Heart Rate Variability: A personal journey

Heart rate variability (HRV) has been a focal point throughout my academic history. To put this into perspective, I have published studies spanning 7 decades focusing on HRV (1969–2022). My interest in HRV started early in graduate school and continues to be an important portal informing my theoretical perspective. This chapter tracks some of this history, which started as an empirical observation and moved through several scientific stages including development of quantitative methods and investigations of neural mechanisms. Along this journey a variety of hypotheses were tested including the relative sensitivity of HRV metrics to neural mechanisms, psychological processes, and medical diagnoses. In addition, the research led to the identification of portals of intervention that have become strategies to optimize mental and physical health. These apparently disparate programs of inquiry have been tightly merged as the Polyvagal Theory (PVT) evolved. In the sections below, I have shared my personal journey through these stages of scientific inquiry and my attempts to integrate the new knowledge in an expansive theoretical model.

Personal history

In the fall of 1966, I arrived at Michigan State University as an entering graduate student in a PhD program in psychology. At that time psychophysiology was emerging as a new discipline bridging psychology and physiology. It was a discipline with a scant literature. Few books and articles on the topic had been published. Only 2 years earlier, a new journal, Psychophysiology, was founded to provide a home for peer-reviewed research in this area. Previously psychophysiological research had been buried in journals such as Experimental Psychology and Psychosomatic Medicine. At the time, I did not appreciate my role as a pioneer, although the founding of the Society for Psychophysiological Research had only occurred 6 years earlier. Before we focus on the state of the emerging discipline of psychophysiology and my role in bringing interest in HRV research, it is important to see psychology and graduate training in psychology from a historical perspective.

On a personal level, my youth may have influenced my understanding of the history of psychology as an academic discipline. A student entering graduate school approaches novelty in ways that are like young children who are born into a preexisting family structure or are confronted with cultural institutions and expectations when they enter school and community. The child assumes that the context is stable and initially sets out to learn the rules without attempting to change them. Similarly, our intellectual perspective of a discipline is distorted by academic experience, and young initiates in a discipline see their field differently from the founders. Although it was clear to me that psychophysiology was new and an innovative approach to investigate historic brain–body or even mind–body questions, I had not fully appreciated that the entire field of psychology was a youthful discipline that only had emerged as an independent discipline during the academic careers of several of my mentors. At Michigan State University, psychology did not become an independent department until 1946, when it separated from the department of philosophy and psychology. A few of my professors started their academic careers in a department dominated by philosophers, not scientists.

As an entering graduate student, I assumed that psychology, as a discipline like biology, physics, and chemistry, was permanently etched into the structure of academics. I did not have a sense that psychology departments were relatively recent additions in many colleges and universities. Nor did I assume that academic disciplines would need to fluidly adapt to a rapidly changing scientific literature. Perhaps, when you are 21 years old, you are less interested in the past; events that occurred 20–50 years before do not appear relevant. Perhaps this was due my own experiences of being born at the end of World War II, a period of rapid change and forward thinking that emphasized the future and did not dwell on the past. As our culture becomes more trauma informed, we start to understand and appreciate the adaptive strategies of culture as it dynamically adjusted to the consequences of the collective trauma and devastation of war and the profound loss of agency felt by many during the Great Depression. Similar to personal trauma, reflection or rumination on societal trauma can numb our nervous system and interfere with our innate need to be social and our intellectual passions to create and discover and even a desire to uncover our roots.

Through the lens of our trauma-informed world, our optimistic dreams of equality and the opportunities to express our intellectual and ethical potential were, in part, an adaptive form of a societal dissociation. In any case, amid civil unrest and protests driven by the Vietnam War and civil rights movement, I was part of an optimistic subculture that was being driven by expansive opportunities for higher education and the rapid growth and accessibility of graduate programs. At the time I entered graduate school, a PhD from a respected program was usually sufficient to be hired without postdoctoral training or additional teaching experience as an assistant professor in a strong PhD-granting department.

This optimism was evident in my incoming classmates. Many came from uneducated families and were the first of their family to attend college. They shared a commitment to education, which several frequently verbalized as a firm desire to level the playing field of opportunities through education. Let's not forget, that in the mid-1960s misogyny was an accepted feature of graduate education. I recall the orientation meeting of all the incoming graduate students, which started with a faculty member looking at the class and inquiring why so many women (about 50%) were in the room. He continued to suggest that most would not complete degrees. All these cultural features were familiar to me as a 21-year-old.

