## 4 Discussion and Future Work
### Recommendations for In Vivo Assessment of Sensor Location  
Nevertheless, there are features within the intraglottal pressure signal that can guide an investigator and help identify when the location of peak contact pressure has been located. Notably, a double-peak should be present in the signal, with the magnitude of the primary contact peak on the order of the subglottal pressure, although VF posturing and medial compression can lead to variations in these ratios. Instructions given to a participant to phonate using pressed versus breathy voice at the same vocal effort during clinical investigations can exploit this dependency by correspondingly amplifying or decreasing the primary contact peak, respectively, while not affecting the magnitude of the secondary peak. This approach may aid in identifying the primary contact peak and thereby aid in locating sensor placement relative to the peak contact pressure location. Additional strategies to aid in sensor placement during clinical examination have been devised, such as placing two sensors on a probe, separated in the inferior-superior direction, to identify both the subglottal and contact pressure simultaneously, thereby guiding probe location through a comparative approach between the two signals [54].  
Probe size relative to inferior-superior contact length should also be carefully considered. While a smaller probe is advantageous in that it provides a higher spatial resolution of the VF contact pressure, positioning becomes increasingly difficult. Contrarily, it is imperative that any pressure probe utilize a dimension in the inferior-superior length that is smaller than the inferior-superior contact length, to avoid biasing the signal by simultaneously measuring the VF contact pressure and the subglottal and/or supraglottal pressure.  
These findings highlight the importance of: (1) utilizing an independent measure to verify contact that is not dependent upon visual observation; (2) designing intraglottal pressure sensors/approaches to prevent disruption of contact mechanics due to intrusion of the physical probe; and (3) considering how the size and positioning of a contact sensor relative to inferior-superior VF contact length may influence the measurement and interpretation of contact pressure results.  
Finally, an additional concern that exists with the Millar Mikro-Cath(tm), but that has not been addressed up to this point, is the sensitivity of the pressure transducer to temperature variations. The benchtop nature of the current investigations facilitated maintaining the transducer at a constant temperature so as to mitigate this problem. The pressure transducer has a quoted temperature sensitivity of \(\pm\)0.27 kPa for a temperature variation from 25-40 \({}^{\circ}\)C. Care should therefore be taken when implementing it in _in vivo_ investigations where thermal shifts may arise due to radiative heat transfer from the lighting source to the transducer, as well as convective heating/cooling due to the warm glottal environment, and the airflow that is passing over the transducer. A strategy for addressing this concern is to zero the signal from the sensor while it is immersed in warm water that is equal to the anticipated/measured temperature of the air passing through the glottis. If this is performed immediately prior to any measurements, it will minimize uncertainties arising from thermal drift.