USMLE Step 1 Respiratory Physiology Review 60 08 Lung Volumes

USMLE Step 1 Respiratory Physiology Review 60 08 Lung Volumes

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Play USMLE Audio MP3 60 08 Lung Volumes Below

Begin 60 08 Lung Volumes Transcription

Now let’s talk about lung volumes. The volume of air flowing into and out of the lungs is a measurable quantity.

What instrument can be used to measure lung volumes and capacities? The name of the instrument begins with the letter S and comes from the Latin word ‘for breath.’

  •  The spirometer is an instrument used to measure lung volume.

The total capacity for the lungs can be divided into four separate, non-overlapping volumes which can be either measured directly by using a spirometer or  calculated from measured volumes. The values obtained are useful when diagnosing some pulmonary disorders and diseases.

In alphabetical order, list the four non overlapping areas. I’ll cue you with the acronym for each.

  • First, ERV

Expiratory reserve volume.

  • Second, IRV

Inspiratory reserve volume.

  • And third, RV

residual volume.

  • And fourth, TV

 

  •  tidal volume.

For the following four questions, I’ll describe one of the lung volumes just listed. Please respond with the proper term.

First, the volume of air that is inspired or expired during eupnoea, or in other words, a normal breath?

  • Tidal volume

Second, the volume of air remaining in the lungs after a maximal expiration. In other words, the volume of air that can never be expelled.

  •   Residual volume.

Third, the maximum volume of air that can be additionally expired after a tidal expiration.

  • Expiratory reserved volume or ERV

And fourth, the maximum volume of air that can be additionally inspired after a tidal inspiration.

  •  Inspiratory reserve volume or IRV.

What’s the normal value for the tidal volume of healthy adult lungs?

  •  The tidal volume of healthy lungs is about 500 milliliters.  

In liters, about how much air is left in the lungs after a maximal expiration?

  •  Normal residual volume is about 1.2 Liters.

What is the normal inspiratory reserve volume of the lungs? Give your answers in liters please.

  •    Normal inspiratory reserved volume is about 3 liters.

What is this a memory key for?

  • After a normal out breath, breathe out a deep sigh.   Expiratory reserve volume.

What is this a memory key for?

  • After a normal breath in, breathe in deeply.     Inspiratory reserve volume.

Student doctor please pause the tape and summarize the spirometer and the four non overlapping volumes of the lungs that were just discussed.

  • The volume of air flowing into and out of the lungs is a measurable quantity. A spirometer can be used to measure lung volumes and capacities. The total capacity of the lungs can be divided into 4 separate, non overlapping volumes which can either be measured directly by using a spirometer or calculated from measured volumes. The values obtained are useful when diagnosing some pulmonary disorders and diseases. The four lung volumes are expiratory reserve volume, ERV; inspiratory reserve volume, IRV; residual volume; and tidal volume. Tidal volume is the volume of air that is inspired or expired during eupnoea, or in other words a normal breath. Residual volume is the volume of air remaining in the lungs after a maximal expiration or the volume of air that can never be expelled. ERV or expiratory reserve volume is the maximum volume of air that can be additionally expired after a tidal expiration. A memory key for this one is after a normal out breath, breathe out a deep sigh. Finally, inspiratory reserve volume, or IRV, is the maximum volume of air that can be additionally inspired after a tidal inspiration. The memory key for this one is after a normal breath in, breathe in deeply. The tidal volume of healthy lungs is about 500 milliliters. Normal residual volume is about 1.2 liters. Normal inspiratory reserve volume is about 3 liters.

 

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