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Fig. 3. The pattern of heart rate variability (HRV) within 250 consecutive
heartbeat intervals (R–R interval) of a single H. unitaeniatus
in (A) normoxia, (B) hypoxia, (C) hypoxia and blockade of adrenergic
receptors, and (D) hypoxia and total (adrenergic and cholinergic receptor)
blockade. The 250 consecutive R–R intervals are displayed as (i) a
tachogram plot, (ii) a frequency histogram in 5 ms bins, and (iii) a power
spectrum of the Fourier transform that shows the frequency and power of
oscillatory components of the R–R interval tachogram.