This dissertation was completed in 2003 after 6 years of research. This bookdown reproduction is being created for the purpose of gradually updating the contents based on 20 years of continued reflection, development and understanding with a target completion date of April 23, 2023 (20 year anniversary of it’s original defense).
The goal of this dissertation was to assess the effect of stress in the work environment on cardiovascular health through assessment of electrocardiograph data. The hypothesis was that psychosocial stress from work affects cardiac regulation in a pathogenic manner. The demand/control model was used to quantify work stress. Cardiac regulation was measured by components of electrocardiogram output: high frequency power (HFP) which represents the parasympathetic autonomic nervous system (ANS); the ratio of low to high frequency power (lo/hi), residual heart rate as well as QT interval variability (QTVI) as measures of sympathetic activity. Thirty-Six males between the ages of 35 and 59 years and free of known heart disease were selected from a larger longitudinal study of healthy subjects and cardiovascular risk based on responses to a subset of questions from the Job Content Questionnaire (JCQ). Subjects were monitored with an ambulatory Holter electrocardiograph. Monitoring began on the morning of a workday followed for 48 continuous hours through the following rest day. Subjects were classified as high and low job strain based on occupational code, responses to the Job Content Questionnaire (JCQ) and a workday diary. High strain subjects exhibited lower parasympathetic activation during the entire 48-hour monitoring period, while measures of sympathetic activation were elevated in the high strain subjects on the workday. Multilevel modeling demonstrated that strain reported on the ambulatory diary was significantly associated with reductions in parasympathetic activity within-subjects. JCQ assessed decision latitude had a significant effect on this relationship with greater within-subject reductions in parasympathetic activity with low decision latitude. One implication of this study is that demands seem associated with short-term alterations in cardiac regulatory control with long-term changes in parasympathetic activity being associated with job control. Preliminary results support the use of ECG data for further analysis of Karasek’s Stress Disequilibrium Model. However, longitudinal studies on larger populations in a wide variety of occupations are needed to fully explore the methods and theories presented. Implications of findings for physiological linkages between strain and disease, testing new job strain based cardiac regulatory hypotheses, as well as for future studies of occupational monitoring are discussed.
Only through the support, care and guidance of so many individuals has it been possible to complete this dissertation. I am indebted to my advisor Robert Karasek; he has been an invaluable mentor providing professional and personal guidance and insight. Kevin Costas has played a critical role in the overall project; I would not have been successful without his support and friendship. It was Professor Karasek’s foresight, which led to the development of the HRV Project, the platform which made this dissertation possible. Additionally, it has been Professor Karasek’s theoretical developments of the Stress Disequilibrium Theory that led to our collaboration on the empirical investigations presented in Chapter Four, and my biological reinterpretation proposed in Chapter One. As the author of this dissertation I plan on submitting Chapters Two and Three for publication as the primary author with the co-author assistance of Professor Karasek. Due to my respect for his work in the development of the theoretical basis for Chapter Four, where I provide initial empirical support for this theory, I would like Professor Karasek to be the primary author of this paper as we prepare it together for publication. I am very grateful for the work and time of my committee members, Bryan Buccholz and David Kriebel, for their constant support and advice on so many diverse aspects of the of this project. I would like to gratefully acknowledge the members of the University of Massachusetts Medical Center and the SEASONS study, Dr. Ira Ockene, Philip Merriam, and Kathy Ruffino for their technical assistance during the data collection process. I am deeply appreciative to the Cardiovascular Electrophysiology Division at Columbia University Medical Center, specifically Dr. Thomas Bigger and Richard Steinman, for their timely and professional processing of the electrocardiogram data, and to the Cardiovascular Electrophysiology Division at Johns Hopkins Hospital, both Dr. Ronald Berger and Barry Fetics for their incredible degree of collaboration, collegiality and hospitality in providing algorithms and training in signal processing of QT intervals. Throughout this process I have had the friendship, mentoring and support of so many individuals from the College of Health Professions, Joseph Dorsey, Janice Stecchi, Susan O’Sullivan, Claire Chamberlain deserve individual mention to the special and critical roles they have each played in my development throughout my years at the university. No one could ask for a more professionally oriented, teaching focused, caring group of colleagues and friends than those that I have had the pleasure of knowing within the College of Health Professions. From a very early age my parents, Nancy and Joseph, have instilled in me a deep sense of respect for education. Many times throughout my life that they saw much more in me than I could see. Their love and support, care and guidance, work ethic and admiration for the human spirit have always been and continue to provide a safe beacon of light in my life. Through the many years of my academic, professional and personal life my family has provided me with the most love and support than it would seem humanly possible. I have been deeply touched by the love of my wife, Traci and my two sons, Timothy and Andrew. This process has placed them under considerable strain and I have, on too many times to count, asked for them to remain understanding of my work and time, which they have always done with smiles. They have provided not only joy and happiness with their caring, understanding and unconditional love, but they have also given me the desire to be a better man.