Critical Perspectives on Racial and Ethnic Differences in Health in Late Life (2004) / Chapter Skim
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15 A Neurovisceral Integration Model of Health Disparities in Aging
15 A Neurovisceral Integration Model of Health Disparities in Aging
Pages 567-603
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From page 567... ...
For example, hypertension rates in African Americans are among the highest in the world, with the age-adjusted rate being more than 50 percent higher than for white Americans. African Americans also develop hypertension earlier and have much higher average blood pressures and higher rates of stage 3 hypertension than whites.
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From page 568... ...
We begin in a broad context within which to view the observed health disparities in the elderly by presenting evidence for the role of autonomic imbalance in disease and negative affective states and dispositions. The notion of appropriate energy regulation as a factor in health and disease is emphasized.
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From page 569... ...
AUTONOMIC IMBALANCE IN DISEASE AND NEGATIVE EMOTIONS There is growing evidence for the role of the autonomic nervous system (ANS) in a wide range of diseases.
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From page 570... ...
The prolonged state of alarm associated with negative emotions likewise places an excessive energy demand on the system. On the way to death, however, premature aging and disease characterize a system dominated by negative affect and autonomic imbalance.
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From page 571... ...
In sum, autonomic imbalance and decreased parasympathetic tone in particular may be the final common pathway linking negative affective states and dispositions, including the indirect effects via poor lifestyle, to numerous diseases and conditions associated with aging as well as increased morbidity and mortality. THE MODEL IN A NUTSHELL A comprehensive model of emotions and health must account for the complex mix of cognitive, affective, behavioral, and physiological
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From page 572... ...
. The neurovisceral integration model (NIM)
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From page 573... ...
For example, a HR change of 72 to 90 bpm can be attained by various permutations of sympathetic and vagal input, including increased sympathetic or decreased vagal activity or some combination of the two, or by other processes such as circulating hormones. Moreover, within the CAN, direct and indirect paths can regulate output to preganglionic sympathetic and parasympathetic neurons.
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From page 574... ...
THAYER AND BRUCE H FRIEDMAN CORTICAL COMPONENTS Medial prefrontal cortex Anterior cngulate Cortex Insula cortex Paraventricular nucleus Central nucleus of the amygdala Lateral hypothalamic area MID-BRAIN Periaqueductal gray matter PONS Parabrachial region MEDULLARY LEVEL Nucleus of the solitarius Nucleus ambiguus Venttrolateral medulla PRIMARY OUTPUTS Stellate ganglion Vagus nerve FIGURE 15-1 Central nervous system structures involved in neurovisceral integration.
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From page 575... ...
Autonomic Regulation Autonomically mediated HRV is useful as an index of neurovisceral integration and organismic self-regulation. The interaction of sympathetic and parasympathetic outputs of the CAN at the sino-atrial node produces the complex beat-to-beat variability that marks a healthy, adaptive organism.
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From page 576... ...
In this view, the prefrontal cortex modulates subcortical motivational circuits to serve goal-directed behavior. When the prefrontal cortex is taken "offline" for whatever reason, a relative sympathetic dominance associated with disinhibited defensive circuits is released.
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From page 577... ...
This neural network permits the prefrontal cortex to inhibit subcortical structures associated with defensive behaviors, and thus promote flexible responsiveness to environmental changes. For example, when faced with threat, tonic inhibitory subcortical control can be withdrawn quickly, leading to sympathoexcitatory survival ("fight or flight")
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From page 578... ...
In addition, subjects with the highest HRV showed the most differentiated emotion-modulated startle effects, whereas those with the lowest HRV showed significant augmentation of startle to neutral foregrounds and marginally potentiated startle to pleasant foregrounds. Thus, individuals with low HRV reacted to neutral, harmless stimuli as if they were aversive and threatening, and also had a tendency to react similarly to positive stimuli.
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From page 579... ...
. Deficits in these cognitive functions tend to accompany aging, and are also present in negative affective states and dispositions such as depression and anxiety.
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From page 580... ...
All subjects exhibited longer reaction times to the color-incongruent words and the dental-related threat words, and thus displayed a difficulty in inhibiting prepotent responses. However, greater HRV was associated with faster reaction times to these words, consistent with the link among vagally mediated HRV, inhibitory ability, and frontal lobe function.
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From page 581... ...
In addition, these data show that low HRV marks increased risk to stress exposure. Significantly, these results provide a connection among stress-related cognitive deficits, high negative affect, and negative health consequences via the common mechanism of autonomic imbalance and low parasympathetic activity.
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From page 582... ...
One key additional factor makes this conceptualization in terms of autonomic imbalance particularly relevant to the health disparities in aging. Whereas the traditional risk factors such as smoking, total cholesterol, obesity, and even hypertension, many of which are used to index allostatic load (Seeman, Singer, Rowe, Horwitz, and McEwen, 1997)
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From page 583... ...
