Vol. 21 • Issue 26 • Page 10
April Gochberg, MA, RRT, could never simply accept conventional wisdom. Twenty years ago, she questioned her respiratory care program professors who insisted lungs simply existed to move air from the mouth to the alveoli for gas exchange.
If form follows function, then why would we possess a complex respiratory system for such a simple job? She wondered whether the lungs, splendidly intricate organs, performed a task that could just as easily be accomplished by a balloon.
“We’ve learned that it is an absolutely perfect system, and every part has a purpose. The lungs manipulate airflow through different angles, adding heat and humidity,” said Gochberg, director of respiratory care at The Christ Hospital in Cincinnati. “We’re dealing with a very delicate system, and everything we do has the potential to cause harm.”
Then 15 years ago, she noticed studies, published in journals like Nature and Journal of Applied Physiology, which applied fractal geometry to the lungs. Even without an advanced math degree, she realized the implications. This more realistic way of viewing the lung had the potential to leap respiratory care and modes of mechanical ventilation forward.
“I became concerned that other professions like radiology could eclipse ours,” she said. “Most key people I talk with have never heard of these concepts. Chaos theory? At best, they might remember the term from a movie.”
Fractals and the RT
Grasping fractal concepts will require a new paradigm for many respiratory therapists.
Mathematically speaking, most people tend to organize the world by Euclidean geometry, which is linear with smooth, straight lines and basically means input equals output, she said. “Linear or Euclidean geometry is a gross simplification of the world around us. Fractal geometry is the geometry of the natural world,” she said. “In ventilation, for example, we take isolated factors like tidal volume and inspiratory time in order to understand them. But the truth is all of those variables happen at once.”
Non-linear math or fractal geometry is foreign to most people. Non-linear math means input is exponentially different from output, like the famous “butterfly effect” that theorizes one flap of an insect’s wings can cause a storm in a distant land. This math proves that initial conditions are critical on output.
In simple terms, a fractal is a rough geometric shape that when split into smaller parts represents a reduced copy of the whole. Created by repetition of simple mathematic algorithms, fractals can describe irregular, real-world objects.
Now don’t worry if that explanation seems a little heady. Computers handle the math so laypeople need only remember that fractals offer insight into natural structures like ferns, flowers, snowflakes and our beloved lungs.
“The beautiful thing about fractal geometry is most of what it talks about can be seen in pictures and nature,” she said. “All you have to do is input the right algorithm.”
For a more respiratory-specific fractal, consider that lungs branch in regular intervals like a tree. That branching follows a mathematical constant called the golden ratio, where the ratio of the two parts equal 1.618. This branching also follows the Fibonacci Sequence-1, 2, 3, 5, 8, 13, 21, 34- so that the sum of the two previous numbers adds up to the third.
“Clinicians are frightened by the mathematical concepts,” said W. Alan Mutch, MD, professor of anesthesiology at the University of Manitoba in Winnipeg, Canada. “And at first it sounds like metaphysics and eastern mysticism, but there is an increasing number of physicians who express interest in this.”
He believes that when you consider how people normally breathe-the variation in timing of every small breath and deep sigh-the process follows a fractal pattern. Then along comes conventional mechanical ventilation in a hospital, and the patient’s natural variation can be obliterated by steady monotonous respiration.
To feel this in action, try this exercise: look at a watch and take identical breaths exactly six seconds apart over and over.
“After two minutes, you’ll drive yourself crazy,” Mutch said. “But that’s what we do when we put people on conventional ventilation.”
Variability and timing of breathing have a fractal signature, meaning a person’s respiratory rate over a month, week or day adheres to a pattern. Ultimately, the variation in the breathing is associated with good health. “Along with heart rate variability, breathing variability can be very accurate ways of tracking outcomes in patients,” he said.
His research into a so-called biologically variable ventilation (BVV) mode incorporates software to allow a ventilator to provide more physiologically natural breathing patterns. It doesn’t change the settings or the patient’s minute ventilation, it just adds variability: If the rate goes up, then the tidal volume goes down and vice versa.
