Anatomy & Physiology of a Flexible Scope: Physiologic Function

Each flexible scope contains a number of internal systems that perform the functions specific to its model. Typically, large-diameter insertion tubes contain more internal components and may potentially have larger operating channels.

Light Transmission - All flexible endoscopes have a light transmission component for proper imaging. The light enters the scope, usually at the light guide connector, through the light guide prong. Some specialty, small-diameter flexible endoscopes have a self-contained battery-powered light source for use when access to a cart system is impractical.

Inside the scope, light travels from the light guide prong to the distal end through a light fiber bundle, a collection of thousands of thin, flexible optical glass fibers. Each individual fiber transports a small portion of light, and together they can produce a very intense bright light. The light exits the scope at the distal end through the light guide lenses, which disperse the light evenly across the visual field.

There is no adjustment capacity within the light fiber system in the scope. All light adjustments are made manually on the light source or automatically within the video cart system. Damage to the fibers results in reduced light transmission.

Image Capturing –Imaging is the primary function of the endoscope. An image is captured at the distal end (using the objective lens system) and is then transferred to the image transmission device directly behind the lens system.

Fiber optic endoscopes use an image fiber bundle (similar to the light fiber bundle) to carry the image to an ocular lens at the control body for viewing. Each of the thousands of fibers carries a small portion of the image, and any black on the image represent one broken fiber.

Video endoscopes (videoscopes) are more common today than fiber optic scopes, and image transmission is by video chip and digital image signal. On video endoscopes, the video chip (or CCD) is located directly behind the objective lens assembly at the distal end. Here the image is converted to a digital signal. It travels through signal wires running through the scope to the light guide connector or video connector. The digital signal then connects directly to or through a cable to the video processor on the cart system. The image can be sent to a variety of monitors, printers or remote locations. The Thinking Cap will provide you with a visual image of a yellow submarine to illustrate this process.
Thinking Cap

Endoscope video chips contain from 100,000 to 1 million pixels. More pixels usually mean better image quality, resolution and color reproduction.

Angulation System - All flexible scopes have an angulation system of wires, guided by knobs on the control body. This system manipulates the bending section for insertion and viewing. The knobs are connected inside the control body housing to either a pulley-and-wire system or a gear-and-chain system that connects to the angle wires. The angle wires are braided stainless steel cables that extend from the control body through the insertion tube and connect to the bending ribs at the distal end. Each wire controls one direction of movement, so two opposite wires work together to provide movement up and down, left and right. The angle wires inside the insertion tube are encased within a protective coil pipe that protects the other internal components from the angle wire.

Biopsy/Suction System - The biopsy and suction channels are part of the same internal system. The biopsy channel is a straight piece of uniform flexible tubing running from the distal end to the control body. The suction channel is similar but runs from the control body to the light guide connector. The suction and biopsy channels are joined in the control body and are controlled by the suction valve controls.

An external suction device connected to the suction channel at the light guide connector provides the suction pressure needed to perform biopsy, and suctioned material then travels back through the biopsy channel at the biopsy port opening.

Some small-diameter specialty scopes do not have a biopsy/suction channel system.

Air/Water System - The air and water internal channels are thin flexible tubes running from the light guide connector to the distal end. Although air and water flow through separate tubes, they are controlled by the same valve on the control body. Air and water exit the scope at the distal end through the air/water nozzles, which direct the flow over the objective lens. Most small diameter scopes do not have air/water capability.

Forcep Raiser Function - Some flexible scopes are equipped with a forcep raiser (also called elevator) at the distal end to deflect accessories passed through the biopsy channel. This small metal arm at the biopsy port opening is attached to a wire that runs inside the insertion tube, connects to a control lever on the control body, and operates much like the angulation system controls. The forceps raising function is most commonly found on duodenoscopes and endoscopic ultrasound scopes.

Fluid and Chemical Resistant Seals – Except for the electrical video connections, the entire outer surface of a flexible scope is chemical and fluid resistant. Any seams between parts are sealed by O-rings, and a standard colonoscope may contain over forty of these O-rings. The chemical- and fluid-resistant coatings on the flexible tubes are themselves flexible, and some parts of the scope are sealed with epoxy. The ends of the bending rubber are sealed with silk or nylon braid and then covered with epoxy. Caps or covers are provided to seal the electrical video connections against fluid. The end result is a device that, when undamaged, can be immersed completely in water or cleaning/disinfecting fluid. In this way, the instrument can be reprocessed over and over.

Next Page: Extending the Life of the Flexible Endoscope

Each scope contains a number of internal systems that perform specific physiologic functions.