Assessment of the human splanchnic venous volume-pressure relation using radionuclide plethysmography. Effect of nitroglycerin.

Abstract

BACKGROUND No method exists to assess human splanchnic venous function, the most important region in terms of vascular capacity. METHODS AND RESULTS We studied 25 stable patients without heart failure or hypertension to develop a method to assess the splanchnic venous volume-pressure (V-P) relation and to determine the effect of nitroglycerin (GTN). We used blood pool scintigraphy to assess changes in regional splanchnic vascular volume (SVV) and low levels of continuous positive airway pressure (CPAP) to passively alter venous pressure and thus, SVV. We postulated that the relation between SVV and the CPAP used would reflect the capacitance of the splanchnic venous bed and that changes in the position of this relation would provide a relative measurement of any change in capacitance. In 12 patients (group 1), the splanchnic vascular V-P curves were recorded before and 2, 9, and 20 minutes after 0.6 mg sublingual GTN; in eight patients (group 2), recordings were made at similar times before and after sublingual administration of placebo; in five patients (group 3), the hemodynamic effects of CPAP were assessed by means of right and left cardiac catheterization. Right atrial and femoral venous pressures increased (p < 0.001) and cardiac output fell (p < 0.05) during CPAP. There was an apparently linear relation between CPAP and SVV (r = 0.74-0.98); SVV increased an average of 7.4 +/- 2.2% (p < 0.001) by 12 cm H2O CPAP: The splanchnic vascular V-P curves were reproducible with minimal variability in SVV (+/- 2%, p > 0.2) in group 2. After administration of GTN, the splanchnic vascular V-P curve shifted away from the pressure axis in a parallel fashion by an average of 9.4 +/- 5.4% (p < 0.001). CONCLUSIONS We have developed a reproducible noninvasive technique that may be used to assess human splanchnic venous V-P relations. We have demonstrated for the first time in humans that GTN exerts its dilatory effect by increasing the unstressed splanchnic venous volume.

Altered mesenteric venous capacitance and volume pooling in cirrhotic rats are mediated by nitric oxide

“…In particular, the linearity of the diameterpressure relationship through the fairly wide range of portal pressure values is now firmly established in the literature. Additionally, the parallel shifts of the D/P line toward the pressure axis with NE also agree with previous studies using an entirely different method of assessing mesenteric venous compliance (nuclear scintigraphy) in dogs (29) and humans (24).…”

Endothelium-Derived Nitric Oxide Contributes to the Regulation of Venous Tone in Humans

“…Although our findings are in contrast to the arterial circulation, in which NO appears to play an important role in the regulation of compliance, 32,33 they parallel those of a number of other studies in which the NO donor glyceryl trinitrate caused a reduction in tone of the venous capacitance bed with no effect on compliance. 34,35 Furthermore these results support the generally held concept that compliance remains relatively constant in the venous bed, whereas changes in unstressed volume are the major determinant of capacitance. 36 -39 …”

“…1,8,30 We have investigated responses in the forearm venous capacitance bed alone, which will not necessarily be mirrored in other capacitance beds, such as the quantitatively more important splanchnic and splenic venous beds. Assessment of these beds in humans, although possible, 34 would be problematic and would require invasive techniques to assess the endothelium.…”

Changes in Intra-Abdominal Visceral Fat and Serum Leptin Levels in Patients With Obstructive Sleep Apnea Syndrome Following Nasal Continuous Positive Airway Pressure Therapy

“…NCPAP treatment may also evoke reflexes associated with increases in lung volume or increases in abdominal pressure and perhaps visceral blood flow. 34 The increase in splanchnic venous volume, 34 decrease in nocturnal blood pressure, 30 and improvement in cardiac function 35 may change blood flow in the body and this would have an effect on the leptin clearance. 36 Another possible mechanism for the decrease in leptin levels after NCPAP treatment is the effect of the circadian rhythm on leptin levels.…”