It is common clinical knowledge that stroke and certain dementing illnesses (e.g., Alzheimer's disease, vascular or multi-infarct dementia), which are the most frequent causes of acquired cognitive and communicative disorders, are regularly predated by cardiovascular disease (CVD). It may be less widely known, however, that CVD can negatively affect the integrity of cognition and communication long before an individual is diagnosed with a major neurological disorder like stroke or dementia.
Given that currently more than 71 million Americans present with one or more forms of CVD (American Heart Association, 2006), it is important for speech, language, and hearing clinicians to be aware of its cognitive and communicative consequences so that at-risk populations receive appropriate referrals for assessment and treatment services.
Forms of CVD and Risk Factors
CVD comprises a variety of medical conditions that compromise the well-being of the cardiac and/or circulatory systems. According to the American Heart Association (AHA, 2006), CVD is the most frequent cause of death in the U.S., killing more than 2,500 individuals each day. If the most common types of CVD were eradicated, it is estimated that life expectancy would increase by at least seven years.
Of the various forms of CVD listed in Table 1 on page 22, hypertension or high blood pressure is the most prevalent, affecting approximately 60 million Americans. Given that one out of every three adults has high blood pressure, it is ominous to learn that in more than 70% of these adults, high blood pressure is not being adequately controlled and that 30% of these adults do not even know they have high blood pressure. Hypertension is also problematic because it is a potent precursor of other forms of CVD such as stroke and congestive heart failure.
A number of risk factors are associated with the chances of developing CVD: smoking, abnormal cholesterol or other blood lipid levels, inactivity, diabetes, obesity, metabolic syndrome, poor nutrition, alcohol abuse, and depression, among others.
Although the prevalence of most CVD risk factors has been decreasing over the past few decades, there is significant concern over escalating rates of diabetes (AHA, 2006). For example, the prevalence of diabetes has increased 60% since 1990. Approximately 171 million Americans are now living with the disease (Mokdad et al., 2003). The vast majority of these cases (i.e., 90%-95%) are age-onset, Type II diabetes mellitus (also sometimes referred to as non-insulin-dependent diabetes). However, children and adolescents are also affected. It is now estimated that one third to one half of all new pediatric diabetes cases are Type II.
Researchers foresee a "cardiovascular epidemic for years to come" (American Heart Association, 2006, p. 6) as the population ages and becomes more vulnerable to CVD. Thus, it is imperative that clinicians be aware of the neural changes and cognitive and communicative symptoms that can accompany CVD even prior to the occurrence of stroke or other major neurological insult or diagnosis.
Neural Changes Associated With CVD
Findings from a growing literature indicate an intimate relationship between the integrity of the central nervous system and cardiovascular well-being (Lim et al., 2004; Verhaegen et al., 2003). It is to be expected, then, that CVD may lead to a number of structural changes within the brain at both the cortical and subcortical levels. For example, atrophy or loss of neural tissue has been detected in terms of an overall reduction in whole-brain volume and enlarged ventricles. Furthermore, certain brain regions, such as the basal ganglia and hippocampus (subcortical structures known to contribute to cognitive functioning) appear particularly vulnerable to CVD-related atrophy.
Pathology markers similar to those observed in Alzheimer's disease (e.g., senile plaque formation) and white matter changes have also frequently been reported. CVD and its risk factors may interfere with the production of certain neurotransmitters. There is some evidence that diabetes may impede production of acetylcholine, a neurotransmitter that has been implicated in a number of cognitive functions. Given the presence and location of these neural changes, it is not surprising that CVD can compromise cognitive and communicative functioning.
Cognitive and Communicative Changes
Literature increasingly documents a variety of cognitive and communicative consequences of CVD. Furthermore, even prior to a CVD diagnosis, having more than one risk factor can jeopardize an individual's cognitive and communicative abilities (Hassing et al., 2004; Pavlik et al., 2005).
Compared to their healthy age- and education-matched peers, individuals with CVD or with multiple risk factors can display problems, accelerated declines, or both in one or more of the following related to cognitive functioning: (a) attention, including sustained attention, processing speed, and attention switching, (b) memory, including immediate and delayed verbal recall, visual memory, and learning efficiency, and (c) executive functioning, including inhibition, planning, reasoning, and cognitive flexibility. Recognition memory for either verbal or nonverbal information, however, appears to be relatively resistant to the detrimental effects of CVD as studies generally report nominal changes within this component of memory.
