Clinical characterization of respiratory large droplet production during common airway procedures using high-speed imaging

During the COVID-19 pandemic, a significant number of healthcare workers have been infected with SARS-CoV-2. However, there remains little knowledge regarding large droplet dissemination during airway management procedures in real life settings. 12 different airway management procedures were investigated during routine clinical care. A high-speed video camera (1000 frames/second) was for imaging. Quantitative droplet characteristics as size, distance traveled, and velocity were computed. Droplets were detected in 8/12 procedures. The droplet trajectories could be divided into two distinctive patterns (type 1/2). Type 1 represented a ballistic trajectory with higher speed large droplets whereas type 2 represented a random trajectory of slower particles that persisted longer in air. The use of tracheal cannula filters reduced the amount of droplets. Respiratory droplet patterns generated during airway management procedures follow two distinctive trajectories based on the influence of aerodynamic forces. Speaking and coughing produce more droplets than non-invasive ventilation therapy confirming these behaviors as exposure risks. Even large droplets may exhibit patterns resembling the fluid dynamics smaller airborne aerosols that follow the airflow convectively and may place the healthcare provider at risk.

The Laryngectomee Substitute Voice: Image Processing of Endoscopic Recordings by Fusion with Acoustic Signals

Objectives: The most radical cancer therapy of the throat is the total excision of the larynx which postoperatively results in the loss of voice. A widely-used method of voice rehabilitation is the insertion of a silicone valve, which establishes an unidirectional connection between trachea and esophagus. Thus, during exhalation, air can be directed from the trachea into the esophagus. This air stream excites tissue vibrations of the esophagus and the hypo-pharynx which act as a substitute voice generator. Purpose of the current study is to present a technique for visualizing the dynamics of the substitute voice generating element.

Methods: Digital high speed videos of the vibrating tissue are simultaneously recorded with the emitted acoustic signal. The high speed sequences are directly evaluated by a three-step knowledge based algorithm. It considers correlation between image and acoustic data, information about the gray value of each pixel, and continuity of tissue vibration. The temporal properties of an image series are investigated by evaluating the time dependent gray value at each pixel position.

Results: The applicability of the algorithm is exemplar-ily demonstrated using the data of one male patient. It enables the identification of the regions within an image series which are mainly responsible for the acoustic signal. Additionally, the dynamics of tissue vibrations are visualized. The main propagation direction can be clearly identified.

Conclusions: The new methodology summarizes the information about endoscopic and acoustic recordings of substitute voice into a single image. The results allow a first estimation of tissue velocity and elastic properties of oscillating tissue.

Normal Voice Production: Computation of Driving Parameters from Endoscopic Digital High Speed Images

Objectives: A central point for quantitative evaluation of pathological and healthy voices is the analysis of vocal fold oscillations. By means of digital High Speed Glottography (HGG), vocal fold oscillations can be recorded in real time. Recently, a numerical inversion procedure was developed that allows the extraction of physiological parameters from digital high speed videos and a classification of voice disorders. The aim of this work was to validate the inversion procedure and to investigate the applicability to normal voices.

Methods: High speed recordings were performed during phonation within a group of five female and five male persons with normal voices. By using knowledge based image processing algorithms, motion curves of the vocal folds were extracted at three different positions (dorsal, medial, ventral). These curves were used to obtain physiological voice parameters, and in particular the degree of symmetry of the vocal folds based upon a biomechanical model of the vocal folds.

Results: The highest degree of symmetry was observed for the medial motion curves. While the dor-sally and ventrally extracted motion curves exhibited similar results concerning the degree of symmetry the performance of the algorithm was less stable.

Conclusions: The inversion algorithm provides reasonable results for all subjects when applied to the medial motion curves. However, for dorsal and ventral motion curves, correct performance is reduced to 85 %.

[Impact of functional mass lesions in professional female singers : Biomechanics of vocal fold oscillation in the register transition regions]

BACKGROUND

The influence of functional mass lesions on vocal fold oscillation patterns in vocally challenging tasks is not yet understood in detail.

