Effects of Lung Volume on Upper Airway Patency During Drug Induced Sleep Endoscopy

DEVICE

Negative Pressure Ventilator

The negative pressure ventilator is an off-the-shelf FDA-approved device designed to treat respiratory patients with hypoventilation syndromes. This ventilator places the torso within a fixed container that is connected to a vacuum source, which inflates the lungs by pulling a negative pressure around the chest and abdomen. After the clinically routine DISE, a negative pressure ventilator will be placed on the participant's chest to increase lung volumes and the DISE evaluation will be repeated to observe changes.

DEVICE

Pulmonary Function Testing (PFT)

PFT is a routine standardized clinical test evaluating lung function, consisting of two parts: spirometry and body plethysmography. In spirometry, participants breathe through a mouthpiece that measures airflow and volume to determine normal and maximal volume of inspiration/expiration. Body plethysmography is performed to calculate residual lung volumes. Participants enter in an enclosed chamber where they breathe through a mouthpiece. Changes in pressure in the sealed chamber during breathing are used to calculate the volume of air that remains in the lung after expiration. A MiniBox+ device may be used. The MiniBox+ device derives total lung capacity (TLC) during tidal breathing by the analysis of gas pressures and airflows immediately preceding and immediately following airway occlusions to calculate the same measures as conventional PFT analysis.

DEVICE

Transcutaneous Phrenic Nerve Stimulation

Phrenic nerve stimulation (PNS) will be performed transcutaneously using a commercially available and FDA approved peripheral neurostimulator. (Digitimer DS8R Bipolar Constant Current Stimulator). The neurostimulator consists of a stimulation generating box connected to electrodes that will be placed over the skin of the neck bilaterally over both phrenic nerves where an bipolar electric current will be used to stimulate the phrenic nerve leading to diaphragm contraction.

Expiratory Reserve Volume (ERV)

Time frame: During PFT

ERV is the volume of extra air that can be forcefully breathed out after exhaling normally. ERV is impacted by body size and altitude and the normal range for adults is about 0.7 to 1.1 liters (L). ERV is obtained as part of the pulmonary function test.

Functional Residual Capacity (FRC)

Time frame: During PFT

FRC is the amount of air remaining in the lungs after a normal exhalation. FRC is impacted by body size and altitude and the normal volume for adults is about 1.8 to 2.4 L. FRC is obtained during the pulmonary function test and is the sum of residual volume (RV; the volume of air remaining after maximum exhalation) and ERV.

Change in VOTE Collapse Patterns - Degree of Obstruction

Time frame: During clinical DISE and intervention DISE

VOTE collapse patterns are obtained during the routine clinical DISE evaluation and during DISE with negative pressure ventilation. The VOTE classification codes degree of obstruction as 0 = no obstruction (no vibration), 1 = partial obstruction (vibration), and 2 = complete obstruction (collapse). Degree of obstruction is determined the velum, oropharynx lateral walls, tongue base, and epiglottis. The measurements obtained without and with negative pressure ventilation will be compared.

Change in VOTE Collapse Patterns - Configuration of Obstruction

Time frame: During clinical DISE and intervention DISE

VOTE collapse patterns are obtained during the routine clinical DISE evaluation and during DISE with negative pressure ventilation. The VOTE classification codes configuration of obstruction for structures with a degree of obstruction greater than 0. The configuration of obstruction is categorized as anteroposterior (anterior structures moving posteriorly against pharyngeal wall), lateral (lateral structures moving towards airway center), or concentric (both anteroposterior and lateral movements). The measurements obtained without and with negative pressure ventilation will be compared.

Change in Critical Closing Pressure (Pcrit)

Time frame: During clinical DISE and intervention DISE

Critical closing pressures are obtained during the routine clinical DISE evaluation and during DISE with negative pressure ventilation. Pcrit assessed pharyngeal collapsibility and is measured as centimeters of water (cm H2O). A Pcrit of less than -10 cm H2O indicates normal breathing. Patients with a Pcrit around -6cm H2O tend to snore but not have OSA. A Pcrit around or greater than 0 cm H2O is seen with obstructive sleep apnea.The measurements obtained without and with negative pressure ventilation will be compared.

Change in Pharyngeal Opening Pressures

Time frame: During clinical DISE and intervention DISE

Pharyngeal opening pressures are obtained during the routine clinical DISE evaluation and during DISE with negative pressure ventilation. Opening pressures are obtained using a positive airway pressure (PAP) titration device. Pharyngeal opening pressures are defined as the minimally effective positive airway pressure that results in non-flow limited breathing. This is measured in cm H2O and ranges from 0 to 25 cm H2O, with 25 cm H2O being the maximum pressure the PAP machine is capable of generating. The measurements obtained without and with negative pressure ventilation will be compared.

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