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ORIGINAL ARTICLES |
From the University of California, San Diego, Department of Psychiatry, San Diego, California.
Address correspondence and reprint requests to Scott C. Matthews, MD, San Diego VA Health Services, 3350 La Jolla Village Drive, Mail Code 116A, La Jolla, CA 92161. E-mail: scmatthews{at}ucsd.edu
| ABSTRACT |
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Methods: Ninety-one healthy volunteer subjects performed reactivity testing while measures of impedance cardiography and autonomic nervous system function were obtained. Subjects completed the Center for Epidemiological Studies Depression Scale (CES-D) and were categorized into either the high depressive (i.e., CES-D
16) or low depressive (i.e., CES-D <16) symptoms group.
Results: Task performance was associated with increases in systemic vascular resistance (SVR) (p = .001), mean arterial pressure (p = .001), and heart rate (p = .005), and decreases in cardiac output (p = .001), heather index (p = .001), and stroke volume (p = .05). After controlling for screening mean arterial pressure, an interaction effect of stress by mood group on SVR (p = .01) was observed; subjects with high amounts of depressive symptoms manifested significantly greater SVR at baseline and in response to a stressor task than did subjects with low amounts of depressive symptoms.
Conclusions: These results suggest a mechanism that may partially explain the increased CV morbidity associated with depressive symptoms. In future studies, it may be useful to examine if treatment of depressive symptoms alters CV reactivity.
Key Words: depressive symptoms systemic vascular resistance reactivity mirror star tracing task
Abbreviations: ANS = autonomic nervous system; CESD = Center for Epidemiological Studies Depression Scale; CO = cardiac output; CV = cardiovascular; DSM-IV = Diagnostic and Statistical Manual, Fourth edition; HI = Heather index; HR = heart rate; HRV = heart rate variability; HRVhf= high-frequency HRV; MAP = mean arterial pressure; MDD = major depressive disorder; MI = myocardial infarction; PNS = parasympathetic nervous system; POMS = Profile of Mood States; MSTT = mirror star tracing task; SNS = sympathetic nervous system; SV = stroke volume; SVR = systemic vascular resistance.
| INTRODUCTION |
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Altered hemodynamic and autonomic nervous system (ANS) functioning have been associated with depressive symptoms, and such alterations may partially explain depressions relationship to increased CV morbidity. MDD has been associated with ANS dysfunction as reflected by: 1) decreased overall heart rate variability (HRV); 2) decreased high-frequency HRV (HRVhf), which specifically reflects parasympathetic nervous system (PNS) activity; and 3) increased low-frequency HRV, which provides an estimate of sympathetic nervous system (SNS) tone (15,2426). Related studies have linked these physiological changes with poor clinical outcomes. Low overall HRV, which reflects either increased sympathetic activation and/or decreased PNS tone, is a strong and independent predictor of post-MI mortality (27,28).
Subclinical depressive symptoms in the absence of psychiatric illness are common, and the "normal range" of these symptoms in the general population is wide. Prior research supports the notion that subclinical mood symptoms are associated with altered CV reactivity both at rest and in response to stress. In one study that examined resting impedance measures underlying blood pressure in healthy volunteer subjects without psychiatric illness, the fatigueinertia and tensionanxiety subscales of the Profile of Mood States (POMS) (29) were negatively correlated with stroke volume (SV). The study also found that the POMS fatigueinertia subscale was negatively associated with cardiac output (CO), and the POMS fatigueinertia subscale was positively correlated with systemic vascular resistance (SVR) (30). Depressive symptoms have also been associated with altered hemodynamic responses to stress. In another study of 60 healthy women with varying levels of subclinical depressive symptoms, performance of a speech task was associated with increased plasma norepinephrine, CO, heart rate (HR), systolic and diastolic blood pressure, and a shorter preejection period, suggesting that subclinical depressive symptoms are associated with increased SNS activity in women performing a speech task (31).
In the current study, two groups of subjects were examined: 1) a group with a high level of depressive symptoms, i.e., Center for Epidemiological Studies Depression Scale (CES-D) (32) of
16, and 2) a group with a low level of depressive symptoms, i.e., CES-D <16. The mirror star tracing task (MSTT), which has been shown to induce robust changes in CV reactivity (3336), was administered while various measures of ANS and hemodynamic functioning were recorded.
