Biomedical Engineering - Life Support Systems

Oral exam

ORAL QUESTION S LIFE SUPPORT SYSTEM – 2021/22 Prof. Maria Laura Costantino Domanda su argomento a piacere + 2 domande della prof COUNTERPULSATOR (IAPB) Domanda a scelta Intra aortic balloon pump – reduce work heart improve the perfusion of the coronaries Catheter + balloon à fermoral artery up to descendin g aorta before the artic diramation Specific position in aortic arch depends on how much we want to perfuse upper districts Compressor + vacuum generator synchronized Diastole à inflation à P ventricole aorta increase à increase coronary perfusion Systole à deflation à flow blood à l ocal depression + displacement à decrease P in LV aorta à work heart decreased Q constant Synchronized - Late def: increase P LV danger - Late inf: eff decreased - Prec def: eff decreased - Prec inf: increase P LV fluido dyn pb danger (less late def, P end systole lower) Cerebral perfusion in danger Invasive – couple weeks: - Balloon damage - Chances survival Gas used CO2: physiologically expelled in case of leakages Low density à pushed easy way inside the catheter à low R PAST ORAL QUESTIONS • ECM O Extra corporeal membrane oxygenator Blood side respiratory assistance System: membrane – tubes – pump – h e – oxy – gas detector Configurations: VA – VV – central cannulation Central cannulation: RA Ao, cardiac support, babies Volemy: 800cc - 1L vs 7L M emebrane: polymeric fibers, blood outside air inside, remix blood micro vortexes, selectively permeable controlled micoporosity 40 - 50A, silicone cont, polypropylene or polymetilpenthene porous Pump: centrifugal, 4 l/m hemolysis, divergent, flowmeter , grav itational drainage He before oxy, t increases affinity hb for oxy decreases No overoxygation Heparin Wash out of CO2, supply of O2 Problem of volemy vs priming volume • VV - ECMO VV: IVC(SVC) – pump – he – oxy – IVC /SVC no cardic support, no fluido dyn prob (physisological flow) , only the venous side, special bilumen cannulae IVC • VA - ECMO VA: femoral vein – pump – he – oxy – femoral artery push up to the descending aorta, bypass of the heart à cardiac support, fluido dyn problems, dead foot syn ( à bypass) • Comparison VA - ECMO and VV - ECMO VA: bypass heart (20%), cardiac support, countrer current fluido dyn problems, countinuous , babies , dead foot syn due to cannula in femoral artery VV: no cardiac support, no fluido dynam prob physiological flow, only venous side, bi lumen cannula only access IVC , no cannula in the arteries à no dead foot syn • Pediatric ECMO Problem of volemy: 300 cc – 100 cc , priming volume miniaturized, saline sol donor blood, but dilute Pumps no sucking action – gravitational drainage Central cannulation or VA (but small vassels) à cardiac support • Component s of the TAH Fully implantable Energy source – Accumulator – converter – VA D • Characteristics of the source and the accumulator in a TAH Source – thermal = radio isotopes : 1) High Tm ( à eff of thermodynamic cycles ) 2) Not dangerous radiations 3) Slow decay 4) High specific power V 5) High power density M à Pu238, 640°C, alpha, 88 years, 2,5 mm Accumulator – thermal – eutettic mixures (meltin g t lower meltin g t single): 1) High Tm, eff rankine > eff joule Thermo el - io conv steep curves with higher eff à eff const small range Eff TE > eff TI Better to work in the point with negative slope • Relative dimensions of accumulator and source of a TAH (Graph). Why the minimum is not in the center? Capacity acc higher cap source Bigger source à thicker shield Acc own shielding cap • Find the best working condition in a steep curve of efficiency (TAH) Point with tangent with negative slope Increase load (stress) higher dissipations à eff decreases Decrease load (relax) high eff no dissip • If the source of a TAH is set with a power between the mean and the max, how should the accumulator be changed and what happens Higher capacity of the source à lower capacity of acc needed à overall dim higher source need thicker shield Patient has to dissipate/use more energy otherwise overheating • How to exploit the efficiency of thermo - ionic conversion Thermo ionic: connection hot sink (acc) cathode, cold sink (body) anode, flow ions Steep curve , small range of loads , point negative slope , dissipations due to friction gas Silent, small, low weight, no moving parts Combination with a thermodynamic cycle à connessione tra due sistemi, il termoionico fa da cold sink ad un termodinamico trasferendogli tutto il calore e l'efficienza totale è più costante rispetto al carico e più alta, eta =eta1+eta2 - moltiplicazione dei due • Thermoionic conversion and Thermo - electric conversion Thermal energy à electrical energy à mechanical work Thermo electric: hot sin k cold sing connected doped semiconducto r so called thermocouple. Flow electros à I Thermo ionic: connection hot sink (acc) cathode, cold sink (body) anode, flow ions, friction gas Adv: high eff (TE better), small, silent, durability , no moving parts Dis: small range of loads high eff , TI friction gas Both Steep curve eff, small range of loads, point negative slope • Consider a patient with a sedentary life and one with an active life: which accumulator would you give to whom? Big or small? Active life à smaller acc Sedentary life à larger acc • Diffusion between 2 compartments at different temperatures Temperatures affects D à diffusion across D1 D2 thin film Higher T à higher D Steady state à acc=0 continuity j1=j2 J1, j2 à int e grate them deltaC different: D1>D2 deltaC1