title: Distension of central great vein decreases sympathetic outflow in humans.
abstract: Classic canine studies suggest that central great vein distension evokes an autonomic reflex tachycardia (Bainbridge reflex). It is unclear whether central venous distension in humans is a necessary and sufficient stimulus to evoke a reflex increase in heart rate (HR), blood pressure (BP), and muscle sympathetic nerve activity (MSNA). Prior work from our laboratory suggests that limb venous distension evokes a reflex increase in BP and MSNA in humans. We hypothesized that in humans, compared with the limb venous distension, inferior vena cava (IVC) distension would evoke a less prominent increase in HR and MSNA. IVC distension (monitored with ultrasonography) was induced by two methods: 1) head-down tilt (HDT, N = 13); and 2) lower-body positive pressure (LBPP, N = 10). Two minutes of HDT induced IVC distension (Δ2.6 ± 0.2 mm, P < 0.001, ~27% in cross-sectional area), slightly increased mean BP (Δ2.3 ± 0.7 mmHg, P = 0.005), decreased MSNA (Δ5.2 ± 0.8 bursts/min, P < 0.001, N = 10), and did not alter HR (P = 0.37). LBPP induced similar IVC distension, increased BP (Δ2.0 ± 0.7 mmHg, P < 0.01), and did not alter HR (P = 0.34). Thus central venous distension leads to a rapid increase in BP and a subsequent fall in MSNA. Central venous distension does not evoke either bradycardia or tachycardia in humans. The absence of a baroreflex-mediated bradycardia suggests that the Bainbridge reflex is engaged. Clearly, this reflex differs from the powerful sympathoexcitation peripheral venous distension reflex described in humans.
authors.affiliation: Pennsylvania State University College of Medicine, Penn State Hershey Heart and Vascular Institute, Milton S. Hershey Medical Center, Hershey, PA 17033, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Cui
authors.forename: Zhaohui
authors.initials: Z
authors.lastname: Gao
authors.forename: Cheryl
authors.initials: C
authors.lastname: Blaha
authors.forename: Michael D
authors.initials: MD
authors.lastname: Herr
authors.forename: Jessica
authors.initials: J
authors.lastname: Mast
authors.forename: Lawrence I
authors.initials: LI
authors.lastname: Sinoway
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D017704:Baroreflex; D001794:Blood Pressure; D002319:Cardiovascular System / Q000294:innervation*; D005260:Female; D018475:Head-Down Tilt; D006339:Heart Rate; D006439:Hemodynamics; D006801:Humans; D008150:Lower Body Negative Pressure; D008297:Male; D018482:Muscle, Skeletal / Q000098:blood supply / Q000294:innervation*; D012018:Reflex; D013564:Sympathetic Nervous System / Q000503:physiopathology*; D013997:Time Factors; D014463:Ultrasonography; D034941:Upper Extremity; D014682:Vena Cava, Inferior / Q000000981:diagnostic imaging / Q000502:physiology*; D055815:Young Adult
keywords: Bainbridge reflex; autonomic; blood pressure control; sympathoexcitation; venous distention