Talking Hearing Aids with Brian Taylor and H. Gustav Mueller

Brian_TaylorGus_Mueller TaylorMueller_2e_FDHA2E

Fitting and Dispensing Hearing Aids, a popular introductory textbook, has just been published in its second edition in September. We managed to listen in to a conversation between its two authors, Brian Taylor and H. Gustav Mueller, who were exchanging some thoughts regarding their new 2nd Edition.

BT:  You know Gus, when we wrote the first edition of this book, I remember us talking about the fact that there seemed to a fair number of professionals who maybe weren’t following Best Practice when they were fitting hearing aids.  We thought that it might simply be because they didn’t exactly know what was called for in Best Practice, or maybe it never had been laid out for them in an orderly manner.

HGM:  And we thought a book like ours might help . . .

BT:  Right.  Do you think it did?

HGM:  I’d certainly like to think so.  We sold a lot of copies, so that’s a good start!  But honestly, when I travel around, I don’t see as much change over the past five years as I thought might happen.  Let’s take pre-fitting testing for instance.  We have some great speech-in-noise tests available for clinical use like the QuickSIN, the BKB-SIN and the WIN.  We talked about all of these in the book, provided step-by-step guidelines, yet I just don’t really see an uptake—for some reason, audiologists and hearing instrument specialists seem to have a love affair with monosyllables in quiet, which really have little use for the fitting of hearing aids.

BT:  Maybe we’re expecting things to happen too fast.  I think it’s good we expanded that section on pre-fitting speech recognition testing in the current book—hopefully more readers will take notice.  And as you know Gus, I’ve always been a fan of the ANL.  I just saw that there has been over 40 articles published on that test in the past 12 years!  That’s another easy-to-do test, and it really provides information that you cannot learn by doing speech recognition testing.

HGM:  Part of Best Practice is picking the right technology for the right person.  I recall you spent a lot of time researching all the new technology that has come out in recent years for this 2nd Edition.

BT:  Things change pretty fast in that area.  I think we’ve added some great new sections on wireless connectivity, frequency lowering, and audio data transfer between hearing aids. Like the first edition, rather than getting into the intricate technical details of various features, we focus on how this technology benefits the patient. For example, in the chapter that covers wireless connectivity and audio data transfer between hearing aids, we write about how these new features enhance benefit in background noise, and how candidates are identified.

HGM:  And, of course, verification of the fitting is critical.  The best hearing aid in the world is no better than a PSAP if it’s programmed wrong.  I think our new section on speechmapping will be extremely helpful for people who are just getting started using probe-mic measures.  As we described, recent research clearly has shown that you can’t simply rely on what you see simulated on the software fitting screen.  As, of course, all those special features that you talked about, such as frequency lowering, need to be verified in the real ear too!

With all that said, however, we also know that verification alone is not enough to demonstrate to patients, their families, and even third-party payers that a new set of hearing aids is worth the investment—so, we can’t forget about outcome measures.

BT: Yes, Gus, it seems there are always a couple of new outcome measures to talk about. With all of the recent research on the impact of untreated hearing loss on other conditions, like cognitive function, social isolation, and overall mental health, we added a section on validated self-reports to measure the impact hearing aid use may have on these common conditions.  Even if you’re not inclined to measure those types of downstream outcomes, we added more detail on using the International Outcome Inventory for Hearing Aids (IOI-HA). As you know, many audiologists and hearing instrument specialists neglect to conduct any outcome measures. We cover the reasons this is a bad idea, and suggest, if you are only going to use one measure, it ought to be the IOI-HA.

HGM:  And you know, some people suggested that it was a little silly for us to use our chapter themes of country music, movies, wine tasting, baseball, and all the others, but I’m glad we kept that going in this 2nd Edition.

BT:  Me too.  Who said you can’t have fun and learn about hearing aid fitting at the same time?  After all, it’s worked all these years for the two of us!

