Toni Brešković

Name: dr. sc. BREŠKOVIĆ TONI dr. med.


Doctoral dissertation full text (pdf)

Mentor: prof. dr. sc.  DUJIĆ ŽELJKO

Qualifying research publications:
Brešković T, Valić Z, Lipp A, Heusser K, Ivančev V, Tank J, i sur.
Peripheral chemoreflex regulation of sympathetic vasomotor tone in apnea divers. Clin
Auton Res. 2010;20:57-63.
IF (JCR 2010) 1.333

Brešković T, Ivančev V, Banić I, Jordan J, Dujić Ž. Peripheral
Chemoreflex sensitivity and sympathetic nerve activity are normal in apnea divers during training season. Auton Neurosci. 2010;154:42-7.
IF (JCR 2010) 1.671

Brešković T, Steinback CD, Salmanpour A, Shoemaker JK, Dujić Ž.
Recruitment pattern of sympathetic neurons during breath-holding at different lung
volumes in apnea divers and controls. Auton Neurosci. 2011;164:74-81.
IF (JCR 2011) 1.858

Sensitivity of peripheral chemoreceptors and activation pattern of sympathetic nervous
system during breath-holding at different lung volumes in apnea divers
Elite breath-hold divers are regularly exposed to repeated massive arterial oxygen
desaturations, which can perturb chemoreflexes. Voluntary breath-holding has already been
recognized as a pronounced sympathoexcitatory stimulus; however pattern of activation of
postganglionic sympathetic neurons which determine the level of sympathetic outflow in men
is poorly investigated.
Aim of this doctoral dissertation is to evaluate the influence of frequent, voluntary
exposures to profound hypoxia, occurring in trained breath-hold divers, on autonomic
regulation characterized by hypersensitivity of peripheral chemoreceptors. The existence of
these chemoreflex disorders was tested after one-month cessation period of apnea trainings.
Finally, the last aim of this dissertation is to assess the activation pattern of sympathetic
nervous system during breath-holding and to compare the responses between the groups of
elite breath-hold divers and healthy control subjects.
These two groups were exposed to breathing of normocapnic hypoxic gas mixture until
reaching 80% of arterial oxygen saturation. Simultaneously, muscle sympathetic nerve
activity (MSNA) was assessed in the peroneal nerve using the technique of
microneurography. Ventilation and various hemodynamic physiological parameters were
measured as well. Similar set of measurements was used in the second experimental protocol.
This protocol included breath-holding at different lung volumes (functional residual capacity
(FRC) and total lung capacity (TLC), respectively). Microneurographic recordings were
analyzed using custom made computer software that enabled identification of individual
sympathetic action potentials (APs) and determination of their characteristics.
The results of studies no. 1 and 2 discarded the existence of acute (throughout the
intensive apnea trainings period) or chronic (after at least one-month training cessation
period) increase in basal level of MSNA and excessive ventilatory response following
exposure to hypoxia in trained breath-hold divers, suggesting normal peripheral
chemoreceptor sensitivity. Consequently, it can be concluded that in the absence of additional
risk factors like hypertension, glucose intolerance or hyperlipidemia, voluntary exposure to
intermittent hypoxia/hypercapnia may not have a negative impact on autonomic, ventilatory,
and cardiovascular regulation.
The results of study no. 3 showed similar recruitment patterns of sympathetic neuron
activity during FRC (isolated chemorefelex stimulation) and TLC breath-holds (combined
activation of baroreflex and chemoreflex) in breath-hold divers and controls. Different
patterns of activation of postganglionic sympathetic neurons were observed depending on
provocation factor (baroreflex vs. chemoreflex). The mechanism by which the same
sympathetic response was elicited during the breath-holds differed between the two groups.
Specifically, the divers exhibited fewer APs per burst at rest but a pronounced increase in the
burst incidence in this group achieved the same overall sympathetic response (number of APs
per unit-time). This observation suggests possible existence of adaptation mechanism by
which the pattern of basal sympathetic outflow can be altered due to regular and frequent
exposures to the level of sympathoexcitation attained during breath-holding

Doctoral dissertation appraisal reports (pdf)
Doctoral dissertation topic proposals (pdf)
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