Heart rate variability are needed to address the LF component (with a lower bound of 0.04 Hz). Although time domain methods, especially the SDNN and RMSSD methods, can be used to investigate recordings of long durations, a substantial part of the long-term variability is day–night differences. Thus, long-term recordings analyzed by time domain methods should contain at least 18 hours of analyzable ECG data that include the whole night. Although cardiac automaticity is intrinsic to various pacemaker tissues, heart rate and rhythm are largely under the control of the autonomic nervous system. The parasympathetic influence on heart rate is mediated via release of
Cardiac excitation-contraction coupling In the SAN cAMP binds to an ion channel involved in action potential initiation, speeding up the production of the action potential (see sinoatrial node for more detail). cAMP also, activates a protein called protein kinase A (PKA). PKA affects both the DHPR and RyR, increasing the rise in Ca within the contractile cells and therefore increasing rate of muscle contraction. PKA also affects the myofilaments as well as a protein called phospholamban (PLB; see sarcoplasmic reticulum for more details), speeding up the rate of Cadecline in the cell and so speeding up muscle relaxation. Parasympathetic nerves work by releasing