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144 oSaAKKEV FT .V .. are these changes^ It is postdlated that tin understanding of thest mechanisms in animal models mav lead to a better understanding of similar processes in a clinical setting. )n the following studies. s'P nuclear magoetic resonance (NMR)was used togenemte data concerning phosphate rrdetabo)ism (IK'r . phosphocreatine: ATP. adenosine ariphosphata P„ inorganic phosphate). Ratios of P,/PZ-r and PCr/A'iP were used to estimate phosphorvlation potential (PP) ahd adenosine diphosphate (ADP) coneentration, both potential regulators ofoxidatna phosphorylation (24) . The P,/PCr ratio would be a better estimator of oxidative pho-cphoq-(ation based on the equation PP' J~ADPT]P) . l P~l x KcK jCrj ' [I) where KcK is the equilibrium constant ol' creatine kinase . H' is the hydrogen ion concentration. and Cr is cteatine (2f. =t) . Howe.rr• at times it is impoisible to interpret information concerning the P. peaks because of its contamination by 2 .3-diphosphoglycerie aeid (2J-DPG) . Therefore . the second ratio. PCr/ATP, can be used to provide similar. if not as sensitive. informaion concerning bioenergetic control mechanisms . Aafrnal Preparoriwr METHdDS Nine cats were anesthetized with nembutal (20-30 mg/kg. ip) and intubated for respiratory maintenance. (Onl% data from seven cats are presented because the shunts were found to be paniallp Ihrombosed in ~tw•o cats at the end of the experiment .) Anesthesia was maintained b% intravenous nembuWl (10-20 nrg/kg, iv) . Intravenous and intraarterial lines were placed for fluid and dmg administmtion, and blood preswte and arterial blood gas monitoring . nespatisrly. Median stcrnotomy was done to expose the hean for surface coil placement . A pericardial cradle was created for support and movement of the hran within the magnetic frcld (to help position the hean in the sensitive volume of the magnet) . A Iwo-turn . 1-cm-diameter surface coil, tuned to 33 .8 MHz for phosphnrus and 8$A MHz for protons• wasattaehed to the left rentricle with cyanoaccrylate. Creation of an abdominal aorta to vena cava shunt was done using 3-mm (id) pol.rthylene tubing which was inserted between the two vessels (/? . 7f). This shunt w-as kept closed wirh a plastic roller clamp until volume overload was required . Each animal was maintained under stable physiological conditions by monitoring and maintaining anerial Wood gases within physiologic range and by mainte• nance of volume and blood pressure status with fluid administration as required . X.t fR JYudres http://legacy.library.ucsf.edu/tid/fpe59c00/pdf Cats were placed in a plexigla$s holder and introduced into a 2 .1-T . 23-em-bore. Oxford magnet . The surface coil used for transmission and reception of radiofrequency signal was tuned to 35.8 MHi (phosphorus) and 88 .4 MHz (protons). The animalsurface coil-magnet combination was made as homogeneous as possible with the magnet shim coils (shimming was dorfe using proton signals . 'H NMR). Pulse width (P W) optimization was performed for each animal-coil interface . For this procedure, a PUBLICATIONS 10347650 • . 028393
® http://legacy.library.ucsf.edu/tid/fpe59c00/pdf VOLUME LOADING EiTECrS ON THE HEART USING "P NMR 145 series of pulses of diH'erent dumsion'(15-50 us) was applied and spectra were acquired with a delay time of 4 s. The pulse width which provided the best signal/noise for PCr and ATP was used for radiofiepuency stimulation for each expnimmt . Opttlmat pulses were between 35 and 30 µs . The schematic repraenlation of pla,ccment of the 1-cm-diameter surface cail on the heart is shown in Frg 1 . Practically a)1 the NMR signal cantributing to the spectrum was generated from the indicated sensitive region . which extends from the heae sullhtt by 4 mm into the myocardium and is roughly ellipsoidally shaped with a diameter varying from 12 to 13 mm . These data were generated by integrating over the threedimensional modulation profile of a suPface coil, BI x sie(ryBJ . 8ased on this infor mation, we do not expect an appreciabfe amount of contamination of the muscle spectrum from blood within the ventricle. t1P NMR spectra were obtained using respiratory and electrocardiographic gating . To do this , the following procedure was used . The respirator was outfened with a switch which was turned on at end expiration . Respiratory informarion along with ECG signal was fed into a uiggering lrox . (built in our lab) . The first QRS. on the ECG, observed by the sensing device in the triggering box. after end expimtion was used to trigger the mdiofrequertcy pulse for NMR spectra acquisition . Each spectrum consisted of 100 seans obtained with a delay tiine of 4 s(based on preset respiration rate main• tained by the ventilator) and an NMR acquisition time of 200 ms per wan, for a total time per spectrum of approximarely 6 min . Since the TI's for PCr. d-ATP, and P, are approximately 4. 1 .5 . and 1 . S s. respectively (26), saturation e&cts wnuid result from using a delay time of 4 s . However. using longer delay times would make data collection times inordinately long . Therefore. MY[e aqe qe~ C~CM Yt~Yn r, NrO .~ fuYm M .aep.M1 n,rpr . F•lo . 1 . Cwn•stcuond diatram of tulfatt eui7 placement an the heart weh a pmale urUhe eendti .
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