The Link Between Cardiovascular and Cognitive Health
The link between the cardiovascular system and cognition has been firmly established. Literature describing this link is vast; however, papers focused on this topic are published in disparate medical journals. If, for example, one is studying papers related to this topic published in cardiology journals, they may miss the papers, on the same topic, published in nursing or psychological journals.
The relatively-recent interest in examining the link between cardiovascular health and cognition, which resembles the studies of “cardiogenic dementia” in the late 1970’s, stems from seeing patterns in hospital readmission of patients with cardiovascular illnesses and related economic costs. In the United States, “Healthcare costs related to HF [Heart Failure] have increased more than 170% over the past decade, with costs for 2010 estimated at over $39 billion. Hospital readmission accounts for a large portion of the cost … 25% of older persons discharged from the hospital with a diagnosis of HF are readmitted within 30 days.”[1] “Central to the treatment of HF is a relatively complex multidrug pharmacological treatment that requires careful biochemical surveillance, strict adherence, and a high level of self-management.”[2] Almeida et al. in their study conclude that cognitive impairment is responsible for the low adherence of many HF patients to this complex self-care regimen.[3] Cognitive deficits due to HF alter patients’ ability “to perform activities of daily living and comply with HF self-care behaviour.”[4] “Heart failure (HF) is a condition that develops after the heart becomes damaged or weakened. HF occurs when the pumping action of your heart is not strong enough to move blood around, especially during increased activity or under stress. In addition, the heart muscle may not relax properly to accommodate the flow of blood back from the lungs to the heart.”[5]
“Cognitive impairment is an umbrella term encompassing everything from mild cognitive impairment at 1 end of the spectrum to dementia at the other end.”[6] Cognitive impairments associated with HF involve multiple processes, such as attention and learning deficits, reduced psychomotor speed, diminished executive function, memory dysfunctions, language impairment, and reduced visuospatial performance.[7] It is important to note that “HF patients … have worse cognitive performances after adjustment for age, socioeconomic status, and education, and also when compared with patients with significant comorbidities.”[8] This implies that the lower cognitive performance in patients is directly related to the presence of heart failure. Additionally, in one study, “patients with more severe HF had poorer total recall memory, visuospatial recall ability, psychomotor speed, and executive functioning.”[9] Thus, the association between HF and cognitive performance is decisively established.
The pathophysiology, or the functional changes, of cognitive impairment in HF patients is currently being studied from multiple perspectives. Some studies have discovered that both anatomic and functional brain abnormalities were found in the HF population. Almeida et al. showed that “participants with HF display a relative loss of cerebral GM [Grey Matter] in various cortical and subcortical regions [of the brain] extending to the frontal lobes, anterior cingulate, and temporal-parietal lobes.”[10] In addition, they found that the posterior cingulate region of the brain, which plays an important role in the successful retrieval of memory traces, showed the greatest reduction in blood flow in HF participants.[11] They suggest that the loss of grey matter density in “subcortical structures and frontal cortex may contribute to compromise attention, memory, and executive function,”[12] and GM loss in anterior cingulate of the brain and areas of the lateral and medial frontal cortex may impair attention, mental associations, and strategic thinking.[13]
Havakuk et al., in their well-researched paper, propose a pathophysiology behind the functional and anatomic brain changes due to HF.[14] To be cautious, they do note that “The mechanism proposed for brain injury in HF is multifactorial and not well understood.”[15] In a simple, yet informative diagram, Havakuk et al. illustrate the multifactorial association between HF and brain injury. To understand this diagram effectively, in their paper, they narrow the definition of cardiocerebral syndrome to, “a state of cognitive impairment of undefined cause in HF patients, beyond that anticipated in age-matched controls, and typically accompanied by anatomic brain changes.”[16] The graph shows that heart failure may trigger a variety of dysfunctions in other bodily systems, which subsequently, result in anatomical brain changes and cognitive dysfunctions.
