Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Nursing

Abstract

Background: The experience of a cardiac event is associated with psychological stress, which is often accompanied by depressive mood, fatigue and sleep disturbance (i.e., psycho-behavioral symptoms). To assist in recovery, cardiac patients can participate in a structured rehabilitation program, which provides monitored exercise and health education. There is limited knowledge, however, as to the extent to which cardiac rehabilitation reduces psycho-behavioral symptoms; nor is there knowledge of the association of these symptoms with stress-related biological mediators. Cortisol and inflammatory mediators (e.g., interleukin 6; IL-6) contribute to cardiovascular disease, and are also associated with greater stress perception, depressive mood, fatigue, and sleep disturbance. Thus, the overall purpose of this study was to evaluate patients over the course of a 12-week cardiac rehabilitation program to examine changes in psycho-behavioral symptoms, cortisol, and IL-6 within the context of cardiac health and quality of life. Methods: Using a prospective longitudinal design, cardiac rehabilitation patients were evaluated prior to program start (T1 -baseline), mid-program (T2 - 6 weeks), and end of program (T3 -12 weeks). Fifty-eight participants were consented, with 40 completing all time points. At each time point, participants completed study questionnaires, and provided a blood sample and saliva (5 samples collected over two days for cortisol diurnal rhythm determination). Levels of IL6 and cortisol were measured using enzyme linked immune-absorbent assays. Two indices of cortisol secretion were calculated: cortisol area under the curve (CAUC) and cortisol awakening response (CAR). Response to exercise (i.e., metabolic equivalent MET levels) and health data, including HDL and LDL levels, were collected from patient records. Data were analyzed using descriptive statistics (Pearson r correlations, student's t-test), general linear models, and multilevel linear modeling. Results: Although perceived stress decreased significantly over the course of cardiac rehabilitation, 35% of participants continued to report high levels of stress at program end (T3). In contrast, depressive mood did not change significantly over rehabilitation, with 16% reporting levels of depressed mood over the cut score at T3. Fatigue decreased significantly over the course of rehabilitation. Participants with greater fatigue had worse cardiac health (i.e., lower MET level at T3 and a significant decrease in HDL). Although sleep quality improved significantly over time, 42% of participants scored above the cut score for sleep disturbance at T3. Both general Quality of Life (QoL) and the Health Functioning subscale (HFSUBa) of QoL improved over the course of cardiac rehabilitation. Furthermore, QoL and HFSUBa were both negatively correlated with depressive mood, disturbed sleep, fatigue, and perceived stress and positively correlated with social support at all three time points. Participants who exhibited a reduced CAR had greater sleep disturbance, higher BMI, and higher circulating Il-6 levels. In contrast, a greater CAR was associated with a higher HDL. Neither CAUC nor CAR predicted cardiac health over rehabilitation or QoL over cardiac rehabilitation. Although Il-6 did not change over rehabilitation, higher IL-6 was associated with lower MET levels, lower HFSUBa, and greater levels of LDL. IL-6 did not predict cardiac health indices nor quality of life over the course of cardiac rehabilitation. Conclusions: Although psycho-behavioral symptoms and QoL improved over the course of cardiac rehabilitation, a substantial proportion of participants continued to report high levels of perceived stress, depressive mood, fatigue, and sleep disturbance at completion of the 12-week program. Moreover, higher fatigue and higher IL-6 were each associated with poorer cardiac health. These findings identify a need for cardiac rehabilitation programs to better address psycho-behavioral symptoms, which reduce QoL and which may hinder participation in and benefit from rehabilitation. Suggested clinical implications are to monitor psycho-behavioral symptoms to identify those at risk, and to provide behavioral interventions. Interventions could include stress reduction techniques, such as deep breathing, measures to promote sleep, and mindfulness meditation which may engage the parasympathetic nervous system to reduce stress, fostering better QoL and improved recovery from cardiovascular disease.

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Creative Commons License
This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 3.0 License.

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