When I elected to go to graduate school, I was enamored by the expansive questions that psychology encompassed. I was especially interested in the internal conflict between intentional behaviors and emotional state. Later, I would focus on the neurophysiological platform for emotion, autonomic state. My research would naturally flow from developing tools to monitor autonomic state (i.e., HRV) to link autonomic state with mental and behavioral processes, to identify mental and physical health vulnerabilities, and develop interventions that would optimize autonomic regulation.

However, when I arrived as an entering student in the broad area of experimental psychology, the available research that professors were studying did not seem to match my interests. At that time the research conducted by the Michigan State faculty in experimental psychology focused on verbal learning, operant learning, classical perception, physiological psychology, and child development. However, within experimental psychology, there were a couple of young faculty members who were interested in the emerging area of psychophysiology, an area that would enable empirical research of some of the historical mind–body questions linking feelings to performance by measuring physiological variables. By the fall of 1967, when I entered my second year of training, I had found a good match in being mentored by David Raskin. David was a young associate professor in his early 30s. He had been trained in physiological monitoring at UCLA by an established scientist, Irving Maltzman. Raskin's area focused on the bridge between learning and autonomic regulation that was a central topic in the scientists who followed Pavlov. These scientists were interested in classical conditioning and the unconditioned reactions to stimuli. In retrospect, the orienting and defensive responses may have been the intellectual trigger for the construct of neuroception in PVT, which functions as a reflexive detection of cues of being either safe or threatening.

I became David's mentee and teaching assistant for an undergraduate laboratory course in psychophysiology and he supervised my master's research (Porges & Raskin, 1969). David had a great influence on my research. He emphasized an empirical and quantitative perspective that effectively balanced my expansive thinking. He provided an opportunity for me to develop skills in monitoring and quantifying autonomic activity. David was a cautious scientist and thought like an engineer. He triggered my interests in designing and fabricating equipment. These interests continue as I have been awarded several patents related to monitoring and regulating autonomic function. A picture of the laboratory equipment used for my Masters' research is illustrated in Figure 8.1. 

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The equipment on the left of the picture is the relay rack that was used to control the stimulus presentation of sounds and lights. This equipment was constructed by the technician in the psychology department from parts scavenged from a government salvage facility available to universities and other public institutions. On the right is a Beckman Dynograph, a physiological monitor with ink pens scrolling out in real time beat-to-beat heart rate changes from a cardiotachometer and electrodermal changes.

It was during the pilot phase of research for my master's thesis that I serendipitously observed systematic changes in heart rate variability during sustained attention. I was interested in identifying mental effort and intentionality from physiological signals. In a way, I was curious about what we could learn about human behavior from our bodily reactions without requiring a verbal response. As I watched the heart rate pattern being displayed on the polygraph paper, I noted that for several of the subjects the beat-to-beat heart rate pattern stabilized during the attention tasks and then returned to a baseline pattern that appeared to be systematically rhythmic at a frequency similar to spontaneous breathing. This was a new phenomenon; there was no literature of a respiratory pattern in beat-to-beat heart rate being sensitive to psychological demands linked to mental effort such as sustained attention. I immediately asked David what he thought. This started a discussion about potential mediating effects of breathing. Was the effect in heart rate being driven by a shift in breathing patterns or was there unique information in the heart rate pattern? We couldn't answer this question since we did not have a sensor to measure respiration. To solve this problem, we temporarily paused the experiment and David purchased a respiration sensor for the Dynograph. After a few weeks I returned to collecting data.

