sid khosla, md
Published on November 27, 2016
Paradoxical vocal fold motion (PVFM) is also known as vocal cord dysfunction (VCD). PVFM/VCD is often misdiagnosed as asthma. It is characterized by abnormal closing of the vocal folds during breathing which causes an airflow obstruction at the level of the larynx. Patients with this disorder complain of not being able to “take air in.”
This video features Dr. Sid Khosla, an associate professor of otolaryngology at the University of Cincinnati. He is nationally known for his expertise in vocal fold and airway reconstruction. His lab is looking at how the vortices change under different asymmetries in unilateral vocal fold paralysis (UVFP) and how effective treatments are in restoring the vortices. He was gracious to answer my question about the video.
Note: The terms vocal cord and vocal fold are synonymous.
TVF: Dr. Khosla, what an interesting video! How is the jet engine technology applied to surgical treatment of PVFM?
Your question is a great one that has a mildly convoluted answer. I have sent you two geeky articles (unfortunately the simplest I can find) that explain how our work is helping treat UVFP (Khosla, S., Oren, L. and Gutmark, E., 2014. An example of the role of basic science research to inform the treatment of unilateral vocal fold paralysis. SIG 3 Perspectives on Voice and Voice Disorders, 24(1), pp.37-50), and my trio thesis on our idea about vortices (Khosla, S., Oren, L., Ying, J. and Gutmark, E., 2014. Direct simultaneous measurement of intraglottal geometry and velocity fields in excised larynges. The Laryngoscope, 124(S2), pp.S1-S13). Since that initial work , it turns out the main goal of vortices is increasing efficiency (it tuns out opera singers use this vortex mechanism more than musical theater singers but that is a different story).
1. In engineering, including aerospace or fluid mechanics (often the same things), vibrations can occur due to something called flow structure oscillations - in the case of vocal fold vibration, the adductors bring the folds together - that is active, but if the conditions are right, air going through the folds then causes vibration (just due to the fact that airflow through the folds changes intraglottal pressures which change intraglottal geometry which changes airflow which changes intraglottal pressure etc… This is known as a flow structure interaction (FSI).
2. Bernoulli plays a role in vocal fold vibration during opening but not during most of closing. During mid to late closing, if the glottis is divergent (divergent shape is what we learn, but it can also be straight), then Bernoulli does not apply. By experiments, we know in divergent folds, that the most negative pressure is in the superior glottis, but Bernoulli suggests that it appears in the inferior glottis. My trio thesis shows why Bernoulli does not apply during closing and that the reason for the negative pressure superiorly during closing is vortices. Rotational flow (also known as vortices) can create negative pressures (like a tornado).
3. Vortices can do two things that are studied in aerospace. One is that vortices cause noise - this is the cause of jet noise and is described by a field known as aeroacoustic. The second is that vortices can cause lift forces but it can also cause bad forces on the wing (which happens when the plane vibrates "experiencing turbulence") it also happens if a plane flies too close because the jet wake is made up of vortices. The field that studies the flow structure interactions (either vibration or collapse) is known as aeroelasticity.
4. The trio thesis describes that vortices form whenever you go from small to large area, but collapse or vibration will also happen if the material is floppy or if the area is below a critical area. In addition to the vocal fold work, which uses aeroelasticity to study vibrations (both experimentally and theoretically), we use aeroelasticity to study dynamic airway collapse in obstructive sleep apnea or in cases such as laryngomalacia (“soft larynx” - immature development of the cartilage of the upper larynx). Aryepiglottic (AE) fold is a triangular opening at the entrance of the larynx. In inspiration with supraglottic collapse you are probably going from small area between the AE folds ( the smaller area due to more collapsible tissue) and larger area (due to the space between AE fold and false fold or AE fold and ventricle).
5. Paradoxical vocal fold motion (PVFM) also known as vocal cord dysfunction (VCD) has multiple causes, but in cases such as laryngomalacia or obstructive sleep apnea (OSA), both aeroelasticity and neurology are involved whereas in classic VCD, there is a large neurological component.
6. In adults, we do see supraglottic collapse in a variety of configurations (anteroposterior, medial lateral, some combo) that is likely mostly mechanical, but this woman was the worst I saw. She would breathe in normally and her false folds would collapse medially to close the membranous gap and the arytenoids flopped anteriorly. The first operation, I found the thickest AE fold muscle I have ever seen) I resected part of the muscle and most of the AE fold bilaterally. It opened up the membrane fold area and she felt better but not great - after the first surgery. In the second surgery I took off some of the medial surface off the superior arytenoid). That solved the collapse but she still did not feel that she got a deep breath (although she could do much more)
7. So this is much more mechanical than regular PVFM. Aerospace studies how airflow causes vibration or forces - we use similar experimental and computation approaches to study how airflow causes tissue oscillations or collapse. I used some of these principles (although they may be very obvious intuitively - certainly the first operation, I am not sure that the second is completely intuitive.
TVF: I can't wait to study your papers. This interview shall be continued….