MATERIALS UND METHODS

Glissandi on the vowel [a:] from 220 to 440 Hz and 440 to 880 Hz were analyzed in three groups of four professional female singers: without a mass lesion or dysphony (group A), with a functional mass lesion (swellings without a great impact on oscillation patterns during stroboscopy; group B), and with organic dysphony (group C). High-speed digital imaging (HSDI; 20,000 fps), and acoustic and electroglottographic (EGG) signals were used for analysis. Based on the EGG sample entropy, time windows for analysis of register transition phenomena were constructed. The voice signals (glottal area waveform, GAW; acoustic and EGG signals) were perceptually rated in terms of the noticeability of registration events.

RESULTS

The absolute sample entropy revealed maxima in fundamental frequency regions where register transitions typically occur. Groups A and B could be distinguished neither by perceptual rating nor based on sample entropy values. In comparison to the other two groups, the absolute sample entropy values of group C were greater in the lower glissando. However, the larger vocal fold oscillatory irregularities were observable for the upper glissando in this group.

CONCLUSION

Functional mass lesions do not influence biomechanics adversely in vocally challenging tasks such as register transitions. The use of sample entropy as a criterion for detection of register transitions is promising, but needs further validation.

[3D visualization and analysis of vocal fold dynamics]

BACKGROUND

Visual investigation methods of the larynx mainly allow for the two-dimensional presentation of the three-dimensional structures of the vocal fold dynamics. The vertical component of the vocal fold dynamics is often neglected, yielding a loss of information. The latest studies show that the vertical dynamic components are in the range of the medio-lateral dynamics and play a significant role within the phonation process.

OBJECTIVES

This work presents a method for future 3D reconstruction and visualization of endoscopically recorded vocal fold dynamics.

MATERIALS AND METHODS

The setup contains a high-speed camera (HSC) and a laser projection system (LPS). The LPS projects a regular grid on the vocal fold surfaces and in combination with the HSC allows a three-dimensional reconstruction of the vocal fold surface. Hence, quantitative information on displacements and velocities can be provided. The applicability of the method is presented for one ex-vivo human larynx, one ex-vivo porcine larynx and one synthetic silicone larynx.

RESULTS

The setup introduced allows the reconstruction of the entire visible vocal fold surfaces for each oscillation status. This enables a detailed analysis of the three dimensional dynamics (i. e. displacements, velocities, accelerations) of the vocal folds.

CONCLUSIONS

The next goal is the miniaturization of the LPS to allow clinical in-vivo analysis in humans. We anticipate new insight on dependencies between 3D dynamic behavior and the quality of the acoustic outcome for healthy and disordered phonation.

Investigation of prescribed movement in fluid-structure interaction simulation for the human phonation process

In a partitioned approach for computational fluid-structure interaction (FSI) the coupling between fluid and structure causes substantial computational resources. Therefore, a convenient alternative is to reduce the problem to a pure flow simulation with preset movement and applying appropriate boundary conditions. This work investigates the impact of replacing the fully-coupled interface condition with a one-way coupling. To continue to capture structural movement and its effect onto the flow field, prescribed wall movements from separate simulations and/or measurements are used. As an appropriate test case, we apply the different coupling strategies to the human phonation process, which is a highly complex interaction of airflow through the larynx and structural vibration of the vocal folds (VF). We obtain vocal fold vibrations from a fully-coupled simulation and use them as input data for the simplified simulation, i.e. just solving the fluid flow. All computations are performed with our research code CFS++, which is based on the finite element (FE) method. The presented results show that a pure fluid simulation with prescribed structural movement can substitute the fully-coupled approach. However, caution must be used to ensure accurate boundary conditions on the interface, and we found that only a pressure driven flow correctly responds to the physical effects when using specified motion.

Pipette aspiration applied to the characterization of nonhomogeneous, transversely isotropic materials used for vocal fold modeling

The etiology and treatment of voice disorders are still not completely understood. Since the vibratory characteristics of vocal folds are strongly influenced by both anatomy and mechanical material properties, measurement methods to analyze the material behavior of vocal fold tissue are required. Due to the limited life time of real tissue in the laboratory, synthetic models are often used to study vocal fold vibrations. In this paper we focus on two topics related to synthetic and real vocal fold materials. First, because certain tissues within the human vocal folds are transversely isotropic, a fabrication process for introducing this characteristic in commonly used vocal fold modeling materials is presented. Second, the pipette aspiration technique is applied to the characterization of these materials. By measuring the displacement profiles of stretched specimens that exhibit varying degrees of transverse isotropy, it is shown that local anisotropy can be quantified using a parameter describing the deviation from an axisymmetric profile. The potential for this technique to characterize homogeneous, anisotropic materials, including soft biological tissues such as those found in the human vocal folds, is supplemented by a computational study.

