Diving Related Changes in the Blood Oxygen Stores of Rehabilitating Harbor Seal Pups (Phoca vitulina)

Hemoglobin concentration and blood shift during dry static apnea in elite breath hold divers

Introduction

Elite breath-hold divers (BHD) enduring apneas of more than 5 min are characterized by tolerance to arterial blood oxygen levels of 4.3 kPa and low oxygen-consumption in their hearts and skeletal muscles, similar to adult seals. Adult seals possess an adaptive higher hemoglobin-concentration and Bohr effect than pups, and when sedated, adult seals demonstrate a blood shift from the spleen towards the brain, lungs, and heart during apnea. We hypothesized these observations to be similar in human BHD. Therefore, we measured hemoglobin- and 2,3-biphosphoglycerate-concentrations in BHD (n = 11) and matched controls (n = 11) at rest, while myocardial mass, spleen and lower extremity volumes were assessed at rest and during apnea in BHD.

Methods and results

After 4 min of apnea, left ventricular myocardial mass (LVMM) determined by 15O-H2O-PET/CT (n = 6) and cardiac MRI (n = 6), was unaltered compared to rest. During maximum apnea (∼6 min), lower extremity volume assessed by DXA-scan revealed a ∼268 mL decrease, and spleen volume, assessed by ultrasonography, decreased ∼102 mL. Compared to age, BMI and VO2max matched controls (n = 11), BHD had similar spleen sizes and 2,3- biphosphoglycerate-concentrations, but higher total hemoglobin-concentrations.

Conclusion

Our results indicate: 1) Apnea training in BHD may increase hemoglobin concentration as an oxygen conserving adaptation similar to adult diving mammals. 2) The blood shift during dry apnea in BHD is 162% more from the lower extremities than from the spleen. 3) In contrast to the previous theory of the blood shift demonstrated in sedated adult seals, blood shift is not towards the heart during dry apnea in humans.

Urinary glucocorticoids in harbour seal (Phoca vitulina) pups during rehabilitation

The glucocorticoid (GC) hormone cortisol is often measured in seals to indicate their stress levels, although other endogenous GCs are usually overlooked. We investigated concentrations of four endogenous GCs in the urine of "orphan" harbour seal pups in rehabilitation. We hypothesised that the GC levels would be elevated if pups were socially isolated, without water access, and with low body mass. Ninety-six samples were collected from 32 pups at four different rehabilitation centres and were analysed by Ultra Performance Liquid Chromatography and Tandem Mass Spectrometry. Median urinary creatinine (Cr) concentrations of endogenous prednisolone (31.6 ng/mg/Cr) and prednisone (31.1 ng/mg/Cr) occurred in similar magnitude to cortisol (37.0 ng/mg/Cr), while median cortisone concentrations were higher (390 ng/mg/Cr). Prednisolone and prednisone concentrations were more strongly inversely related to pup growth rate and pup mass than cortisol and cortisone. Concentrations of all four GCs decreased with mass gain for pups with water access but did not decrease for pups without water; linear mixed models indicated the interaction between these trends was significant for cortisol and cortisone, but not for prednisolone or prednisone. These results indicate the potential value of measuring all four of these endogenous GC hormones in phocid seal pups.