How is the physiology of ventilation?

Goal is facilitating CO2 release with normal PaO2 Delivery of breath occurs with every change in transpulmonary pressure (mouth: pleura gradient) Spontaneous breathing chest wall expansion, diaphragm descent and muscle contraction create negative pressure within pleural space, which allows gas flow through conducting airways to respiratory units. So, negative pressure ventilators (NPV) create subatmospheric pressure around the chest to expand thoracic cavity. They lack diaphragm movement so alveolar ventilation is not as efficient Positive pressure ventilators (PPV) favor flow of gases down conducting airways overcoming pleural pressure