Measurement of the elasticity modulus of soft tissues

A measurement setup combined with a Finite Element (FE) simulation is presented to determine the elasticity modulus of soft materials as a function of frequency. The longterm goal of this work is to measure in vitro the elasticity modulus of human vocal folds over a frequency range that coincides with the range of human phonation. The results will assist numerical simulations modeling the phonation process by providing correct material parameters. Furthermore, the measurements are locally applied, enabling to determine spatial differences along the surface of the material. In this work the method will be presented and validated by applying it to silicones with similar characteristics as human vocal folds. Three silicone samples with different consistency were tested over a frequency range of 20-250 Hz. The results of the pipette aspiration method revealed a strong frequency dependency of the elasticity modulus, especially below 100 Hz. In this frequency range the elasticity moduli of the samples varied between 5 and 27 kPa.

[Basic research on vocal fold dynamics: three-dimensional vibration analysis of human and canine larynges]

BACKGROUND

The understanding of normal and pathological vocal fold dynamics is the basis for a pathophysiological motivated voice therapy. Crucial vocal fold dynamics concerning voice production occur at the medial part of the vocal fold which is seen as the most critical region of mucosal wave propagation. Due to the limited size of the larynx the possibilities of laryngeal imaging by endoscopic techniques are limited.

MATERIAL AND METHODS

This work describes an experimental set-up that enables quantification of the entire medial and superior vocal fold surface using excised human and in vivo canine larynges.

RESULTS

The data obtained enable analysis of vocal fold deflections, velocities, and mucosal wave propagation. The reciprocal dependencies can be examined and different areas of vocal fold dynamics located. The vertical components obscured in clinical endoscopy can be visualized. This is not negligible.

CONCLUSIONS

In particular it is shown that the vertical deflection, which cannot be observed by clinical examination, plays an important part in the dynamics and therefore cannot be omitted for therapeutic procedures. The theoretically assumed entrainment and influence of the two main vibration modes enabling normal phonation is confirmed.

High-speed video analysis of the phonation onset, with an application to the diagnosis of functional dysphonias

An objective method for the diagnosis of functional dysphonias is presented. The mathematically motivated approach was evaluated on 71 female subjects with normal voice or functional dysphonia. Using digital high-speed recordings, the phonation onset process was recorded in real-time for 8-10 different sound pressure levels for each subject. From these recordings two parameters were mathematically estimated, reflecting the phonation onset dynamics. The growth of the vocal fold amplitudes during the phonation onset process was described by a parameter a for which its lower threshold value a(th) was extrapolated. This threshold reflects the myoelastic tonus within the vocal folds. The second parameter was the maximum sound pressure level L(max). It allows conclusions on voice efficiency with respect to the necessary subglottal pressure and the myoelastic forces. Due to the significant differences of these parameters between the pathological groups and normal voices, the presented method is a stable and objective tool for medical diagnosis.

[Diagnosis of functional voice disorders by using the high speed recording technics]

INTRODUCTION

Malfunctions of the human voice with unknown causes are denoted by "functional voice disorders". The high speed video imaging technique (HVT) allows the recording of the oscillating vocal folds in real time. A new method is presented, describing different types of oscillation and their onset mathematically. A precise classification of the kind of functional voice disorders is possible.

METHODS

For 71 young women, from the HVT recordings two parameters were mathematically estimated, reflecting the phonation onset dynamics: The threshold value A(th), corresponding with the myoelastic tone of the vocal folds and a maximum sound pressure level of speech L(max), characterising the efficiency of voice.

RESULTS

Both values are sensitive for functional voice disorders and enable a differentiation between these pathologies.

DISCUSSION

Significant differences of the computed parameters between the pathological groups and normal voices substantiate the presented method as a stable and objective tool for medical diagnosis.

