Cardiovascular and cerebral hemodynamics during static and dynamic breath-holding.

PURPOSE: The study investigated the changes in cardiovascular and cerebral hemodynamics elicited by the diving response during static (SBH) and dynamic (DYNBH) breath-holding (BH) in moderately trained recreational breath-hold divers (BHDs).

METHODS

Nineteen BHDs (42.9 ± 7.8 years, 5.7 ± 2.5 years of breath-hold practice) participated in the study. Cardiovascular and cerebral hemodynamics, along with muscle and pre-frontal cortex oxygenation, were continuously tracked throughout a single SBH and DYNBH by means of arterial volume clamp, transcranial Doppler ultrasound, and near-infrared spectroscopy. In addition, neuron-specific enolase (NSE) was measured pre- and post-BH to evaluate potential neuronal stress.

RESULTS

At the end of BH, the manifestations of the diving response were similar in both conditions, characterized by a bradycardic response (SBH: - 14 ± 6%, p < 0.05; DYNBH: - 13 ± 18%, p < 0.05) and an increase in total peripheral resistance (SBH: + 127 ± 46%, p < 0.05; DYNBH: + 116 ± 110%, p < 0.05). Mean middle cerebral artery blood velocity increased significantly more during SBH (+ 139 ± 17%, p < 0.05) than DYNBH (+ 109 ± 23%, p < 0.05). Relative changes in pre-frontal cortex deoxygenated hemoglobin were higher during DYNBH compared to SBH (+ 350 ± 106% vs. + 128 ± 27%, p < 0.05). NSE levels did not change pre- and post- SBH and DYNBH.

CONCLUSION

Due to relatively attenuated increase in cerebral blood velocity, DYNBH resulted in a greater imbalance between oxygen supply and pre-frontal oxygen consumption than SBH. However, NSE levels remained unchanged from baseline values, suggesting that no acute neuronal damage occurred in either condition.