Assessment of End Expiratory Lung Volumes in Healthy Subjects Using High Flow Oxygen (Vapotherm®)
Condition: Healthy Adult Volunteers
Study type: Interventional

Summary: 
      Respiratory distress is a common problem in an intensive care unit. There are multiple
      mechanisms that are used to help patients who are in respiratory distress including
      mechanical ventilation, continuous positive airway pressure (CPAP), bilevel positive airway
      pressure (BiPAP), high flow oxygen, and oxygen supplementation through nasal cannula or a
      facemask.

      The purpose of this study is to evaluate the mechanism by which Vapotherm, a high flow oxygen
      system, provides breathing support. Vapotherm provides high flow oxygen at different flow
      rates, meaning one can increase the amount of oxygen flow to help with breathing support. The
      investigators believe that this high flow oxygen system may provide similar breathing support
      that a continuous positive airway pressure machine (CPAP) machine does.
    

Detailed description: 
      High flow nasal cannula oxygen therapy (HFNC) is a method of oxygen delivery now commonly
      used in persistently hypoxic patients refractory to conventional modes of oxygen
      supplementation (i.e. nasal cannula, facemask, non-rebreather facemask). Initially used in
      neonates, it is now increasingly popular in the adult population. While the investigators
      know how HFNC provides oxygen supplementation, the physiologic mechanism of correcting
      hypoxemia is still unclear. There are five mechanisms of hypoxemia, four which correct with
      oxygen supplementation - decreased fraction of inspired oxygen (FiO2), hyperventilation,
      ventilation-perfusion (V/Q) mismatch, and diffusion defect; and one that does not - shunt.
      The hypoxemia refractory to supplemental oxygen suggests the presence of physiologic shunt.
      The conventional non-invasive therapy to reduce shunt fraction requires raising
      end-expiratory lung volumes by raising end-expiratory airway pressures using the application
      of continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP).
      The Vapotherm® (Vapotherm®, Stevensville, Maryland) product of high flow oxygen therapy
      (Precision Flow®) is one the investigators frequently use in intensive care units at the
      University of Maryland Medical Center. It does not create a leak proof seal in the nose as
      seen in CPAP and BiPAP. Positive pressure generation has been studied in another high flow
      oxygen system called Optiflow™ (Fisher & Paykel Healthcare, Ltd., Auckland, New Zealand).
      However this device differs from Vapotherm® in that its nasal bores are large and create a
      seal in each nares thereby affected both ventilation and the level of positive end expiratory
      pressure (PEEP) generation. Additionally, these studies measured positive expiratory lung
      pressures, not volume. Positive end expiratory alveolar pressure and increase expiratory lung
      volumes in adults have not yet been demonstrated using Precision Flow®.

      HFNC is intriguing because studies and clinical data have shown it is a relatively
      non-invasive method of oxygen delivery that appears to correct hypoxemia better than other
      non-invasive methods. It is more comfortable than a CPAP machine and thus is better tolerated
      among patients, especially those who are critically ill and possibly altered. While it has
      been used in neonates for some time, its use with adults is new and needs more research.

      The investigators hypothesis is that HFNC corrects persistent hypoxemia by producing
      increased end-expiratory lung volumes thus keeping alveoli open throughout the respiratory
      cycle which other oxygen supplements are unable to do. Using healthy volunteers the
      investigators will measure end expiratory lung volumes on HFNC and compare them to those
      obtained with CPAP at graded pressures.
    

Intervention name(s): HFNC; CPAP
Intervention type(s): Device; Device
Intervention description(s): Graded high flow nasal cannula oxygen at 10, 20 , 30, and 40 liters per minute (LPM) to each subject and end-expiratory lung volume measured by respiratory inductive plethysmography.; Graded contiuous positive airway pressure at 5, 10 , 15, and 20 cm H2O applied to each subject and end-expiratory lung volume measured by respiratory inductive plethysmography.
Other intervention name(s): High flow nasal cannula oxygen, Precision Flow®, Vapotherm®; Continuous positive airway pressure, Respironics(R)
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: None (Open Label)
Primary purpose: Basic Science