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Relationship between cardiac cycle length and ventricular relaxation rate in the chick embryo
V Cheanvechai1, S F Hughes, D W Benson
1Division of Cardiology, Children's Memorial Hospital, Northwestern University Medical School, Chicago, Illinois.
Insights
During chick embryo development, faster heart rates (shorter cycle lengths) correlate with improved ventricular relaxation (decreased tau). This relaxation rate is dependent on both maturation and cycle length, with a plateau observed at shorter cycle lengths.
Area of Science:
- Developmental Biology
- Cardiovascular Physiology
- Biophysics
Background:
- Cardiac development involves intricate changes in heart rate and relaxation dynamics.
- The ventricular relaxation rate constant, tau, is a key parameter reflecting diastolic function.
- Understanding the relationship between cycle length and tau is crucial for characterizing cardiac maturation.
Purpose of the Study:
- To investigate the association between decreasing cardiac cycle length and the ventricular relaxation rate constant, tau, during chick embryo development.
- To determine if tau is dependent on developmental stage and/or acute changes in cardiac cycle length.
- To explore potential mechanisms underlying the observed tau-cycle length relationship.
Main Methods:
- Ventricular pressure data was analyzed using the function P(t) = P0e-t/tau to estimate tau.
- Tau was determined in Hamburger-Hamilton stage 17-27 chick embryos at intrinsic cycle lengths.
- Cardiac cycle length perturbations were induced using a hot-cold probe technique in stage 24 embryos to assess tau's response.
Main Results:
- Intrinsic cardiac cycle length decreased significantly from stage 17 to 27 in developing chick embryos.
- Tau decreased linearly with decreasing cycle length during development (r = 0.39, p < 0.005).
- In stage 24 embryos, cycle length perturbations revealed a nonlinear relationship, with tau plateauing at cycle lengths shorter than intrinsic.
Conclusions:
- Ventricular relaxation rate (tau) is dependent on both embryonic maturation and cardiac cycle length.
- A plateau in the tau-cycle length relationship at shorter cycle lengths suggests developmental limitations, potentially involving the calcium transport system.
- These findings provide insights into the dynamic regulation of diastolic function during early cardiac development.
Abstract:
We hypothesized that during chick embryo cardiac development, cycle length decrease (heart rate increase) may be associated with developmental changes in the ventricular relaxation rate constant, tau, which can be estimated from ventricular pressure decrease by the function P(t) = P0e-t/tau, where P0 = pressure at the time of minimum time derivative of ventricular pressure and t = time. Natural logarithm conversion results in a linear relation between In P(t) and t with slope of -1/tau. We determined tau in Hamburger-Hamilton stage 17-27 (d 3-5) embryos (n = 35) at intrinsic cycle length and in stage 24 embryos (n = 5) during cardiac cycle length perturbations with the hot-cold probe technique. Regression analysis of In P(t) from the minimum dP/dt until t = 30 ms was used to estimate tau. Intrinsic cycle length decreased during development from stage 17 to 27 and tau decreased linearly as cycle length decreased (r = 0.39, p less than 0.005). Thus, during early development, both tau and cycle length decrease (relaxation rate and heart rate increase). In stage 24 embryos, cycle length perturbation yielded a nonlinear cycle length-dependent relation with tau, with a plateau at cycle lengths less than intrinsic, i.e. tau decreased with cycle length decrease to intrinsic cycle length, then tau plateaued with further cycle length decrease. These findings demonstrate that ventricular relaxation rate is both maturation and cycle length dependent. The plateau effect of the tau-cycle length relationship may be due to developmental limitations of the calcium transport system.