 

Book Review: Auditory-Verbal Therapy reviewed by Helen M. Morrison, Ph.D., CCC/A, LSLS Cert. AVT

AVT book - artwork -v8

Auditory-Verbal Therapy: For Young Children with Hearing Loss and Their Families, and the Practitioners Who Guide Them, by Warren Estabrooks, Karen MacIver-Lux and Ellen A. Rhoades, Plural Publishing, 2016.

Reviewed by Helen M. Morrison, Ph.D., CCC/A, LSLS Cert. AVT

 

 

 

Auditory-Verbal Therapy provides a thorough, 21st century resource for professionals, families, and students. Each chapter is organized in a way that technical information is accompanied by suggestions for practical application, making it a likely “go-to” reference that will be consulted frequently.

The history of Auditory-Verbal therapy (AVT) described in the first chapter is comprehensive and much needed in order to ensure that the story of the approach is not lost to current and future generations of professionals and families. The book is clear about the principles of AVT, what it is and is not, all while demonstrating how AV therapy has evolved to apply evidence-based practices that meet the needs of today’s diverse families and children.

A highlight of the book is a systematic review of literature concerning AVT that utilizes the most current techniques and standards for scientific rigor to describe the state of evidence supporting the approach. The chapters that address audiological procedures and hearing technology are current and provide a basis for deeper reading of the topics discussed. The book addresses each of the knowledge domains that Auditory-Verbal therapists apply in practice, including comprehensive developmental milestones, emergent literacy, inclusion and specific strategies for parent coaching.

An important section of this book provides a rationale and framework for planning and implementing AVT sessions, followed by a series of case studies and lesson plans written by experienced AV therapists that apply this framework. The children and families in these case studies and lessons represent a range of ages, diagnoses, additional disabilities, and cultural/economic situations. The lesson plans at first glance may not seem like conventional lesson plans. They illustrate how important teaching within the conversational context is in AVT, beginning with initial greetings and entering the therapy room or home. Following the child’s lead and exploiting teachable moments are highlighted.

Finally, families from across the global community tell their own stories, demonstrating the universality of the approach. The families not only hail from many different countries, but they are each unique in their cultural and economic situations, types of hearing loss and the ages at which their children entered AVT. Many of the children in these families have challenges in addition to hearing loss.

This book is a must-have for anyone who works with children with hearing loss and their families. The information has value for professionals and families across the communication options that families might choose. This book is essential for professionals working to attain Listening and Spoken Language Specialist certification. It will guide their learning during their certification period and serve as a foundational source for examination preparation.

AudiologyNOW! 2016 Author Signing Schedule

AudiologyNOW! attendees – Meet our authors and connect with experts in the field! Stop by the Plural booth (#301) for the following Meet the Author sessions: 


Thursday, April 14, 11:00 am – 12:00 pm
Meet Marc Fagelson, BA, MS, PhD 
Co-editor of Tinnitus: Clinical and Research Perspectives

Marc Fagelson   Tinnitus


Thursday, April 14, 3:00 – 3:30 pm
Meet Mark DeRuiter, MBA, PhD and Virginia Ramachandran, AuD, PhD
Authors of Basic Audiometry Learning Manual, Second Edition 

Mark DeRuiter   Virginia Ramachandran   Basic Audiometry Learning Manual, Second Edition


Friday, April 15, 11:00 – 11:30 am
Meet Ruth Bentler, PhD, H. Gustav Mueller, PhD, and Todd A. Ricketts, PhD
Authors of Modern Hearing Aids: Verification, Outcome Measures, and Follow-Up  

Ruth Bentler   H. Gustav Mueller   Todd A. Ricketts  Bentler_MHA.jpg

Congratulations to Ruth Bentler, 2016 recipient of the Jerger Award for Research in Audiology. 


Friday, April 15, 1:00 – 2:00 pm
Meet Anne Marie Tharpe, PhD
Co-editor of Comprehensive Handbook of Pediatric Audiology, Second Edition

Anne Marie Tharpe   Comprehensive Handbook of Pediatric Audiology

Congratulations to Anne Marie Tharpe, 2016 recipient of the Marion Downs Award for Excellence in Pediatric Audiology. 

