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Burlington, VT
The authors are affiliated with the Vermont Lung Center, Department of Medicine, College of Medicine, University of Vermont.
Correspondence to: Charles Irvin, PhD, Vermont Lung Center, Department of Medicine, College of Medicine, University of Vermont, 149 Beaumont Ave, HSRF 226, Burlington, VT 05405; e-mail: Charles.Irvin{at}uvm.edu
Performance of a maximum cardiopulmonary stress test is perhaps one of the most informative tests we have in the armamentarium of the pulmonary function laboratory. Yet, the results generated from such a test are easily the most difficult set of results one has to interpret. The reasons for this are several. First, the response of the body to muscular exercise is in itself complex,1 and, second, the number of variables or end points measured are numerous. But last, the principal difficulty is that the integration of the complex response, the number of variables, and the clinical situation try even the most experienced practitioner. As a result, this exceptionally useful endeavor is misunderstood and accordingly underutilized.
When we both started as directors of pulmonary function laboratories, we found that cardiopulmonary stress testing was difficult for all of the above reasons, but we also had additional problems. First, while numerous tomes on exercise have been published, most deal with the intricacies of the cardiovascular response or with formulating the "exercise prescriptions." As such, these resources are pitched at cardiologists or exercise physiologists. There are in fact few resources for a largely pulmonary practice. In particular, most of these treatises fail to discuss blood gas determinations and their integration into the cardiopulmonary response. Finally, most of these texts do not consider other issues, such as ventilatory limitations, central to the practice of pulmonary medicine.
But the biggest shortcoming of most treatments of the subject is the lack of any real attempt at providing a framework for the preparation of a cogent, and hence useful, interpretation of results. This is a serious shortcoming because there are only a few references that provide any real guidance in the interpretation of cardiopulmonary stress test results. The excellent books by Wasserman and colleagues2 and Jones3 provide important chapters on the finer points of techniques and equipment, and on the normal response to exercise. However, we have never found the case presentations in either the text or the flow charts for interpretation terribly helpful. For integration and interpretation guidelines, we have always recommended a short article by Becklake,4 which helps to provide a useful perspective as to why one performs exercise testing, especially when the outcome variables are simple and limited. But, far and away the single most useful article is the one by Younes,5 containing now well-worn pages of excellent case presentations. Last, the seminal studies of Jones6 and Hansen et al7 provided us with normal data and hence a framework for the final touches to a useful interpretation. However, this all changed when a joint committee of the American Thoracic Society and the American College of Chest Physicians published a statement on cardiopulmonary exercise testing (CPET).8
We approached this latest addition to our limited references on cardiopulmonary testing with a great deal of anticipation. This is because we think there was a real need for an all-encompassing work to pull together the many needs of those of us engaged in CPET, namely, a background of exercise physiology, clarification of important technique issues, normal values, protocols, guidelines for interpretation, and illustrative case presentations germane to pulmonary medicine.
We approached our review of this American Thoracic Society/American College of Chest Physicians statement by considering the final product in light of its stated purpose: "... to provide a comprehensive, conceptually balanced, reader-friendly, and practical document about CPET...." First, there is no doubt that the statement is comprehensive, and it is so in a major way. The statement encompasses some 66 journal pages and has 545 references. Clearly, this impressive work includes all of the basic information one would expect to find in this type of reference document. Indeed, the statement could practically stand alone as a textbook, and we both feel that it will be a welcome reference source. The tables were especially helpful at summarizing key points related to the indications for and technical aspects of testing. The table outlining the reproducibility of selected exercise variables was especially useful, as this will be of great assistance in the interpretation of results. On the perspective of pulmonary medicine and issues related to lung disease, the discussion of flow-volume loop analysis during exercise was excellent and well-illustrated with figures. While the discussions of such issues as peak oxygen uptake (
O2) vs maximum O2 were also valuable, the statement would have been strengthened if it had included a discussion of the concept of the definition of exercise limitation. Often there is discordance between work (watts) and O2 in clinical testing, making the interpretation and final determination of exercise tolerance difficult. As work performed seems to be such a particularly applicable concept,4
we might suggest that defining normal exercise tolerance in terms of predicted work rather than O2 would be the most realistic approach.