Interruption of this ongoing state is associated with inhibition and negative feedback. In the context of our model of neurovisceral integration, vagal control of cardiovascular function (as well as activity of the prefrontal cortex)
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From page 584... ...
The inability to inhibit attention to harmless stimuli leads to a positive feedback loop that spirals out of control. Thus, worry becomes the preferred response to an ever-widening range of situations, maintaining anxiety in the face of disconfirming data.
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From page 585... ...
, which suggests that the association was at least partly due to "pure" worry tendencies and not entirely to the disposition to express negative affect. In a related study from the same lab in older, part-time students, further evidence accrued for a causal role for worry.
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From page 586... ...
. Another way in which perseverative thinking may be causally related to autonomic imbalance and disease is by decreased vagally mediated HRV.
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From page 587... ...
This network of reciprocally interconnected structures allows the prefrontal cortex to inhibit subcortical activity associated with defensive behavior, and thus foster flexible control of behavior in response to changing environmental demands. As noted earlier, disruption of this network might lead to disinhibition of defensive perseverative behaviors, including hypervigilance.
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From page 588... ...
Central Concomitants of Perseverative Behavior Perseverative behavior is associated with depression, anxiety, and hostility among other negative affective states and dispositions. The current discussion will be restricted to anxiety and hostility, based on a recent review of the physiological concomitants of rumination and depression (Siegle and Thayer, 2003)
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From page 589... ...
The amygdala is often held to be the key limbic structure in emotional behavior. For example, electrical stimulation of the amygdala has been associated with a range of defensive behaviors, including increased cortisol, heart rate, and blood pressure (see Davis and Whalen, 2001, for review)
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From page 590... ...
Finally, it is clear from these findings and theoretical considerations that hypervigilance and perseveration have physiological consequences, that is, signs of stress and limbic-induced autonomic imbalance such as low HRV, elevated HR and cortisol, and particularly elevated blood pressure and peripheral resistance (the so-called "vigilance reaction"; see Winters et al., 2000)
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From page 591... ...
. Physiological concomitants include autonomic imbalance as indexed by decreased HRV, decreased prefrontal cortex activity, increased amygdala activity, excess and prolonged cortisol responsivity, altered immune function, increased blood pressure and peripheral resistance responses in anticipatory coping, increased blood pressure and peripheral resistance during recovery from stress, sustained and prolonged pupil dilation, and poor tolerance to and delayed recovery from stress in general.
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From page 592... ...
. In the United States, for example, perceived interpersonal discrimination has been associated with a number of factors associated with autonomic imbalance, such as depression and psychological stress, high blood pressure, low birthweight, poor selfrated health, smoking, and physical inactivity (Karlsen and Nazroo, 2002)
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From page 593... ...
The fact that autonomic imbalance continues to predict morbidity and mortality into old age when other risk factors have lost their predictive power adds further to the utility of the neurovisceral integration model in the understanding of health disparities in the elderly. Preliminary Data in Support of the Model We recently completed a pilot study that sought to examine in an elderly African-American sample some of the aspects of the model we have outlined.
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From page 594... ...
These results underscore the multiple levels of system function that may contribute to health disparities in cardiovascular disease, especially hypertension. A series of carefully selected genetic polymorphisms implicated in cardiovascular disease will be studied in future work to assess genetic contributions to autonomic balance.
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From page 595... ...
For example, depression, which has been suggested as a primary factor in the greater rates of hypertension in African Americans, was associated with both poor affective regulation and increased peripheral resistance. As detailed earlier, increased peripheral resistance is associated with autonomic imbalance via sustained activity in the amygdala and with hypervigilance and perseverative thinking.
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From page 596... ...
The neurovisceral integration model offers a framework to integrate such work across levels of analysis. It is key that the central nervous system be included, which entails neuroimaging and neuropsychological research to tap brain processes that support and accompany the many complex factors involved in health and disease in aging.
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From page 597... ...
. African Americans and high blood pressure: The role of stereotype threat.
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From page 598... ...
. Autonomic balance revisited: Panic anxiety and heart rate variability.
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From page 599... ...
. Heart rate variability is inversely related to cortisol reactivity during cognitive stress.
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From page 600... ...
. Activity in medial prefrontal cortex correlates with vagal component of heart rate variability during emotion.
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From page 601... ...
. Inhibitory control and affective processing in the prefrontal cortex: Neuropsychological studies in the common marmoset.
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From page 602... ...
. Heart rate variability: A measure of cardiac autonomic tone.
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From page 603... ...
. Effect of angiotensin-converting enzyme insertion/deletion polymorphophism DD genotype on high-frequency heart rate variability in African Americans.
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