2016 Awards and Honors

We are thrilled to announce the winners of the 2016 Plural Publishing Research Awards given in honor of the late Dr. Sadanand Singh, Plural’s founder. These two scholarships are awarded by the Council of Academic Programs in Communication Sciences and Disorders and the honorees and their faculty sponsors will be acknowledged at the annual CAPCSD meeting award banquet, in San Antonio, TX on March 31.

At the MS/AuD level, the award went to Chelsea Hull of the University of Nebraska-Lincoln. Working with advisor Dr. Sherri Jones, Chelsea is researching the impact of Sound Field Amplification (SFA) devices, specifically the REDCAT amplification system, on student academic outcomes and teacher perspectives of this amplification system on academic improvement.

CAPCSD Scholarship Chelsea Hull

Chelsea Hull                                                         Au.D. Student                                             University of Nebraska-Lincoln

At the PhD level, the award was given to Nancy Quick of the University of North Carolina. Under advisor Dr. Melody Harrison, the focus of Nancy’s research is on investigating the impact of underlying linguistic sources of knowledge on spelling among children with hearing aids, cochlear implants and normal hearing, utilizing a multilinguistic analytic approach.

CAPCSD Scholarship Nancy Quick

Nancy Quick, M.S. CCC-SLP               University of North Carolina at Chapel Hill PhD Candidate in Speech and Hearing Sciences, Class of 2017

Congratulations Chelsea and Nancy on your achievements!


Continue reading

The Changing Indications for Cochlear Implantation

Theodore R. McRackan, MD Otology, Neurotology, and Skull Base Surgery

By Ted McRackan, MD, co-editor of Otology, Neurotology, and Skull Base Surgery: Clinical Reference Guide

Cochlear implantation is the gold standard for treatment of severe to profound sensorineural hearing loss. Cochlear implants (CIs) were approved by the Food and Drug Administration (FDA) in 1985 and have been suggested to be the most successful neural prosthesis created to date. Over 300,000 cochlear implants have been performed worldwide, with over 50,000 performed in the past year alone. Cochlear implantation involves a surgical procedure whereby an electrode array is placed in the cochlea of the inner ear, which is organized in a tonotopic fashion with decreasing characteristic frequency along its length. Modern CIs contain between 12 and 22 electrodes, which are spaced with the intention of each electrode stimulating a unique area of the spiral ganglia of the auditory nerve. Cochlear implants work by having an external microphone and an external processor convert an acoustic signal to an electrical signal. It is then sent to a speech processor, which is designed to enhance the signal and reduce noise before sending the information to the spiral ganglion through the CI electrode array.

Cochlear implantation is currently at an exciting time point due to the combination of improving technology and proven outcomes that has led to rapid expansion of its indications. The FDA approved the first single-channel CI electrode for adults in 1984, followed by the multichannel electrode in 1987. Cochlear implants were then approved in 1990 for children older than 2 years, in 1998 for children over 18 months, and ultimately in 2000 for children older than 12 months. There has been a recent push to implant children younger than 12 months due to evidence that children implanted at this age are more likely to catch up to normal-hearing peers at an earlier time point. Three major obstacles have hampered this movement. First, obtaining accurate hearing diagnostic testing in a timely manner can often be difficult in those less than 12 months. Second, there is a slight increased risk of surgical complications due to the low blood volume in this age group. Third, it can be extremely difficult to perform cochlear implant programming in this age group. Nonetheless, the clear benefits of early implantation likely outweigh these risks. Pediatricians, audiologists, and otolaryngologists are encouraged to identify infants with hearing loss as soon as possible for hearing rehabilitation. The earlier this is performed, the earlier children with profound hearing loss can be identified, and the earlier they can be implanted, leading to better CI outcomes.

