Chest wall dynamics during voluntary and induced cough in healthy volunteers

Abstract

Coughing both protects the airways from foreign material and clears excessive secretions in respiratory diseases, and therefore requires high expiratory flows. We hypothesised that the volume inspired prior to coughing (operating volume) would significantly influence the mechanical changes during coughing and thus cough flow. Sixteen healthy volunteers (6 female, mean age 31 ± 10 years) performed six single voluntary coughs from four different operating volumes (10%, 30%, 60% and 90% of vital capacity) followed by three peals of voluntary and citric acid-induced coughs. During coughing we simultaneously measured (i) chest and upper abdominal wall motion using opto-electronic plethysmography (OEP), (ii) intra-thoracic and intra-abdominal pressures with a balloon catheter in each compartment and (iii) flow at the mouth. Operating volume was the most important determinant of the peak flow achieved and volume expelled during coughing, but had little influence on the pressures generated. The duration of single coughs increased with operating volume, whereas coughs were much shorter and varied little during peals. Voluntary cough peals were also associated with significant blood shift away from the trunk. In conclusion, this study has shown that operating volume is the most important determinant of cough peak flow and volume expelled in healthy individuals. During peals of coughs, similar mechanical effects were achieved more rapidly, suggesting a modification of the motor pattern with improved efficiency. Future studies investigating cough mechanics in health and disease should control for the influence of operating volume.

Figure 1. Signals collected: flow at the mouth, trunk volume (V_tr), oesophageal (P_oes) and gastric (P_gas) pressures during single voluntary cough (A) and voluntary peal of coughs (B)

The volume setting procedure required inspiration to TLC (1–2) followed by expiration to the required operating volume (2–3). In A the subject then performed a single voluntary cough, consisting of a compressive phase (3–4) and expulsive phase (4–5). In B a peal of coughs was performed, each containing a compressive/expulsive phase, with the final expulsive phase completing at point 5.

Figure 2. Changes in trunk volume

A, changes in trunk volume during single voluntary coughs from increasing operating volume, expressed as a percentage of vital capacity, mean ± 95%CI (n= 16). Volume change is shown for the total trunk ΔV_TR and the individual compartments, pulmonary rib cage ΔV_RCp, abdominal rib cage ΔV_RCa and the abdomen ΔV_Ab. *Significant differences for all pairwise comparisons P < 0.001 (after Bonferroni correction). B, changes in trunk volume during single voluntary coughs expressed as a proportion of the operating volume (n= 16). ^‡Significant increases in the proportion of operating volume expelled above that for 10% of VC.

Figure 3. Effect of operating volume on changes in trunk volume, peak flow and peak pressures in the abdomen and chest for single voluntary coughs (A–C) and during peals of voluntary coughs (D–F)

Values are mean ± 95%CI. Note for peals, the x axis displays the coughs in order of decreasing operating volume to allow comparison with single coughs i.e. the first, middle and then last cough. *Significant differences for all pairwise comparisons, P < 0.001 (after Bonferroni correction). ^§Significant differences for all pairwise comparisons, P≤ 0.001 (after Bonferroni correction). For volume, flow and P_gas measurements, n= 16 whereas for P_oesn= 8.

Figure 4. Effect of operating volume on the compressive and expulsive phases of voluntary coughs

A shows effect on duration in single coughs; *significant differences for all pairwise comparisons, P < 0.001 for total cough duration and expulsive phase duration but not compressive phase duration. C shows effect on duration in peals of coughs; ^†significant fall in total cough duration. The volume changes during these phases are shown in B for single coughs; *significant differences for all pairwise comparisons, P < 0.001 for volume change during expulsive and compressive phases and peals of coughs (D); *significant differences for all pairwise comparisons, P < 0.001 for volume change during expulsive and compressive phases. All data are mean ± 95%CI (n= 16).

Figure 5. Volume tracings of trunk, integrated flow at the mouth, gas compression and blood shift during a peal of cough in an individual subject (A). Mean volume variation of trunk, integrated flow at the mouth, gas compression and blood shift during peals of cough for all subjects (B)

Values are taken at the end of the first compression phase and at the end of cough peal.

Figure 6. Volume changes (A) and peak pressures (B) during citric acid-induced cough peals, for first, middle and last coughs of peal i.e. high to low operating volume

Values are mean ± 95%CI. *Significant differences for all pairwise comparisons of operating volume but pressure measures did not change significantly. For volume and P_gas measurements, n= 16 whereas for P_oes, n= 8.