Ahmed Khattab Thanks for the message. However, I do think the original math is correct. It's worked out more explicitly here: samples.jbpub.com/9780763781187/81187_CH02_FF.pdf (page 90 of the book, or page 22 of the uploaded pdf) Please let me know if it still seems in error.

Eric's Medical Lectures I don't know how to thank you for your reply. It turns out that it's just a matter of rearranging the equation. My mistake. Thank you for the clarification.

Ahmed Khattab No problem! I do make mistakes in these videos, and I honestly appreciate viewers pointing them out. Thanks for watching!

I did not get that calculation

Thanks for the feedback, and that's a great suggestion! I'm super behind in fulfilling requests, so I can't guarantee when I'll be able to get to it, but will add CSF, pleural fluid, and ascites fluid analysis to the list of upcoming topics.

By validity, are you asking about how accurately the tests are in discriminating different forms of pulmonary disease? Or how reproducible they are? Or how much clinicians actually use them in practice? (I'm happy to discuss any of these in the final video in the series.)

Eric's Medical Lectures Dear Dr Strong, By validity, I am refering to the criteria for acceptability for each test. For example, for spirometry, is there maximal effort; no cough or glottic closure during the first second ;good start-of-test; back-extrapolated volume less than 5% of FVC or 150 mL,tracing shows 6 seconds of exhalation or an obvious plateau, 3 acceptable spirograms obtained; 2 largest FVC values within 150 mL; 2 largest FEV1 values within 150 mL and finally reporting the highest FVC and highest FEV1, even if they come from separate maneuvers and that the FEV1/FVC ratio is derived from these values. There are criteria for acceptability for dilutional lung volumes, body box and the different techniques for diffusion capacity. Would you be able to elaborate on these in a separate lecture on pulmonary function test. Thank you. Sincerely, Raleigh

Raleigh Lee Raleigh, I'm very sorry, but I think you just exhausted my own knowledge on this particular issue. This level of detail is critical in the PFT lab, but by the time I see a PFT report, the technicians have already taken care of this. Thus, I don't know more about it. However, unless you are working as a PFT technician, it seems unlikely you'll need this information in routine clinical care. (though I can imagine one might potentially need to know this for pulmonary boards...)

Yes, you are correct. If only spirometry is ordered without a lung volume test, one might intepretate the result as "restrictive lung disease" based on the reduced vital capacity measured by sprometry.

I've been wanting to do a video on breath sounds for a while, but unfortunately, I've been dissatisfied with the quality of the breath sound recordings I've made. They are much harder to clean up than heart sounds were, and I've put it on hold until I either get a better recording stethoscope or manage to make cleaner recordings with what I have.

I hope he/she properly attributed them!

No and I'll explain why! For example, in the helium test, the patient begins to breathe the air containing helium at the end of tidal exhalation (i.e. when the FRC is contained in his lungs). When the stopcock is closed it is true that helium is distributed throughout the lung but in an air volume that corresponds only to the FRC. I got it?

@@giuseppevallese4153 Thank you!! Yes this makes more sense now

@nada amraoui Try to think that when the patient begins to breathe the circuit is closed and a single environment (reservoir + lungs [FRC]) is created in which the helium is distributed homogeneously. That's why the final helium concentration is the same in the reservoir and lungs. Clear?

In the absence of a pneumothorax (air in the pleural space around the lung), any air located within the thorax would necessarily be within the lung (with the exception of air in the esophagus, which is negligible in volume).

@@StrongMed Thank you for your response. The reason I'm asking is because I'm interested in measuring air volume within inflated lungs using CT. I am just curious whether quantifying the volume of the lungs=quantifying the volume of the air. Seems like this is true given your response, but if you have anything to add please do! Thank you again.

@@hollyhermann-sorensen5974 Yes, the volume of the lungs on CT is close enough to the air volume that these can be assumed to be equal for any common clinical application. (i.e. the volume of lung tissue

@@StrongMed Thank you SO MUCH for this response. This sets my mind at ease. I'm quantifying the air spaces of some anesthetized animals using CT at known inflated conditions. Someone recently asked me whether this method was comparable to whole body plethysmography as I'm quantifying tissue + air versus just changes in air volume. I feel now like I can say that they are basically the same thing. Thank you again!

yeah its like the only reason I watched the video lol. "ok, pleth, here it comes, and its skipped."