USMLE Step 1 Respiratory Physiology Review 61 13 Dead Space

USMLE Step 1 Respiratory Physiology Review 61 13 Dead Space

On these “Gold Standard Step 1 Facts” pages you will find Free:

  • USMLE Audio Review files from our “Gold Standard USMLE Reviews”
  • Transcriptions of those files
  • And videos (as they become available)

The idea is that you can review for the USMLE online by:

  • Listening to the Audio
  • Following along with the transcription
  • Or by watching the video (if available)

If you like what you here, you can purchase the entire Gold Standard Step 1 MP3 audio USMLE review for your iPhone, iPod, or computer here.

Let’s start our USMLE Review with Anatomy from the Gold Standard USMLE Step 1 Audio Review program.

Play USMLE Audio MP3  61 13 Dead Space  Below

Begin 61 13 Dead SpaceTranscription

Before we discuss the three kinds of dead space that exist in the lungs, let’s just list them. I’ll cue you with the first letter of each.
First, P

  • – physiological dead space

Second, A

  • Anatomical dead space

And Third, A

  • Alveolar dead space

Not all inspired air is delivered to the alveoli. Some of it remains in the air ways that comprise the conducting zone of the respiratory system.
Under resting conditions, what percent of each tidal volume of inspired air remains in the air ways?

  • 25 to 35 percent

Which of the three kinds of dead space is the volume of air that remains in the airways?

  • The anatomical dead space is the volume of air that remains in the airways.

When tidal volume is increased, does most of the extra inspired air ventilate the alveoli, the dead space, or about equal?

  • When tidal volume is increased, most of the extra air ventilates the alveoli.

In contrast, how does increasing the number of breaths per minute affect ventilation of alveoli and dead space?

  • Alveolar ventilation and dead space ventilation are both increased proportionally.

When an area of the lungs is either over ventilated or under perfused, what will its ventilation perfusion ratio be?

  • The VQ ratio is greater than 1 in lung regions that are over ventilated or under perfused

What about a lung area where there is no blood flow? What will the VQ ratio for that area equal?

  • In lung regions with no blood flow, the VQ ratio equals infinity.

Whenever the ventilation perfusion ratio is greater than one up to infinity, we have wasted ventilation. What kind of dead space results from ventilation of alveoli that are either under perfused or not perfused at all?

  • Alveolar dead space

Finally, we come to the third kind of dead space. What is it called and what does it consist of?

  • Physiological dead space is the total dead space in the lungs. That is, anatomical dead space plus alveolar dead space.

Student doctor, please pause the tape and summarize what we’ve discussed about dead space.

  • The three kinds of dead space that exist in the lungs are physiological dead space, anatomical dead space, and alveolar dead space. Not all inspired air is delivered to the alveoli; some of it remains in the airways that comprise the conducting zone of the respiratory system. Under resting conditions, 25 to 35 percent of each tidal volume of inspired air remains in the airways. This represents the anatomical dead space. When tidal volume is increased, most of the extra air ventilates the alveoli. In contrast, when a number of breaths per minute is increased, alveolar ventilation and dead space ventilation are both increased proportionally. The VQ ratio is greater than 1 in lung regions that are over ventilated or under perfused. In lung regions with no blood flow, the VQ ratio equals infinity. Whenever the VQ ratio is greater than 1 up to infinity, we have wasted ventilation. Alveolar dead space results from ventilation of alveoli that are either under perfused or not perfused at all. Finally, physiological dead space is the total dead space in the lungs. That is, anatomical dead space plus alveolar dead space.

 

****END OF TRANSCRIPTION****

Want More USMLE Step 1 Review Facts?

boardprep.net

Leave a Reply