I was gonna leave out the explanation to the others, but I'll hit 'em just fot the heck of it.
a. Bronchospasm doesn't really reduce the surface area. It is an obstructive process that is worse w/exhalation, and with time the pt becomes so inflated that diaphragmatic excursion is impaired. With diaphragmatic impairment the logical outcoe is a loss of the ability to ventilate, and hence, smaller tidal volumes.
b.CPAP: the idea behind CPAP is a constant pressure holding the airways open during SPONTANEOUS VENTILATION. Now, if you think about the expiratory cycle, it's a passive event. If the result of the passive event is movement of air out of the trachea, then it logically follows that anything that increases the pressure gradient (cpap produces a pressure opposing the tracheal expiratory pressure) in the opposite direction will decrease the flow. Decreased flow is decreased volume, which is a decreased Vt. One other thing, CPAP during GA (like peep) doesn't recruit new alveoli, it just prevents the closure of airways, and alveoli. That being said, Vd isn't really effected either way, but a decrease in Vd is prevented b/c CPAP is maintaining the status quo of the ventilation: perfusion ratio.
c.PEEP: Is a burst of pressure at the END of and expiratory cycle in an INTUBATED AND MECHANICALLY VENTILATED pt, that serves to prevent alveolar/small airway collapse collapse (think prevention of reaching closing capacity volume). The Vt is not really increased in this, and it's common to make that assumption. Some think that b/c you get a burst of volume at the end of the exp cycle, then you are taking in larger volumes and hence a greater Vt, and also b/c you have a larger number of alveoli, you ventilate more. The flaw here is that the P burst during end expiration prevents closure of airways and prevents the exhalation of the final 20-30 cc which translates to a slightly smaller Vt. Also you dont actually recruit alveoli with peep, all you do is hold open the ones that are already open. If you want to increase the # of alveoli, then you have to use a recruitment manuever such as holding a 40-50 mmH2O for 30 seconds or sitting pt up, using a sigh cycle on the vent, or something else.
d. Explanation above
e. With a PE you effectively eliminate the pulmonary blood flow, and ventilation w/o flow is the definition of Vd n hence increased Vd.
Again, I don't know the answer for sure, but logic and reason guided these answers. If something is off, please post it so I/we can learn from it.
BTW tnx 4 saying I'm ready for boards, but I don't think u can ever be too ready for those durned things.
