Lung mechanics

what is the analogy with elasticity

think of it like a balloon; can be difficult to expand at first but as more air goes in compliance goes up and elesticity goes up

why is compliance of inpsiration less then compliance with expiration

because you have to get over the threshold first with inspiration (like a balloon) because you have to overcome the surface tension first

with emphysema: what is compliance, elasticity, and expamsion and collapsing of lungs?

increased compliance but not enough elasticity

easy to expand the lungs (breathe in) but hard to collpase them (breathe out)

with fibrosis: what is compliance, elasticity, and expamsion and collapsing of lungs?

too elastic and not enough compliance

easy to collapse (breathe out) but hard to expand (breathe in)

expain the law of laplace with surface/collapsing pressure of small alveoli versus bigger alveoli

small alveoli has higher collapsing pressure

What is neonatal rspiratory distress syndrome and how do we treat it?

born before 24 GW: no sulfactant

treat with injection of steroids in the mother to help keep the alveoli of the fetus open

explain trachea versus terminal bronchioles with resistance

terminal brnchioles have less resistance (would think becuase they are smaller its more resistnce, but they are like capillaires becuase they all together have a greater combined surface area; parallel flow)

Explain the changes in airway resistance/air flow with sympathetic vs parasympathetic stimulation

symp: dilation (adrenergic beta-receptor agonists); epinephrine, isoproterenol, and albuterol

para: constriction (muscarinic agonists); muscarine and carbachol

What are the pro-inflammatory mediators and what do they cause?

histamine and leukotrienes; constriction of airway

explain compensatory bronchoconstriction

decrease in PCO2 → increased pH → bronchoconstriction (less air gets to the less perfused areas)

explain the interdependence of alveoli (like in asthma)

the status of one alveolus will affect the surrounding ones

explain viscocity of air and how that plays a role in airway resistance

more viscous air is harder to breath (more resistance)

this is why helium is in the O2 tanks for divers, because it is less viscous and easier to breathe

transmural pressure and lung collapse

the transmural pressure has to be positive to keep lung from collapsing

so the intrapleaural pressure can be positive (usually neg) and the lung not collapse as long as the alveolar pressure is still geater

How to calculate transmural pressure

alveolar pressure - intraplaural pressure