system clearance than an indicator of VLF fluctuations of the BOLD signal arising from perturbed neuronal activity3. The BOLD signal indicated underlying vascular and respiratory factors in the brain which then shown elevated variability in the BOLD signal. 

The brain signal showed that Alzheimer’s patients increased rSDbold in clusters of the voxels distributed around the basal ganglia and the white matter around the lateral ventricles. With the findings it was then compared to the patterns of neurodegeneration with regional rSDBold changes3. Within brain signal variability it is then associated with declined Mini Mental State Examination (MMSE). The comparison brought to the attention that BOLD signal variability was associated with lower cognitive function scores during the exam. The comparison was then the voxel-wise group-level difference between the AD and control groups in rSD maps of full band MREGBOLD and in SD maps of cardiac (SDcard), respiratory (SDresp), and VLF (SDVLF) band data. This showed that rSD maps of the full band and SD maps of cardiac and respiratory parts of the signal overlapped spatially. Moreover, the SDcard showed widespread increases extending beyond the corresponding findings for full band rSDBOLD in the AD group. The SDresp maps indicated group differences in bilateral frontal and temporoparietal areas, left sensorimotor cortex, medial frontal and temporal gyri.3

While using three different Fmri data sets it has come to the conclusion that brain signal variability increase in Alzheimer’s disease. 

References

1. Alzheimer’s Assosiation, 2021 

2. https://cfmriweb.ucsd.edu/Research/whatisfmri.html

3. Tuovinen, T., Kananen, J., Rajna, Z. et al. The variability of functional MRI brain signal increases in Alzheimer's disease at cardiorespiratory frequencies. Sci Rep 10, 21559 (2020). https://doi.org/10.1038/s41598-020-77984-1

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