Relationship of peak flow rate and peak velocity time during voluntary coughing

Airway mechanics alters generation of cough motor pattern

Effects of sequential increase in airway resistance: no, low (5 kPa.s/l), high (24 kPa.s/l), and complete block in the inspiratory or expiratory phase of mechanically induced cough on the cough motor pattern were studied in 16 anesthetized (pentobarbital) spontaneously breathing cats (3.70±0.15 kg, 11♂, 5♀). Esophageal pressure and electromyographic activities of the diaphragm during inspiration and abdominal muscles during expiration were analyzed. No significant changes in the number of coughs occurred. Inspiratory occlusion caused a prolongation of cough inspiratory phase, cough inspiratory diaphragm activity, and all cough-related activity. Inspiratory occlusion along with high resistance increased inspiratory esophageal pressure amplitude, total cough cycle duration and the time between maximum activity of the diaphragm and abdominal muscles. High expiratory resistance and occlusion resulted in increased cough expiratory esophageal pressure amplitude, a longer active portion of cough expiration, and cough abdominal activity. Expiratory occlusion also prolonged cough expiratory phase, all cough activity, and total cough cycle. Significantly increased airway resistance and occlusion induce secondary, in addition to mechanical, changes in cough by significantly modulating the generated cough motor pattern. A certain level of resistance appears to be successfully compensated, resulting in minimal changes in coughing characteristics, including expiratory airflow and the rising time of the airflow. Afferent feedback from the respiratory tract, particularly volume feedback, represents a significant factor in modulating cough, mainly under various pathological conditions in the respiratory system.

Interferometric laser imaging for respiratory droplets sizing

Due to its importance in airborne disease transmission, especially because of the COVID-19 pandemic, much attention has recently been devoted by the scientific community to the analysis of dispersion of particle-laden air clouds ejected by humans during different respiratory activities. In spite of that, a lack of knowledge is still present particularly with regard to the velocity of the emitted particles, which could differ considerably from that of the air phase. The velocity of the particles is also expected to vary with their size. In this work, simultaneous measurements of size and velocity of particles emitted by humans while speaking have been performed by means of Interferometric Laser Imaging Droplet Sizing (ILIDS). This technique allowed us to detect emitted particles with size down to 2 µm as well as to quantify all three components of the velocity vector and the particle concentration. The outcomes of this work may be used as boundary conditions for numerical simulations of infected respiratory cloud transmission.

Graphical abstract

A review on the transmission of COVID-19 based on cough/sneeze/breath flows

COVID-19 pandemic has recently had a dramatic impact on society. The understanding of the disease transmission is of high importance to limit its spread between humans. The spread of the virus in air strongly depends on the flow dynamics of the human airflows. It is, however, known that predicting the flow dynamics of the human airflows can be challenging due to different particles sizes and the turbulent aspect of the flow regime. It is thus recommended to present a deep analysis of different human airflows based on the existing experimental investigations. A validation of the existing numerical predictions of such flows would be of high interest to further develop the existing numerical model for different flow configurations. This paper presents a literature review of the experimental and numerical studies on human airflows, including sneezing, coughing and breathing. The dynamics of these airflows for different droplet sizes is discussed. The influence of other parameters, such as the viscosity and relative humidity, on the germs transmission is also presented. Finally, the efficacy of using a facemask in limiting the transmission of COVID-19 is investigated.

Measurements of exhaled airflow velocity through human coughs using particle image velocimetry

The sudden outbreak of coronavirus (COVID-19) has infected over 100 million people and led to over two million deaths (data in January 2021), posing a significant threat to global human health. As a potential carrier of the novel coronavirus, the exhaled airflow of infected individuals through coughs is significant in virus transmission. The research of detailed airflow characteristics and velocity distributions is insufficient because most previous studies utilize particle image velocimetry (PIV) with low frequency. This study measured the airflow velocity of human coughs in a chamber using PIV with high frequency (interval: 1/2986 s) to provide a detailed validation database for droplet propagation CFD simulation. Sixty cough cases for ten young healthy nonsmoking volunteers (five males and five females) were analyzed. Ensemble-average operations were conducted to eliminate individual variations. Vertical and horizontal velocity distributions were measured around the mouth area. Overall cough characteristics such as cough duration time (CDT), peak velocity time (PVT), maximum velocities, and cough spread angle were obtained. The CDT of the cough airflow was 520-560 m s, while PVT was 20 m s. The male/female averaged maximum velocities were 15.2/13.1 m/s. The average vertical/horizontal cough spread angle was 15.3°/13.3° for males and 15.6°/14.2° for females. In addition, the spatial and temporal distributions of ensemble-averaged velocity profiles were obtained in the vertical and horizontal directions. The experimental data can provide a detailed validation database the basis for further study on the influence of cough airflow on virus transmission using computational fluid dynamic simulations.

