Design, development and validation of a new laryngo-pharyngeal endoscopic esthesiometer and range-finder based on the assessment of air-pulse variability determinants

Abstract

Background: Laryngo-pharyngeal mechano-sensitivity (LPMS) is involved in dysphagia, sleep apnea, stroke, irritable larynx syndrome and cough hypersensitivity syndrome among other disorders. These conditions are associated with a wide range of airway reflex abnormalities. However, the current device for exploring LPMS is limited because it assesses only the laryngeal adductor reflex during fiber-optic endoscopic evaluations of swallowing and requires a high degree of expertise to obtain reliable results, introducing intrinsic expert variability and subjectivity.

Methods: We designed, developed and validated a new air-pulse laryngo-pharyngeal endoscopic esthesiometer with a built-in laser range-finder (LPEER) based on the evaluation and control of air-pulse variability determinants and on intrinsic observer variability and subjectivity determinants of the distance, angle and site of stimulus impact. The LPEER was designed to be capable of delivering precise and accurate stimuli with a wide range of intensities that can explore most laryngo-pharyngeal reflexes.

Results: We initially explored the potential factors affecting the reliability of LPMS tests and included these factors in a multiple linear regression model. The following factors significantly affected the precision and accuracy of the test (P < 0.001): the tube conducting the air-pulses, the supply pressure of the system, the duration of the air-pulses, and the distance and angle between the end of the tube conducting the air-pulses and the site of impact. To control all of these factors, an LPEER consisting of an air-pulse generator and an endoscopic laser range-finder was designed and manufactured. We assessed the precision and accuracy of the LPEER's stimulus and range-finder according to the coefficient of variation (CV) and by looking at the differences between the measured properties and the desired values, and we performed a pilot validation on ten human subjects. The air-pulses and range-finder exhibited good precision and accuracy (CV < 0.06), with differences between the desired and measured properties at <3 % and a range-finder measurement error of <1 mm. The tests in patients demonstrated obtainable and reproducible thresholds for the laryngeal adductor, cough and gag reflexes.

Conclusions: The new LPEER was capable of delivering precise and accurate stimuli for exploring laryngo-pharyngeal reflexes.

Keywords: Accuracy; Airway; Biomedical engineering; Biomedical equipment; Biomedical imaging; Bronchoscopy; Calibration; Deglutition; Endoscopes; Esthesiometer; Fiber lasers; Larynx; Mechanoreceptor; Medical diagnosis; Optical fibers; Pharynx; Range finder; Reflex; Reliability; Repeatability and reproducibility of results; Sensory thresholds; Telemeter.

Figures

Fig. 1

Air-pulse generator block diagram

Fig. 2

Diagram of the LPEER and endoscope assembly, where the air-pulse path (blue) and the optical fiber (red) represent a typical configuration

Fig. 3

Sketch of the different configurations to measure pressures. a Calibration setup, where the tube is connected to the calibration port I2 (see Fig. 1). b Pressure drop measurement using the Kistler probe 7261 using a 3-way stopcock open to the atmosphere. c Assembly to measure the pressure of the air-pulses and the effect of the distance and impact angle. d Assembly similar to that used by Aviv and Hammer to measure the air-pulses [29, 31, 34]. e Assembly to measure the impact force (pressure) using a precision balance. In this last case, the balance plate is horizontal, and the air-pulses arrive from the top. f Picture of the Kistler sensor, where the cover and the transducer can be distinguished. g Sensor MPX2010D, where the air-pulse impacts the cavity hole that is placed in face of the distal end in the Aviv and Hammer studies configuration (d)

Fig. 4

Optical fiber assembly, range-finder polar grid and distance calculation. a Laser optical fiber assembly at the endoscope distal end; b polar grid; and c distance calculation using a pinhole camera model [41]. 1 polar grid, 2 image captured from the target surface, 3 center of the polar grid (coincides with the center of the captured image); the polar grid includes circles corresponding to the estimated distances between the endoscope distal end and the target surface as follows: 5: 1.78 mm (used to center the endoscopic camera), 6 3, 7:6, 8:9, 9:12, and 10:15 mm. 4 Laser spot. Distance calculation: a the distance used in the pin-hole camera model from the focal point (camera point) to the image plane; b the distance between the real point of the laser spot impact and the point of intersection of the camera model axis (endoscope axis) and the object plane axis; c the distance between the point of impact of the laser spot if the laser axis were parallel to the endoscope axis and the real point of impact of the laser spot (only the radial component is considered); L the distance between the laser optical fiber (laser axis) and the axis of the camera (endoscope axis) on the image plane; x the distance between the camera image plane and the object plane in millimeters; and y the distance on the image plane between the centroid of the laser spot and the center of the image in pixels (radius)

Fig. 5

Distance measuring block

Fig. 6

Air-pulse visualization in a dark room using chemical fog. The air-pulse morphology is similar to a vortex ring

Fig. 7

Distance determined using the endoscopic laser range-finder (telemeter) vs distance determined using the high-precision micrometer. The middle line represents the linear regression line and the upper and lower lines represents its 95 % confidence interval (95 % CI)