Jack C. de la Torre expands the scope of the link between heart dysfunction and cognitive impairment beyond heart failure.[17] He states, “Epidemiological findings indicate that a broad spectrum of cardiovascular risk factors, including heart failure … are reported to contribute to cognitive dysfunction and decline affecting performance in executive functions, attention, learning, psychomotor speed, verbal fluency, mental alertness, and memory.”[18] In a central figure in his paper, de la Torre illustrates the “cardiovascular risk factors reported to promote progressive cognitive decline leading to dementia in elderly population.”[19]
By referring to previous studies de la Torre connects various cardiovascular risk factors to a variety of cognitive dysfunctions. According to de la Torre, the “Cardiovascular disease and the risk factors that characterize it promote brain hypoperfusion[20] in the aging individual by inducing cerebral hemodynamic deficits and reducing blood flow to the brain through various vasculopathic pathways.”[21] The cascade of events occur in the following order: “Cardiovascular pathology begets chronic brain hypoperfusion which begets progressive cognitive decline.”[22] In another figure in his paper, he illustrates this cardiovascular disease cascade in cognitive decline.
He describes the above figure as the “Hypothetical model based on the collective evidence available showing how cardiovascular risk factors give rise to disturbed hemodynamic flow patterns inducing cerebral hypoperfusion.” He states, “Chronic insufficiency of blood flow to the brain may reach a critically attained threshold of cerebral hypoperfusion (CATCH) responsible for lowered energy substrate delivery and creation of neurono-glial energy crisis, initially in brain regions where memory and learning are localized.”[23] [Italics mine] Picano et al. explains, “Since it is unable to store energy, the brain function depends on continuous delivery of oxygen and glucose through blood flow… Because of the high metabolic demand for oxygen in the brain, limited cerebral blood flow may lead to neurovascular unit energy crisis and cerebral hypoperfusion is a very early event in the hypothetical cascade leading to cognitive decline.”[24]
In their paper, Picano et al. widen, even further, the pathophysiological link between cardiovascular disease and cognitive impairment to include the seven major rings of the cardiovascular hemodynamic chain. According to Picano et al., “Normal brain perfusion requires that all rings of the physiological chain be intact, since a chain can only lift the weight that its weakest link can bear.”[25] The seven rings of the cardiovascular chain are: the lung, the heart, the large elastic vessels (aorta), the baroreflex, the cerebrovascular arteries, the small cerebral vessels, and the cerebrospinal venous system.[26] “An anatomic or functional alteration of each segment can lead to impaired cerebrovascular perfusion and increased risk of dementia, although frequently these conditions are not isolated and are often mutually interrelated.”[27] Picano et al. illustrate this interrelationship in the following simplified figure.
They equate the relationship between vascular health and cognitive health to the relationship between tree roots and tree leaves, respectively. Healthy leaves (well-performing cognition) require healthy roots (healthy vascular system). In their paper, they simplify this relationship in the following figure. To better grasp the figure they clarify the terms, “cognitive reserve” and “vascular reserve.” “Cognitive reserve refers to the brain’s ability to cope with either increasing activities or damage. The concept of cognitive reserve is a predominantly functional one.”[28] “Vascular reserve refers to the vessel’s ability to cope with increasing activity or damage, and is commonly measured as the ability to increase regional flow after a hyperemic stimulus, such as carbon dioxide in the brain, adenosine in myocardium or ischemia in the forearm.”[29] The clinician or an individual who aims to treat the cognitive impairment is regarded as the gardener.
