Thomas V. Mccaffrey, MD, PhD

It is my pleasure to introduce Dr Ingo Titze as the recipient of this year's American Laryngological Association Award. The purpose of this award is to acknowledge the accomplishments of a distinguished contributor to laryngology. Dr Titze is presently the University of Iowa Distinguished Professor of Speech, Science, and Voice in the Department of Speech Pathology and Audiology and the School of Music. He is also Director of the National Center for Voice and Speech and the Wilbur James School Voice Research Center of the Denver Center for the Performing Arts. His initial training was in electrical engineering, and he received a master's in electrical engineering from the University of Utah and a PhD in physics from Brigham Young University.

His interests in vocal music and speech led him to the Department of Speech Pathology and Audiology at the University of Iowa. He has risen to become the University of Iowa Foundation Distinguished Professor in this department. He has written over 150 articles in scientific journals, primarily relating to the physical basis of the production of speech and voice. He has edited two books on vocal fold physiology and has authored the book entitled Principles of Voice Production. He has been honored as the recipient of the William and Harriet Gould Award for Laryngeal Physiology, the Jacob Javits Neuroscience Investigation Award, the Claude Pepper Award, and the Quintana Award. Dr Titze's unique background as an engineer and physicist interested in the voice production, as well as an active singer himself, has produced a unique perspective on the primary function of the larynx, which is the production of voice. On behalf of the American Laryngological Association, I am happy to present this award to Dr Ingo Titze.

Response Of The Recipient Of The American Laryngological Association Award

Ingo Titze, PhD

I'm very honored and humbled to have this opportunity to be amongst you giants in the field of laryngology. I was introduced to this field about 25 years ago by Hans von Leden, into whose office I stumbled when I was a youngster and wanted to find out what I could learn and how I could contribute to the study of the human larynx, and from then on there have been some 25 years of studies. I want to thank Dr Paul Ward, Dr McCaffrey, and others who have given me this opportunity today, and I feel that the best way that I could honor this society is to take maybe 10 minutes and just give you kind of a quick overview of some of the things that we have discovered in the past and how it relates to surgery on the human larynx. So if you bear with me, I am most comfortable in the scientific domain. If I could just point out some of the fundamental research on the mechanics of the vocal folds and then relate them to some surgical considerations that have resulted.

The first thing that we discovered about 20 years ago is that the vocal fold vibration is based on normal modes in bounded tissue. A normal mode is a very characteristic type of vibration whose amplitude and frequency depend on not only the elastic properties of the tissue, but all of the boundary geometry that is associated with it. As you see here in the two distinct modes of the top plate of a guitar, in mode 1 the entire plate is moving uniformly up and down. The rings indicate that this is moving together. In another mode the left half of the plate is moving in the opposite direction to the right half. That opposite direction, one moving in and one moving out, is always present in this mode. It is a definite characteristic of that bounded medium that is in vibration.

Likewise, in the vocal folds, it has been discovered now that there are two very principal modes of vibration. One you can think of as a compressional mode, where all the tissue vertically is moving in the same direction in and out, and there is no phase difference between the top and the bottom. In the second mode, there is always an opposite movement between the top part and the bottom part of the vocal folds, so the two margins move out of phase by 180 degrees. This is very much like that model structure that you saw in the guitar plate. When you combine these two together, you get the very characteristic movement in the coronal view of the vocal folds that we have come to know and rely on now.

We found that 90% of the vibration of normal vocal fold movement is explained by these two modes. The impact that has had on surgical considerations is that boundaries are very important to the movement. For example, the vocal processes must always be free from obstruction and close together, but not quite touching, in the ideal state. We have also learned that a visually normal vocal fold does not guarantee vibrational symmetry. It's the viscoelastic properties, the properties inside that you don't see, that must also be similar enough to allow the two modes of the left side and the right side to be entrained by the common airflow. Otherwise, we have found that very chaotic vibration can result. The bottom of the vocal fold, the lower margin, should be in a similar abductory position as the top one.

Another discovery had to do with the mucosa, which I call here the epithelium and the superficial layer. Together they serve as the energy transmitter between the airflow and the vocal folds. If you are going to get any energy from the airflow into the vocal folds, to get them to vibrate, then the mucosa must always have this shear mode, as we called it, the out-of-phase mode. Otherwise, there can be no energy transfer from one to the other. This shear mode is facilitated by the biphasic nature that is found in that region, namely, a combination of liquid and solid.

The impact that has on surgical consideration is that first of all, hydration in this mucosal area, both internal and on the surface, is extremely important, and many papers have been written on that now. If any substitute or augmentative material is to be placed in the mucosa, it must be of low viscosity, which translates molecularly into a small molecular size, to assimilate the balance between liquids or proteoglycans and structural glycoproteins, as Dr Gray has recently described in his papers, and the solid nature of the material, which is the extracellular matrix. Of course, we all know already that any type of scar formation must be avoided in the larynx.

If we turn now to the vibration of the mucosa, we see that this can be represented by a model structure with two masses on springs, and notice the deformation of the mucosa in going from one shape to another. Every vibratory cycle is extremely important, and hence the deformation characteristics must be very clearly defined in that tissue.

I would like to now say one thing about the vocal ligament, which has been another major discovery. It has been found that the vocal ligament is the essential member of the vocal folds for high pitches. This is very appropriate for singers. That ligament can support stress at least 10 times greater than the highest active stress that can be found in the laryngeal muscles, either the cricothyroid or the thyroarytenoid. The collagen and elastin fibers in that vocal ligament must be very dense, they must run parallel, and they must be unobstructed in their stringlike vibration. It is also important for the ligament to be relatively thin, so that the cricothyroid muscle can put a lot of tension on this region when it contracts. The surgical implications of this are that injections or implantations near the vocal ligament can encumber its motion. If there are excisions or growths near the ligament, they should not reduce the already thin cross-sectional area, because the chain is no stronger than its weakest link. Any bonding of fibrous material to the ligament should be limited so as not to locally batten it, because that would also encumber its normal mode vibrational structure.

Finally, I would just like to say that for the future, the most exciting research that we are doing is that vocal fold vibration is not only facilitated by what we find in the vocal folds themselves, but is also dependent on the supraglottal airway, and we are finding now that a narrow epilarynx tube, that is, the region in the false folds and the ventricles, can lower the phonation threshold and facilitate phonation. That will have future impact, and there will be recommendations, I am sure, that come forth for resections in the false folds and epiglottal structures that may make it more difficult or more easy to get the vocal folds into vibration.

With that little overview, I would I like to thank you once again for a wonderful quarter-century of research in the larynx, and hope to do another such length of research.