Validation of a questionnaire for assessing physical fitness in cardiac patients

Background: Physical fitness is an important factor in the tertiary prevention of cardiac patients.

Aims: To develop and validate a simple tool for the evaluation of the fitness of cardiac patients.

Methods: In this study, 154 cardiac patients: 119 men and 35 women, mean age 63.1±11.2 years; 92.2% NYHA=1, 4.5% NYHA=2, 3.2% NYHA=3; 64.3% on beta-blockers; entering the cardiac rehabilitation program at Sheba Medical Center, gave informed consent and filled-in a 24-hour recall physical activity questionnaire. Information on medication use and on their performance on a symptom-free limited treadmill test, i.e. measured estimated VO2 (ml/kg/min) and resting heart rate (bpm), were obtained from the medical chart.

Results: Statistically significant differences in measured physical fitness were found according to working status (p < 0.001), level of education > 12 years vs < 12 years (p < 0.001), and reported sports related physical activity (p < 0.01).

A linear-regression equation for predicting the measured estimated VO2 includes the overall physical activity index calculated from the physical activity questionnaire, sex, age, BMI, type of coronary heart disease (acute myocardial infarction, coronary artery bypass graft, percutaneous coronary intervention, chronic heart failure, duration of illness, resting heart rate, use of beta blockers and level of education. The correlation coefficient between measured VO2 values and calculated values is r=0.6. Categorizing the study sample to high and low physical fitness according to the VO2 median value, the validity of the equation was good: sensitivity=61.2%, specificity=65.2%, positive predictive value=68.4%, negative predictive value=57.7%.

Conclusions: The prediction equation for assessing VO2 in cardiac patients is a simple, inexpensive tool, which may be used for monitoring changes in the patients' physical fitness. This tool may assist the physician in following a cardiac patient's response to physical activity recommendations and improving fitness when the ergometric stress test availability is low.

Key words: Physical activity, Physical fitness, Questionnaire, Cardiac patients, Maximal Oxygen Consumption