Among mammals, there is an inverse semilogarithmic relation
between heart rate and life expectancy. The product of these variables, namely,
the number of heart beats/lifetime, should provide a mathematical expression
that defines for each species a predetermined number of heart beats in a
lifetime. Plots of the calculated number of heart beats/lifetime among mammals
against life expectancy and body weight (allometric scale of 0.5 x 10(6)) are,
within an order of magnitude, remarkably constant and average 7.3 +/- 5.6 x
10(8) heart beats/lifetime. A study of universal biologic scaling and mortality
suggests that the basal energy consumption/body atom per heart beat is the
same in all animals
(approximately 10(-8) O2 molecules/heart beat). These data yield a mean value of
10
x 10(8) heart beats/lifetime
and suggest that life span is predetermined by basic energetics of living cells
and that the apparent inverse relation between life span and heart rate reflects
an epiphenomenon in which heart rate is a marker of metabolic rate. Thus, the
question of whether human life can be extended by cardiac slowing remains moot
and most likely will only be resolved by retrospective analyses of large
populations, future animal studies and clinical trials using bradycardic
therapy. Journal of the American College of Cardiology, 1997; 30:1104-1106
Ref. see
also