Novel assisted cough system based on simulating cough airflow dynamics

Abstract

Cough is a defensive behavior that protects the respiratory system from infection and clears airway secretions. Cough airflow dynamics have been analyzed by a variety of mathematical and experimental tools. In this paper, the cough airflow dynamics of 42 subjects were obtained and analyzed. An identification model based on piecewise Gauss function for cough airflow dynamics is proposed through the dimensionless method, which could achieve over 90% identification accuracy. Meanwhile, an assisted cough system based on pneumatic flow servo system is presented. The vacuum situation and feedback control are used to increase the simulated peak cough flow rate, which are important for airway secretion clearance and to avoid airway collapse, respectively. The simulated cough peak flow could reach 5 L/s without the external assistance such as manual pressing, patient cooperation and other means. Finally, the backstepping control is developed to generate a simulated cough airflow that closely mimics the natural cough airflow of humans. The assisted cough system opens up wide opportunities of practical application in airway secretion clearance for critically ill patients with COVID 2019 and other pulmonary diseases.

Graphic abstract

A review on the applied techniques of exhaled airflow and droplets characterization

In the last two decades, multidisciplinary research teams worked on developing a comprehensive understanding of the transmission mechanisms of airborne diseases. This article reviews the experimental studies on the characterization of the exhaled airflow and the droplets, comparing the measured parameters, the advantages, and the limitations of each technique. To characterize the airflow field, the global flow-field techniques-high-speed photography, schlieren photography, and PIV-are applied to visualize the shape and propagation of the exhaled airflow and its interaction with the ambient air, while the pointwise measurements provide quantitative measurements of the velocity, flow rate, humidity and temperature at a single point in the flow field. For the exhaled droplets, intrusive techniques are used to characterize the size distribution and concentration of the droplets' dry residues while non-intrusive techniques can measure the droplet size and velocity at different locations in the flow field. The evolution of droplets' size and velocity away from the source has not yet been thoroughly experimentally investigated. Besides, there is a lack of information about the temperature and humidity fields composed by the interaction of the exhaled airflow and the ambient air.

Numerical Analysis of Airway Mucus Clearance Effectiveness Using Assisted Coughing Techniques

Cough is a protective respiratory reflex used to clear respiratory airway mucus. For patients with cough weakness, such as chronic obstructive pulmonary disease, neuromuscular weakness disease and other respiratory diseases, assisted coughing techniques are essential to help them clear mucus. In this study, the Eulerian wall film model was applied to simulate the coughing clearance process through a computational fluid dynamics methodology. Airway generation 0 to generation 2 based on realistic geometry is considered in this study. To quantify cough effectiveness, cough efficiency was calculated. Moreover, simulations of four different coughing techniques applied for chronic obstructive pulmonary disease and neuromuscular weakness disease were conducted. The influences of mucus film thickness and mucus viscosity on cough efficiency were analyzed. From the simulation results, we found that with increasing mucus film thickness and decreasing mucus viscosity, cough efficiency improved accordingly. Assisted coughing technologies have little influence on the mucus clearance of chronic obstructive pulmonary disease models. Finally, it was observed that the cough efficiency of the mechanical insufflation-exsufflation technique (MIE) is more than 40 times the value of an unassisted coughing technique, which indicates that the MIE technology has a great effect on airway mucus clearance for neuromuscular weakness disease models.

CFD Simulation of Airflow Dynamics During Cough Based on CT-Scanned Respiratory Airway Geometries

The airflow dynamics observed during a cough process in a CT-scanned respiratory airway model were numerically analyzed using the computational fluid dynamics (CFD) method. The model and methodology were validated by a comparison with published experimental results. The influence of the cough peak flow rate on airflow dynamics and flow distribution was studied. The maximum velocity, wall pressure, and wall shear stress increased linearly as the cough peak flow increased. However, the cough peak flow rate had little influence on the flow distribution of the left and right main bronchi during the cough process. This article focuses on the mathematical and numerical modelling for human cough process in bioengineering.

