SCALING SUBMAXIMAL CARDIOVASCULAR DATA

Cardiovascular variables have traditionally been scaled relative to body surface area (BSA, ratio scaling) to eliminate the effects of body size. The appropriateness of this scaling method has been questioned (Turley & Wilmore, Med. Sci. Sports Exerc., 30:S242, 1998). Allometric scaling is a newer technique to normalize data. PURPOSE: Determine the most appropriate method of scaling submaximal cardiovascular variables. METHODS: Cardiac output (Q) and stroke volume (SV) were measured at absolute (50 W) and relative (60% VO2max) power outputs on a cycle ergometer in 422 women and 337 men ages 17–65. BSA values ranged from 1.28–2.74. The allometric exponent b was determined from the equation Y=aXb (Y=SV or Q, X=BSA, and a = constant). RESULTS: Values of b for Q (0.36 and 0.71) and SV (0.80 and 0.93) at 50 W and 60% VO2max, respectively, were significantly different (p ≤ 0.05) from 1.00 (the value necessary if ratio scaling truly normalizes the physiological value) except for SV at 60%. Further, the scaled physiological values (Y/BSA1.00 and Y/BSAb) were correlated to BSA. The Pearson Product Moment Correlation coefficients were as follows: If properly normalized the physiological value (Y/X1.00 or Y/Xb) should be devoid of a relationship (r = 0.00) with the scaling value (BSA). CONCLUSION: Traditional ratio scaling does not truly normalize cardiovascular variables in this large data set. Determining the appropriate exponent b from the equation Y=aXb is a more appropriate method of scaling submaximal cardiovascular values.Table: No Caption Available