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Potreba za disanjem tijekom zadržavanja daha rezultira nastankom nevoljnih dišnih pokreta. Ovom se studijom željelo utvrditi pokreću li IBM-e kritične razine hiperkapnije i/ili hipoksije tijekom maksimalne apneje. Zbog toga su određivani plinovi u arterijskoj krvi tijekom maksimalnog voljnog zadržavanja daha. Jedanaest zdravih ispitanika zadržavalo je dah nakon što su prethodno udisali zrak, hiperoksično-normokapničnu, hipoksično-normokapničnu i normooksično-hipekapničnu mješavinu plinova. Prethodno udisanje plinskih mješavina olakšalo je nastup IBM-a, skraćujući vrijeme njihova nastupa za oko 46% (hiperoksični uvjeti), odnosno za oko 80% (hipoksični uvjeti) u usporedbi s prethodnim udisanjem zraka. Zamijećena jaka korelacija (r=0.83, p=0.002) između parcijalnog tlaka ugljičnog dioksida (PaCO2) i trenutka nastupa IBM-a, a nakon prethodnog udisanja hiperoksične i hiperkapnične plinske mješavine, govori u prilog postojanja mogućeg PaCO2 praga za nastup IBM-a, koji iznosi oko 6.5 ± 0.5 kPa. Prag za parcijalni tlak kisika u arterijskoj krvi (PaO2) pri kojem nastupa IBM nije se mogao odrediti. Međutim, zamijetili smo da je nastup IBM-a, tijekom maksimalne apneje, barem djelomice ovisan o međuodnosu PaO2 i PaCO2. Prema tome, ova studija ukazuje na složen odnos između O2 i CO2 u arterijskoj krvi i fiziološkog odgovora na maksimalno zadržavanje daha., The growing urge to breathe that occurs during breath-holding results in development of involuntary breathing movements (IBMs). The present study determined whether IBMs are initiated at critical levels of hypercapnia and/or hypoxia during maximal apnoea. Arterial blood gasses at the onset of IBM were monitored during maximal voluntary breath-holds. Eleven healthy men performed breath holds after breathing air, hyperoxic–normocapnia, hypoxic–normocapnia, and normoxic–hypercapnia. Prebreathing of the gas mixtures facilitated the IBM onset, reducing the time-to-onset for ~46% (hyperoxic condition) and for ~80% (hypoxic condition) compared to the normoxic air breathing time. A strong correlation (R = 0.83, P = 0.002) between arterial partial pressure of CO2 (PaCO2 ) at IBM onset after pre-breathing hyperoxic and hypercapnic gas mixtures was observed, suggesting the existence of a possible IBM PaCO2 threshold level of ~6.5 ± 0.5 kPa. No clear “threshold” was observed for partial pressure of arterial O2 (PaO2 ). However, we observed that IBM onset was influenced, in part, by an interaction between PaO2 and PaCO2 levels during maximal apnoea. This study demonstrated the complex interaction between arterial blood-gases and the physiological response to maximal breath holding.

Background and Goal of Study: Spinal anesthesia is a preferred method of anesthesia for lower limb surgery. Antinociceptive synergism between local anesthetics and opioids is well studied. Dexmedetomidine, selective alpha2-agonist, is relatively new as an intrathecal agent. The main goal of this study was to compare dexmedetomidine with opioids as adjuvant to spinal anesthesia, in terms of its ef fect on postoperative analgesia, as well as its ef fect on hemodynamic stability in elderly patients. Materials and Methods: Spinal anesthesia was performed on thirty ASA Grade II and III geriatric patients undergoing hip surgery. Before the procedure all patients received 500 mL of i.v. saline. Noninvasive blood pressure, heart rate and SpO2 were noted every 5 minutes. NRS(numeric rating scale) was assesed 2, 4, 6, 8, 10 and 12 hours af ter spinal block. Patients were randomly assigned into two groups: control group (n=15) received levobupivacaine by body height nomogram with 2.5 mcg (0.5 mL) of sufentanil, while subject group (n=15) received levobupivacaine by body height nomogram with 5 mcg of dexmedetomidine. Groups were compared by hemodynamic parameters(systolic pressure, pulse) and NRS score in early postoperative stage of recovery. Results and Discussion: Baseline patients’ characteristics were comparable in both groups. Analysis of hemodynamic data showed that incidence of hypotension, defined as systolic blood pressure lower than 90 mmHg, was not significantly dif ferent between groups. When comparing analgesic ef fect, dexmedetomidine showed significantly better analgesic ef fect than opioids 10 and 12 hours af ter spinal block (p=0.03 and p

