Acute volume loading studied in cat myocardium with ³¹P Nuclear magnetic resonance

Abstract

To study the effects of acute volume loading on myocardial metabolic and mechanical function, seven cats were volume loaded via anastomosis of the abdominal aorta to the vena cava (AV shunt). Metabolic effects were evaluated with 31P nuclear magnetic resonance (NMR). Mechanical function was evaluated with heart rate X systolic blood pressure product (HR X SBP). Shunts were opened for 1-2 h during which time phosphocreatine (PCr), adenosine triphosphate (ATP), inorganic phosphate (Pi), and HR X SBP were monitored. High-energy phosphate energetics as determined by Pi/PCr and PCr/ATP ratios were correlated with HR X SBP. Opening of the AV shunts was associated with an increase (four cats) or a decrease (three cats) in HR X SBP. Pi/PCr ratios increased and PCr/ATP ratios decreased in cats with an increase in HR X SBP. In cats with a decrease in HR X SBP, Pi/PCr and PCr/ATP generally did not change significantly. In summary, acute volume loading could be associated with an increase or decrease in myocardial external work as evaluated by HR X SBP, accompanied by metabolic changes suggestive of appropriate induction of state 3 metabolism (active metabolic state: ADP + Pi----ATP) in those cats with increased mechanical work, and minimal change in bioenergetics in cats with no or minimal increase in mechanical work. These induced metabolic responses to myocardial mechanical loading can be evaluated with 31P NMR techniques and may provide insight into in vivo metabolic control mechanisms.

In vivo phosphorus-31 NMR spectroscopy of abnormal myocardial high-energy phosphate metabolism during cardiac stress in hypertensive-hypertrophied non-human primates

“…NMR spectroscopy [18] in an acute, close-chested procine model with a surface coil directly sutured to the anterior epicardial surface of the left ventricle has demonstrated that creatine kinase flux and concentrations of PCr and ATP were independent of work load over a 2.5-fold range of cardiac rate-pressure products in response to the infusion of norepinephrine (2-5 micrograms/minute). Cat hearts appear more sensitive to changes in work than canine hearts [20]. Cat hearts appear more sensitive to changes in work than canine hearts [20].…”

In vivo Mechanisms of Myocardial Functional Stability during Physiological Interventions

“…Cardiac and respiratory gating were used to trigger both the satu ration and acquisition radio frequencies (RF). A rep resentative set o f 3IP spectra obtained during satura tion o f yP-ATP in a volume o f myocardial tissue (ap proximately 2 cm2) [1] is shown in figure 2. Progres sive saturation o f the yP-ATP was associated with a progressive decrease in PCr peak area.…”

“…Both the light guide and surface coil were positioned so that they did not overlie visible surface coronary ves sels. A multibundle fiberoptic light guide, 4 mm in diameter, was placed into the light guide holder and used in conjunction with a custom-built fluorometer to measure N A D H fluorescence [1],…”

In vivo Myocardial Bioenergetics during Acute Volume and/or Pressure Loading in a Canine Model: A ³¹P NMR Study

“…Using a program which models the sensitivity pro file of a surface coil [22], we determined that practi cally all of the 11P NMR signal was obtained from left ventricular myocardium. The average wall thickness of the dog left ventricle at end systole was 1-1.2 cm (measured with piezoelectric crystals at the end of each experiment).…”

“…To do this, the respirator was instrumented with a switch which was turned on at end expiration. This signal plus a signal from a pressure transducer (which monitored the dog's systemic arterial pressure) were fed into a triggering box (built in our laboratory) [22]. The first positive upstroke from the pressure transducer during the end expiration period was used to trigger the radiofrequency stimulation.…”