Heart Rate Variability (HRV) and Its Relationship with Cognitive Decline

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

Introduction

Life expectancy has increased, so the group of people over 60 years old has grown worldwide (World Health Organization, 2015), including Mexico. With increasing age, it is expected that various cognitive functions will 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 about 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 the mental abilities that allow us, human beings, to correctly interpret and manage information that comes from the environment. Adequate 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 neural tissue. This alters both brain function and cognitive performance.

Among the most common changes are difficulties in perceptual abilities, memory and learning, impairments in visuospatial and constructional skills, greater 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 (Ardilla, 2012). 

These previously mentioned changes 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 decline 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, diagnostic criteria include the patient’s or an informant’s concern about changes in cognition relative to their previous state, the presence of impairments in cognitive functions, the preservation of functional independence, although 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 by age.

For example, as one ages, the heart experiences a decrease in heart rate and ventricular relaxation becomes slower. These cardiovascular alterations are also accompanied by structural and functional modifications at the brain level, as well as less efficient regulation of the autonomic nervous system, which plays a key role in the body’s physiological regulation (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 the deterioration of the cardiovascular system, thereby increasing the risk of chronic diseases such as arterial hypertension. Among these risk factors are progressive degeneration of the arteries and 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, which is 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 organism is to respond to different situations and higher 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 lower capacity of the organism to adapt and respond to different physiological stimuli (Almeida-Santos et al., 2016).

HRV can be measured using an electrocardiogram (ECG) or using a photoplethysmograph (PPG), which detects changes in 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). 

It has been shown that high HRV is associated with greater psychological well-being, better emotional self-regulation, and a lower risk of physical and mental illnesses. In contrast, low HRV may indicate a less flexible organism, with a lower 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 communicate in turn with other structures, such as the amygdala and some 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 body.

Because of this relationship between the brain and the heart, 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 control the heart properly. That is, since the heart and brain are closely connected, changes in one of these systems can directly influence the other. 

In this sense, low HRV has been linked to 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 poorer 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 executive function performance, as well as 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, although 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 view of all the above, in the second part of this article we will delve into HRV biofeedback and how it works, providing evidence about its effects on improving cognitive functioning and ethical considerations.

Bibliografía

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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