Basics Of Breathing

Basics Of Breathing

When a person inspires, the diaphragm contracts and pulls the lungs downward. This produces negative pressure within the alveoli that is transmitted to the airway; air is then drawn in. During expiration, passive relaxation of the chest wall musculature allows the chest cavity to naturally recoil to elastic neutrality. Between each regular inhalation and exhalation, there is a brief expiratory pause when intrathoracic pressures match atmospheric pressures. This process is referred to as spontaneous negative pressure breathing. Ventilator breathing is markedly different in that ventilated lungs have air pushed rather than drawn into them. This is referred to as positive pressure ventilation. Positive pressure ventilation can be provided invasively (as when a patient is intubated and on full ventilatory support) or non-invasively (continuous positive airway pressure [CPAP] or bi-level positive airway pressure [BiPAP]).