Abstract
Experienced freedivers can endure prolonged breath-holds despite severe hypoxemia and are therefore ideal subjects to study apnea-induced cerebrovascular reactivity. This multiparametric study investigated CBF, the spatial coefficient of variation as a correlate of arterial transit time and brain metabolism, dynamics during prolonged apnea. Fifteen male freedivers (age range, 20-64 years; cumulative previous prolonged breath-holds >2 minutes and 30 seconds: 4-79,200) underwent repetitive 3T pseudocontinuous arterial spin-labeling and 31P-/1H-MR spectroscopy before, during, and after a 5-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. Correlation of temporal and regional cerebrovascular reactivity to blood gases and cumulative previous breath-holds of >2 minutes and 30 seconds in a lifetime was assessed. The spatial coefficient of variation of CBF (by arterial spin-labeling) decreased during the early breath-hold phase (-30.0%, P = .002), whereas CBF remained almost stable during this phase and increased in the late phase (+51.8%, P = .001). CBF differed between the anterior and the posterior circulation during all phases (eg, during late breath-hold: MCA, 57.3 ± 14.2 versus posterior cerebral artery, 42.7 ± 10.8 mL/100 g/min; P = .001). There was an association between breath-hold experience and lower CBF (1000 previous breath-holds reduced WM CBF by 0.6 mL/100 g/min; 95% CI, 0.15-1.1 mL/100 g/min; P = .01). While breath-hold caused peripheral lactate rise (+18.5%) and hypoxemia (oxygen saturation, -24.0%), cerebral lactate and adenosine diphosphate remained within physiologic ranges despite early signs of oxidative stress [-6.4% phosphocreatine / (adenosine triphosphate + adenosine diphosphate); P = .02]. This study revealed that the cerebral energy metabolism of trained freedivers withstands severe hypoxic hypercarbia in prolonged breath-hold due to a complex cerebrovascular hemodynamic response.
Highlights
BACKGROUND AND PURPOSEExperienced freedivers can endure prolonged breath-holds despite severe hypoxemia and are ideal subjects to study apnea-induced cerebrovascular reactivity
The spatial coefficient of variation of CBF decreased during the early breath-hold phase (Ϫ30.0%, P ϭ .002), whereas CBF remained almost stable during this phase and increased in the late phase (ϩ51.8%, P ϭ .001)
This study revealed that the cerebral energy metabolism of trained freedivers withstands severe hypoxic hypercarbia in prolonged breath-hold due to a complex cerebrovascular hemodynamic response
Summary
Fifteen male freedivers (age range, 20 – 64 years; cumulative previous prolonged breath-holds Ͼ2 minutes and 30 seconds: 4 –79,200) underwent repetitive 3T pseudocontinuous arterial spin-labeling and 31P-/1H-MR spectroscopy before, during, and after a 5-minute breath-hold (split into early and late phases) and gave temporally matching venous blood gas samples. Correlation of temporal and regional cerebrovascular reactivity to blood gases and cumulative previous breath-holds of Ͼ2 minutes and 30 seconds in a lifetime was assessed. Maximum breath-hold studies are rare, and CBF evaluations were, until now, exclusively performed with Doppler sonography, which revealed a continuous elevation of flow velocity in the MCA of around 100%.19,20. PET-estimated absolute CBF was, for example, consistently lower than phasecontrast MR imaging, while Doppler and ASL differed substantially in relative CBF change in a drug-stimulation trial.[23,24] These differences are not surprising and can be explained by different influential factors acting on the respective flow parameters. An awareness of a vessel-selective CVR is, crucial when interpreting ASL measurements in focal ischemic lesions after prolonged clinical conditions of apnea
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