Realistic mouth-throat models developed and validated by Virginia Commonwealth University can be used in place of the USP throat to provide clinically relevant in vitro testing and improved drug deposition prediction. 3D printed polymer and stainless steel models are available.

In both models, the inlet (upstream) accepts the same sized inhaler mouthpiece adaptor used in conjunction with the USP throat inlet. The downstream outlet of both models also connects with a Nephele Mixing Inlet (NMI). The combination of NMI and realistic mouth throat model plus a breath simulator facilitates inhaler testing with both a realistic mouth throat geometry and flow profiles through an inhaler that simulate inhalations (irrespective of the constant flow rate through the cascade impactor).

Models are available in three sizes, Small, Medium and Large. The Small and Large versions are scaled based on the reported mean and standard deviation of airway volumes and dimensions across the normal adult population, as reflected in the Medium model. This allows for testing that reflects the variability observed in in vivo testing across the population.

Polymer Mouth Throat Model Technical Details

Realistic Throat ModelsPolymer mouth throat models are available in three sizes, Small, Medium and Large for use with either the NGI or ACI.

Models are robust and made from solvent-resistant polymer. They are lightly frosted inside to permit coating with artificial mucus, which is widely used in the realistic in vitro evaluation of inhaled products.

Purchasers assume responsibility for solvent compatibility (samples of polymer can be provided) since RDD does not warrant that they are appropriate for particular experimental applications.


Polymer Mouth Throat Models
Small VCU Realistic Mouth Throat Model for NGI VTN-S
Medium VCU Realistic Mouth Throat Model for NGI VTN-M
Large VCU Realistic Mouth Throat Model for NGI VTN-L
Small VCU Realistic Mouth Throat Model for ACI VTA-S
Medium VCU Realistic Mouth Throat Model for ACI VTA-M
Large VCU Realistic Mouth Throat Model for ACI VTA-L

Stainless Steel Realistic Mouth Throat Model Technical Details

Stainless steel mouth-throat models are available in Small, Medium and Large versions.

The interior of the stainless steel models are dimensionally identical to their polymer counterparts but have several design enhancements that provide additional flexibility when designing in vitro studies to assess real-world inhaled product performance. The two-piece design of the stainless steel model allows separation of aerosol into ‘mouth’ and ‘throat’ regions to provide a more detailed picture of aerosol deposition of inhaled particles that do not progress into the cascade impactor. Separation into 'mouth' and 'throat' fractions also facilitates the validation of in silico models.

Using one of two patented downstream adaptors, stainless steel mouth-throat models can be used in conjunction with the Next Generation or Andersen Cascade Impactor, or the adaptor can be omitted to permit direct connection to a Pulmoguardfilter (or equivalent with a 27.3 mm ID patient end connection). This allows for Aerodynamic Particle Size Distribution (APSD) and Total Lung Dose (TLD) to be evaluated using the same mouth-throat model, which reduces cost and potentially improves comparability across data sets.

The stainless-steel models are robust and resistant to a wider range of drug recovery solvents than the polymer models, and the interior surface is amenable to coating with artifical mucus.

Purchasers assume responsibility for solvent compatibility of all mouth-throat models since RDD does not warrant that they are appropriate for particular experimental applications.


Stainless Steel Mouth Throat Models  
Small VCU Realistic Mouth Throat Model VTF-S
Medium VCU Realistic Mouth Throat Model VTF-M
Large VCU Realistic Mouth Throat Model VTF-L
Adaptors for use with Cascade Impactors  
Connector to NGI NGI-C
Connector to ACI ACI-C

Relevant Publications

The Mouth-Throat geometry was developed and described in:

  • In vitro tests for aerosol deposition. I: Scaling a physical model of the upper airways to predict drug deposition variation in normal humans
    Delvadia RR, Longest PW, and Byron PR
    Journal of Aerosol Medicine and Pulmonary Drug Delivery 2012, 25(1): 32-40
  • In vitro prediction of regional drug deposition from dry powder inhalers
    Delvadia RR, Byron PR, Longest PW, and Hindle M
    Respiratory Drug Delivery 2010 (2010), Vol 3: 907-911
  • Stepping into the trachea with realistic physical models: Uncertainties in regional drug deposition from powder inhalers
    Byron PR, Delvadia RR, Longest PW, and Hindle M
    Respiratory Drug Delivery 2010 (2010), Vol 1: 215-224
  • Effects of oral airway geometry characteristics on the diffusional deposition of inhaled nanoparticles
    Xi J, and Longest PW
    ASME Journal of Biomechanical Engineering 2008, 130: 011008
  • Transport and deposition of micro-aerosols in realistic and simplified models of the oral airway.
    Xi J, and Longest PW
    Annals of Biomedical Engineering 2007, 39: 572-591


Nephele Mixing InletsNephele Mixing Inlets allow for variable flow rate, such as that produced by a patient, when used with cascade impactors (NGI and ACI) to establish aerodynamic particle size distribution (APSD) of inhaled drug following inhaler actuation.

