Abstract
PurposeThe aim of the study was to assess changes in subarachnoid space width (sas-TQ), the marker of intracranial pressure (ICP), pial artery pulsation (cc-TQ) and cardiac contribution to blood pressure (BP), cerebral blood flow velocity (CBFV) and cc-TQ oscillations throughout the maximal breath hold in elite apnoea divers. Non-invasive assessment of sas-TQ and cc-TQ became possible due to recently developed method based on infrared radiation, called near-infrared transillumination/backscattering sounding (NIR-T/BSS).MethodsThe experimental group consisted of seven breath-hold divers (six men). During testing, each participant performed a single maximal end-inspiratory breath hold. Apnoea consisted of the easy-going and struggle phases (characterised by involuntary breathing movements (IBMs)). Heart rate (HR) was determined using a standard ECG. BP was assessed using the photoplethysmography method. SaO2 was monitored continuously with pulse oximetry. A pneumatic chest belt was used to register thoracic and abdominal movements. Cerebral blood flow velocity (CBFV) was estimated by a 2-MHz transcranial Doppler ultrasonic probe. sas-TQ and cc-TQ were measured using NIR-T/BSS. Wavelet transform analysis was performed to assess cardiac contribution to BP, CBFV and cc-TQ oscillations.ResultsMean BP and CBFV increased compared to baseline at the end of the easy phase and were further augmented by IBMs. cc-TQ increased compared to baseline at the end of the easy phase and remained stable during the IBMs. HR did not change significantly throughout the apnoea, although a trend toward a decrease during the easy phase and recovery during the IBMs was visible. Amplitudes of BP, CBFV and cc-TQ were augmented. sas-TQ and SaO2 decreased at the easy phase of apnoea and further decreased during the IBMs.ConclusionsApnoea increases intracranial pressure and pial artery pulsation. Pial artery pulsation seems to be stabilised by the IBMs. Cardiac contribution to BP, CBFV and cc-TQ oscillations does not change throughout the apnoea.
Highlights
Maximal apnoea performed by elite breath-hold divers results in extreme hypercapnia and hypoxia
Mean blood pressure (BP) and cerebral blood flow velocity (CBFV) increased compared to baseline at the end of the easy phase and were further augmented by involuntary breathing movements (IBMs). cc-TQ increased compared to baseline at the end of the easy phase and remained stable during the IBMs
Amplitudes of BP, CBFV and cc-TQ were augmented. sas-TQ and SaO2 decreased at the easy phase of apnoea and further decreased during the IBMs
Summary
Maximal apnoea performed by elite breath-hold divers results in extreme hypercapnia and hypoxia. Resulting chemostress augments sympathetic excitation, which in turn increases the blood pressure (BP) contribution to cerebral blood flow (CBF) [1,2]. A maximal apnoea performed by elite apnoea divers consists of two distinct phases. The beginning of the second period, the struggle phase, is marked by the onset of involuntary breathing movements (IBMs) that increase in both magnitude and frequency until the end of the apnoea [11,12,13]. Cross et al [13] reported that increases in both BP and CBF velocity in the IBMs phase were primarily due to increasing cardiac output (CO). During the IBMs phase, an increase in CBF velocity variability at the IBMs passband frequencies (0.20–0.80 Hz) was proposed [13]. Willie et al [14] indicated that the IBMs per se do not augment CBF
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