Empirical Eigenfunctions and medial surface dynamics of a human vocal fold

OBJECTIVES

The purpose of this investigation was to use an excised human larynx to substantiate physical mechanisms of sustained vocal fold oscillation over a variety of phonatory conditions. During sustained, flow-induced oscillation, dynamical data was collected from the medial surface of the vocal fold. The method of Empirical Eigenfunctions was used to analyze the data and to probe physical mechanisms of sustained oscillation.

METHODS

Thirty microsutures were mounted on the medial margin of a human vocal fold. Across five distinct phonatory conditions, the vocal fold was set into oscillation and imaged with a high-speed digital imaging system. The position coordinates of the sutures were extracted from the images and converted into physical coordinates. Empirical Eigenfunctions were computed from the time-varying physical coordinates, and mechanisms of sustained oscillation were explored.

RESULTS

Using the method of Empirical Eigenfunctions, physical mechanisms of sustained vocal fold oscillation were substantiated. In particular, the essential dynamics of vocal fold vibration were captured by two dominant Empirical Eigenfunctions. The largest Eigenfunction primarily captured the alternating convergent/divergent shape of the medial surface of the vocal fold, while the second largest Eigenfunction primarily captured the lateral vibrations of the vocal fold.

CONCLUSIONS

The hemi-larynx setup yielded a view of the medial surface of the vocal folds, revealing the tissue vibrations which produced sound. Through the use of Empirical Eigenfunctions, the underlying modes of vibration were computed, disclosing physical mechanisms of sustained vocal fold oscillation. The investigation substantiated previous theoretical analyses and yielded significant data to help evaluate and refine computational models of vocal fold vibration.

The laryngectomee substitute voice: image processing of endoscopic recordings by fusion with acoustic signals

OBJECTIVES

The most radical cancer therapy of the throat is the total excision of the larynx which post-operatively results in the loss of voice. A widely-used method of voice rehabilitation is the insertion of a silicone valve, which establishes an unidirectional connection between trachea and esophagus. Thus, during exhalation, air can be directed from the trachea into the esophagus. This air stream excites tissue vibrations of the esophagus and the hypo-pharynx which act as a substitute voice generator. Purpose of the current study is to present a technique for visualizing the dynamics of the substitute voice generating element.

METHODS

Digital high speed videos of the vibrating tissue are simultaneously recorded with the emitted acoustic signal. The high speed sequences are directly evaluated by a three-step knowledge based algorithm. It considers correlation between image and acoustic data, information about the gray value of each pixel, and continuity of tissue vibration. The temporal properties of an image series are investigated by evaluating the time dependent gray value at each pixel position.

RESULTS

The applicability of the algorithm is exemplarily demonstrated using the data of one male patient. It enables the identification of the regions within an image series which are mainly responsible for the acoustic signal. Additionally, the dynamics of tissue vibrations are visualized. The main propagation direction can be clearly identified.

CONCLUSIONS

The new methodology summarizes the information about endoscopic and acoustic recordings of substitute voice into a single image. The results allow a first estimation of tissue velocity and elastic properties of oscillating tissue.

Normal voice production: computation of driving parameters from endoscopic digital high speed images

OBJECTIVES

A central point for quantitative evaluation of pathological and healthy voices is the analysis of vocal fold oscillations. By means of digital High Speed Glottography (HGG), vocal fold oscillations can be recorded in real time. Recently, a numerical inversion procedure was developed that allows the extraction of physiological parameters from digital high speed videos and a classification of voice disorders. The aim of this work was to validate the inversion procedure and to investigate the applicability to normal voices.

METHODS

High speed recordings were performed during phonation within a group of five female and five male persons with normal voices. By using knowledge based image processing algorithms, motion curves of the vocal folds were extracted at three different positions (dorsal, medial, ventral). These curves were used to obtain physiological voice parameters, and in particular the degree of symmetry of the vocal folds based upon a biomechanical model of the vocal folds.

RESULTS

The highest degree of symmetry was observed for the medial motion curves. While the dorsally and ventrally extracted motion curves exhibited similar results concerning the degree of symmetry the performance of the algorithm was less stable.

CONCLUSIONS

The inversion algorithm provides reasonable results for all subjects when applied to the medial motion curves. However, for dorsal and ventral motion curves, correct performance is reduced to 85%.