Spence P A, Montgomery W D, Santamore W P
Division of Thoracic and Cardiovascular Surgery, University of Louisville, KY 40292, USA.
J Thorac Cardiovasc Surg. 1995 Oct;110(4 Pt 1):952-62. doi: 10.1016/s0022-5223(05)80162-x.
Despite the superior long-term patency of arterial grafts, surgeons are often reluctant to use arterial grafts on coronary vessels that supply large areas of myocardium because postoperative shock may occur. We hypothesized that supramaximal flow through small arterial conduits would decrease distal intraluminal pressure, thereby reducing afterload on the smooth muscle and rendering the arterial graft vulnerable to spasm. Fourteen internal thoracic and eight gastroepiploic arteries were harvested from adult pigs (220 to 250 pounds). Arteries were mounted on a computer-controlled perfusion system with inflow pressure at 80 mm Hg and outflow resistance adjusted to simulate normal (in situ) or supramaximal (coronary artery bypass graft) flow demands. Artery pressures and flow rates were measured at baseline and after norepinephrine was added to the system. Internal thoracic arteries had no hemodynamic response to norepinephrine at normal flow. Under supramaximal flow demands, large internal thoracic arteries (2.5 to 3.0 mm) had no hemodynamic response to norepinephrine. However, for small internal thoracic arteries (2.1 to 2.9 mm), norepinephrine reduced distal internal thoracic arterial pressure (63.2 +/- 2.2 to 27.0 +/- 1.9 mm Hg) and flow rate (99.4 +/- 5.0 to 45.4 +/- 2.7 ml/min, median effective dose = 9.12 x 10(-9) mol/L). Under normal flow demands, the flow rate in gastroepiploic arteries (1.0 to 2.0 mm diameter) decreased (14.1 +/- 0.5 to 4.8 +/- 0.8 ml/min, p < 0.05) only at high concentrations of norepinephrine (median effective dose = 1.26 x 10(-6) mol/L). Supramaximal flow demands reduced distal gastroepiploic arterial pressure (77.5 +/- 0.5 to 49.5 +/- 3.8 mm Hg, p < 0.05), which resulted in a greater decrease in flow rate (80.0 +/- 3.7 to 6.8 +/- 1.6 ml/min, p < 0.05) at lower concentrations of norepinephrine, (median effective dose = 3.24 x 10(-8) mol/L, p < 0.05). In four studies in internal thoracic arteries and eight in gastroepiploic arteries, arteries were cut in half, reattached, and reperfused. The proximal half of the internal thoracic artery did not respond to norepinephrine, but the distal half had a 53% +/- 7% decrease in flow. Both gastroepiploic artery halves reacted and flow rate decreased by 88% +/- 2% (proximal half) and 89% +/- 3% (distal half). In conclusion, small arterial conduits develop large transconduit pressure gradients under supramaximal flow demands. Under these conditions, arteries are very sensitive to vasoconstrictors and flow may cease with higher drug concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)
尽管动脉移植物具有出色的长期通畅性，但外科医生通常不愿在为大面积心肌供血的冠状动脉上使用动脉移植物，因为术后可能会发生休克。我们推测，通过小动脉导管的超最大流量会降低远端管腔内压力，从而降低平滑肌的后负荷，并使动脉移植物易发生痉挛。从成年猪（220至250磅）身上采集了14条胸廓内动脉和8条胃网膜动脉。将动脉安装在计算机控制的灌注系统上，流入压力为80毫米汞柱，调节流出阻力以模拟正常（原位）或超最大（冠状动脉搭桥术）流量需求。在基线时以及向系统中添加去甲肾上腺素后，测量动脉压力和流速。胸廓内动脉在正常流量下对去甲肾上腺素无血流动力学反应。在超最大流量需求下，大的胸廓内动脉（2.5至3.0毫米）对去甲肾上腺素无血流动力学反应。然而，对于小的胸廓内动脉（2.1至2.9毫米），去甲肾上腺素降低了胸廓内动脉远端压力（从63.2±2.2毫米汞柱降至27.0±1.9毫米汞柱）和流速（从99.4±5.0毫升/分钟降至45.4±2.7毫升/分钟，半数有效剂量=9.12×10⁻⁹摩尔/升）。在正常流量需求下，胃网膜动脉（直径1.0至2.0毫米）仅在高浓度去甲肾上腺素（半数有效剂量=1.26×10⁻⁶摩尔/升）时流速降低（从14.1±0.5毫升/分钟降至4.8±0.8毫升/分钟，p<0.05）。超最大流量需求降低了胃网膜动脉远端压力（从77.5±0.5毫米汞柱降至49.5±3.8毫米汞柱，p<0.05），这导致在较低浓度去甲肾上腺素（半数有效剂量=3.24×10⁻⁸摩尔/升，p<0.05）时流速有更大降低（从80.0±3.7毫升/分钟降至6.8±1.6毫升/分钟，p<0.05）。在对胸廓内动脉的4项研究和对胃网膜动脉的8项研究中，将动脉切成两半，重新连接并再灌注。胸廓内动脉的近端部分对去甲肾上腺素无反应，但远端部分流速降低了53%±7%。胃网膜动脉的两半均有反应，流速分别降低了88%±2%（近端部分）和89%±3%（远端部分）。总之，在超最大流量需求下，小动脉导管会产生较大的跨导管压力梯度。在这些条件下，动脉对血管收缩剂非常敏感，较高的药物浓度可能会使血流停止。（摘要截短至400字）
