RETURN TO TABLE OF CONTENTS
Winter 2004 

Q&A: Mark VanNess, PhD, & Chris Snell, PhD

Working to understand why activity causes relapse inCFIDS

Mark VanNess, PhD, and Chris Snell, PhD, are among the few exercise physiologists studying CFIDS. They, and their colleague Staci Stevens (a member of the federal CFS Advisory Committee and a person with CFIDS), use their knowledge of energy production and utilization to better understand why CFIDS patients feel so much worse after activity. Dr. VanNess is an assistant professor and Dr. Snell a professor in the Department of Sport Sciences at the University of the Pacific.

Q: What is exercise physiology?

VanNess: I break exercise physiology into two parts, the first being the acute responses to exercise, looking at changes in muscle contraction, energy delivery, heart rate, blood flow and processes like these when you exercise. The second part is teaching athletes or people with health conditions to operate at a higher level of efficiency and higher work output as a result of training. We’re studying the acute response to exer- tion in our CFIDS research.

Q: What exercise testing do you do with your CFIDS subjects?

Snell: We use either a treadmill or a cycle ergometer that is manufactured to work at different outputs.

VanNess: We do a cardiopulmonary analysis where we collect the expired air for analysis of oxygen utilization and carbon dioxide production, and we also measure blood pressure and heart rate response to exercise. With those variables you can look at the patients’ resting levels and then, as they start doing exercise, look at the acute responses — the responses that provide energy during exercise.

With the maximal exercise test, you take subjects all the way up to their peak exertion, so you’re able to measure their peak oxygen utilization and carbon dioxide production, and how well they’re able to activate their heart to bring heart rate up and increase systolic blood pressure.

Snell: As you increase your effort you’re no longer able to supply sufficient oxygen to active muscles to completely metabolize the energy. So you go into a secondary energy system, called the anaerobic energy system, which is quite deviously designed to allow you to continue to work even though you’re not using oxygen to produce the energy. In anaerobic metabolism the byproducts of exertion are not completely metabolized, so you end up with lactic acid building up in the bloodstream, eventually compromising your ability to continue working. You enter a condition called “oxygen debt.” It’s like being overdrawn at the bank — you have to pay it back before you can start spending again.

VanNess: Our research is unique in that we have looked at determination of anaerobic threshold in CFIDS . In order to determine anaerobic threshold you have to do an incremental exercise test to peak effort.

Q: Your research has also shown that CFIDS patients have a lower anaerobic threshold than healthy sedentary controls. What does that mean?

VanNess: If athletes spend too much time above their anaerobic threshold, they become exhausted and have to rest. We think the same applies to CFIDS patients. If their aerobic metabolism is lower than expected, then they’d spend more time above that anaerobic threshold doing their regular activities. That may be producing prolonged recovery time and more exhaustion after activities of daily living.

Snell: In real terms, anaerobic threshold is the point at which you should stop working if you expect to recover in a reasonable amount of time. We can establish that very accurately with an exercise test and match that to a specific heart rate. A heart rate monitor can be used by the patient as a biofeedback mechanism to determine the point where they need to stop activity if they want to be able to function the next day. So it’s becoming a useful, practical way people can monitor output during the day to allow them to stay within their energy envelope.

Q: What else have you learned about CFIDS?

Snell: We have access to the baseline data for 189 Phase III Ampligen treatment trial subjects. So we have a large subject pool of what we think have been consistently diagnosed CFIDS patients. We’ve found that those who have abnormal RNase-L activity (an indication of immune activation) are lower func-tioning than those who don’t.

VanNess: The maximal exercise test is a very good measure of a patient’s functional capacity. If you look at the results of an exercise test and you’re not familiar with CFIDS, the patient’s function (but not the oxygen and carbon dioxide exchange measures) looks like that of a patient with cardiovascular or pulmonary disease. The exercise test can be used to rule out these other causes of fatigue when making a CFIDS diagnosis.

Q: Does your data compare with the findings of orthostatic intolerance in CFIDS?

VanNess: We’ve looked at the systolic blood pressure response to exercise. And, interestingly enough, it is blunted quite profoundly in patients with CFIDS . I think it’s two ways of looking at the same thing: orthostatic intolerance is an inability to regulate blood pressure within normal parameters. I think the same thing occurs during exercise when you’d normally see a large rise in systolic blood pressure to provide blood flow during exercise. Patients with CFIDS don’t activate that system well, so they may have a failure to perfuse (send blood to) muscle tissues during exercise.

Q: What CFIDS research studies are you planning?

Snell: We have two other ideas that we’re pursuing on a small scale. One of them is the idea of doing two exercise tests separated by 24 hours. In a healthy individual when you do two exercise tests a day apart, the results are about the same. In a CFIDS patient, because of the post-exertional malaise, peak oxygen consumption is dramatically less on the second exercise test. We’d like to get funding to examine that a little more closely and not just describe the phenomenon, but try to determine why it’s so much less the second day.

The second idea is trying to use the exercise test as a standardized stressor to look at post-exertional malaise. We’ll look at some of the immune and hormonal responses and neurocognitive effects after exercise. So, we want to truly describe what post-exertional malaise entails in a CFIDS patient.