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.
|Original language||English (US)|
|Journal||American Journal of Physiology - Heart and Circulatory Physiology|
|State||Published - Aug 1 2013|
All Science Journal Classification (ASJC) codes
- Cardiology and Cardiovascular Medicine
- Physiology (medical)