When aerosols from inhalers are sampled through realistic throat geometries such as the VCU Realistic Throat Models (above), and in combination with the Nephele Mixing Inlet, investigators can compare the APSD of aerosols that penetrate the throat (and thus enter the lung) under various flow conditions likely to be used by patients.

Technical Details

All Nephele Mixing Inlets are manufactured with hard-anodized aluminum housings and a stainless steel inner nozzle. While all components are intended to be solvent resistant, prolonged exposure to washing solutions and mobile phase should be avoided.

Nephele Mixing Inlets gently merge a particle-free sheath air stream with a second central air stream containing an aerosol, with virtually no turbulence and minimal aerosol losses. A Nephele Mixing Inlet mounted between the aerosol entry port (for example, a VCU Realistic Throat Model or USP throat) and the inlet to the cascade impactor allows the impactor to be operated at a constant flow rate (e.g., 60 LPM) while allowing a lower fixed or variable flow rate to draw aerosol from the inhaler device and throat model. A typical experimental set-up is shown below.

Mixing Inlet Diagram
Experimental Set Up for Breath Profile Simulator – Nephele Mixing Inlet.
Adapted from Olsson et al, Respiratory Drug Delivery 2010, pp 225-234.

Mixing Inlet  
Nephele II Mixing Inlet for Andersen Cascade Impactor NMI-II
Nephele III Mixing Inlet for Next Generation Impactor NMI-III

The Original Nephele Mixing Inlet is available by special order only and requires an adaptor to fit NGI.

Relevant Publications

The Nephele Mixing Inlet has been described in the following studies:


Dosage Unit Sampling ApparatusDosage Unit Sampling Apparatus (DUSA) for Metered Dose Inhalers (MDIs) and Dry Powder Inhalers (DPIs) are used in inhaler testing to determine the amount of drug emitted from an inhaler. DUSAs from RDD Online are compliant with USP Chapter <601> and EP Chapter <0671> specifications.

Technical Details

The standard collection tube and associated caps are manufactured from Dupont™ Delrin®, which is inert, resistant to most solvents, and contains no extractables. Rinsing caps are fitted with fluorinated ethylene propylene (FEP) encapsulated silicone O-ring seals to virtually eliminate leakage and extractables with the majority of drug recovery solvent systems. Caps are quick-seal, ¼ turn to full positive stop: easy to assemble/disassemble reproducibly, independent of the torque applied by the technician.

The compendial method for delivered dose determination from a DPI, requires a 4 kPa pressure drop across the device. The corresponding flow rate through the inhaler can be measured with the Collection Tube with Pressure Tap (NE-D002B). The DUSA for DPIs is capable of sampling at a variety of flow rates up to 100 LPM. Standard Collection Tubes without a pressure tap (NE-D002A) are available for subsequent dose collections, once the test flow rate has been established.

Starter Kits include:

  • One collection tube (DPI Starter Kit also includes Collection Tube with Pressure Tap)
  • One filter support assembly: accommodates filter and readily produces airtight seal, fitted with hose barb to connect to vacuum pump.
  • One cap (with FEP encapsulated silicone seal) with hose barb to connect to a flow meter, which permits easy setting and confirmation of the target airflow rate prior to use of the DUSA.
  • Two rinsing caps (with FEP encapsulated silicone seals)
  • A starter pack of glass fiber filters (25-mm for MDI / 47-mm for DPI)

In practice, most companies usually find it convenient and more efficient to supplement the starter kit described above with additional collection tubes and rinsing caps. The same filter support assembly can be used respectively with multiple DUSAs to achieve faster sample preparation.

Dosage Uniformity Sampling Apparatus



Starter Kit



Collection Tube w/Two Rinsing Caps



DPI Collection Tube with Pressure Tap



Two Rinsing Caps



Filter Support Assembly



Cap with Hose Barb



Set of 10 FEP Encapsulated Silicone Seals



Pack of Glass Fiber Filters




Pediatric Airway Model - RealisticRDD provides computational airway models which can be used to test aerosol deposition, flow field characteristics, or for the construction of computational fluid dynamics (CFD) geometries.

