Chapter 22 - Respiratory Physiology

Premature infants often lack adequate surfactant. How does this affect their ability to breathe?

A lack of surfactant increases surface tension in the alveoli and causes them to collapse between breaths. In other words, it markedly decreases lung compliance.

What is the driving force for pulmonary ventilation?

A pressure gradient created by changes in the thoracic volume (inspiration and expiration)

What is the clinical name for the condition when air enters the pleural cavity?

Pneumothorax

Explain why slow, deep breaths ventilate the alveoli more effectively than do rapid, shallow breaths.

Slow, deep breaths ventilate the alveoli more effective because a smaller fraction of the tidal volume of each breath is spent moving air into and out of dead space.

Inspiration

The period when air flows into the lungs

Expiration

The period when gases exit the lungs

Atmospheric pressure (Patm)

The pressure exerted by the air (gases) surrounding the body and is relative to describing respiratory pressures.

Positive respiratory pressure

The pressure in any respiratory area that is higher than atmospheric pressure.

Give 3 reasons in why resistance in the airways is typically low.

1) The diameters of most airways are relatively large. 2) For smaller airways there are many in parallel, making their combined diameter large. 3) Air has a low viscosity.

What is atmospheric pressure at sea level?

760 mm Hg (the pressure exerted by a column of mercury 760 mm high). This pressure can also be expressed in atmospheric units: atmospheric pressure = 760 mm Hg = 1 atm.

Zero respiratory pressure is equal to _______________________________?

Atmospheric pressure

Respiratory pressures are always described relative to what?

Atmospheric pressure (Patm)

What causes the intrapulmonary pressure to decrease during inspiration?

Because of the increase in thoracic cavity volume brought about by the muscles of inspiration.

Breathing, aka pulmonary ventilation, consists of what 2 phases?

Inspiration and expiration

What happens to a lung if air enters the pleural cavity?

The lungs on the side of the pleural cavity where air is entering will collapse.

What causes the parietal vacuum (negative pressure) inside the pleural cavity?

The opposing forces acting on the visceral and parietal pleurae. The visceral pleurae are pulled inward by the lungs' natural tendency to recoil and the surface tension of the alveolar fluid. The parietal pleurae are pulled outward by the elasticity of the chest wall.

Negative respiratory pressure

The pressure in any respiratory area that is lower than atmospheric pressure. For example, a respiratory pressure of -4 mm Hg indicates a pressure that is lower than atmospheric pressure by 4 mm Hg (760 - 4 = 756 mm Hg). In this case, 756 mm Hg is the absolute pressure in that region.

Intrapulmonary (intra-alveolar) pressure (Ppul)

The pressure in the alveoli that rises and falls with the phases of breathing, but it always equalizes with the atmospheric pressure eventually.

Intrapleural pressure (Pip)

The pressure in the pleural cavity that fluctuates with breathing phases, but is always about 4 mm Hg less than intrapulmonary pressure (Ppul) - that is it is always negative relative to intrapulmonary pressure.