Figure 1.
Experimental set-up of the shadowgraph imaging system.
Schematic of the layout with the large, 1-m diameter, spherical concave f/5 mirror and subject test area at one end, and the high-speed camera with the LED light-source and the image capture system (laptop) approximately 10 m away at the other end of the environmental chamber. Note that the schematic diagram has been shown previously to describe this experimental set-up [8].
Figure 2.
Example of a ‘before’ (A) and ‘after’ (B) digitized shadowgraph image of a human volunteer coughing.
These types of images were used to obtain the cough dynamic parameters shown in Figure 3. The blue crosses in image B represent the (x,y) coordinates of the digitized airflow boundary at that point, as seen by one of the independent observers. The software algorithm measured the resolved detectable distance in the ‘x’ direction (B), as this was the clinically important parameter reflecting the horizontal propagation distance of the cough. It also measured the maximum detectable 2-D projected area resolved in the horizontal direction of the cough as seen in the side-on view of the shadowgraph visualization of the cough aerosol.
Table 1.
Characteristics of the 20 healthy human volunteers used in the cough imaging.
Figure 3.
Combined plots of all the coughs produced by the 20 healthy volunteers.
These demonstrate the cough airflow dynamic parameters measured in these experiments. A: cough ‘propagation distance-velocity-time’; B: ‘2-D projected area-expansion rate-time’. The parameters digitized directly from the recorded images (propagation distance and 2-D area) are shown by solid red lines with the actual data points as empty circles, with reference to the left y-axis, labeled with the red font. The derived parameters (velocity and 2-D area expansion rate) are shown by thinner, dotted blue lines, with reference to the right y-axis, labeled with the blue font.
Figure 4.
A shadowgraph still image of a cough captured from video.
This demonstrates the typical bifurcation of the cough air-stream as a volunteer coughs into his sleeve.