The statement was conceptually balanced, with an excellent discussion of the controversial issues surrounding direct vs indirect determination of the anaerobic threshold, the relationship of O2 pulse to stroke volume, and the difference between maximum minute ventilation (E) and maximal ventilatory capacity during exercise, the latter being of particular interest to pulmonologists. One of the major virtues of this document is that many different authorities contributed to its writing. The result is a final statement with balance.
Unfortunately, the virtue of having many authors and a comprehensive treatment of this difficult topic leads to some shortcomings. One of the main problems is simply the organization of the document. So much information is packed into so tight a format that reading the statement will be for most a labor of love. In particular, the organization of the statement makes it difficult at times to find topics and to keep them organized in a logical framework. Perhaps more bold headings, with better spacing between topics may have improved the visual impact. This shortcoming is serious enough that it will not allow us just to hand it out to our fellows and have any hope that they will read it. In addition, certain topics are discussed in great detail, such as technical aspects, but others of equal importance are only summarized, in particular the discussions on preoperative evaluation, pulmonary rehabilitation, and respiratory impairment. It would have been nice to see a few simple tables associated with these topics that would have outlined data regarding the minimal O2 required to tolerate lung resection surgery (eg, 10 mL/ min/kg), the recommended exercise targets for pulmonary rehabilitation (eg, 60% maximum O2), or categories of impairment based on O2 (eg, > 25 mL/min/kg.) Hopefully, as the field progresses there will be another chance at redoing the document. If so, we might also be so bold as to suggest a few alternative structures. Since most readers will be using the document for information about interpretation, perhaps the technical aspects should have been separated. Indeed, the entire document could be much more approachable if it were published in parts, with one part covering technical and theoretical issues, and the others focusing on practical points of testing and interpretation. Nevertheless, having participated in such endeavors, we recognize the labor that went into this statement and congratulate the authors on their Herculean achievement.
As with any authoritative statement, concepts are best illustrated by example, or, as are included here, case studies. The examples are nicely laid out and very well explained. As such, they will be invaluable to the real important activity of becoming facile with the interpretation of the often overwhelming data set of a CPET. Our only gripe is that there were not nearly enough examples. Moreover, with the commercial equipment currently available, one cannot find a data presentation format that includes all of the essentials outlined by the document. In particular, it is most useful to analyze exercise data graphically, yet most systems do not provide predicted values on the graphs for such variables as maximal E, E vs carbon dioxide output, E/O2 ratio and E/carbon dioxide output vs O2, physiologic dead space ventilation, O2 pulse, or the O2 vs work relationship. We would therefore call on industry to standardize the graphic display of data, including these predicted values, in order to facilitate interpretation. If they were to do so, all would benefit.
In summary, there is no doubt that the current statement certainly provides the most up-to-date and authoritative compilation of information about CPET. The user must approach this statement with zeal, however, in order to not become overwhelmed. However, the effort will be more than worthwhile because when the reader lays the statement down on completion, he/she will undoubtedly be able to approach the CPET armed with the information needed to become more expert in CPET testing and interpretation.
Footnotes
This research was supported by National Institutes of Health-National Heart, Lung, and Blood Institute grants HL 56638, HL 60793, and PO1 HL 67004, and by the Centers of Biomedical Research Excellence program PO1 RR-15557 (of the National Center for Research Resources).
References
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 W. W. Stringer, K. Wasserman, C. G. Irvin, and D. A. Kaminsky Statement on Exercise: American College of Chest Physicians/American Thoracic Society--Exercise for Fun or Profit? Chest, March 1, 2005; 127(3): 1072 - 1074. [Full Text] [PDF]
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C. M. Kirsch, D. A. Kaminsky, and C. G. Irvin Measuring the Work of Exercise Chest, September 1, 2004; 126(3): 1006 - 1007. [Full Text] [PDF]
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