Francis B A, Cortes A, Chen J, Alvarado J A
University of California, San Francisco, Department of Ophthalmology 94143, USA.
Ophthalmology. 1998 Sep;105(9):1708-14. doi: 10.1016/S0161-6420(98)99042-X.
This study aimed to ascertain whether the Optimed, Krupin, and Ahmed drainage devices function as valves that vary resistance depending on flow conditions to maintain pressure within a desired range.
Experimental study.
The three devices and a control cannula were submerged in fluid and perfused with balanced salt solution using a computer-driven apparatus that continuously monitors flow (Q) and pressure (P). In one set of experiments, the flow rates were maintained at 2, 5, 10, 25, or 50 microliters/min until steady-state pressures were achieved. In another set of experiments, the flow rate was increased linearly from 0 to 100 microliters/min over 15 to 20 minutes.
The resistance of each implant was calculated from the first set of experiments by dividing the change in pressure (P) by the change in flow (Q) between successive perfusion rates. Flow-pressure curves were plotted from the experiments in which perfusion rate was increased linearly.
Resistance remained relatively constant for the cannula (0.18-0.24 mmHg/microliter/min), the Krupin (0.09-0.25 mmHg/microliter/min), and the Optimed implants (0.04-0.08) throughout the tested flow rates. For the Ahmed device, conversely, resistance decreased proportionally (2.86-0.05 mmHg/microliter/min) to the increase in flow. When flow rate was increased linearly from 0 to 100 microliters/min, the Optimed and Krupin devices as well as the cannula generated a linear pressure response with a constant slope. The pressure in the two devices increased at a rate of 0.11 mmHg/microliter compared to 0.23 mmHg/microliter/min for the cannula. The flow-pressure curve for the Ahmed implant was distinct with a steep initial pressure rise and an essentially constant pressure of 12 mmHg thereafter.
The Optimed and Krupin devices displayed resistance and pressure responses to various flow conditions that were similar to those of a cannula or flow resistor. In these devices, resistance remained relatively stable and pressure increased linearly with flow. The Ahmed device, conversely, functioned as a valve that closely regulated pressure within a desired range by decreasing or increasing resistance as a function of flow.
本研究旨在确定Optimed、Krupin和Ahmed引流装置是否起到阀门的作用，根据血流情况改变阻力，从而将压力维持在所需范围内。
实验研究。
将这三种装置和一个对照套管浸入液体中，使用计算机驱动的仪器用平衡盐溶液进行灌注，该仪器可连续监测流量（Q）和压力（P）。在一组实验中，流速保持在2、5、10、25或50微升/分钟，直至达到稳态压力。在另一组实验中，流速在15至20分钟内从0线性增加至100微升/分钟。
通过第一组实验计算每个植入物的阻力，即通过相继灌注速率之间的压力变化（P）除以流量变化（Q）。根据流速线性增加的实验绘制流量-压力曲线。
在整个测试流速范围内，套管（0.18 - 0.24 mmHg/微升/分钟）、Krupin装置（0.09 - 0.25 mmHg/微升/分钟）和Optimed植入物（0.04 - 0.08）的阻力保持相对恒定。相反，对于Ahmed装置，阻力随流量增加成比例降低（2.86 - 0.05 mmHg/微升/分钟）。当流速从0线性增加至100微升/分钟时，Optimed和Krupin装置以及套管产生具有恒定斜率的线性压力响应。这两种装置中的压力以0.11 mmHg/微升的速率增加，而套管为0.23 mmHg/微升/分钟。Ahmed植入物的流量-压力曲线明显不同，初始压力急剧上升，此后基本保持在12 mmHg恒定。
Optimed和Krupin装置对各种血流情况的阻力和压力响应与套管或流量电阻器相似。在这些装置中，阻力保持相对稳定，压力随流量线性增加。相反，Ahmed装置起到阀门的作用，通过根据流量降低或增加阻力，将压力紧密调节在所需范围内。
