A Virtual Voyage Into the Lungs
By David Brown
The first landmark on the tour is the vocal cords, the A-shaped portal to the trachea and the labyrinthine world of the lungs that lies beyond.
The fiber-optic bronchoscope slides through cords without problems. It's time to pause briefly, take a deep breath and look around. But whoa! What's happening now? The patient is coughing, and the image of his trachea on the video screen looks as if it's being buffeted with gale-force winds.
Oops. Guess we didn't give enough local anesthetic on the way down. A little more lidocaine you can see it squirt out through one of the "ports" on the bronchoscope's tip and all's calm again. The only motion is a faint rocking of the left-hand side of the image on the screen. It's the heart, beating unseen and insistently a few inches from where we're stopped right now.
Next up is the right mainstem bronchus, the route into the right lung.
A trip into the human lungs is exciting under any circumstances. What's especially amazing about this one is that it's happening inside a "virtual" chest cavity. The patient stretched before us consists of a rubber manikin face attached to a six-foot metal box.
The box is not nearly wide enough to contain a model of the human lungs. And it's unlikely to contain a beating artificial heart. So what's in it?
"It's full of trade secrets," says Joseph L. Tasto, a physician and engineer at HT Medical Systems in Rockville. He declines to lift the top. But one fact is known. This virtual tour of the respiratory tree is possible only because of the Visible Human Project.
HT Medical's bronchoscopy simulator is one of the most dramatic applications of the Visible Human Project, which has rendered thousands of images of human anatomy into digital code.
In the next decade, other computerized simulations using the enormous data base 15 gigabytes (about 120 billion digital units, or bits) for the man, 40 gigabytes for the more detailed woman are likely to make their way into medical education. The applications may allow people to insert endotracheal tubes, start intravenous lines, perform colonoscopies all without risk or pain to real patients.
Bronchoscopy is done hundreds of times a year in most large hospitals, primarily to find and biopsy lung tumors. It's occasionally also used to diagnose lung infections or identify sites of bleeding.
In the procedure, a thin fiber-optic tube is pushed through a nostril into the back of the throat and then into the trachea. From there, the doctor can explore the bronchi and their segments, which eventually become too narrow to accommodate the scope. The doctor controls the scope's direction by bending its tip, via a linkage that comes up the tube, and then advancing the entire tube.
Imagine standing in your front door and exploring the downstairs of your house with a garden hose whose tip you control only crudely. That's more or less what bronchoscopy is like.
This procedure is an especially good candidate for simulation because a physician performing ite has a limited repertoire of physical manipulations and must rely on a limited amount of sensory feedback to tell how it's going. All of those inputs and outputs can be reproduced when the vast detail of the Visible Human data set is married to clever programming, robotics and electronics.
In the simulation, a real though somewhat modified bronchoscope is threaded through the manikin's nostril and into the chest cavity box. Images it encounters are endowed with tactile properties.
For example, the inner surface of the trachea has a specific resistance, and when the bronchoscope tip "touches" it during the virtual examination, the person holding the scope feels the physical resistance. The program can further stipulate that. if local anesthetic hasn't been dripped in at the right place and in the right amount, that "touch" will stimulate a cough.
The bronchoscope's lens tip occasionally fogs during the simulated procedure, as it does in real life, and can be cleared with a squirt of virtual saline from one of the ports. The simulator even allows the operator to biopsy a virtual tumor with a virtual alligator forceps that, as in the real instrument, is one of the hand controls. The biopsy site then bleeds.
E. James Britt, a pulmonary physician at the University of Maryland School of Medicine in Baltimore, has tried the HT Medical simulator and provided consultative advice to the company. It will be a useful training tool, he believes.
"The model only responds well to the appropriate hand motions so that a lot of wasted motion doesn't get you very far," he said recently. "It's realistic enough, in terms of a driving challenge, to separate people based on their skills."
At the moment, physicians who complete the three years of fellowship training required to become a pulmonary specialist don't have their bronchoscopy skills directly tested when they apply for certification. In the future, simulators will make that possible and probably mandatory.
The more immediate use for the devices, however, is to teach people how to do the procedure. Currently, plastic models are used for that purpose, but they never change. At about $27,000, a simulator is far more expensive than a model but also far more versatile. It can be programmed to offer examinations on dozens of different virtual patients, each with its own dimensions, limitations and complications.
Britt says 75 to 100 bronchoscopies are required for a person to become proficient. The first 25 teach the basic of eye-hand coordination of the procedure. In the second 25, a trainee learns how to do a routine case. The last 25 to 50 provide skills and confidence to handle at least some unexpected problems.
Bronchoscopy is a safe procedure, with few deaths or serious complications. But it's not risk-free. Furthermore, the ability to do it quickly can come in very handy when a patient is very ill.
"Any device that allows you to make more bronchoscopists facile sooner is an advantage," Britt says, "mostly for the comfort of the patients."
© Copyright 1999 The Washington Post Company