The Department of Otorhinolaryngology - Head & Neck Surgery at The University of Texas Medical School at Houston
Department of Otorhinolaryngology

Optical Rhinometry and Nasal Provocation Testing


Nasal provocation testing (NPT) represents a direct means of evaluating the nasal end organ response to suspected inhalant allergens. The antigen is introduced into the nasal cavity and response in terms of nasal mucosal swelling is then monitored. In a positive hypersensitivity response, the nasal mucosa swells from the influx of venous blood and the cross-sectional area of the nasal airway is reduced. In most European countries, NPT is well standardized and is incorporated into the clinical evaluation of inhalant allergies.¹ The clinical use of NPT in the United States has been limited. Rather, the diagnosis of allergies has relied primarily on history and either skin testing or measurements of serum allergen-specific IgE levels.

Inhalant allergies are first suggested by a clinical history of allergy symptoms such as rhinorrhea, sneezing, watery/itchy eyes, and nasal congestion. For confirmation and identification of inciting allergens, patients undergo either skin or blood testing (modified radioallergosorbent test (mRAST)). Several investigators have argued that skin test results have unreliable correlations with nasal challenges unless coupled with serum IgE levels in a patient with allergic rhinitis symptoms.² Given limitations of skin testing and mRAST for the diagnosis of clinically relevant inhalant allergies, NPT represents an alternative diagnostic tool for inhalant allergies.

The response to NPT is typically assessed by acoustic rhinometry or anterior rhinomanometry. Acoustic rhinometry transforms the analysis of a sound pulse within the nasal cavity to an area-distance plot. However, this technique involves placement of a tube within the anterior aspect of the nasal cavity and malpositioning of the nasal tube can lead to distortion. Anterior rhinomanometry measures the pressure difference between the nasopharynx and the naris and unilateral air flow to calculate the nasal resistance to airflow. Although well standardized, it is not valid in subjects with septal perforations or unilateral complete obstruction.

Optical rhinometry has recently been introduced as a means of assessing nasal airway patency. A wavelength light emitter and an optical sensor are placed across the nasal bridge. One of the 3 wavelengths emitted, 800-nm, corresponds to the isobestic point of hemoglobin. Consequently, changes in hemoglobin within the nasal tissue is measured independent of its oxygenation state. Hemoglobin levels within the nasal tissue provide a means of assessing nasal congestion. Rhinolux (Rhios GmbH, Germany), one such optical rhinometer, assesses nasal airway patency by detecting changes in blood flow into the nasal mucosa.

Schematic representation of the Rhinolux

This image depicts the optical rhinometer. A) Schematics of the optical sensor which consists of an optical emitter and detector that resides in the nasal pieces of a spectacles-like frame B) Optical sensor is placed across the nasal bridge during measurements.

Patient wearing the Rhinolux

Patient wearing the Rhinolux

graph

This is a graphic representation of readings from the optical rhinometer in allergic subject undergoing nasal challenge with histamine and then oxymetazoline in one nasal cavity followed by histamine challenge in the contralateral nasal cavity.

References
  1. Malm, L., R. Gerth van Wijk, and C. Bachert, Guidelines for nasal provocations with aspects on nasal patency, airflow, and airflow resistance. International Committee on Objective Assessment of the Nasal Airways, International Rhinologic Society. Rhinology, 2000. 38(1): p. 1-6. Link
  2. Gergen, P.J. and P.C. Turkeltaub, The association of individual allergen reactivity with respiratory disease in a national sample: data from the second National Health and Nutrition Examination Survey, 1976-80 (NHANES II). J Allergy Clin Immunol, 1992. 90(4 Pt 1): p. 579-88. Link