Use of cochlear implantation in patients with residual hearing has been another area of rapid expansion. It was initially thought that all hearing would be lost with cochlear implantation and that if hearing was preserved, patients would not be able to process electrical and acoustic hearing. However, through the trials of the Cochlear Hybrid electrode and the MED-EL EAS electrode, it appears that both are possible. Through these and other trials, most patients had preserved residual hearing after cochlear implantation. Additionally, these patients showed improved hearing outcomes compared to patients without residual hearing. At the present time, it is not clear whether this preserved hearing is sustainable over time. This is an active area of investigation and will continue to be studied for years. Nevertheless, this technology has greatly expanded the indications for cochlear implantation beyond traditional candidacy.

As discussed above, it was previously thought that individuals would not be able to process combined electrical and acoustic hearing. However, cochlear implantation in patients with residual hearing proved this incorrect. This has led to the more widespread use of CIs in individuals with single-sided deafness. Current standard treatment for single-sided deafness includes devices that essentially ignore the deafened ear. However, with cochlear implantation, hearing can be restored to that ear. This was initially performed in patients with severe tinnitus in the deafened ear but is now being more commonly performed in the absence of tinnitus. Further work is certainly needed to develop a more comprehensive understanding of cochlear implantation in this population, but preliminary data show decreased head shadow effect and improvement in binaural summation, spatial release from masking, and potentially sound localization.

Beyond cochlear implantation, the use of auditory brainstem implants (ABIs) in children is another area of expansion. Although this has been performed in Europe for years, it is only more recently being performed in the non-neurofibromatosis type II population in the United States. Several centers have active clinical trials to perform ABIs in children unlikely to benefit from cochlear implantation due to either absent cochlear nerves or cochlear malformations. This is an unfortunate population as they have limited hearing rehabilitation options. Auditory brainstem implants provide an opportunity for hearing in this population, and the neurotology community is excited to hear the results of these trials.

We have come a long way since Bill House developed the first single-channel CI. As outcomes and technology continue to improve, the indications for cochlear implantation will grow. The audiology and otology communities are eager to see what the future holds for cochlear implantation.

About the Author
Dr. Theodore R. McRackan is an assistant professor of otolaryngology at the Medical University of South Carolina. He received his medical degree from the Medical University of South Carolina and completed his otolaryngology residency at Vanderbilt University. Dr. McRackan then completed his fellowship in neurotology-skull base surgery at the House Ear Clinic. His professional interests include neurotologic outcomes and quality of life research. Dr. McRackan and Derald E. Brackmann, MD co-edited Otology, Neurotology, and Skull Base Surgery, which serves as both a study resource for qualifying exams and a portable clinical reference guide. This text features a concise and approachable outline format, contributions by leaders in the field, and key topics such as anatomy and embryology, hearing loss, cochlear implantation, skull base tumors, vestibular disorders, and pediatric otology. View sample pages and place your order at www.PluralPublishing.com.

Tinnitus: In the Brain of the Beholder

Marc_Fagelson    Baguley_PTINN    David_Baguley

 

By: Marc Fagelson, BA, MS, PhD and David M. Baguley, BSc, MSc, MBA, PhD

Co-editors of Tinnitus: Clinical and Research Perspectives

Most audiologists and patients understand tinnitus to be the perception of a sound that is not connected in any way to an environmental event. For some patients, the sound produces minimal discomfort and is noticeable only a fraction of the time. Other patients are not so fortunate, and their tinnitus may persist and prove distracting when they are in the presence of other sounds or when they try to communicate. A relatively small proportion of patients with tinnitus, still probably more than 10 million people worldwide, have bothersome tinnitus that consistently reduces their quality of life and affects most routine activities. Such patients often respond to tinnitus as though its presence merits the attention and concern consistent with that demanded by a sound that is recognized as a threat. These patients illustrate some of the more confounding elements of tinnitus: it is a sound experience that may produce, or be associated with, powerful emotions and physiologic responses consistent with those demonstrated in fear-avoidance research.

