Abstract
This study investigated different methods of scaling submaximal cardiac output (Q)
and stroke volume (SV) to best normalize for body size (body surface area [BSA], height
[Ht], weight [Wt], and fat-free mass [FFM]). Q and SV were measured at both an absolute
(50 W) and a relative power output (60 % of V·O2max ) in 337 men and 422 women, 17 to 65 years of age. Traditional ratio scaling was examined
in addition to allometric scaling, where scaling exponents (b ) were determined for each body size variable (x) that best normalized the physiological
outcome variables (y) for body size (y = a x
b
). With ratio scaling, regardless of the body size variable (x = BSA, Ht, Wt, FFM),
there was no evidence of a linear relationship between x and y (y = Q or SV). A linear
relationship is a necessary condition for appropriate normalization. Further, when
ratio-scaled variables (e.g., Q/BSA) were correlated to the body size variable (e.g.,
BSA) by which they were scaled, significant (p ≤ 0.05) relationships still existed
for BSA, Ht, Wt, and FFM. Thus, ratio scaling did not meet either criteria for normalizing
Q and SV for body size. In contrast, when allometrically-derived scaling exponents
were used to normalize Q and SV (e.g., Q/BSA
b
), the resulting scaled values were uncorrelated (i.e., size-independent) with BSA,
Ht, Wt, or FFM. These results were independent of age, sex or race. In summary, ratio
scaling did not appropriately normalize Q and SV for differences in body size, while
allometric scaling did result in size-independent values. Thus, individually-derived
allometric exponents should be applied to body size variables to most appropriately
adjust Q and SV for body size.
Key words
Allometric scaling - ratio scaling - cardiac index - stroke volume index
References
2 -to-body size relationship among children and adults.
J Appl Physiol.
1995;
79
958-967
KRTurley@Harding.edu