Balloon Vs. Tree
Even the way the lungs inflate follows fractal geometry, said B‚la Suki, PhD, a professor of biomedical engineering at Boston University and another researcher of fractal-based ventilation modes.
“The airways are organized into a fractal tree so the collapsed lung doesn’t expand smoothly like a balloon,” he said. “It inflates in discrete steps, or avalanches, as air enters the gas exchange region through the fractal airway tree.”
He led a study in 1998 to examine ventilation strategies in a computer model of the lung. Conventional ventilation caused smaller airway branches to collapse with increased resistance and reduced gas exchange, but variable ventilation was able to keep the in silico lung open.1“Variable ventilation can be helpful to pop open those blocked alveoli, significantly improving gas exchange,” Suki said.
In several studies, researchers have confirmed BVV can better ventilate lungs in cases of injury or status asthmaticus, but the exact algorithm the computer should use remains elusive.2,3 Or perhaps any variation at all will offer equal benefit. In a study published this year, Mutch and colleagues compared physiology-driven variability to completely random variability, which amounted to white noise. The two modes resulted in no statistical differences.4“You can talk about this in theory, but proving it has been difficult. Truly understanding the underpinnings of BVV requires complex math and real computing power that was not available before,” he explained. “Now clinicians need to see a device so they can measure outcomes.”
One other theory asserts that variability might depend on genetics, tying it to a certain species oreven to a specific
disease state. “If you give some kind of variably, the worst-case scenario is no improvement,” Suki said.
Great Potential
“If the ARDS Network trials proved anything, it was that therapists were kind of barbaric with ventilators. We were destroying the lung,” Gochberg said of findings from a multi-center study.
However, recent years have brought improvements in vent care and a shift to the type of gentler ventilation advocated by the National Heart, Lung and Blood Institute.
Just as RTs have the ability to adopt those lung protective strategies, she feels they can grasp this potentially important evolution too.
“When I speak to therapists about this, they get abuzz,” she said. “They immediately understand the implications.”
Consider that 17 years ago Tom Petty, MD, said chronic obstructive pulmonary disease is not just a lung disease but rather a systemic disease. Fractal geometry might be able to show airway abnormalities long before obstruction occurs.
“How great will it be when you can show 28-year-old smokers what changes have already happened in their lungs and when airflow obstruction will begin?” she asked.
Still, physicians and other health care staff might have difficulty understanding the science, and this means BVV might not become a reality for some time.
“There may be a need for a generational change,” Mutch said. “Most doctors I work with are not comfortable with this level of mathematics.”
It’s essential that RTs understand this concept, Gochberg concluded. “There’s so much more to patient care than meets the eye. Waveforms are just the tip of the iceberg. I’ve been talking to people about fractals for 15 years. If we get left behind, it won’t be anyone’s fault but our own.”
Shawn Proctor, associate editor, can be reached at [email protected].
References
1. Suki B, et al. Life-support system benefits from noise. Nature. (1998; 393, 6681: 127-8).
2. Mutch WA, Buchman TG, et al. Biologically variable ventilation improves gas exchange and respiratory mechanics in a model of severe bronchospasm. Crit Care Med. (2007; 35, 7: 1749-55).
3. McMullen MC, Girling LG, Graham MR, et al. Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation. Anesthesiology. (2006; 105, 1: 91-7).
4. Froehlich KF, Graham MR, Buchman TG, et al. Physiological noise versus white noise to drive a variable ventilator in a porcine model of lung injury. Can J Anaesth. (2008; 55, 9: 577-86).
Fractally Thinking
Terms to keep in mind when thinking about fractal geometry:
• Golden Ratio: a classical mathematical constant when a ratio of two parts equal 1.618.
• Fibonacci Sequence: a set of numbers common in nature. These increase so that the sum of the two previous numbers add up to the third. For example: 1, 2, 3, 5, 8, 13, 21, 34.
• Fractal: a rough geometric shape that when split into smaller parts represents a reduced copy of the whole.