Voluntary cough intensity and its influencing factors differ by sex in community-dwelling adults

Background:

Cough peak flow (CPF) is widely used for measuring voluntary cough intensity. However, the respective factors that affect CPF are not known. The aim of this study was to determine the factors affecting CPF by sex in community-dwelling adults.

Method:

We recruited participants using posters exhibited at a public gymnasium. Participation was voluntary, and all participants provided informed consent. Nonsmoking community residents (102 males, 49.6 ± 20.2 years of age; 101 females, 51.4 ± 18.4 years of age) participated in this study. The main outcome measures were sex differences in CPF, respiratory function, respiratory muscle strength, thorax extension, and grip strength. Factors affecting CPF by sex were analyzed using multiple regression analysis.

Results:

All parameters were higher in men than in women. CPF was affected by thorax expansion at the tenth rib, inspiratory muscle strength and forced expiration in 1 s in men, and thorax expansion at the tenth rib, inspiratory reserve volume, and expiratory muscle power in women. A weak negative correlation was observed between CPF and age (p = −0.24, p < 0.05) in women.

Conclusions:

The factors affecting CPF differed by sex in community-dwelling adults.

Clinical Trial Number: UMIN000023912

Western Cold and Flu (WeCoF) aerosol study--preliminary results

BACKGROUND

Influenza virus is responsible for annual deaths due to seasonal epidemics and is the cause of major pandemics which have claimed millions of human lives over the last century. Knowledge about respiratory virus transmission is advancing. Spread is likely through the air, but much work remains to be done to characterize the aerosols produced by infected individuals, including viral particle survival and infectivity. Although coughs have been characterized, little work has been done to examine coughs from infected individuals. The WeCoF project aims at providing evidence to support prevention measures to mitigate person-to-person influenza transmission in critical locations, such as hospitals, and during pandemics.

FINDINGS

A novel experimental cough chamber facility - the FLUGIE - has been developed to study the far-field aerodynamics and aerosol transport of droplets produced by the coughs from humans naturally-infected with influenza. The flow field of each cough is measured using Particle Image Velocimetry (PIV). A preliminary study involving 12 healthy individuals has been carried out in order to quantify the strengths of their coughs at a distance of 1 m from the mouth. The spatially averaged maximum velocity was determined and the average value was 0.41 m/s across 27 coughs of good data quality. The peak value of velocity was also extracted and compared with the average velocity.

CONCLUSIONS

Preliminary results show that there is significant air motion associated with a cough (on the order of 0.5 m/s) as far away as 1 m from the mouth of the healthy person who coughs. The results from this pilot study provide the framework for a more extensive participant recruitment campaign that will encompass a statistically-significant cohort.

Volitional control of reflex cough

Multiple studies suggest a role for the cerebral cortex in the generation of reflex cough in awake humans. Reflex cough is preceded by detection of an urge to cough; strokes specifically within the cerebral cortex can affect parameters of reflex cough, and reflex cough can be voluntarily suppressed. However, it is not known to what extent healthy, awake humans can volitionally modulate the cough reflex, aside from suppression. The aims of this study were to determine whether conscious humans can volitionally modify their reflexive cough and, if so, to determine what parameters of the cough waveform and corresponding muscle activity can be modified. Twenty adults (18-40 yr, 4 men) volunteered for study participation and gave verbal and written informed consent. Participants were seated and outfitted with a facemask and pneumotacograph, and two surface EMG electrodes were positioned over expiratory muscles. Capsaicin (200 μM) was delivered via dosimeter and one-way (inspiratory) valve attached to a side port between the facemask and pneumotachograph. Cough airflow and surface EMG activity were recorded across tasks including 1) baseline, 2) small cough (cough smaller or softer than normal), 3) long cough (cough longer or louder than normal), and 4) not cough (alternative behavior). All participants coughed in response to 200 μM capsaicin and were able to modify the cough. Variables exhibiting changes include those related to the peak airflow during the expiratory phase. Results demonstrate that it is possible to volitionally modify cough motor output characteristics.

