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VOLUME LOADING EFFEe'fS ON THE HEART USING "P NMR
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FiG . 10. Relatiomhiptaher AV alunl openedl d,htpenYn4yee chynPe frum eunlm7 ofP,/P(Y to pefeenteae
ehang from eontrol of HR a SBP for all points,n time dur,np olume loading for all u .tn alt, Nme thn
then appears to be a Iinear tetannn .hip 4vuxn tAerc pnropcd vrfaMet narch wat not ew{hm w-hen
individual data utrc anaretd :,.e .. as HR x SBP increased P,/P(T intremed Thn indican tnn as rn&
load mcro0.s. meaboOa mdummi, Iregulnionl of oudun .e phorpnmllmion is prubabl) appmpuate for
the incrnsad merhamcal orL loads .
Acute volume loaditly produced by creation of abdominal aona .•vena cava shunts
(12. ?1 . 36) was associated with variable changes in NR x SBP . some cats with an
increase and some wilh a decrease in HR x SBP . These responses were probxbly
closely relaed to each animal's baseline homcostalic condition and/or ability ofregex
recruitmem secondarc to volume loading . Metabolic responses to .nlume overload
as reflected by changes in P./PCr and PCr/ATP generally paralleled mechanical re•
sponses : i.e. . an increase in HR x SRP was associated with an increase in P,/PCr and
a decrease in PCr/ATP and a decrease in HR x SBP was associated with a slight
inerease . decrease . or no change in P,/PCr and a slighl decrease. inerease. or no change
in PCr/ATP. Hoariern when group data were analyzed
. the P,/PCr ratio wasgenemlhincreased during volume loading and appeared to be Iinearl,v related to HR X SBP•
even though this relationship was not linear in each individual animal . This indicates
that the P,/PCr ratio may be a go,x1 measure of metabolic induction and stability
during myocardial loading conditions (when _^,3•DPG does not obscure the P, peak) .
The P,/PCr response to volume loading generally appeared to be greater than the
PCr/ATP response. This is reasonable because both parameters (P, and PCrI of the
P,/PCr ratio change during intenenlion . whereas only one parameter of the PCr/ATP
catio ostensibly changes. These changes in P,/PCr and/or PCr/ATP ratios may regulate
the increase in oxidame phosphor)1ation whice may result from increasing the work
of the hean: i .e. . phosphorylation potential as eslimated by P,/PCr and ADP cmncen•
nation as estimated b. PCr/ATP appear to be regulators of myocardial metabolism
during acute volume loading .
In conclusion . acute .rolumc loading in cats uus associated with hioenergetic changes
as measured by "P NhlR . Oxidative phospor.lafion . asestimated by P,/PCr and PCr/
d,TP ratios. eas changed during acute snlume overload as dem,mstrated Man increase
and/la decrease in P,/PCr and PCr/ATP. The changes in P,IPCr and PCr/ATP may
ah as mesxngers for enryme induction to ultimately increase oxidative phosphory-
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