Fig. 2.

Two deep dives (A: a 16.5-min, 176-m dive; B: a 10.5-min, 143-m dive) and 2 shallow dives (C: a 11.0-min, 43-m dive; D, a 7.6-min, 14-m dive) illustrate potential contributions of exercise and pulmonary stretch receptor reflexes to changes in the cardiovascular dive response and heart rate (5, 12, 26). Relative lung volume was calculated as 1/(1 + [depth/10]), with depth in meters. In all cases, the heart rate profiles generally paralleled changes in depth and relative lung volume during descent and ascent. Increases in heart rate during the active ascent phases of feeding lunges of deep dives were not associated with changes in relative lung volume but were more likely related to exercise and the locomotory cost of the lunge. In artifact-free heart rate profiles of 13 lunges during deep dives, heart rate increased 2.5 ± 1.00 times above the before-ascent minima. Peak heart rates during the 13 lunges averaged 8.5 ± 3.53 bpm. During shallow dives, changes in activity as well as in relative lung volume potentially contributed to the increases in heart rate observed during transient ascents during the bottom phases of the dives. The common, often single-beat oscillations in heart rate observed during ascents in all of the dives are typical in other marine mammals and penguins (1).