Flow dynamics and characterization of a cough

Airborne disease transmission has always been a topic of wide interests in various fields for decades. Cough is found to be one of the prime sources of airborne diseases as it has high velocity and large quantity of droplets. To understand and characterize the flow dynamics of a cough can help to control the airborne disease transmission. This study has measured flow dynamics of coughs with human subjects. The flow rate variation of a cough with time can be represented as a combination of gamma-probability-distribution functions. The variables needed to define the gamma-probability-distribution functions can be represented by some medical parameters. A robust multiple linear regression analysis indicated that these medical parameters can be obtained from the physiological details of a person. However, the jet direction and mouth opening area during a cough seemed not related to the physiological parameters of the human subjects. Combining the flow characteristics reported in this study with appropriate virus and droplet distribution information, the infectious source strength by coughing can be evaluated.

PRACTICAL IMPLICATIONS

There is a clear need for the scientific community to accurately predict and control the transmission of airborne diseases. Transportation of airborne viruses is often predicted using Computational Fluid Dynamics (CFD) simulations. CFD simulations are inexpensive but need accurate source boundary conditions for the precise prediction of disease transmission. Cough is found to be the prime source for generating infectious viruses. The present study was designed to develop an accurate source model to define thermo-fluid boundary conditions for a cough. The model can aid in accurately predicting the disease transmission in various indoor environments, such as aircraft cabins, office spaces and hospitals.

Impaired efficacy of cough in patients with Parkinson disease

STUDY OBJECTIVES

Aspiration pneumonia, a leading cause of death in patients with Parkinson disease (PD), usually occurs at the advanced stages of the disease. We investigated both motor and sensory components of cough and induced-sputum substance P (SP) concentrations in patients with early and advanced stages of PD to assess whether cough efficacy is impaired in PD.

SUBJECTS

Fifteen female patients with early stages of PD (Hoehn and Yahr stage II-III), 10 patients with advanced stages of PD (Hoehn and Yahr stage IV), and 15 age-matched female control subjects were investigated.

MEASUREMENTS

The motor component of cough efficacy was assessed by monitoring voluntary maximal cough peak flow. The sensory component of cough efficacy was assessed by measuring cough reflex sensitivity to citric acid inhalation. Sputum SP concentrations were measured in sputum induced by hypertonic saline solution inhalation.

RESULTS

The mean (+/- SD) cough peak flow rates in patients with both early PD (230 +/- 74 L/min; p < 0.005) and advanced PD (186 +/- 60 L/min; p < 0.0001) were significantly weaker than that in control subjects (316 +/- 70 L/min). Cough reflex sensitivity in patients with advanced PD (46.7 +/- 49.3 g/L) was significantly lower compared to control subjects (14.5 +/- 16.6 g/L; p < 0.01) and patients with early PD (11.2 +/- 14.8 g/L; p < 0.005). The sputum SP concentration was significantly lower in patients with advanced PD (11.2 +/- 8.4 pg/mL) compared to that in control subjects (35.6 +/- 15.4 pg/mL) and patients with early PD (28.5 +/- 16.4 pg/mL).

CONCLUSION

In the early stages of the disease, mainly the motor component of cough was impaired. In advanced stages of the disease, both the motor and sensory components of cough were impaired. Sputum SP concentration significantly declined in patients with advanced PD. The results suggest that the combination of impaired motor and sensory components of cough may play an important role in the development of aspiration pneumonia in PD.

Simulation of cough in man by magnetic stimulation of the thoracic nerve roots

Normal cough requires abdominal muscle contraction. We have previously reported contraction of the abdominal muscles elicited by a single percutaneous magnetic stimulation of the thoracic nerve roots. We hypothesized that paired magnetic twitches could generate sufficient tension in the abdominal muscles to simulate cough. Therefore, six normal subjects were stimulated at the T10 intervertebral level in the seated position. We measured the gastric pressure elicited by paired magnetic stimuli (pTw Pga) with interstimulus intervals in the range of 10 ms (100 Hz) to 999 ms (1 Hz). In the second part of the study we evaluated paired stimuli (at the frequency found to produce the greatest response) using a valve to simulate the function of the glottis; the valve was arranged such that it opened once mouth pressure exceeded a predetermined threshold. Mean pTw Pga during stimulation for the 6 subjects was 74 cm H2O (range, 30-109), and mean peak flow was 209 L/min (range, 128-345 L/min). These values were increased if the subject took a prior inspiration or had previously made a vigorous expiratory effort. Comparable values for a maximal natural cough were 212 cm H2O and 649 L/min. We conclude that paired magnetic thoracic nerve root stimulation produces gastric pressure and expiratory flow of an order of magnitude comparable to a natural cough.