Characteristics of an In Vivo Canine Model of Phonation With a Constant zyxw Air Pressure Source Sina Nasri, MD; Ali Namazie, MD; Ming Ye, MD; Jody Kreiman, PhD; Bruce R. Gerratt, PhD; Gerald S. Berke, MD Many previous studies of laryngeal biomechan- ics using in vivo models have employed a constant air flow source. Several authorshave recently suggested that the lung-thorax system functions zyxwvu as a constant pressure source during phonation. This study de- scribes an in vivo canine system designedto maintain a constant peak subglottic pressure (Psub) using a pressure-controlling mechanism. Increasing levels of recurrent laryngeal nerve (RLN) stimulationresulted in a significant rise in re- sistance followed by a plateau. For a given p*& flow decreased significantly and precipitously with in- creasing stimulation and then quickly plateaued. VO- cal intensity increased With increasing RLN stim- ulation until a peak was reached. After this peak, intensity dropped until a plateau was reached, corre- sponding to the flow zyxwvuts minimum. At a given Psub, in- creasing levels of RLN stimulation resulted in a nor- mal distribution of vocal efficiencies. LARYNGOSCOPE, 108:746-751,1996 INTRODUCTION Recent debate has centered on the question of whether the lung-thorax system acts as a constant air pressure source or a constant air flow source in provid- ing the vocal tract with the aerodynamic energy need- ed for speech production. The majority of biomechani- cal studies examining pressure-flow characteristics of the larynx have been designed with the flow generated From the Division of Head and Neck Surgery, Stanford University Medical Center (s.N.), Stanford, Calif., and the Division of Head and Neck Surgery, University of California, Los Angeles, School of Medicine (A.N., M.Y., J.K., B.R.G., G.s.B.), Los Angeles. Editor’s Note: This Manuscript was accepted for publication January 5,1996. This research was supported by NIDCD grant #RO1 DC 00855-01. This study was performed in accordance with the US. Public Health Service’s Policy on Humane Care and Use of Laboratory Animals, the Na- tional Institutes of Health‘s Guide for the Care and Use of Laboratory Aui- mals, and the Animal Welfare Act (7 U.S.C. et seq.). The animal use protocol was approved by the Institutional Animal Care and Use Committee of the University of California, Los Angeles. Send Reprint Requests to Sina Nasri, MD, Division of Head and Neck Surgery, Stanford University Medical Center, Stanford, CA 94305-5328. by the lung-thorax system as an independent variable and the subglottic pressure (Psub) as a dependent vari- able, implying that the system is flow regulated.I4 The concept of pressure regulation was supported by the interlabial tube leak experiments of Putnam et a1.6 These investigators discovered that as the cross- sectional area of the leak tube increased, flow through the tube also increased. They concluded that pressure was controlled, while flow was allowed to vary. The concept of active pressure regulation has been more recently challenged by the theory that the lung-thorax unit provides a constant air pressure without the need for any active feedback mechanism.6 In this view, mus- cular activity and the elastic recoil of the lung-thorax unit combine to maintain pressure levels passively. Some authors have assumed a constant pressure source in their theoretic formulations of sound produc- tion. In Ishizaka and Flanagan’s network model for the synthesis of voiced sounds,7 a constant excess pressure in the lungs was employed as an approxima- tion of P&,. The notion of pressure maintenance was addressed in 1986 by Warren.8 He claimed that the primary goal of the lung-thorax system was the regu- lation of air pressure in order to generate a driving force above a minimum level. In another study, War- ren et al.9 assumed that pressures were maintained by reflexive changes in the resistance of the vocal tract or by alterations in the level of muscular contraction. This implied the existence of a feedback mechanism through which the pressure or the acoustic quality of the voice was monitored and regulated. To block the auditory feedback loop, auditory masking studies of articulatory quality were performed.10 These studies demonstrated that peak intraoral pressures remained above a certain level regardless of the auditory mask- ing, suggesting that constant pressures are main- tained without the need for an auditory perceptual feedback regulation mechanism. The present investigation was undertaken to ex- amine the characteristics of a constant pressure source of phonation using an in vivo canine model. The z Laryngoscope 106: June 1996 Nasri et al.: Phonation Model 745