Modification of the cylindrical approximation improves conductance catheter determination of left ventricular volumes in small hearts

J Mol Cell Cardiol23 (Supplement III) (1991) p-2-1 4 MODIFICATION OF THE CYLINDRICAL APPROXIMATION IMPROVES CONDUCTANCE CATHETER DETERMINATION OF LEFT VENTRJCULAR VOLUMES IN SMALL HEARTS Richard S, Szwarc, Reena Sandhu, Roberto Diaz, Lee N. Benson, John G. Cdes, Gregory J Wilson. Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada. We compared conductance cathater (CC) stroke volumes to those derived by thermodilution (TD) in 9 piglets (1.7-3.2 kg) and 5 pigs (16.8-22.0 kg). To increase the sample size, we volume loaded each animal, generating a range cardiac outputs. Absolute volumes, corrected for parallel conductance (V& as determined by the method of dilution, were compared to In vitro, syringe calibrated volumes. The CCflD stroke volume ratio (ar) in neonates was found to be 0.56 (r=O.86) and in older pigs 0.67 (r=O.92) as compared to 0.8, the value reported for adult humans (Circulation 70, No.5, 812-623, 1964). To account for the discrepancy, we tested the theory that catheter electrode height (EH) becomes mote important as the centre-to-centte distance between electrodes (L) is reduced. We hypothesirecl that the electrode surface exposed to the current field beyond the centres results in an artificially low conductance measurement. This was proven empirically by measuring thevolume of cylinders using catheters with varying EH and gave rise to the modified time varying volume formula: V(t)= l/cr (L*. rho. (7+EH/L,JG(r) - oVJ where rho is resistance of blood and G(t) is the measured conductance. Applying the new formula, Q became 0.72 In neonates and 0.75 in pigs. The remaining difference from 0.8 may be partially due to the temperature dependence of rho which we found to increase in pigs by 2.2ncm per 1-C drop (we measured rho continually at body temperature). Using the modified volume formula, the CC can be used to obtain continuous in sit0 estimates of left ventricular volumes in small hearts with the same degree of accuracy es in larger hearts.

f’4&15PATHOLOGlCAL EVALUATION OF THE SUSCEPTIBILIN OF THE ADULT AND THE NEONATAL RABBIT MYOCARDIUhtTO ISCHEMIAAND REPERFUBIONINJURY Stanley L Herman,Alex D Romaschin,John G Coles, Ivan M Rebeyka,GregoryJ Wilson. ResearchInstitute,The Hospital for Sick Children,Toronto, Ontario,Canada. Myocardial inury was evaluated in the adult and neonatal rabbit myocardiumto determine differences in susceptibiltyto ischemialreparfusionusing H&E stained sectionsfor light microscopy, and by electronmicroscopy. Rabbitswere divided into age groups: 7-10 days - neonate [n=24],and 2 4 months- adults [n=24]. Heartswere retrogradeiyperfusedwith oxygenated Krebs-Henseleitbuffer at 3$C, with a perfusionpressure of 75 mmHg in both groups. Hearts were stabilized for 30 minutes (control),then underwent30 minutes of ischemie at 37OC, followedby 1 hour of reperfusion,Heartswere removedfrom the perfusionsystem at the end of the controlperiod [n=S/agegroup], or after 2 hours continuousperfusion[n=8/agegroup], or following 1 hour reperfusion[r&/age group], sectionedinto 3-5 mm sections,and each sectionwas stainedwith Wphenyltetrazoliumfor 20 minutesat 370C to quantify extent of necrosis. No necroticregionswere observti in either age group at control, or during continuous perfusion, nor was there\any evidence of myocardial damage at the LM or EM level. Following ischemiaand reperfusion,the adult hearts exhibited 40&.4%(SD) necrosiswhich was confirmedby LM and EM. No necrosiswas observedin the neonatewith tetrazolium,but minutefoci of necrosiswere observedwith LM and EM. In conclusion,pathological evaluationcombininghistochemicai,histological,and ultrastructuraltechniques clearly demonstratesthat the neonateis more resistantthan the adult to myocardialischemialreperfusioninjury.

p-2-1 Fj THE ADULT BUFFER PERFUSED RAWT MYOCARDKJMIS MORE SENBITWE TO OXtDATiVE INJURY THAN THE NEONATEFOLLOWiNGl$CHEMtA AND 1 HOUR OF REPERFUStON” Stanley L Herman,Alex D Romaschin,John G Coles, Ivan M Rebeyka, GregoryJ Wilson.Researchinstitute,The Hospital for Sick Children,Toronto,Ontario, Canada. To determinethe importanceof oxygen free radical injury in the neonate,conjugateddienes [CD] a marker of lipid peroxidationwere measuredfoitowinga period of ischemiaand rep&&ion. Rabbits were divided into age groups: J-10 days - neonate p, n=tQ and 2 4 months- adults (A, ntl6]. Animalswere anaes&etiied, and their hearts were excised, mountedon a retrogradeperfusionsystem, and perfusedwith oxygenated Krebs-Henseleit buffer at 37oC, at perfusionpressure of 75 mmHg in both groups. Hearts were stabilized for 30 minutes(control), then underwent30 minutesof &hernia at 370C, followedby 1 hour of reperfusion.LV biopsies were taken at the end of the stabilizationPeriod[n&age group] , and following 1 hour of reperfusion(n&age group]. Fatty acids were extracted from the tissue and conjugated dienes were quantified by HPLG. The results are expressed as pmoles of dieneslgram tissue dry weigh&SE. The control levels of CD were not significantlydifferent between the age groups [A 34&i&7.37, N 35.1&9.26]. At 1 hour of reperfusionthere was a significantincreasein CO levels @<0.05]relative to contfol levels in both groups [A 337,[email protected],N 74.39&4.39],as well as a signiilcantdifference [p&.POOl] between the two age groups. We conclude that the normal adult myQC3tiUm is more sensilve to oxidatiie injury than the normatneonatal myocardium, furthersupportingour previouswork [JMCC 1990;22(supl iil):S.117. ‘Supportedby the OntarioHeart and Stroke Foundation. S.58