Revisiting Use of the Ebbeling Prediction Equation - The College ...


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Revisiting Use of the Ebbeling Prediction Equation - The College ...

  1. 1. 1 Revisiting Use of the Ebbeling Prediction Equation Sonya M. Arzola, MS Project Director The Geneva Foundation working at Brooke Army Medical Center Department of Nursing Research Fort Sam Houston, TX 78234-6200 Stacey Young-McCaughan, RN, PhD Professor University of Texas Health Science Center San Antonio School of Medicine, Department of Psychiatry San Antonio, TX 78229-3900 Maximal oxygen consumption (VO2 max) is one commonly used index of cardiorespiratory fitness. It can either be directly measured or indirectly calculated using a regression equation to predict VO2 max from a combination of variables such as age, heart rate, speed and/or time at either maximal or submaximal work load on an ergometer or other field test. Direct measurement has evolved over the years from volumetric gas analyzers, to semi-automated systems, to automated systems (i.e., the metabolic cart). The direct measurement of VO2 max requires trained staff using costly, specialized equipment. It can be time consuming for both the patient and the staff. Thus, indirectly measuring VO2 max can be more practical in a busy clinical or cost-constrained environment. The Ebbeling formula is an equation that can be used to predict VO2 max from a 4-minute single-stage submaximal treadmill walking protocol [1]. Speed, heart rate, age, and gender are used to determine VO2 max using the formula: VO2 max = 15.1 + (21.8) (speed in mph) - (0.327) (heart rate in bpm) - (0.263) (speed) (age in years) + (0.000504) (heart rate) (age) + (5.98) (gender where 0 = female and 1 = male) The Ebbeling formula was selected to determine VO2 max as a measure of cardiorespiratory fitness in a quasi-experimental, repeated-measures study designed to assess how persons within six months of completing treatment for cancer do over the 18-months following participation in a 12-week exercise program comparing them to patients who did not participate in the program [2]. While the Ebbeling protocol is not specific to patients with cancer or older Professionalization of Exercise Physiologyonline Vol 12 No 6 June 2009
  2. 2. 2 persons, the protocol and formula were chosen over direct measurement of VO2 max during maximal testing for this study because physician supervision was not required for patients without existing disease and because patients could better tolerate the 4-minute test administered five times over 18-months. Also, the formula had been shown to be reliable and valid [1] and computer software was available that quickly calculated the predicted VO2 max [3]. During baseline testing patients were allowed two- to four-minutes to warm-up on the treadmill and find a comfortable speed between 2.0 and 4.5 mph at a 0% grade that elicited a heart rate between 50% and 70% of age predicted maximal heart rate (APMHR). During the four-minute exercise phase patients walked at the speed determined during the warm-up phase plus a 5% grade [1]. Subsequent testing was conducted at the same speed and grade. In the process of analyzing the data the research team was puzzled by the calculated VO2 max values until it was realized that two key elements of the structure of the prediction formula had been inadvertently overlooked. First Key Element Overlooked We were studying exercise rehabilitation in patients with cancer. The incidence of cancer increases with age [4] and as anticipated, our study sample had a mean age of 60 years with a range of 31 to 86 years. Unexpectedly however, we found that as individuals aged instead of calculating increases in predicted VO2 max with decreases in heart rate, predicted VO2 max decreased with decreases in heart rate. This change from the expected inverse relationship between heart rate and predicted VO2 max to an unexpected direct relationship between heart rate and predicted VO2 max occurred at age 65. In re-evaluating the prediction equation it was obvious that the negative coefficient 0.327 has an increasingly larger negative effect on the calculation with increasing age while the positive coefficient 0.000504 has a decreasingly positive effect with increasing age. Ebbeling clearly states that the protocol was developed in a population of typically healthy subjects ranging in age from 20 to 59 years [1]. Although it is mathematically possible to apply the formula to an older population as we did, this was not appropriate. Second Key Element Overlooked To avoid the practice effect of exercise testing where the individual being tested performs better because of familiarity with the equipment, the research team standardized the speed at all testing times determined at baseline. Although the formula was not specifically developed to assess change over time, the research team used it to assess change over time anticipating that trained study participants would more easily complete the testing protocol at subsequent testing periods and that this would be reflected as an increase in VO2 max. However, there was very little variability in the calculated VO2 max.
  3. 3. 3 In re-evaluating the prediction equation, it was obvious that change in speed, which the research team had kept constant over time, has the greatest effect on the calculated VO2 max. As compared with speed that has a large positive coefficient of 21.8 and thus a large impact on the calculated VO2 max, heart rate has a relatively small impact on the calculated VO2 max with a small negative coefficient of 0.327 in one term and a very small positive coefficient of 0.000504 in another term. By standardizing the speed for all testing time points, we inadvertently eliminated the influence of change in speed over time. Lessons Learned The Ebbeling protocol is an easily conducted, generally well-tolerated, and robust approach to assess cardiorespiratory fitness recommend for both clinical care and research studies. However, both clinicians and researchers should be cautioned to only use prediction equations in the populations for which they were developed and tested. And when testing individuals over time, repeated measurement of the variable of interest over time should be carefully chosen as not to inadvertently obscure change. Recommendations for Future Research Future research should develop predication equations for older persons as well as those with chronic conditions like cancer. Cardiorespiratory fitness has been repeatedly shown to be predictive of both health benefit and disease reduction. Sensitive and specific measures will help to better define those benefits in selected populations and test interventions to further improve health and reduce disease burden. References 1. Ebbeling, C.B., et al. (1991). Development of a single-stage submaximal treadmill walking test. Medicine & Science in Sports Exercise. 23(8):966-73. 2. Arzola, S.M., S. Young-McCaughan, and S.A. Dramiga. (2007). The Ebbeling protocol: Tolerability in patients completing treatment for cancer. Journal of Cardiopulmonary Rehabilitation and Prevention. 27:315-339. 3. Ng, N.K. (1995). METCALC software: Metabolic calculations in exercise and fitness. Champaign, IL: Human Kinetics. 4. American Cancer Society. Cancer Facts & Figures 2008. Atlanta: American Cancer Society; 2008. Disclaimer: The views of these authors are their own and do not purport to reflect the position of the Army Medical Department, Department of the Army, or the Department of Defense. Acknowledgement: Funding for this work was made possible through the Uniformed Services University of the Health Sciences TriService Military Nursing Research Grants Program (MDA HU0001-05-1-TS03, TSNRP N05-
  4. 4. 4 006). The authors would like to gratefully acknowledge Travis Vaught for his assistance calculating the age at which the relationship between heart rate and VO2 max, and Jim Mintz, PhD for his assistance helping us understand the regression equation. Classification: UNCLASSIFIED Caveats: NONE