What this model highlights, which is in harmony with numerous other papers on the link between cardiovascular health and cognition, is that “The same lifestyle and environmental factors modulating cognitive function also modulate vascular function… The recommendations of neurobiologists to prevent cognitive decay by lifestyle and environmental intervention closely mirror those of cardiologists to prevent vascular disease progression.”[30] They are:
Quitting smoking
Achievement and maintenance of ideal body weight
Regular exercise
Reduced intake of saturated fat and sugars
Decreasing the level of stress which is best achieved by improving one’s family, community and societal relationships
They note, “An integrated physical, cognitive, and dietary program of environmental enrichment allows the neurobiologist and the cardiologist to kill but two birds (brain and vessel protection) with one stone (lifestyle changes).”[31]
Abete et al.’s “heart-brain continuum hypothesis”[32] agrees with Picano et al.’s practical recommendations in order to maintain healthy cognitive abilities; however, they shift the focus from the seven rings of cardiovascular hemodynamic chain to a “cardiovascular disease continuum,” which begins with cardiovascular risk factors, particularly hypertension, and ends with dementia. Their analysis shows, “The presence of hypertension during middle-age represents the key point for the development of left ventricular hypertrophy and atrial fibrillation. All these conditions, together with CAD [Coronary Artery Disease], may lead to chronic heart failure and the end of cardiovascular continuum.” They continue, “Each step of the cardiovascular continuum represents a potential risk factor for the development of cognitive impairment … and consequently, if the risk factor is not abolished, to the development of dementia.”[33] They consider the mechanisms behind cognitive impairment to be “thrombo-embolic and/or reduction of cardiac output”[34] due to cardiovascular risk factors. Thromboembolism is the obstruction of a blood vessel by a blood clot that has become dislodged from another site in the circulation. They have illustrated their hypothesis in the following figure.
The evidence linking cardiovascular activities to cognition is plenty. Commenting on the current evidence available, Angermann et al. state, since “Cognitive impairment (CI), CVD and heart failure (HF) frequently co-occur, the precise mechanisms underlying CI have remained difficult to disentangle.”[35] However, they conclude, “There is unequivocal evidence that cognition matters in CVD [Cardiovascular Disease] and HF.”[36] Similarly, Harrison et al. states, “a strong positive association was observed between the different vascular risk models and future cognitive decline or incident cognitive impairment or dementia.”[37] Kerola et al. also agree that “Cardiovascular risk markers have repeatedly been linked to changes in cognition.”[38] In one of the latest studies on this topic, published in 2017, Cannon et al. conclude, “We have demonstrated strong associations between HF and cognitive problems,”[39] and “Compared with matched controls with no HF, those with HF have significantly increased risk of cognitive impairment.”[40] In their systematic review and meta-analytical study, they have taken careful measures to indicate that the high prevalence of cognitive impairment in HF patients is “robust and not driven by poor-quality studies.”[41]
Although there may be various models, hypotheses, and theories about how the heart, specifically, and the cardiovascular system, generally, are linked to cognition, there is little doubt that they are indeed associated with one another and the performance of the former, both directly and indirectly, affects the performance of the latter. Picano et al.’s allegory of the constant gardener brings to mind and affirms an old famous adage, which is just as relevant today as it was when it was uttered, “A healthy mind is in a healthy body.”
REFERENCES:
[1] Bauer, Lisa C., Julene K. Johnson, and Bunny J. Pozehl. "Cognition in heart failure: an overview of the concepts and their measures." Journal of the American Association of Nurse Practitioners 23, no. 11 (2011): 577-585.
[2] Cannon, Jane A., Peter Moffitt, Ana Cristina Perez-Moreno, Matthew R. Walters, Niall M. Broomfield, John JV McMurray, and Terence J. Quinn. "Cognitive impairment and heart failure: systematic review and meta-analysis." Journal of cardiac failure (2017).
[3] Almeida, Osvaldo P., Griselda J. Garrido, Christopher Beer, Nicola T. Lautenschlager, Leonard Arnolda, and Leon Flicker. "Cognitive and brain changes associated with ischaemic heart disease and heart failure." European heart journal 33, no. 14 (2012): 1769-1776.
[4] Pressler, Susan J., Usha Subramanian, David Kareken, Susan M. Perkins, Irmina Gradus-Pizlo, Mary Jane Sauvé, Yan Ding et al. "Cognitive deficits in chronic heart failure." Nursing research 59, no. 2 (2010): 127.
[5] “Heart Failure,” Heart and Stroke Foundation. Accessed November 15, 2017. https://www.heartandstroke.ca/heart/conditions/heart-failure
[6] Cannon, Jane A., Peter Moffitt, Ana Cristina Perez-Moreno, Matthew R. Walters, Niall M. Broomfield, John JV McMurray, and Terence J. Quinn. "Cognitive impairment and heart failure: systematic review and meta-analysis." Journal of cardiac failure (2017).
