Acute arterio-venous fistula occlusion decreases sympathetic activity and improves baroreflex control in kidney transplanted patients

Background. The acute bradycardia induced by the occlusion of an arteriovenous fistula (AVF), known as the Nicoladoni-Branham sign, is considerably larger than that which occurs during carotid sinus massage. This suggests increased arterial baroreflex sensitivity during acute AVF occlusion. Moreover, the influence of acute AVF occlusion on muscle sympathetic nerve traffic (MSNA, by microneurography) is unknown. We therefore assessed the effects of acute AVF occlusion on baroreflex sensitivity and on MSNA in patients with stable functional kidney grafts and patent AVF. Methods. We measured blood pressure (BP), MSNA (n = 11), heart rate (HR), cardiac output (CO) and arterial baroreflex sensitivity (n = 18) at baseline and during acute, 30-s pneumatic AVF occlusions in 23 renal transplanted recipients. Results. During the first 5 s of the AVF occlusion, mean BP increased from 98±4 to 112±4 mmHg (P<0.0001) while MSNA decreased to 28±5% of baseline values (P<0.0001) and HR decreased from 71±3 to 61±3 b.p.m. (P<0.0001). The largest increases in BP were accompanied by the most marked decreases in MSNA (r=-0.79, P=0.003) and HR (r=-0.49; P=0.01) during the first 5 s of the AVF occlusion. During AVF occlusion baseline CO of 6.9±0.3 decreased to 5.6±0.3 l/min (P<0.0001) while baroreflex sensitivity increased from 101 to 17±2 ms/mm Hg (P<0.001). Conclusions. Arterial baroreceptor activation and increased arterial baroreflex sensitivity decrease heart rate during AVF occlusion. In addition, our study is the first to demonstrate that arterial baroreflex activation decreases sympathetic nerve traffic during the Nicoladoni-Branham sign.