Drivers of the dive response in pinnipeds; apnea, submergence or temperature?

The mammalian dive response (DR) is described as oxygen-conserving based on measures of bradycardia, peripheral vasoconstriction, and decreased ventilation (V̇E). Using a model of simulated diving, this study examined the effect of nonapnoeic facial submersions (NAFS) on oxygen consumption (V̇O2). 19 participants performed four 2-min NAFS with 8 min of rest between each. Two submersions were performed in 5 °C water, 2 in 25 °C water. Heart rate (HR) was collected using chest strap monitors. A tube connected to the inspired port of a non-rebreathing valve allowed participants to breathe during facial submersion. Expired air was directed to a metabolic cart to determine V̇O2 and V̇E. Baseline (BL) HR, V̇O2, and V̇E values were determined by the average during the 2 min prior to facial submersion; cold shock response (CSR) values were the maximum during the first 30 s of facial submersion; and NAFS values were the minimum during the last 90 s of facial submersion. A 2-way repeated-measures ANOVA indicated that both HR and V̇E were greater during the CSR (92.5 ± 3.6 beats/min, 16.3 ± 0.8 L/min) compared with BL (78.9 ± 3.2 beats/min, 8.7 ± 0.4 L/min), while both were decreased from BL during the NAFS (60.0 ± 4.0 beats/min, 6.0 ± 0.4 L/min) (all, p < 0.05). HRCSR was higher and HRNAFS lower in 5 °C versus 25 °C water (p < 0.05), while V̇E was greater in 5 °C conditions (p < 0.05). V̇O2 exceeded BL during the CSR and decreased below BL during the NAFS (BL: 5.3 ± 0.1, CSR: 9.8 ± 0.4, NAFS: 3.1 ± 0.2 mL·kg−1·min−1, p < 0.05). The data illustrate that NAFS alone contributes to the oxygen conservation associated with the human DR.

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Effects of training on forced submersion responses in harbor seals

Journal of Experimental Biology ◽

10.1242/jeb.204.22.3877 ◽

2001 ◽

Vol 204 (22) ◽

pp. 3877-3885 ◽

Cited By ~ 1

Author(s):

P. D. Jobsis ◽

P. J. Ponganis ◽

G. L. Kooyman

Keyword(s):

Heart Rate ◽

Blood Flow ◽

Muscle Blood Flow ◽

Muscle Oxygenation ◽

Metabolic Efficiency ◽

Harbor Seals ◽

Doppler Flowmetry ◽

Muscle Deoxygenation ◽

Training Protocol ◽

Dive Response

SUMMARY In several pinniped species, the heart rates observed during unrestrained dives are frequently higher than the severe bradycardias recorded during forced submersions. To examine other physiological components of the classic ‘dive response’ during such moderate bradycardias, a training protocol was developed to habituate harbor seals (Phoca vitulina) to short forced submersions. Significant changes were observed between physiological measurements made during naive and trained submersions (3–3.5 min). Differences were found in measurements of heart rate during submersion (naive 18±4.3 beats min–1versus trained 35±3.4 beats min–1), muscle blood flow measured using laser-Doppler flowmetry (naive 1.8±0.8 ml min–1 100 g–1versus trained 5.8±3.9 ml min–1 100 g–1), change in venous PO2 (naive –0.44±1.25 kPa versus trained –1.48±0.76 kPa) and muscle deoxygenation rate (naive –0.67±0.27 mvd s–1versus trained –0.51±0.18 mvd s–1, a relative measure of muscle oxygenation provided by the Vander Niroscope, where mvd are milli-vander units). In contrast to the naive situation, the post-submersion increase in plasma lactate levels was only rarely significant in trained seals. Resting eupneic (while breathing) heart rate and total oxygen consumption rates (measured in two seals) were not significantly different between the naive and trained states. This training protocol revealed that the higher heart rate and greater muscle blood flow in the trained seals were associated with a lower muscle deoxygenation rate, presumably secondary to greater extraction of blood O2 during trained submersions. Supplementation of muscle oxygenation by blood O2 delivery during diving would increase the rate of blood O2 depletion but could prolong the duration of aerobic muscle metabolism during diving. This alteration of the dive response may increase the metabolic efficiency of diving.

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Temperature effect on the human dive response in relation to cold water near-drowning

Journal of Applied Physiology ◽

10.1152/jappl.1984.56.1.202 ◽

1984 ◽

Vol 56 (1) ◽

pp. 202-206 ◽

Cited By ~ 46

Author(s):

J. S. Hayward ◽

C. Hay ◽

B. R. Matthews ◽

C. H. Overweel ◽

D. D. Radford

Keyword(s):

Heart Rate ◽

Water Temperature ◽

Cold Water ◽

Breath Holding ◽

Breath Hold ◽

Cold Stimulation ◽

Near Drowning ◽

Voluntary Hyperventilation ◽

Dive Response ◽

Breath Hold Duration

To facilitate analysis of mechanisms involved in cold water near-drowning, maximum breath-hold duration (BHD) and diving bradycardia were measured in 160 humans who were submerged in water temperatures from 0 to 35 degrees C at 5 degrees C intervals. For sudden submersion BHD was dependent on water temperature (Tw) according to the equation BHD = 15.01 + 0.92Tw. In cold water (0–15 degrees C), BHD was greatly reduced, being 25–50% of the presubmersion duration. BHD after brief habituation to water temperature and mild, voluntary hyperventilation was more than double that of sudden submersion and was also dependent on water temperature according to the equation BHD = 38.90 + 1.70Tw. Minimum heart rate during both types of submersions (diving bradycardia) was independent of water temperature. The results are pertinent to accidental submersion in cold water and show that decreased breath-holding capacity caused by peripheral cold stimulation reduces the effectiveness of the dive response and facilitates drowning. These findings do not support the postulate that the dive response has an important role in the enhanced resuscitatibility associated with cold water near-drowning, thereby shifting emphasis to hypothermia as the mechanism for this phenomenon.

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