Acute changes in forearm venous volume and tone using radionuclide plethysmography

In this investigation blood pool scintigraphy was validated as a method to study acute changes in human forearm veins. Changes in regional forearm vascular volume (capacity) and the occluding pressure-volume (P-V) relationship induced by sublingual nifedipine (NIF) and nitroglycerin (GTN) were recorded in 16 patients with simultaneous data collection by the radionuclide and the mercury-in-rubber strain-gauge techniques. The standard error of estimate (s(yx)) between successive control measurements using the radionuclide method was 3.1% compared with 3.2% for th strain gauge method. The venous P-V curves were highly reproducible using both techniques. Strain gauge and radionuclide measurements of acute changes in forearm venous volume correlated well (r = 0.86; s(yx) = 7%, n = 156). After 20 mg of NIF or 0.6 mg of GTN, mean heart rate increased from 71 ± 10 to 77 ± 9 and from 68 ± 10 to 75 ± 11 beats/min, respectively, and group systolic blood pressure decreased from 128 ± 22 to 120 ± 19 and from 136 ± 18 to 126 ± 23 mmHg, respectively (P < 0.05). At venous occluding pressures of 0 and 30 mmHg, the forearm vascular volume did not change after NIF (2 ± 4 and -1 ± 4%; P > 0.05), whereas it increased after GTN (8 ± 5 and 12 ± 7%; P < 0.001). The forearm venous P-V relationship did not change after NIF, whereas a significant rightward shift (venodilation, with an increase in unstressed volume) occurred after GTN. We conclude that blood pool scintigraphy is a reliable technique to assess acute changes in human forearm venous volume and venous P-V relationship.