Importance of REM

@Hearing_Potential said:

Think a little more. You get better HL audiogram because insertphones are calibrated for a larger volume than the average female ear canal so the sound pressure is louder than expected. But once the very positive RECD is taken into account the SPL hearing loss is in reality worse than the HL audiogram, hence greater listening difficulties for the same HL level of hearing loss.

You cropped my quote there, about why the residual volume will track the fitted volume.

Also no, your argument makes no sense:

Volume small = relative (in-canal) measurement SPL up = better result = LOWER HL = Lower Prescription O/P SPL = relatively suits smaller canal.

Volume Large = Relative (in-canal) measurement SPL down = worse result = Higher HL = Higher Prescription O/P SPL = relatively suits larger canal.

Volume Average = Relative (in-canal) measurement SPL normal = average result = expected HL = as per Prescription O/P SPL = suits average canal.

You lost your logic somewhere in your interpretation.

That’s why your voice always sounds louder in an elevator than Carnegie Hall. And men are just more stubborn/willing to ignore degrees of loss than Women, probably for a similar reason that they establish an interest in lawnmowers or outboard engines……or are just worse at self-determination of medical issues in general: possibly because they are less risk averse in general/not so good with the stigma vs. communication benefits of hearing aid wear.

I actually don't disagree with most of what you've written, however your interpretation for the purposes of comparing HL hearing thresholds measured using insertphones between people isn't correct.

As we both agree, someone with a smaller ear canal size will have better HL thresholds than someone tested with the same calibrated insertphones who has a larger ear canal volume. A fair comparison can only be made by measuring their RECD and converting the HL audiogram into SPL.

When you do this for two people with identical HL audiograms, the SPL loss will be larger for a smaller ear canal volume if all other things are equal. Hence why females with smaller ear canals and the same HL audiogram as males with larger ear canal volumes might experience greater listening difficulties: soft speech may be less intelligible to them depending on the audiogram configuration.

When ear canal volumes differ and you've performed the hearing test using insertphones you need to compare the SPL audiogram whether this is within the same person such as an infant whose ear canal is growing or between people with different ear canal sizes in order for the comparison to be entirely accurate and fair.

Does that make sense? Do you see the logic in this now? Please note, I'm hypothesizing this to be a contributing factor to the perception that women with lesser degrees of HL loss seek hearing assistance earlier. I'm not saying it is the only contributing factor. You've already acknowledged many differences between men and women. There's no reason why this cannot also be included in that list.

Could this debate not be resolved with a simple demo? Using software that shows SPLogram, input the same audiogram for two dummy patients and below average RECD for one and above average for the other. How do the SPLograms differ?

If it is this simple to observe in software, why are audiologists short changing patients by not measuring RECD? The assumption that average is close enough seems flawed if a patient wants best personalized care.

@user490 said:

If it is this simple to observe in software, why are audiologists short changing patients by not measuring RECD?

Possibly three reasons:

1 It's a self-correcting 'issue'.

2 It would demand a re-write of the long defined accepted standards for hearing tests and thereby potentially open a can of worms in terms of both legal and medical decision making.

3 The extent to which it makes a difference - usually the over implementation of output in smaller residual canal volumes has been well understood for years - and REM normally illustrates them anyway. Added to the fact that people will either complain about the loudness or, like in the case of most slightly open fits, the 'EXTRA' LF is just radiated out of the ear canal.

Are those good reasons? They seem flimsy and/or don't cover all cases. They seem similar to arguments against REM. Measuring RECD is an extra step, likely once per adult patient unless there is lots of weight gain or loss (is that accurate and how much is enough to alter RECD)? It doesn't seem unreasonable given the audiologist fees. Legal standards in the US are minimum standard of care, not maximums. Top providers often exceed the minimum by a lot. Is the UK different? What argument can you make for any material risk to the patient from measuring RECD and applying it in the way discussed here?

@user490 said:

How can patients tell whether insertion gain or speech mapping is being used based upon the screen display or other information?I think I've had speech mapping.

On an audioscan verifit system it will usually say speechmap or insertion gain somewhere on the screen. I cannot recall what it looks like on other systems as I've only really used speech mapping on them. Insertion gain historically used non-speech stimuli, but I'm not sure whether that's a hard and fast rule.

@user490 said:

Top providers often exceed the minimum by a lot.

This is really what it comes down to in the end. Many clinicians will only do things if it is part of the minimum standard of care but top clinicians will do whatever they can to maximize your chances of success.

No Stephen, it is the reality of the differences of how insertphones and supraural headphones are calibrated and positioned and something neither of us were educated in during our audiology training. "Less effected" by something isn't the reverse of anything, rather this information is complimentary to what you already know.

You haven't acknowledged corrections to the errors in your arguments in my responses and don't seem interested in properly engaging with them. That's your choice. As you're clearly disinterested in this information I'm not going to try and convince you further.

@mindsil said:

What I'm saying is that NAL-NL2 was also likely developed without taking this into account itself so where does that leave us?

NAL-NL2 incorporates the RECD for the transformation of HL thresholds into SPL for both the speechmapping and insertion gain methods of measuring the output of a hearing aid in the ear. The difference is that for insertion gain, the real ear unaided response measured is used in the calculation of targets, correcting for individual ear canal acoustics. The RECD is used solely for audiogram transformation from HL to SPL. For speech mapping the RECD is used for both the HL to SPL conversion of the audiogram and the generation of prescription targets.

If your audiogram was tested using headphones, the positioning of the headphones outside of the ear canal means that the total air volume of the system is going to be closer to the coupler size used to calibrate the headphone vs an insertphone which is still calibrated using a fixed coupler but is placed inside an ear at different insertion depths and plays sound into a cavity that is more variable in size relative to the coupler used to calibrate them. This will introduce more error that requires correction for an insertphone vs headphones.

Irrespective of which method of verification I was using, I would personally want to measure an RECD, but if you're verifying using real-ear insertion gain with an audiogram that was obtained using headphones and measuring the real-ear unaided response (REUR) then this will provide the next best option for accurate generation of prescription gain targets because it is less likely to be affected by transducer calibration differences and includes some measure of your individual ear canal acoustics.

Have you done any practical application checks for yourself on this? Identified a clear example of when a fitting on a small adult ear was compromised by using averaged RECD values and demonstrated the difference after using RECD? That would be interesting to see.

For headphones vs inserts, I can tell you that I will often check with one or the other when I am unsure about the results and want to double check. I've seen a lot of audiograms come in with apparent air bone gaps, especially in 250 - 1khz that when I check with headphones, they disappear. Personally I think it has to do with inserts being round and canals being a bit more oval so there are a fair number of people that the seal is almost never perfect. You'd need a custom insert of sorts.

Another thing I've come to do for myself is when I'm testing bone conduction, I'll try a few soundfield presentations to see where they respond. If the results are inconsistent, I'll retest with a more concentrated interest. It feels like a better version of PTA SRT agreement, to be honest.

I have found every once in awhile there will be a massive difference in results between headphones and inserts. Sometimes one direction or the other. I think my methods are consistent and that I know to observe things like collapsed canals and other factors, so I'm open to what you're saying. I also think there's parts that I still question. And it just gets to the point for me of, enough talk, let's measure it.

@mindsil said:

Have you done any practical application checks for yourself on this? Identified a clear example of when a fitting on a small adult ear was compromised by using averaged RECD values and demonstrated the difference after using RECD?

It's part of my daily clinical practice. You can see the difference in the gain targets every time you go from an average to a measured RECD, so it's something you can check as part of your routine workflow. I don't keep the average RECD data (targets) though, because it isn't what was used in the end.