Ventilation Flashcards
(12 cards)
Ventilation and tidal volume
The movement of air in and out of the lungs, the volume of air that enters the lungs in single breath.
Flow is directly proportional to the pressure difference and inversely proportional to airway resistance.
Patm - Palv
The driving pressure gradient that determines the direction of air flow.
Pip
The pressure in the intrapleural cavity that balances the tendency of the lungs to collapse and the chest wall to expand. Approx. 756mmHg or -4mmHg compared to the Palv.
Ptp
(Palv - Pip) ≈ 4mmHg
Transpulmonary pressure, the main determinant of lung size.
Opposed the elastic recoil of the lung.
Pcw
(Pip - Patm) ≈ -4mmHg
The pressure across the chest wall.
Opposed the elastic recoil of the chest wall.
Pip during ventilation
Falls from -5mmHg to -8mmHg, increasing the elastic recoil of the lung as it inflates
Palv during ventilation
Falls slightly due to the expansion of volume (boyle’s law) becoming slightly subatmospheric. Air flows down this pressure gradient.
what causes the lungs to expand? to recoil?
Expand - Pip falls and transpulmonary pressure increases such that Palv becomes atmospheric.
Recoil - Pip returns to regular and Ptp does too, alveolar air is compressed and Palv > Patm.
Mechanisms of (atelectasis)
Chest wall is pierced WITHOUT damage to the lung. Atmospheric air enters the interpleural space causing Pip to match. atmospheric. Ptp is eliminated and the innate elastic recoil of the lungs and chest wall causes them to collapse and spring out, respectively.
Anatomic dead space
Approx. 150mL
Physiological (functional) dead space
When ventilation and perfusion become mismatched and gas exchange is inefficient.
Effect of breathing patterns on alveolar ventilation
By manipulating tidal volume and frequency of breaths, patients may have the same minute ventilation, but taking in to account the dead space ventilation, they may receive severely different amounts of alveolar exchange.
