Radionuclide analysis of the forearm venous pressure-volume relationship: response to nitroglycerin

By means of equilibrium radionuclide forearm venous occlusion plethysmography, we studied 12 adult men without heart failure. By using stepwise increases in venous occlusion pressure (0, 10, 20, and 30 mm Hg), we found that the relationship between venous cuff pressure and forearm radionuclide volume was consistently linear (r greater than 0.985). When sublingual nitroglycerin (NTG) was administered (0.8 mg), the venous pressure-volume relationship was consistently shifted rightward (reducing the slope and increasing the intercept). This resulted in large increases in venous capacitance, as shown by other workers using alternative techniques. Increased venous distensibility due to NTG was caused by an entire shift of the venous pressure-volume relationship rather than increased capacitance at one occlusion pressure. Equilibrium radionuclide venous occlusion plethysmography is a sensitive way to characterize venous pressure-volume relations. In addition, by using radionuclide blood pool component imaging to evaluate venous compliance, concern over fluid transudation seen with standard strain gauge venous plethysmographic techniques can be ignored, particularly at higher occlusion pressures.