Analysis of Heart Rate Adaptation to Temperature
E. ZERBST
With 3 Figures
Abstract
The capacity adaptation of the heart rate to increasing or decreasing temperature is determined by ion concentrations of the extracellular space and by the ion
permeabilities of the pacemaker membrane. Parameters (driving forces, velocity
coefficients and compartment dimensions) are qualitatively determined by experimental arrangements. The parameter-relations are identical in frog, rat and dog
heart. The causal mechanisms of adaptation are derived by coordinating the experimental data with the requirements satisfying flux-equilibrium and irreversible
thermodvnamics.
A sudden increase of temperature at the pacemaker of the heart results
in a steep frequency acceleration; however, in spite of the constancy of the
newly achieved temperature level the pacemaker impulses subsequently
decrease to a medium steady state rate. The phenomenon of this overshooting frequency in short term adaptation to temperature reminds us of
influences expected by feedback regulations. The question may be raised,
whether another possibility for understanding this regulatory mechanism
can be considered [61L. V. BERTALAK'FFY described the characteristics of first-order-regulations
in thermodynamically open reactions [1]. The kinetics of these systems
exhibit overshooting and undershooting processes as a consequence of a
parameter variation; it is exactly the same phenomenon which is observable
in capacity adaptation to temperature.-In our previous studies we tried to
clear up the problem whether an equivalent mechanism for the adaptation
of heart rate to temperature exists. These experiments were done on hearts
of frogs, rats and cats; the question was: What components of the ion transport kinetics at the membrane of heart pacemakers (i.e. driving forces,
velocity coefficients and fluxes) are parameters of adaptation? The experimental results obtained have been correlated with the kinetics of simple
steady state systems. After having coordinated the experimental results
with the properties of thermodynamically open systems, a hypothesis on
short term capacity-adaptation was proposed and examined carefully by
specially designed experiments.
E. ZERBST
With 3 Figures
Abstract
The capacity adaptation of the heart rate to increasing or decreasing temperature is determined by ion concentrations of the extracellular space and by the ion
permeabilities of the pacemaker membrane. Parameters (driving forces, velocity
coefficients and compartment dimensions) are qualitatively determined by experimental arrangements. The parameter-relations are identical in frog, rat and dog
heart. The causal mechanisms of adaptation are derived by coordinating the experimental data with the requirements satisfying flux-equilibrium and irreversible
thermodvnamics.
A sudden increase of temperature at the pacemaker of the heart results
in a steep frequency acceleration; however, in spite of the constancy of the
newly achieved temperature level the pacemaker impulses subsequently
decrease to a medium steady state rate. The phenomenon of this overshooting frequency in short term adaptation to temperature reminds us of
influences expected by feedback regulations. The question may be raised,
whether another possibility for understanding this regulatory mechanism
can be considered [61L. V. BERTALAK'FFY described the characteristics of first-order-regulations
in thermodynamically open reactions [1]. The kinetics of these systems
exhibit overshooting and undershooting processes as a consequence of a
parameter variation; it is exactly the same phenomenon which is observable
in capacity adaptation to temperature.-In our previous studies we tried to
clear up the problem whether an equivalent mechanism for the adaptation
of heart rate to temperature exists. These experiments were done on hearts
of frogs, rats and cats; the question was: What components of the ion transport kinetics at the membrane of heart pacemakers (i.e. driving forces,
velocity coefficients and fluxes) are parameters of adaptation? The experimental results obtained have been correlated with the kinetics of simple
steady state systems. After having coordinated the experimental results
with the properties of thermodynamically open systems, a hypothesis on
short term capacity-adaptation was proposed and examined carefully by
specially designed experiments.