## 2 In Vivo Intraglottal/Subglottal Pressure (ISP) Probe  
Figure 1 displays a photograph of the dual-sensor ISP probe and its dimensions. The width of the probe tip was 4.4 mm, and the probe tip length (before curvature began) was 28 mm. The thickness of the probe at the sensor locations was maximally 1.9 mm, which is larger than in previous devices (0.4 mm [7; 8] and 0.29 mm [9]) due to the dimensions of the pressure sensing elements. The larger footprint was deemed satisfactory due to the ultimate placement of the probe on a non-vibrating vocal fold of patients with a unilateral cordectomy. Simultaneous measurement of intraglottal and subglottal pressures was accomplished using two miniature pressure-sensitive sensors originally designed for heart valve and arterial pressure measurement for cardiovascular function assessment (Mikro-Cath Pressure Catheter, Millar, Inc., Houston, TX, USA). The pressure sensing elements consisted of diffused, piezoresistive semiconductors with a dynamic range of \(-\)6.7 kPa to 40 kPa (\(-\)70 cm H\({}_{2}\)O to 400 cm H\({}_{2}\)O) and a flat frequency response up to 10 kHz. The pressure sensing elements are embedded in ovoid capsules 4.8 mm long and 1.17 mm in diameter and are each connected to flexible cables 120 cm long. The two catheters are connected, via extender adapter cables, to a two-channel signal conditioning unit (PCU-2000, Millar, Inc.) that provides electrical isolation, analog knobs for zero control, and a flat frequency response of 0-1000 Hz. The ISP probe specifications are able to sense peak vocal fold impact stresses that have been reported in humans to be in the range of 0.4-3.2 kPa (4-33 cm H\({}_{2}\)O) [7] and subglottal pressures for loud phonation in the range of 0.6-1.5 kPa (5.9-15.4 cm H\({}_{2}\)O) [18]. Calibration of the pressure sensors is typically performed to account for sensor enclosures (e.g., silicone embeddings) by submerging the probe in a graduated cylinder filled with water, noting the voltage level at a given submergence depth (i.e., hydrostatic pressure) for each sensor, and computing a best-fit line to the data. The two pressure sensors were placed inline at the exposed distal end of a custom rigid cannula whose curvature was designed to match that of a common laryngeal injector device typically used in outpatient settings for the injection of materials to medialize a paralyzed vocal fold [19]. The sensors were positioned 7.6 mm apart so that the distal sensor would not touch the vocal folds (thus, measuring  
Figure 1: In vivo intraglottal/subglottal pressure (ISP) probe with inline, dual pressure sensors at the tip (arrows) for simultaneously measuring intraglottal and subglottal pressure during phonation. Shown are (**a**) the ISP probe with a Ford injector-like handle and two-channel signal conditioning electronics and (**b**) a zoomed-in view of the distal end of the ISP probe showing dimensions of the two inline pressure sensors embedded in epoxy. the aerodynamic subglottal pressure), while the proximal sensor would be positioned intraglottally to measure vocal fold collision pressures during phonation. The sensing elements of the Mikro-Cath devices employed are directional and, thus, sensitive to pressures on only one side of each capsule. We are planning to use the probes in patients who have had a hemi-laryngectomy to treat laryngeal cancer. The resulting laryngeal anatomy of these patients will allow the position of the probe to be more easily stabilized against the nonvibrating side of the glottis (mimicking an excised hemi-larynx setup) instead of trying to position the probe between two vibrating vocal folds, which has proven to be extremely challenging in previous studies (e.g., interferes with phonation) [7; 9]. The ISP probe displayed in Figure 1 is a right-handed probe designed to record from patients with a left unilateral cordectomy, where the intraglottal pressure sensor comes into contact with the functioning right vocal fold during phonation.