The relationship between fatigue and cardiac functioning

Background: Although characteristics such as heart rate (HR) and blood pressure (BP) are commonly reported in studies of the relationship between fatigue and cardiac functioning, few reports examine how cardiac function parameters such as cardiac output (CO) and stroke volume (SV) relate to fatigue. This study examined the relationship between self-reported fatigue and hemodynamic functioning at rest and in response to a public speaking stressor in healthy individuals. Methods: A total of 142 individuals participated in this study. Subjects were placed in low-, moderate-, or high-fatigue groups based on their Profile of Moods State fatigue scale. Heart rate, SV, and CO were determined using impedance cardiography at rest and during a speaking stressor. Stroke volume and CO values were converted to stroke index (SI) and cardiac index (CI) by adjusting for body surface area. Data were analyzed with hierarchical regression analysis and a 3 (group) X 3 (stress period) mixed model analysis of variance. Results: At rest, fatigue was not associated with BP or HR but was significantly associated with decreased CI (P <.001; 95% confidence interval, -0.046 to -0.014) and stroke index (SI) (P=.002; 95% confidence interval -0.664 to -0.151), even after controlling for demographic variables and depressive symptoms. Heart rate and BP increased, as expected, from baseline to preparation to speaking stressor (F-1,F-124 = 118.6 and F-1,F-122=46.450, respectively) (P <.001 for both). More interestingly, there were effects on SI and Cl of fatigue (P<.03 for both) and stress (P<.03 for both); high-fatigue individuals had lower SI and CI levels than moderate- and low-fatigue individuals both at rest and in response to the stressor. Conclusion: This study demonstrates that fatigue complaints may have hemodynamic correlates even in ostensibly healthy individuals.