| Abstract | Cilj disertacije: Svrha ovog istraživanja bila je ispitati mogu li se vaskularne promjene u perifernoj i cerebralnoj cirkulaciji izazvane ronjenjem spriječiti oralnim dodavanjem antioksidansa. Nadalje, ispitali smo hipotezu da će promijenjeni hemodinamski parametri nakon zarona SCUBA dovesti do promjena cerebralnog protoka krvi u mirovanju i tijekom vježbanja.
Materijali i metode: Ovo kliničko istraživanje provedeno je u Zavodu za integrativnu fiziologiju Medicinskog fakulteta Sveučilišta u Splitu. U prvoj fazi istraživanja, 14 ronioca izvelo je jedno podvodno ronjenje na 18-metarskoj morskoj dubini tijekom 47 minuta. 12 ronioca sudjelovalo je u naknadnom istraživanju koja je uključivalo udisanje 60% kisika pod atmosferskim tlakom tijekom 47 minuta. Prije oba istraživanja sudionici su 6 dana unosili vitamin C (2 g/dan) ili placebo. Nakon 2 tjedna ispiranja, studija je ponovljena s različitim stanjima. Vazodilatacija ovisna o endotelu brahijalne arterije procijenjena je prije i nakon intervencije pomoću tehnike dilatacije posredovane protokom (FMD). U drugoj fazi istraživanja, 16 ronioca izvršilo je jedan zaron na na 18-metarskoj morskoj dubini tijekom 47 minuta. Nadzorna laboratorijska mjerenja provedena su tjedan dana kasnije. Transkranijski Doppler ultrazvuk korišten je za mjerenje intrakranijskih brzina krvi.
Rezultati: FMD je smanjen za ~32,8% i ∼21,2% nakon zarona u ispitivanju s placebom i vitaminom C, a posthiperoksično stanje u ispitivanju s placebom za ∼28,2% (P<0,05). Ovo smanjenje FMD-a umanjeno je za ~10% nakon dodavanja vitamina C u hiperoksičnoj studiji (P>0,05). Povišenje brzine intrakranijalne krvi 30 minuta nakon izranjanja na površinu od ronjenja smanjeno je u studiji s vitaminom C u usporedbi s ispitivanjem placeba (P<0,05). Disanje O2 nije imalo postintervencijskih učinaka na intrakranijalne brzine (P>0,05). Profilaktičko uzimanje vitamina C učinkovito je poništilo perifernu vaskularnu disfunkciju nakon izlaganja 60% O2, ali nije ukinulo smanjenje FMD-a nakon post-zarona. Prolazna povišenja intrakranijalnih brzina nakon zarona smanjena su vitaminom C. Nakon zarona u mirovanju, srednja brzina cerebralne arterije (MCAv) povišena je 15 i 30 minuta nakon izranjanja (za 3,3±5,8, odnosno 4,0±6,9 cm/s; P <0,05); brzina stražnje cerebralne arterije (PCAv) povećana je 30 minuta nakon izranjanja (za 3,0±4,5 cm/s; P<0,05). Tijekom vježbanja nakon ronjenja, MCAv i PCAv povećali su se na 150 W, nakon čega je uslijedio pad prema početnoj liniji na 180 W (P<0,05). Nismo pronašli razliku u CBV tijekom vježbanja između terenskih i laboratorijskih studija (P<0,05).
Zaključci: Ova otkrića ističu diferencijalni utjecaj vitamina C na perifernu i cerebralnu cirkulaciju nakon ronjenja, koji su samo djelomično posredovani hiperoksijom. Također, novo otkriće ove studije jest prolazno povišenje intrakranijalnih brzina u mirovanju unutar 30 minuta nakon SCUBA ronjenja. |
| Abstract (english) | Objectives: The aim of this study was to examine if the diving-induced vascular changes in the peripheral and cerebral circulation could be prevented by oral antioxidant supplementation. Furthermore, we examined the hypothesis that the altered hemodynamic parameters following a SCUBA dive will lead to differential changes in CBF at rest and during exercise.
Materials and methods: This study was conducted in Department of Physiology, University of Split School of Medicine. In the first study phase, 14 divers performed a single scuba dive to 18-meter sea water for 47 min. 12 divers participated in a follow-up study involving breathing 60% of oxygen at ambient pressure for 47 min. Before both studies, participants ingested vitamin C (2 g/day) or a placebo capsule for 6 days. After a 2-wk washout, the study was repeated with the different condition. Endothelium-dependent vasodilator function of the brachial artery was assessed pre- and postintervention using the flow-mediated dilation (FMD) technique. In the second study phase, 16 divers completed a single dive at a depth of 18-meter sea water with a 47-min bottom time. A follow-up laboratory based study was conducted 1-week later. Transcranial Doppler ultrasound was used to measure intracranial blood velocities.
Results: FMD was reduced by ∼32.8% and ∼21.2% postdive in the placebo and vitamin C trial and posthyperoxic condition in the placebo trial by ∼28.2% (P<0.05). This reduction in FMD was attenuated by ∼10% following vitamin C supplementation in the hyperoxic study (P>0.05). Elevations in intracranial blood velocities 30 min after surfacing from diving were reduced in the vitamin C study compared with the placebo trial (P<0.05). O2 breathing had no postintervention effects on intracranial velocities (P>0.05). Prophylactic ingestion of vitamin C effectively abrogated peripheral vascular dysfunction following exposure to 60% O2 but did not abolish the postdive decrease in FMD. Transient elevations of intracranial velocities postdive were reduced by vitamin C. Following the dive at rest, middle cerebral artery velocity (MCAv) was elevated 15 and 30 min after surfacing (by 3.3±5.8 and 4.0±6.9 cm/s, respectively; P<0.05); posterior cerebral artery velocity (PCAv) was increased at 30 min after surfacing (by 3.0±4.5 cm/s; P<0.05). During exercise following the dive, both MCAv and PCAv increased up to 150W followed by a decrease towards baseline at 180W (P<0.05). We found no difference in CBV during exercise between field and laboratory studies (P<0.05). .
Conclusions: These findings highlight the differential influence of vitamin C on peripheral and cerebral circulations following scuba diving, which are only partly mediated via hyperoxia. Also, the novel finding of this study is the transient elevation in resting intra-cranial velocities within 30 min following a SCUBA dive. |
