Respiratory mechanics during submersion and negative-pressure breathing.

Publisher Website
Google Scholar
Abstract
During submersion up to the neck the expiratory reserve volume of the sitting subject is reduced to 11% of the vital capacity in air, the same decrease is obtained breathing from a tank at [long dash]20.5 cm H2O. The decrease of lung volume is mainly due to the cranial displacement of the abdomen; although at the end of spontaneous expirations during submersion the diaphragm is stretched almost as far as at full expiration, it is relaxed, whereas during a full expiration it contracts. The end-expiratory pressures across the rib cage, the diaphragm, and the abdominal wall are: [long dash]19, [long dash]14, and [long dash]13 cm H2O during submersion, and [long dash]23.5, [long dash]11.5, and [long dash]12 during NPB. Notwithstanding the lack of the gravitational effect of the abdomen during submersion, the shape of the chest wall is almost the same as during negative-pressure breathing because of the low compliance of the rib cage. During submersion the airways resistance increases by 58% because of the lung volume decrease; during negative-pressure breathing it increases by 157%, the extra increase being due to the compression of the extrathoracic airways.