Cardiovascular reactivity of younger and older adults to positive-, negative-, and mixed-emotion cognitive challenge

Abstract

Although aging is associated with progressive increases in blood pressure level, previous research has been inconsistent as to whether older adults show greater or lesser cardiovascular reactivity (CVR) to emotion than do younger adults. There is reason to believe that these inconsistencies could be clarified by examining age-related differences in hemodynamic profile revealed by measuring the pattern of cardiac output and total peripheral resistance associated with changes in blood pressure reactivity. Accordingly, the present study examined the performance, CVR, and hemodynamic profile of younger and older adults during encoding and recognition of word pairs involving four valence types: positive, negative, mixed (positive/negative), and neutral word pairs. Results revealed higher baseline blood pressure, increased CVR characterized by a vascular hemodynamic profile, and more rapid recovery (especially during encoding) for older than for younger participants. Results are discussed in light of research and theory on the relationship between aging and cardiovascular health.

Introduction

Aging is associated with progressive increases in blood pressure (Starr and Bulpitt, 1996) and increased cardiovascular disease risk (Tunstall-Pedoe, 1991). In addition, research suggests that, compared with younger adults, older adults experience increased blood pressure reactivity to psychological challenge (Faucheux et al., 1983, Garwood et al., 1982, Jennings et al., 1990). However, it appears that older adults do not necessarily show greater cardiovascular reactivity than younger adults in all situations, with some research suggesting that older adults are less reactive to emotional stimuli (Labouvie-Vief et al., 2003, Levenson et al., 1991, Tsai et al., 2000). Because prolonged or exaggerated reactivity to psychological stress contributes significantly to the development of cardiovascular disease (Carroll et al., 2001, Light et al., 1992), further research is needed to better understand the circumstances under which older adults are prone to experience greater reactivity than younger adults.

Some researchers argue that older adults focus more on emotion regulation goals than younger adults, and that this is evidenced by an information-processing bias in older adults, especially in relation to memory for content that is positively valenced rather than negatively valenced (Fernandes et al., 2008, Kennedy et al., 2004, Mather and Carstensen, 2003, Mather and Carstensen, 2005, Spaniol et al., 2008). However, findings regarding an age-related positivity bias have been inconsistent (Gruhn et al., 2005).

Although the positivity bias in older adults could serve to buffer physiological reactions to negatively valenced information, some research suggests that regulating negative emotion may itself be cognitively and physiologically demanding. For example, in relation to the cognitive demands of maintaining a positivity bias, older adults who do well on tests measuring cognitive control show greater positivity effects than those doing poorly (Mather and Knight, 2005, Petrican et al., 2008). However, when distracted, and thus less able to engage cognitive resources in the service of emotion regulation goals, older adults no longer show a positivity effect in attention or memory, but instead show a negativity bias (Knight et al., 2007, Mather and Knight, 2005). Also, even when younger and older adults perform similarly on behavioral measures of emotion processing (i.e., when doing valence ratings for emotional pictures) while processing negatively valenced stimuli, recent event-related fMRI research findings suggest that older adults show greater functional connectivity than younger adults between the right amygdala and ventral anterior cingulate cortex (Jacques et al., 2010). This greater functional connectivity in older adults could reflect increased emotional regulation efforts in response to negative emotion.

Questions arise as to the differential effects of emotion processing on younger and older adults’ cardiovascular reactivity when considering two distinct strands of cardiovascular research conducted to date: one assessing reactivity in response to active and challenging cognitive tasks (Jennings et al., 1990), which has demonstrated higher cardiovascular reactivity in older adults relative to younger adults; the other assessing cardiovascular reactivity to less cognitively (though more emotionally) challenging situations such as viewing emotional film clips (Tsai et al., 2000). In the absence of specific task demands (e.g., instructions to learn the information presented), and in the absence of an effort to evaluate how much information is actually processed (e.g., in the context of a memory test), there is no way of knowing what study participants are actually doing when viewing a film. Similarly, it is difficult to assess the level of cognitive challenge in other studies of emotion processing and cardiovascular reactivity in younger and older adults, including studies that ask participants to recall autobiographical memories (Labouvie-Vief et al., 2003, Levenson et al., 1991). In the current study, this problem is addressed by placing a consistent cognitive burden on both younger and older adults (i.e., “remember this list of word pairs”), while varying the emotional content of the information presented for learning (i.e., word pairs of neutral, negative, positive, and mixed emotional content).

