Fig. 1From: The physiological basis and measurement of heart rate variability in humansRelationship between heart rate (HR) and R-R interval (RRi). Note the hyperbolic behavior of HR (bpm) as a function of RRi (ms); same increase in RRi (ΔRRi = 100 ms) results in markedly different changes in HR (ΔHR) according to the chronotropic RRiBack to article page