Heart Rate Variability (HRV)

Background

Physiological systems continuously interact according to their own regulatory mechanisms. Consequently, functions of these systems may be coupled. This is well described by the coupling between the systems that control breathing and those that control heart rate. In normal control subjects, there is a continuous periodic modulation in the heart rate within each breathing cycle, and the amplitude of this modulation depends nonlinearly on the breathing frequency, a mechanism known as respiratory sinus arrhythmia. Central sleep apnea may be associated with bradycardia and asystole, and obstructive apnea may be associated with severe bradycardia at the end of apneas and with tachycardia when breathing resumes.