Precision Rehabilitation to Enhance Exercise Tolerance

Reid Mitchell is a MSc candidate in Dr. Jordan Guenette’s Cardiopulmonary Exercise Physiology (CPEP) Laboratory at St. Paul’s Hospital. He holds an undergraduate degree in Kinesiology from UBC.

Having grown up in Ontario in an active family that encouraged physical activity, exercise, and sport from a very young age, I often take for granted the benefits and opportunities that accompany regular physical activity. This is especially true in Vancouver, an outdoor oasis, where the ocean meets the mountains and a mild climate plays host to more activities than I could ever imagine. However, not everyone shares the same capacity or tolerance for exercise. Individuals with chronic diseases, for example, are often limited in their physical activities. Consequently, they may struggle with tasks of daily living, such as walking up stairs, doing laundry, or taking a shower. To minimize their discomfort, these tasks are often avoided leading to physical inactivity, which places a significant burden on both the individual and the society at large.

In the CPEP lab, our mission is to better understand the factors that lead to exercise intolerance across the spectrum of health and chronic lung disease. Specific to disease, our aim is to counteract the negative cycle of physical inactivity and worsening symptoms. As a member of this lab, I have had the opportunity to contribute to research that may directly impact the quality of life of those living with chronic obstructive lung disease, cystic fibrosis, and interstitial lung disease. I’ve also played a role in mentoring physical therapy students during their research placement. For example, we recently completed an award winning (CSEP 2016) project which compared the accuracy of non-invasive surface electrode stickers placed on the chest to an invasive esophageal electrode catheter to measure breathing muscle activity as a diagnostic tool for disease progression and exertional dyspnea. One of our research group’s largest projects is a multi-center randomized control trial, that has been implemented at eight different sites across Canada, to determine the impact and feasibility of cycling rehabilitation in idiopathic pulmonary fibrosis while breathing supplemental (60%) oxygen. My role as an exercise trainer in this study has been eye opening, and I find immense satisfaction in having a direct impact on a patient’s ability to exercise and improve his or her ability to perform physical activity. However, this is just a start. Much more can be done to improve current pulmonary rehabilitation programs.

We are now entering an era of “precision” or “personalized” medicine. Currently, our health care system primarily operates by use of generalized treatment plans for individuals presenting with symptoms common to a particular illness. However, each individual is unique in terms of the co-morbidities they present with, the interaction of these different co-morbidities, and the severity of their symptoms. For example, in pulmonary rehabilitation, these patients are limited by immense breathing discomfort coupled with a low tolerance for cycling exercise, the predominant modality used in these programs. Therefore, if we can find ways to reduce their breathing discomfort and allow them to tolerate exercise for longer and/or at a higher intensity, we may be able to optimize the benefits these patients gain from exercise training. One parameter in these programs that has received little attention is cycling cadence, or pedal rate. Recent work in cyclists, suggests that pedaling rate may represent a balance between leg muscle fatigue and stress on the cardiorespiratory system. Pedaling at too high a rate causes excess breathing ventilation, which could exaggerate breathing discomfort. On the other hand, a low pedal rate leads to greater leg muscle fatigue while potentially minimizing breathing discomfort so that exercise duration can be extended. Thus, pedaling rate may be the key to optimizing rehabilitation programs. Even marginal gains in exercise intensity and volume will lead to a host of physiological benefits and an improved overall quality of life.

In order to investigate this relationship my Master’s research project is focusing on the impact of cycling cadence on subjective breathing discomfort; leg muscle activation; the work it takes to breath; as well as leg muscle oxygenation and blood flow. Oxygen is essential for exercise and is dependent on blood flow for delivery to the active muscles. Thus, blood flow to these regions could represent the key to understanding this pedal rate effect. To determine blood flow, we inject a biological tracer molecule (indocyanine green) into the venous circulation while the participant is cycling. The dye travels through the arterial circulation where the concentration of the dye increases in the active muscles and this change in concentration is used to calculate a relative measure of blood flow. Due to the invasiveness of this procedure, my Master’s thesis will be conducted on healthy, highly fit cyclists. However, we hope the results of this novel investigative study will lead to similar projects in chronic lung disease to better optimize rehabilitation programs.