The demographic characteristics of patients and healthy controls are given in . Within healthy control subjects there were more females, and they were younger. Thirteen of 19 patients had very severe COPD (stage IV according to GOLD), 11/19 (58%) had a significant hyperinflation (TLC > 120%), and all patients had significant air trapping as witnessed by an increased reserve volume (RV).
Characteristics of study participants
Safety of humor intervention in patients with severe COPD
One patient, hospitalized for an exacerbation of a very severe COPD at the time of the study insisted on not applying oxygen during the humor intervention. He normally was under long-term oxygen-therapy. After 10 minutes of intervention he was exhausted, required oxygen, and did not want to continue with the study. Back in his hospital room he felt well and did not experience any discomfort related to the study. The problem was probably not a bronchospasm, but the fact that laughing led to increased oxygen and ventilatory demands. None of the other participants suffered neither from bronchospasm nor respiratory discomfort during the whole 24 hours.
Effect of the humor intervention on static lung volumes
The intervention led to a reduction of TLC in patients with COPD (mean reduction: 0.31 ± 0.54 [−0.36; 1.55] mL, 5 ± 9 [−6; 24] %, predicted, p = 0.04, (), but not in controls (mean reduction: 0.24 ± 0.28 [−0.10; 0.58] mL, 5 ± 6 [−2; 13] %, predicted, p = 0.9). The effect was rather short-lived and no longer present 2 hours after the intervention. The responses varied significantly between subjects. Twenty-two (CI 95% 7 to 46) % (4/18) of patients and 20 (CI 95% 4 to 56) % (2/10) of healthy individuals reduced their TLC by more than 10%, predicted. The reduction of TLC in responders ranged between 580 and 1550 mL or 10 and 24%, predicted. When analyzing the responders separately the reduction of TLC was accompanied by a reduction of the residual volume (RV; mean reduction of 992 ± 448 [range 460; 1600] mL, 33 ± 12%, p < 0.001; ). No change was observed for the functional residual capacity (FRC; mean change 28 ± 850 [range −710–420] mL, −0.8 ± 21%, p = 0.87). The vital capacity (VC) did not change significantly.
Figure 2 Effect of the humoristic intervention on total lung capacity (TLC) over a time period up to 24 hours in patients with COPD (panel A) and healthy controls (panel B). Shown are responses as partial residuals of the fitted regression model. Responders decreased (more ...)
Figure 3 Comparison of the change in static lung volumes between baseline and time 0 hour after the humor intervention in TLC-responders compared to non-responders. Reduction of TLC in responders in response to the humor intervention was primarily due to a reduction (more ...)
Video-analysis and questionnaires for the assessment of psychological wellbeing
Patients, as well as controls, responded similarly to the humor intervention in terms of smiling and laughing (Kruskal-Wallis p = 0.18). Responders among patients with COPD smiled more frequently during the intervention compared with nonresponders (p = 0.04).
The intervention improved cheerfulness in patients (p = 0.02) and controls (p = 0.02) without lowering degrees of state seriousness and state bad mood (both ns). The changes in terms of psychological wellbeing of patients with COPD and healthy controls were comparable, but patients with COPD had higher degree of seriousness at baseline. The latter might also be related to the age difference between patients and controls.
Independent predictors of TLC-response
Multiple linear regression analysis was used in an exploratory fashion to identify independent predictors of response. The frequency of smiling (p = 0.018) and TLC at baseline (p = 0.021) proved to be the only independent predictors of TLC-response.
Analysis of real-time breathing pattern
During the intervention and in order to adapt for a higher demand in oxygen uptake and minute ventilation in response to physical activity and emotion, patients mainly increased their breathing frequency, whereas controls increased their tidal volumes (). Representative examples of responses to laughter are shown in .
Results of real-time breathing pattern during the humor intervention
Figure 4 Spirogram from the real-time monitoring of the breathing pattern showing the varying instant effect of laughter on the end-expiratory lung volume (EELV) in patients with COPD. Intense laughter can lead to dynamic hyperinflation in some patients with severe (more ...)