A multimodal catheter for characterizing airway collapse in obstructive sleep apnea (OSA) was introduced at Photonics West in 2019. This newly developed device showed the potential for improved diagnosis of OSA with the aim to distinguish which patients would benefit from one of the variety of treatments currently available. We build upon these findings and present preliminary results for in-vivo studies that highlight the ability of fiber Bragg grating (FBG) based pressure and temperature measurements to characterize upper airway obstruction during OSA. Significantly, our recent data is derived from a sleep study in a human subject with diagnosed OSA during natural sleep as it is considered that upper airway collapse occurs differently when awake or in a drug induced state. We demonstrate how pressure measurements from 10mm spaced FBGs can determine the location of the site(s) of collapse. Using video recordings from the catheter integrated micro-camera, we also identify the mechanism of collapse and associated anatomical features. Combining the video capture with the simultaneous and temperature independent optical measurements we present evidence of upper airway collapse during natural sleep. It is considered that improved diagnostic data of this kind would advance the ability of clinicians to better guide subsequent therapeutic interventions.