Cardiovascular and cerebral hemodynamics during static and dynamic breath-holding

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

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 S_BH and DYN_BH 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.

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

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