Although few investigators have explored whether CVD might negatively affect communication abilities, initial research suggests that hearing and language might be vulnerable. For example, reduced pure tone thresholds and signs of cochlear impairment have been reported (e.g., Torre et al., 2005); additionally, these audiological changes appear more commonly or prominently in women than men.
In terms of language abilities, most research has focused on evaluating the integrity of basic receptive (e.g., spoken word-to-picture matching) or expressive vocabulary skills (e.g., confrontation naming). Findings from these studies suggest that vocabulary changes are unlikely, but that in at least a few patients, conspicuous word retrieval difficulties can develop (e.g., Lim et al., 2004).
Initial data also suggest that higher level lexical-semantic processing abilities might be more sensitive to CVD-related changes. For example, Hassing et al. (2004) found that compared to their age-matched peers without diabetes, elderly adults with Type II diabetes demonstrated faster rates of decline on a test that required identification of synonyms.
Few CVD investigations have included language tests that go beyond single-word processing abilities. One study, however, identified progressive auditory comprehension difficulties for sentence-level material in adults with congestive heart failure (Murray et al., in preparation). Whereas approximately 40% of the sample performed below the 16th percentile on the Revised Token Test at the beginning of the study, close to 50% of the sample was scoring below the 16th percentile 12 months later.
These preliminary findings highlight the need to characterize further the relationship between CVD and cognitive and communicative functioning. Future research should (a) examine those cognitive and communicative abilities that have thus far received little or no empirical examination (e.g., divided attention, visual memory, expressive and receptive grammar, figurative language processing); and (b) incorporate a broader spectrum of assessment tools, given that up to this point a relatively limited set of tests has been utilized (e.g., reliance on only Trails A and B to assess attention; Boston Naming Test to assess spoken word retrieval).
Undeniably, individuals who present with one or more forms of CVD, and even those who present with only CVD risk factors are at risk for a number of cognitive and communicative difficulties. Accordingly, audiologists and SLPs can make important contributions to CVD management.
Complete hearing and cognitive-communicative evaluations are warranted: These assessments will yield results that can help quantify patients' and their caregivers' subjective complaints as well as monitor the outcomes of CVD treatment programs. Assessment should include informal observations and interviews as not all cognitive-communicative symptoms are easily characterized by formal, structured tests; and some research suggests that data from subjective measures are particularly potent predictors of functional outcome (Kiessling & Henriksson, 2005).
Because more basic aspects of cognition and communication appear relatively resistant to CVD-related changes, assessment should primarily focus on evaluating complex or high-level cognitive (e.g., attention switching, working memory) and linguistic abilities (e.g., comprehension of lengthy material in stressful listening or reading conditions, and understanding of implied information). This means that assessment must extend beyond administering brief screening tools such as the widely used Mini Mental Status Examination, and incorporate more comprehensive measures that allow in-depth evaluation of specific cognitive or linguistic functions (e.g., Test of Everyday Attention, Behavioral Assessment of Dysexecutive Syndrome, Test of Language Competence-Extended Version).
CVD treatments are typically multi-component programs consisting of various combinations of education, lifestyle changes (e.g., exercise, diet, smoking cessation), pharmacotherapy (e.g., antihypertensives, anticoagulants), and surgery. Given that research supports a positive relationship between cognitive-communicative status and adherence to these multi-component treatment regimens (e.g., Musselman et al., 2003), audiologists and SLPs can clearly play important roles in treating individuals with CVD.
Table 2 (at right) suggests several ways in which clinicians might directly or indirectly contribute to multi-component CVD treatments. Because nominal research pertains to the involvement of audiology, speech-language pathology, or both in CVD treatment programs, formal investigation is needed to determine which, if any, of the recommendations in Table 2 can significantly improve CVD outcomes.
CVD encompasses a variety of disorders that can compromise the integrity of hearing, language, and other cognitive abilities in individuals of all ages. Traditionally, clinicians have been involved only when CVD results in a neurological event such as stroke or a progressive disorder such as dementia. The above review indicates that a larger population of individuals with CVD or its risk factors might benefit from the involvement of audiologists and SLPs.
The need remains for further research to document the extent to which CVD and its risk factors can impair cognitive-communicative abilities, and to determine how audiologists and SLPs can effectively and efficiently contribute to current approaches to assessing and treating CVD.