We hypothesized that high levels of depressive symptoms would be associated with increased SNS (both alpha and beta adrenergic) output and decreased PNS tone in response to stress. Support for these hypotheses would add to an existing body of literature suggesting a relationship between subclinical depression and altered CV reactivity, and may speak to a putative mechanism that may partially mediate the relationship between subclinical depressive symptoms and CV morbidity.
| METHODS |
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16) or low depressive (i.e., CES-D <16) symptoms group. Subjects were excluded if they had MDD or another Axis I psychiatric diagnosis, according to the Diagnostic and Statistical Manual, Fourth edition (DSM-IV). To decrease the amount of medical comorbidities, all subjects were between 18 and 50 years old and between 85% to 150% of ideal body weight. Women who were taking oral contraceptives or hormonal replacement therapy, menopausal women, and those who were pregnant were excluded. However, restrictions regarding the timing of the menstrual cycle were not imposed. Hypertensive subjects who were currently receiving antihypertensive medication completed a careful tapering program followed by a 3-week drug washout. Any patient whose blood pressure was >180/110 mm Hg while off treatment left the protocol and returned to active treatment.
Reactivity Testing
Reactivity testing was performed within approximately 2 weeks of the screening visit. Subjects were tested in a sound-attenuated room at 8:30 am while seated in a comfortable reclining chair. On arrival to the laboratory, subjects rested quietly for 30 minutes. After this acclimatization phase, subjects rested quietly for an additional 3 minutes (resting baseline) and then performed the MSTT. The MSTT has been used extensively in psychophysiological experiments to probe CV reactivity and has been shown to induce changes in blood pressure (BP) and SVR (3336). In this task, subjects trace the outline of a star using its mirror image for 3 minutes.
During resting baseline and during performance of the MSTT, electrocardiography (ECG; model 78352C; Hewlett Packard; Andover, MA), impedance cardiography (Minnesota Impedance Cardiograph 304B; Surcom, Minneapolis, MN), and BP (Colin Pilot, Houston, TX) were monitored continuously to obtain dependent measures of ANS and hemodynamic functioning. To record the impedance cardiography measures, impedance cardiographic tape was applied in a standard tetrapolar configuration. A BP cuff and ECG electrodes in a modified lead I or lead II configuration that maximized the R wave were then applied. The ECG, BP, and impedance waveform signals were recorded and relayed to an analog-to-digital converter (DT2801; Data Translation; Marlboro, MA), sampling at 1 kHz per channel and stored in a computer for subsequent review, artifact rejection, and calculation. These data were collected in 3-minute epochs. The review and calculation of HRV were performed using a program developed at the University of Miami, Behavioral Medicine Research Center (37,38). This program calculated the variables of LF power and HF power from spectral analyses. Stroke volume (SV), SVR, and Heather index (HI) were calculated using standard formulas from BP, ECG, and impedance cardiography data (39). Details of the instrumentation and calculation (40) of the physiological variables have been previously described in detail. SVR and HI provide sensitive and reliable measures of alpha and beta SNS activity, respectively (39). Parasympathetic activation is reflected in HRVhf (41).
Analyses
The dependent variables were HR, HRVhf, HI, SV, MAP, CO, and SVR. To examine main effects of stress and interaction effects of stress by depression on these dependent variables, a two (task, i.e., baseline versus stress) by two (mood group, i.e., high/low depression) repeated-measures analysis of variance (SPSS for Windows 9.0; SPSS, Chicago, IL (42)) was performed. Then, to control for the potential confounding variables of gender and ethnicity, data were analyzed using a two (task, i.e., baseline versus stress) by two (gender, i.e., male versus female) by two (ethnicity, i.e., Euro-American versus black) by two (mood group, i.e., high/low depression) repeated-measures analysis of variance.
A post-hoc analysis of simple effects was then performed. Independent-samples t tests were performed to compare SVR during the baseline condition between the high and low depressive symptoms groups, and to compare SVR during performance of the MSTT between the high and low depressive symptoms groups. Paired t tests were performed to compare SVR during baseline with SVR during performance of the MSTT within the high and low depressive symptoms groups.
| RESULTS |
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The repeated-measures analysis revealed a main effect of stress on several variables of interest. Task performance was associated with significant increases in SVR (p = .001), MAP (p = .001), and HR (p = .005), and significant decreases in SV (p = .05), CO (p = .001), and HI (p = .001). More interestingly, an interaction effect of stress by mood was observed on SVR (F[1,88] = 7.43, p < .01). Subjects with high depressive symptoms responded to stress with a particularly pronounced increase in SVR (Fig. 1). This interaction remained significant after controlling for ethnicity, gender, and screening MAP (F[1,82[rsqb = 7.87, p < .01). The analysis of simple effects revealed significant increases in SVR from baseline to task within the high depressive symptoms (p < .0001) and within the low depressive symptoms (p < .0001) groups. Independent-samples t tests revealed significant differences in SVR between the high and low depressive symptoms groups both during baseline (p < .05) and during performance of the MSTT (p < .005). There were no significant interactions of ethnicity by stress or gender by stress on SVR. No significant interactions of stress by mood group on HR, HRVhf, HI, MAP, CO, or SV were observed (Table 2).