Razvojem računala i numeričkih metoda pojavili su se uvjeti za numeričko modeliranje složenih strujanja kao što je strujanje krvi u arterijskom krvotoku. Cilj ovog rada je provesti numeričku simulaciju strujanja krvi kroz arterijsku premosnicu. U radu je definiran matematički model nestlačivog, izotermnog, laminarnog, 3D pulsirajućeg strujanja unutar krvne žile s krutom stijenkom. Izrađena su i analizirana dva geometrijski različita modela spajanja premosnice na zdravi dio krvne žile: spoj u obliku koljena i spoj u obliku račve. Pulsirajuće strujanje krvi ostvareno je propisivanjem vremenskog profila volumenskog protoka krvi na ulazu u domenu i ugradnjom Windkessel modela s 3 elementa kao rubnog uvjeta na izlazu iz domene. Uloga Windkessel modela je uzimanje u obzir podatljivosti krvne žile, perifernog otpora mikrocirkulacije i ulazne impedancije aortnog zaliska. Intenzitet oscilatornosti smičnih naprezanja uzet je u obzir umnoškom 𝑂𝑆𝐼 ∙ 𝜏𝑤, u kojem faktor 𝑂𝑆𝐼 iskazuje stupanj promjene smjera smičnog naprezanja, a 𝜏𝑤 predstavlja srednju vrijednost smičnog naprezanja na stijenci krvne žile. Iznos tog umnoška se koristi kao kriterij za procjenu uvjeta za stvaranje hiperplazije (zadebljanje stijenke krvne žile). Simulacija je provedena u programskom paketu OpenFOAM dok je analiza rezultata napravljena u programu ParaView i gnuplot. Rezultati simulacije pokazuju da su zbog nagle promjene smjera strujanja krvi i postojanja oštrih rubova vrijednosti smičnog naprezanja veće u slučaju spoja premosnice i krvne žile u obliku račve u usporedbi sa spojem u obliku koljena. Također su u slučaju spoja u obliku račve i vrijednosti umnoška 𝑂𝑆𝐼 ∙ 𝜏𝑤 nekoliko puta veće u području gdje se u stvarnim uvjetima očekuje nastanak hiperplazije. With the development of computers and numerical methods, the conditions for numerical modeling of complex flows such as blood flow in the arterial blood stream appeared. The aim of this work is to run a numerical simulation of blood flow through an arterial bypass. In this thesis is defined mathematical model of incompressible, isothermal, laminar, 3D pulsating flow inside a blood vessel with a rigid wall. Two geometrically different models of joining the bypass to a healthy part of the blood vessel were created and analyzed: a joint in the form of a knee and a joint in the form of a fork. The pulsatile blood flow was achieved by prescribing the time profile of the volume blood flow at the entrance to the domain and incorporating the Windkessel model with 3 elements as a boundary condition at the exit from the domain. The role of the Windkessel model is to consider the compliance of the blood vessel, the peripheral resistance of the microcirculation and the input impedance of the aortic valve. The intensity of oscillatory shear stress is considered by the product 𝑂𝑆𝐼 ∙ 𝜏𝑤, in which the OSI factor expresses the degree of change in the direction of wall shear stress, and 𝜏𝑤 represents the mean value of wall shear stress on the blood vessel wall. The amount of this product is used as a criterion for evaluating the conditions for the formation of hyperplasia (thickening of the blood vessel wall). The simulation was carried out in the OpenFOAM software package, while the results were analyzed in the ParaView and gnuplot. The simulation results show that due to the sudden change in blood flow direction and the existence of sharp edges, the wall shear stress values are higher in the case of the junction of the bypass and blood vessel in the form of a fork compared to the junction in the form of a knee. Also, in the case of joint in the form of a fork, values of the product 𝑂𝑆𝐼 ∙ 𝜏𝑤 are several times higher in the area where the occurrence of hyperplasia is expected in real conditions.

Coronary artery disease is a common and serious disease which is a consequence of plaque build-up in the coronary arteries. As a result, the artery cross-sectional area is reduced which restricts the blood flow. In this study, a numerical analysis of the blood flow through an idealised stenosed artery is presented. The effects of rheological models of blood on the flow characteristics is studied. Blood is modeled as a Newtonian, a generalized Newtonian and a viscoelastic fluid. For generalized Newtonian fluid modelling, the Carreau-Yasuda model is used. For viscoelastic fluid modelling, the simplified Phan-Thien-Tanner (sPTT) model is used. Flow is studied as steady and transient for three different stenosis geometries at Reynolds number values of 50 and 200. Results show that the Carreau-Yasuda model predicts the smallest boundary layer size and significantly lesser velocity magnitudes at the artery axis in comparison to the other models. The differences between model predictions are more noticeable when the stenosis is more severe and at higher velocities. Koronarna bolest srca je česta i ozbiljna bolest koja nastaje kao posljedica nakupljanja plaka na koronarnim arterijama. Uzrokuje smanjenje površine poprečnog presjeka arterije što otežava protok krvi. U ovom radu napravljena je numerička analiza strujanja krvi kroz idealiziranu stenotičnu arteriju. Analiziran je utjecaj reološkog modela krvi na strujne karakteristike. Krv je modelirana kao Newtonovski, generalizirani Newtonovski te viskoelastični fluid. Za modeliranje generaliziranog Newtonovskog fluida korišten je Carreau-Yasuda model, a za modeliranje viskoelastičnog fluida korišten je pojednostavljeni Phan-Thien–Tanner (sPTT) model. Proučavano je stacionarno i nestacionarno strujanje za tri različite geometrije stenoze pri vrijednostima Reynoldsovog broja 50 i 200. Rezultati pokazuju da Carreau-Yasuda model predviđa najmanji granični sloj i znatno manje magnitude brzina u osi arterije u usporedbi s ostalim modelima. Razlike između modela su primjetnije kada je stenoza veća te pri većim brzinama strujanja.