Heart rate variability (HRV) and its relation to cognitive decline

Neuropsychologist Sofía Fonseca Moreno analyzes how heart rate variability (HRV) influences cognitive decline in old age.

Introduction

The life expectancy has increased, so the group of people over 60 years old has grown worldwide (World Health Organization (WHO), 2015), including Mexico. With increasing age, it is expected that various cognitive functions begin to decline. However, that decline can be severe enough to compromise the quality of life of those who suffer from it (Aveleyra & Ostrosky, 2007; Forte et al., 2019; Mejía-Arango et al., 2007).

Given this situation, it is important to know interventions that promote healthy cognitive aging, such as heart rate variability (HRV) biofeedback, an intervention based on scientific evidence (Moss, 2004). 

Cognitive functions and aging

What are cognitive functions?

The cognitive functions have been defined as those mental abilities that allow us, human beings, to correctly interpret and manage information coming from the environment. A proper cognitive functioning is essential, since it enables us to perform all our activities of daily living (ADLs) optimally, such as reading, driving, writing, speaking, reasoning, planning, etc. Some of these cognitive functions are attention, memory, language, and executive functions (Aveleyra & Ostrosky, 2007; Forte et al., 2019). 

Cognitive changes associated with aging

During aging various changes occur, such as deterioration of certain brain structures and loss of nervous tissue. This modifies both brain functioning and cognitive performance.

Among the most common changes are difficulties in perceptual skills, memory and learning, alterations in visuospatial and constructional skills, increased difficulty incorporating new information, and a slowing of motor responses. Changes in language and verbal processes may also occur, although in some cases these functions show some resistance to decline and can even improve in advanced age (Ardila, 2012). 

These changes mentioned above are considered normal. However, when they progress enough to affect a person’s quality of life and daily functioning (Forte et al., 2019), they may be related to cognitive impairment that is no longer part of normal aging, such as mild cognitive impairment (MCI) (Aveleyra & Ostrosky, 2007).

What is mild cognitive impairment (MCI)?

Mild cognitive impairment is a condition characterized by the presence of a significant decline in one or more cognitive functions, but that does not substantially interfere with the person’s functional autonomy (American Psychiatric Association, 1994).

According to the National Institute on Aging and the Alzheimer’s Association, the diagnostic criteria include concern by the patient or an informant about changes in cognition relative to prior status, the presence of cognitive impairments, the preservation of functional independence, albeit with greater slowness or errors, and the absence of clinical signs indicating dementia (Albert et al., 2011; McKhann et al., 2011). Although it is not a type of dementia, MCI does represent an important warning sign, since the probability of progression from mild cognitive impairment to dementia is estimated between 10% and 15% (Albert et al., 2011).

Heart rate variability and aging

The changes in cognitive functions that occur during aging do not occur in isolation, but are related to other physiological processes that are also affected with age.

For example, as one ages, the heart experiences a decrease in heartbeat frequency and ventricular relaxation is slower. These cardiovascular alterations are also accompanied by structural and functional changes at the brain level, as well as less efficient regulation of the autonomic nervous system, which plays a key role in the physiological regulation of the organism (Bozkurt et al., 2016). In this context, an association has been observed between the state of the autonomic nervous system and cognitive performance in older adults (Shaffer & Venner, 2013). 

With aging, various factors contribute to cardiovascular system deterioration, thereby increasing the risk of chronic diseases such as arterial hypertension. Among these risk factors are progressive arterial degeneration and the accumulation of fat in the vascular walls, which reduce the internal diameter of blood vessels and hinder adequate blood flow. In particular, hypertension in the older adult population is a highly prevalent condition at this stage of life and is associated with a higher risk of cognitive decline and neurodegenerative diseases (Almeida-Santos et al., 2016).

What is HRV?

Heart rate variability (HRV) is an indicator of autonomic nervous system regulation, responsible for controlling involuntary functions such as breathing, digestion and heart rate. HRV is a phenomenon of the cardiac cycle defined as the variation in time in milliseconds between consecutive heartbeats and is a signal of how well the autonomic nervous system functions. This measure indicates how flexible and adaptable the body is to respond to different situations, and greater variability indicates better regulation (Acharya et al., 2006; Thayer et al., 2012). 

Global autonomic regulation of the heart decreases with aging, which causes a progressive reduction in heart rate variability, thus reflecting a reduced capacity of the organism to adapt and respond to different physiological stimuli (Almeida-Santos et al., 2016).

HRV can be measured by electrocardiogram (ECG) or using a photoplethysmograph (PPG), which detects changes in blood pulse volume. From these heart rate measurements, it is possible to analyze heart rate variability (HRV) using different analyses, such as time-domain or frequency-domain analysis (Acharya et al., 2006). 

Evidence shows that high HRV is associated with greater psychological well-being, better emotional self-regulation, and lower risk of physical and mental illnesses. In contrast, low HRV may indicate a less flexible organism, with reduced capacity to adapt to demanding or stressful situations (Acharya et al., 2006; Moss, 2004).

Relationship between the cerebral cortex, HRV and cognitive functions

Some brain structures participate in the regulation of heart rate and HRV. Specifically, some areas of the brain, such as the medial and orbital prefrontal cortex, help modulate heart rate through the vagus nerve (Williams et al., 2019).

These brain regions in turn communicate with other structures, such as the amygdala and certain brainstem nuclei, which together regulate heart activity (Gianaros et al., 2004). This means that HRV not only reflects the state of the cardiovascular system, but also the degree of control the brain has over the organism.

Due to this brain–heart relationship, consequently, when there is a problem in this regulatory system, the blood flow to these brain areas can be affected, which reduces their capacity to properly control the heart. That is, given that the heart and the brain are closely connected, changes in one of these systems can directly influence the other. 

In this sense, low HRV has been associated with poorer performance in various cognitive functions:

1. For example, it has been found that lower HRV is associated with worse performance in both short- and long-term verbal memory.
2. Likewise, reduced HRV has been linked to lower language performance, and resting HRV levels have been shown to predict attentional performance.
3. An association has also been reported between lower HRV and poorer performance in executive functions, as well as in visuospatial skills.
4. Additionally, individuals with low HRV have shown poorer performance and greater decline in processing speed.

However, these findings should be interpreted with caution, since there is also evidence, albeit to a lesser extent, that does not confirm these associations, which suggests that more research is needed to clarify the nature of this relationship. (Forte et al., 2019; Thayer et al., 2012).

Conclusion

In light of all the above, in the second part of this article we will delve into HRV biofeedback and how it works, providing evidence on its effects on improving cognitive functioning and ethical considerations.

Bibliography

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“This article has been translated. Link to the original article in Spanish:”
La variabilidad de la frecuencia cardíaca (VFC) y su relación con el deterioro cognitivo