Models are emailed to registrants as attachments in Solidworks (EASM or EPRT) file formats. EASM and EPRT files can be opened and viewed using the free Solidworks' eDrawings Viewer. The eDrawing Viewer can be used to evaluate model dimensions and save models in STL file format, for constructing meshes or rapid prototypes.

Use of these geometries (or similar versions) in publications should cite the relevant studies and that the model was downloaded from this website.

Adult Upper Tracheobronchial (TB) Models

Adult Upper Airway ModelADULT UPPER TRACHEOBRONICHIAL (TB) MODELS were developed by the Respiratory and Aerosol Dynamics Research Group of Virginia Commonwealth University (School of Engineering, led by Dr. Worth Longest).

  • Medium: Original TB geometry based on the measurements of Yeh and Schum (1980) applied to "physiologically realistic bifurcation units" (Heistracher and Hofmann 1995) and scaled to a FRC of 3.5 L (ICRP 1994).
  • Small: Small geometry based on the medium configuration and scaled by a length factor of 0.748.
  • Large: Large geometry based on the medium configuration and scaled by a length factor of 1.165.

Relevant Publications

  • Physiologically realistic models of bronchial airway bifurcations.
    Heistracher T and Hofmann W
    Journal of Aerosol Science 1995, 26(3): 497-509.
  • Human Respiratory Tract Model for Radiological Protection
    Elsevier Science Ltd., New York 1994.
  • Models of human lung airways and their application to inhaled particle deposition.
    Yeh HC and Schum GM
    Bull. Math. Biology 1980, 42: 461–480.

The medium TB geometry was developed and described in:

  • Characterization of respiratory drug delivery with enhanced condensational growth (ECG) using an individual path model of the entire tracheobronchial airways.
    Tian G, Longest PW, Su G, and Hindle M
    Annals of Biomedical Engineering 2011, 39(3): 1136-1153.
  • Development of a stochastic individual path (SIP) model for predicting the tracheobronchial deposition of pharmaceutical aerosols: Effects of transient inhalation and sampling the airways.
    Tian G, Longest, PW, Su G, Walenga RL, and Hindle M
    Journal of Aerosol Science 2011, 42: 781-799.

The small TB model was designed to mate with small MT, medium TB with medium MT and large TB with large MT. In addition one medium model was adjusted to represent the presence of cartilaginous rings in the trachea. The small, medium and large TB geometries were described and used in:

  • In vitro tests for aerosol deposition. I: Scaling a physical model of the upper airways to predict drug deposition variation in normal humans.
    Delvadia RR, Longest PW, and Byron PR
    Journal of Aerosol Medicine and Pulmonary Drug Delivery 2012, 25(1): 32-40.

Pediatric Airway Models

PEDIATRIC AIRWAY MODELS of the pediatric mouth-throat region (oral cavity, pharynx and larynx) and nose-throat region (nasal cavity, pharynx, larynx) that represent this airway region during oral or nasal inhalation from an inhaler were developed in the Pharmaceutical Physics Laboratory of Boehringer Ingelheim Pharma GmbH & Co. KG by the research team consisting of Deborah Bickmann, Andree Jung, and Dr. Herbert Wachtel.

Realistic (5 years): Volume of ~39.8 cm3

Pediatric Airway Model - Realistic

Idealized (5 yrs): Volume of ~50.3 cm3.

Pediatric Airway Model - IdealizedThis value excludes the volume of the mouthpiece holder). The idealized model resembles a re-dimensioned version of the Alberta Throat (Warren Finlay). The idealized MT geometry interfaces an inhaler-dependent mouthpiece adapter. The respective adapters are filled with 2-component silicone resin; in this way they mate the mouthpieces of the inhalers so that there is a zero inhaler insertion depth and zero inhaler angle with respect to the horizontal plane of the mouth of the MT.

Realistic Nose-Throat (5 yrs): Volume of ~22.3 cm3

Pediatric Nose-Throat Geometry

Relevant Publications

Model Request Form


All equipment is supplied according to the following Terms and Conditions:

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RDD Online, LLC warrants only that this RDD® equipment supplied was manufactured in accordance with its specifications. RDD Online, LLC, disclaims all other expressed and implied warranties including the implied warranty of merchantability and fitness for a particular purpose. The sole remedy of the buyer for any breach of this warranty is, at RDD Online’s option, to repair or replace the unit, or to refund the purchase price. This option applies only to new, unused equipment that is returned to RDD Online within 2 months of delivery.

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