Respiratory dynamics during laughter

Lung and chest wall mechanics were studied during fits of laughter in 11 no rmal subjects. Laughing was naturally induced by showing clips of the funni est scenes from a movie by Roberto Benigni. Chest wall volume was measured by using a three-dimensional optoelectronic plethysmography and was partiti oned into upper thorax, lower thorax, and abdominal compartments. Esophagea l (Pes) and gastric (Pga) pressures were measured in seven subjects. All fi ts of laughter were characterized by a sudden occurrence of repetitive expi ratory efforts at an average frequency of 4.6 +/- 1.1 Hz, which led to a fi nal drop in functional residual capacity (FRC) by 1.55 +/- 0.40 liter (P < 0.001). All compartments similarly contributed to the decrease of lung volu mes. The average duration of the fits of laughter was 3.7 +/- 2.2 s. Most o f the events were associated with sudden increase in Pes well beyond the cr itical pressure necessary to generate maximum expiratory flow at a given lu ng volume. Pga increased more than Pes at the end of the expiratory efforts by an average of 27 +/- 7 cmH(2)O. Transdiaphragmatic pressure (Pdi) at FR C and at 10% and 20% control forced vital capacity below FRC was significan tly higher than Pdi at the same absolute lung volumes during a relaxed mane uver at rest (P < 0.001). We conclude that fits of laughter consistently le ad to sudden and substantial decrease in lung volume in all respiratory com partments and remarkable dynamic compression of the airways. Further mechan ical stress would have applied to all the organs located in the thoracic ca vity if the diaphragm had not actively prevented part of the increase in ab dominal pressure from being transmitted to the chest wall cavity.