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| DISCUSSION |
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These results are consistent with a study by Yu et al., which reported that SVR at rest was positively correlated with scores on the POMS fatigueinertia subscale (30). Our study provides complementary evidence that extensive depressive symptoms, as revealed by the CES-D, are associated with increased SVR at rest. Reservations have been raised about the validity of using baseline measures of CO and therefore SVR (49). The current study extends our previously noted observations of baseline differences to differences observed when subjects are stressed, an area in which impedance cardiography measures are on firmer ground. In this context, we found that depressive symptoms are associated with greater SVR during stress.
Interestingly, we observed no significant interactions of stress by mood group on MAP, CO, HR, HRVhf, HI, or SV. Additionally, when the high and low depressive symptom groups were analyzed together, MSTT performance was associated with decreased HI, a sensitive measure of beta-adrenergic tone. Additional research using multiple tasks in a large sample of patients with various degrees of depressive symptoms is needed to fully explain this finding. Perhaps MDD is associated with central ANS changes that result in dysfunction across a broad range of CV measures, whereas the presence of subsyndromal symptoms affects peripheral ANS changes reflected in increased SVR. Also of note is the fact that the MSTT has been previously shown to affect primarily SVR through increased alpha-adrenergic tone (36,50), and additional research using multiple different tasks is needed to understand the role that specific tasks may play in selective activation of the alpha adrenergic nervous system.
The current study suggests a mechanism whereby subclinical levels of depression may have deleterious CV effects. Prior research has described a dose-response relationship between depressive symptom severity and CV events. In one cohort study of generally healthy outpatients, an increase in depressive symptoms over time was significantly associated with MI, stroke, and death (51). In a related study, increased depressive symptoms were associated with an increased risk of subsequent cardiac mortality. In that study, cardiac patients with a CES-D score of
16 relative to cardiac patients with a CES-D score of <16 had a relative risk of subsequent cardiac mortality of 1.6, and noncardiac patients with a CES-D score of
16 relative to noncardiac patients with a CES-D score of <16 had a relative risk of subsequent cardiac mortality of 1.5 (52).
Although the underlying mechanism that explains the relationship between depressive symptoms and CV morbidity remains incompletely understood, some of the same physiological alterations that have been proposed to contribute to CV morbidity in MDD have also been described in patients with subclinical levels of depression. For example, altered platelet function has been demonstrated in patients with subclinical depressive symptoms (53). Although the current study suggests that depressive symptoms are associated with alterations in CV reactivity, further research is needed to replicate this finding and to understand whether altered CV reactivity is associated with adverse CV outcomes in patients with subclinical depressive symptoms.
There are a number of next steps suggested by this study. First, a research diagnostic interview was not administered. Although subjects were excluded if they had a MDD or other DSM-IV Axis I psychiatric illness, a standardized diagnostic measure was not used, and we cannot definitively rule out the presence of MDD. Second, only 24 subjects had high levels of depression. In future research, it would be useful to study a larger group of subjects that includes both a subgroup of subjects with MDD as well as a subgroup of subjects with a broad range of subsyndromal depressive symptoms. Additionally, because there is ample research showing the values obtained from a single reactivity paradigm administered at a single time have limited reproducibility, future studies might also profitably compare the hemodynamic and autonomic effects of depressive symptoms in terms of responses elicited by multiple stressors on several occasions (54). What is needed to interpret and understand the biologic significance of the current findings is a study in three groups of subjects (i.e., MDD, subclinical depressive symptoms, and healthy volunteers) that implements multiple tasks (i.e., one task such as the MSTT that probes alpha adrenergic functioning, as well as a second task that perturbs the beta adrenergic system) on several occasions. Although the current data do not support general statements about the effects of depressive symptoms on cardiovascular reactivity, and the specific biologic significance of the observed depression by stress interaction on SVR remains uncertain, our study does provide a useful groundwork for follow-up studies that may examine how the presence, and potentially treatment, of depressive symptoms affects CV reactivity.
| NOTES |
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This work was supported by grants HL36005, HL44915, RR00827, and 5T32MH18399 from the National Institutes of Health.
DOI:10.1097/01.psy.0000160467.78373.d8
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