[7] Bauer, Lisa C., Julene K. Johnson, and Bunny J. Pozehl. "Cognition in heart failure: an overview of the concepts and their measures." Journal of the American Association of Nurse Practitioners 23, no. 11 (2011): 577-585.
[8] Havakuk, Ofer, Kevin S. King, Luanda Grazette, Andrew J. Yoon, Michael Fong, Noa Bregman, Uri Elkayam, and Robert A. Kloner. "Heart Failure-Induced Brain Injury." Journal of the American College of Cardiology 69, no. 12 (2017): 1609-1616.
[9] Pressler, Susan J., Usha Subramanian, David Kareken, Susan M. Perkins, Irmina Gradus-Pizlo, Mary Jane Sauvé, Yan Ding et al. "Cognitive deficits in chronic heart failure." Nursing research 59, no. 2 (2010): 127.
[10] Almeida, Osvaldo P., Griselda J. Garrido, Christopher Beer, Nicola T. Lautenschlager, Leonard Arnolda, and Leon Flicker. "Cognitive and brain changes associated with ischaemic heart disease and heart failure." European heart journal 33, no. 14 (2012): 1769-1776.
[11] Ibid., P. 1774
[12] Ibid., P. 1775
[13] Ibid.
[14] Havakuk, Ofer, Kevin S. King, Luanda Grazette, Andrew J. Yoon, Michael Fong, Noa Bregman, Uri Elkayam, and Robert A. Kloner. "Heart Failure-Induced Brain Injury." Journal of the American College of Cardiology 69, no. 12 (2017): 1609-1616.
[15] Ibid., P. 1611
[16] Ibid., P. 1613
[17] de la Torre, Jack C. "Cardiovascular risk factors promote brain hypoperfusion leading to cognitive decline and dementia." Cardiovascular psychiatry and neurology 2012 (2012).
[18] Ibid., P.3
[19] Ibid.
[20] “Brain perfusion” is the blood flow to the brain. “Brain hypoperfusion” is when lower-than-normal level of blood flows to the brain.
[21] Ibid., P.7
[22] Ibid.
[23] Ibid., P.4
[24] Picano, Eugenio, Rosa Maria Bruno, Gian Franco Ferrari, and Ubaldo Bonuccelli. "Cognitive impairment and cardiovascular disease: so near, so far." International journal of cardiology175, no. 1 (2014): 21-29.
[25] Ibid., P. 23
[26] Ibid.
[27] Ibid.
[28] Ibid., P. 21
[29] Ibid., P. 22
[30] Ibid., P. 26
[31] Ibid.
[32] Abete, Pasquale, David Della-Morte, Gaetano Gargiulo, Claudia Basile, Assunta Langellotto, Gianluigi Galizia, Gianluca Testa, Vincenzo Canonico, Domenico Bonaduce, and Francesco Cacciatore. "Cognitive impairment and cardiovascular diseases in the elderly. A heart–brain continuum hypothesis." Ageing research reviews 18 (2014): 41-52.
[33] Ibid., P. 49
[34] Ibid.
[35] Angermann, Christiane E., Anna Frey, and Georg Ertl. "Cognition matters in cardiovascular disease and heart failure." (2012): 1721-1723.
[36] Ibid., P. 1723
[37] Harrison, Stephanie L., Jie Ding, Eugene YH Tang, Mario Siervo, Louise Robinson, Carol Jagger, and Blossom CM Stephan. "Cardiovascular disease risk models and longitudinal changes in cognition: a systematic review." PLoS One 9, no. 12 (2014): e114431.
[38] Kerola, Tuomas, Raimo Kettunen, and Tuomo Nieminen. "The complex interplay of cardiovascular system and cognition: how to predict dementia in the elderly?." International journal of cardiology 150, no. 2 (2011): 123-129.
[39] Cannon, Jane A., Peter Moffitt, Ana Cristina Perez-Moreno, Matthew R. Walters, Niall M. Broomfield, John JV McMurray, and Terence J. Quinn. "Cognitive impairment and heart failure: systematic review and meta-analysis." Journal of cardiac failure (2017).
[40] Ibid., P. 469
[41] Ibid.