During the 1960s computers were not available in individual psychology laboratories. In fact, this was a time when the major computational tools in psychology departments were mechanical calculators. As I was completing graduate school, this was replaced by a digital desktop calculator. Most graduate students tediously conducted their analyses using these now archaic devices. However, those of us collecting large arrays of beat-to-beat data had several additional challenges. First, we had to quantify the beat-to-beat tracings from the Dynograph (see Figure 8.1). This was done with a millimeter ruler. Thanks to the innovation of the cardiotachometer heart rate was a calibrated deflection on the paper. Prior to the cardiotachometer, heart rate was derived by measuring the interval between R-waves on the paper. However, with this technique precision was dependent on paper speed. Thus, more precision required more paper and paper for the Dynograph was very expensive. Heart rate was sampled second-by-second within the experimental conditions. Similarly, respiration was analyzed by counting the frequency of inspirations and mean amplitude of completed inspirations within each experimental condition. As each value was scored, it was entered into a notebook. With this notebook, I would go to the computer center and create IBM punch cards via a machine like a typewriter that punched a hole in the card for every value I typed. Then I carried hundreds of data cards to the mainframe computer (CDC 3600/CDC 6400) to conduct the analyses of variance. Prior to the analyses, the data were subjected to a two-pass verification process during which the data were reentered and compared with the original card. If there were no differences, a verification notch was punched on the right edge of the card and the data could be submitted for analyses and placed in a queue. Often the delay between submitting data and analyses would be several days. Once analyzed, a large printout was placed in a bin that the user could retrieve. If a mistake was made on the format card, which instructed the computer what columns had specific data, a few days later you would pick up a very slim printout with the word ERROR prominently displayed. This type of error could cause major delays in completing the work and even scheduling thesis defenses.

Now back to the findings from this HRV study. Based on our intuitive scoring of the data, we calculated the variance of the second-by-second heart rate. First, the results documented that the traditional variables of heart rate, respiration amplitude, and respiration frequency exhibited a systematic reaction during attention and were not selectively sensitive to variations in attentional demands. Basically, during the attention tasks breathing became more rapid and shallow, while mean heart rate increased. Over repeated trials the task effect on heart rate dissipated. Interestingly, the HRV data uniquely documented differential task demands linking suppression of HRV with sustained attention. This finding documenting that mental effort resulted in a reduction of HRV was followed by my dissertation focused on linking HRV to reaction time performance and heart rate reactivity.

As I was finishing my masters' research, David moved from Michigan State University to the University of Utah. When he left, serendipitously I started to work with Hiram Fitzgerald, a young assistant professor in his late 20s. Hi was a developmental psychologist with an interest in infancy and early development. It was through Hi's benevolent mentorship that I was welcomed into the world of developmental psychology, which has greatly enriched my theoretical perspective. His influence led to my interest in neonatal and prenatal autonomic regulation. The dissertation uncovered another important finding in my HRV journey. It documented both the HRV level prior to the task and the suppression of HRV during the predicted reaction time. These findings set the stage for future research in individual differences and mental effort. The findings also influenced my research agenda by directing me into the interdependent challenges of understanding the neural mechanisms mediating HRV, developing methodologies to quantify HRV, and studying the maturation of the neural mechanisms.

The academic marketplace was far different from what it is now. When I finished my PhD at the age of 25 there was an expectation that I would have an academic job. This expectation was not atypical, and during my 4th year in graduate school I was offered attractive positions. I accepted a position at West Virginia University with an expectation that I would create a developmental psychophysiology research program. WVU had an optimistic perspective and the psychology department was expanding, hiring both a young cohort and also seasoned, established full professors. The department had a plan to become a visible program with a strength focusing on life-span developmental psychology. This seemed like a perfect place to start my academic career. At WVU I was given access to research space in the university hospital's newborn nursery, where I studied the heart rate patterns of newborns to visual and auditory stimuli and conducted a study on temporal conditioning. After 2 years, I left WVU to move to the University of Illinois at Urbana-Champaign, where I joined the department of psychology. Over the next 50 years I have been in several universities and affiliated with several academic programs; however, my research has continued to be focused on the autonomic nervous system and the important information that can be obtained through the quantification of HRV. Rather than elaborating on how my research bridged numerous disciplines and applications, the remaining part of the chapter provides a history of the antecedent science that preceded my work. It is an opportunity for me to honor those whose work provided the scholarly platform for mine.

• Excerpted from Polyvagal Perspectives: Interventions, Practices, and Strategies. Copyright (c) 2024 by Stephen W. Porges. Used with permission of the publisher, Norton Professional Books, a division of W. W. Norton & Company, Inc. All rights reserved.
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• Author photo by Marina Kushnir.