Association Analyses Between Cough Droplet Concentrations and Human Lung Function

Research Article

Austin J Public Health Epidemiol. 2015; 2(2): 1023.

Association Analyses Between Cough Droplet Concentrations and Human Lung Function

Chen SC1,2*, Lin CW¹ and Lei KI¹

¹Department of Public Health, Chung Shan Medical University, Taiwan

²Department of Family and Community Medicine, Chung Shan Medical University Hospital, Taiwan

*Corresponding author: Szu C. Chen, Department of Public Health, Chung Shan Medical University, Taichung, Taiwan

Received: August 13, 2015; Accepted: September 29, 2015; Published: October 23, 2015


Purpose: Cough droplets are generated in human airways. Human respiratory tract activities and lung function are linked to a number of processes resulting in the introduction of droplets with infectious content into indoor air. The scope of this work was to measure the droplet experiment and associated with lung function variables.

Methods: A droplet experiment has been performed for measuring the coughed droplet characteristics from 18 nonsmoking healthy volunteers and tested simple lung function variables (Forced Expiratory Volume in 1 second (FEV1), Forced Vital Capacity (FVC), and Peak Expiratory Flow (PEF)) between genders. A 15-channel Grimm dust monitor (Grimm 1.108, Germany) were used to measure the real-time exhaled droplets. Mann-Whitney U tests and independent-sample t test were applied to compare gender-specific differences in particle concentrations and lung function variables. The association analyses between exhaled droplet concentrations and lung function were performed using SPSS, version 17.0.

Results: The average peak concentration was determined to be 60,000 particles/L for total subjects, with a reading of 80,000 and 40,000 particles/L for males and females, respectively. Results showed that droplet concentrations for males were significantly higher than those for females (Mann-Whitney U test, p < 0.05). There was a significant gender difference in FEV1 (L), FVC (L) and PEF (L/sec) variables (Independent-sample t test, p < 0.01).

Conclusions: There was a non-significant relationship between exhaled droplet concentrations and human lung function variables. However, this research could provide an opportunity for understanding how gender-specific, and inter/intra-subject analyses affects exhaled particle concentration and lung function variables.

Keywords: Droplet experiment; Cough; Lung function; FEV1; Influenza


Influenza continues to be a major public health concern because of the disease burden and the inherent potential for severe pandemic. Influenza transmission results from virus-exposed susceptible hosts showed that spread could occur by means of either small or large droplets [1,2]. However, human respiratory tract activities, lung function and environmental factors are linked to a number of processes resulting in the introduction of droplets with infectious content into indoor air.

The mechanisms for exhaled particle formation were connected to high air velocities in the airways during exhalation [3]. Dynamic compression of airways occurring during forced expiratory flow, e.g. during cough, may cause instabilities in the layer of Respiratory Tract Lining Fluid (RTLF) and mucus. Subsequently this may produce droplets, presumably being torn off from shaking and vibrating airways walls [3]. In specific, activities such as talking, coughing, sneezing, and breathing could generate different types of respiratory droplets. It was characterized the droplet concentration and size distribution by previously studies [4-9]. Several studies used optical technology (i.e., optical particle counters) to test particle size distribution or concentration for various human respiratory activities [7,10,11], even including new methods to sample and detect virus loads from exhaled respiratory aerosols [12-14]. In an interesting study, Yang et al. [4] measured the size distribution of coughed droplets and nuclei and identified the effect of age and gender on the size distribution and concentration. Results showed that the difference in average droplet size between males and females was insignificant (p > 0.1); however, the variation in droplet concentration between males and females was significant (p < 0.1).

With respect to lung function, assessment of such parameters has gained importance as an index of cardiopulmonary status. Indeed, measurement of Forced Vital Capacity (FVC), forced expiratory volume in 1 second (FEV1), and Peak Expiratory Flow (PEF) are indicators of ventilator capacity within the respiratory system. Lung function may be influenced by several factors, including age and gender [15,16]. Aging causes structural changes to the respiratory system, encompassing modifications that occur to the lungs, rib cage respiratory muscles, and, ultimately, respiratory drive [15]. With respect to gender, there were differences between males and females in terms of inspiratory time, expiratory time, and total time of the respiratory cycle. Spirometry is a well-known and widely used measurement tool in detection, differentiation, and diagnosis of various respiratory diseases. It is also beneficial for monitoring disease progression and improvement following therapeutic intervention [17].

A paucity of studies has examined exhaled droplets as a function of lung parameters in healthy individuals. One study by Schwarz et al. [18] investigated in detail the influence of respiratory variables on exhaled particle number and size distribution during tidal breathing in 21 healthy volunteers. Results showed: (1) increasing tidal volumes dominantly influenced particle number emission while flow rates had little effect; (2) reproducibility within subjects was high, but there was a large variation of particle emission between subjects; and, (3) the ratio of functional residual capacity to total lung capacity was found to correlate with exhaled particle numbers.

Taken together, the first goal of this research was to conduct the droplet experiment for measuring exhaled droplet characteristics of healthy volunteers and test simple lung function variables (FEV1, FVC, and PEF). Secondly, this study aimed to analyze the association between droplet concentration and variables like gender and assess inter-subject variations.

Materials and Methods

Particle measurement

The sampling methods were partly adopted from Xie et al. [5] and Loudon and Roberts [19]. A schematic of the experimental setup is shown in (Figure 1). A small, air-tight box was constructed from Perspex with the dimensions of 36.6 cm × 50.8 cm × 30.5 cm inside [5,19] and placed in a clean room equipped with a central filtration system. An entry hole of 100 mm in diameter was cut for the purpose of respiratory droplet expulsion from a subject’s mouth at nearly twothirds of the height of the front wall (Figures 1A &1B). (Figure 1B) also shows the position of the subject with the sampling hole.