The large body of research concerned with cardiovascular reactions to stress reflects strong interest in blood pressure reactivity, which is justified in light of the fact that blood pressure level is the single most important predictor of cardiovascular disease (MacMahon, 2000, Prospective Studies Collaboration, 2002). However, although previous studies of emotion processing in older adults included a variety of measurements of cardiovascular function (Labouvie-Vief et al., 2003, Levenson et al., 1991, Tsai et al., 2000), blood pressure responses have not previously been examined in that context. Accordingly, in the present study, we examined systolic (SBP) and diastolic blood pressure (DBP) in addition to heart rate (HR). Furthermore, we examined the key underlying physiological parameters of cardiac output (CO) and total peripheral resistance (TPR), which are known to influence blood pressure level and reactivity. CO is the volume of blood pumped by the left ventricle into the aorta each minute, and the simultaneous measurement of blood pressure and CO makes it possible to derive TPR from the relation, TPR = mean arterial pressure (MAP)/CO (Guyton and Hall, 1997).

Gregg et al. (2002) have proposed a model derived from physiological theory, which explains variations in blood pressure in terms of hemodynamic profile characterized by the dynamic compensatory relationship between CO and TPR. The model takes account of the homeostatic regulation of blood pressure whereby an increase in either CO or TPR tends to be “compensated” by an accompanying decrease in the other variable (Gregg et al., 2002, Guyton and Hall, 1997). This means that blood pressure responses of similar magnitude may be accompanied by markedly different patterns of CO and TPR reactivity, and that marked CO and TPR reactivity can occur with no change in blood pressure (i.e., CO increases and is fully compensated by decreases in TPR and vice versa; Gregg et al., 2002). Independent empirical studies have shown that hemodynamic profile is a more reliable predictor of everyday cardiovascular responses than blood pressure reactivity (Gregg et al., 2005, Ottaviani et al., 2006, Ottaviani et al., 2007).

The terms myocardial and vascular reactivity have been used to describe responses characterized, respectively, by uncompensated increases in CO (predominance of beta-adrenergic responding) and TPR (predominance of alpha-adrenergic responding) (Gregg et al., 1999). Marked and persistent myocardial responding is believed to increase the risk of cardiovascular disease due to tissue over-perfusion and endothelial damage from shear stress, whereas marked and persistent vascular responding is believed to contribute to impaired vascular contractility and atherosclerosis. Compared to a myocardial profile, a vascular profile is believed to contribute over time to greater increased cardiovascular disease risk (Julius, 1988, Palatini and Julius, 2009). To our knowledge, the present study is the first to examine myocardial and vascular response profiles in the context of emotion processing in younger and older adults.

Taking account of previous research findings, we hypothesized that older adults would have higher baseline blood pressure than younger adults. Second, we hypothesized that, after controlling for baseline blood pressure, older adults would show greater blood pressure reactivity to cognitive challenge than younger adults. Third, we hypothesized that, relative to younger adults, the act of regulating any negative emotion experienced while learning negative- and mixed-emotion word pairs would increase the cognitive and physiological burden of the learning task for older adults (i.e., negative- and mixed-emotion regulation was hypothesized to be relatively demanding). This in turn, would result in increased blood pressure reactivity to negative- and mixed-emotion word-pair learning as compared to positive-emotion and neutral word pairs in the older adult sample relative to younger adults. The alternative hypothesis in this context, based on previous findings that older adults show lower reactivity to emotions during less cognitively challenging tasks, was that older adults would learn negative- and mixed-emotion word pairs with a similar blood pressure response to that observed during the learning of both positive and neutral information. Finally, based on previous research demonstrating increased vascular responding while coping with noxious stimuli (Gregg et al., 2002), we examined whether any lower reactivity observed in older adults to negative-emotion challenges was associated with important changes in hemodynamic profile. More specifically, we hypothesized that older adults would demonstrate increased vascular responding to negative emotion independent of changes in blood pressure.