Means for load variation during echocardiographic assessment of the Frank-Starling relationship

Elucidating the relationship between cardiac preload and renal perfusion under pneumoperitoneum

INTRODUCTION

Pneumoperitoneum is associated with a well-described decrease in renal blood flow, but it remains unclear whether a decrease in cardiac preload is responsible. Our aim was to characterize the relationship between cardiac preload and renal perfusion during pneumoperitoneum.

METHODS

Eleven pigs were submitted to three 30 minute study periods: 1) Baseline (n=11): no interventions, 2) Pneumoperitoneum (n=11): 12 mmHg CO2 pneumoperitoneum, 3) Preload Reduction: pneumoperitoneum and nitroglycerin infusion (n=8); or pneumoperitoneum and hemorrhage to a mean arterial pressure (MAP) of 40 mmHg (n=3). Echocardiographic measurements of left ventricular end-diastolic diameter (LVEDD) were used as an index of preload. Renal cortical perfusion (RCP) was measured using laser doppler flowmetry.

RESULTS

LVEDD decreased from 4.2 +/- 0.5 to 4.1 +/- 0.6 cm (p=0.02) with pneumoperitoneum and then to 4.0 +/- 0.5 cm (p=0.03) with the addition of nitroglycerin. There was no statistically significant change in RCP with pneumoperitoneum (33.5 +/- 8.4 to 28.5 +/- 8.4 ml/min/100g tissue, p=0.2), but it decreased to 18.5 +/- 11.3 ml/min/100g tissue (p=0.001) with the addition of nitroglycerin. The correlation between RCP and LVEDD was weak (0.35, p=0.003), whereas correlation between RCP and MAP was superior (R=0.59, p<0.0001).

CONCLUSIONS

While decreasing preload under extreme lab conditions also decreases RCP, simply creating a pneumoperitoneum of 12 mmHg does not. The decrease in renal blood flow associated with pneumoperitoneum is likely not solely a function of preload.

Real-time three-dimensional echocardiography to construct clinically ready, load-independent indices of myocardial contractile performance

BACKGROUND

Real-time 3-dimensional echocardiography (RT3DE) reliably determines intracardiac chamber volumes without left ventricular (LV) geometric assumptions, yet clinical assessment of contractile performance is often on the basis of potentially inaccurate, load-dependent indices such as ejection fraction.

METHODS

In 6 chronically instrumented dogs, RT3DE estimated LV volumes at various loading conditions. Preload recruitable stroke work and end-systolic pressure-volume relationships were constructed. RT3DE-derived indices were compared with similar relationships determined by sonomicrometry.

RESULTS

Highly linear preload recruitable stroke work and end-systolic pressure-volume relationships were constructed by RT3DE and sonomicrometry. Mean preload recruitable stroke work slopes correlated between methods, but volume intercepts differed as a result of geometric assumptions of sonomicrometry. Conversely, RT3DE-derived end-systolic pressure-volume relationships did not correlate well with sonomicrometry.

CONCLUSIONS

These data are unique in reporting load-independent measures of LV performance using RT3DE. These techniques would strengthen evaluation of LV function after myocardial ischemia or cardiac operation, in which frequent changes in ventricular geometry or loading conditions confound functional assessment by more traditional methods.