A person’s experience with tinnitus may be complex and multi-faceted. Some patients link tinnitus to traumatic events, perhaps those that triggered the tinnitus onset. Other patients report psychological conditions such as anxiety and depression appear to exacerbate tinnitus and may be reinforced by tinnitus-related negative associations. Often, tinnitus severity is dictated not by the sound, but by the patient’s interpretation of and response to the sound. In this regard, the power of tinnitus to exert influence over a person’s life is in the eye, or ear, of the beholder.

Tinnitus interventions, then, may be viewed as proceeding along parallel tracks: abolishing or attenuating the sound may be the target of a treatment strategy, or the patient’s response to tinnitus may be the target of a management strategy. Both approaches are considered in detail, and with many examples, in Tinnitus: Clinical and Research Perspectives. Continue reading

Must-see TV – Audiology is a hot topic this week

Authors_in_the_News

Recently a few of our authors have been on television! They are experts in the field of audiology and we are happy to share their wisdom and success.

Ruth Bentler, PhD was on Charlie Rose’s Brain Series speaking about the brain and hearing. Specifically she detailed some of the history of the hearing aid and the future of hearing loss awareness and acceptance. Just want to see Ruth? Skip to the 20 minute mark.

Brian Taylor, AUD was interviewed on hearing health by Morgan Fairchild for the new show Baby Boomers in America on the LifeTime Network. He discusses the importance of early detection and maintained audiologic care.

Follow the Signs- Protect Your Hearing

Do you have difficulty hearing and following conversations in noisy restaurants and crowded rooms? Are male voices easier to understand than female voices? Do you experience ringing or buzzing sounds in your ears? If you answered “Yes” to any of these questions, you may have a hearing loss and need to visit an audiologist. Audiologists are healthcare professionals that specialize in evaluating, diagnosing, treating and managing hearing loss and balance disorders in adults and children.

Untreated hearing loss affects your ability to understand speech, negatively impacting you socially and emotionally. Hearing loss can affect people of all ages; not just seniors. Over 36 million American adults have some degree of hearing loss. The statistics are shocking, especially knowing that over half of those 36 million Americans are younger than age 65.

Protect Your Hearing12 million Americans have hearing loss as a result of noise exposures. Over 5 million of those people are under the age of 18. Noise induced hearing loss is a permanent and preventable disability that can affect your quality of life. Follow these easy steps to protect your hearing:

  • Walk away from the noise
  • Turn down the volume
  • Wear proper ear protection

Hearing loss is an increasing preventable health concern in this nation. Taking time to see an audiologist for regular hearing screenings and knowing the signs of hearing loss can protect your hearing. This October is both Audiology Awareness Month and Protect Your Hearing Month! Follow the guide below to avoid extended exposure to loud noises and celebrate by preventing hearing damage; or go to the American Academy of Audiology’s website to see what you can do to spread awareness this month.

Noise Levels Poster

Guest Post by Melanie Lewis: Hearing Loss

Foreword:

Our guest post this week, by Melaine Lewis with Hearing Direct, explains the details of hearing loss and recommended courses of action.

-Plural Team

HEARING LOSS

EarHearing loss can occur due to a number of reasons, these can be due to changes that the body undergoes (age-related) or more man-made reasons such as exposure to harmful noise. According to Kochkin’s 2008 survey (*MarkeTrak VIII) 35 million Americans are thought to present  the symptoms of impaired hearing and the number is projected to increase to 40 million by 2025.

The biggest group and the subject of this post are the age-related (Presbycusis) hearing loss suffers whose condition is often misunderstood. Many sufferers chose to ‘accept’ diminished hearing as a given fact, though modern healthcare offers means to mange the condition so its influence on daily lives is minimized.

What Is Age-Related Hearing Loss?

Let’s start by explaining what it isn’t. It isn’t a condition that an individual can control like noise induced hearing loss nor does it normally lead to complete hearing loss.

It is a gradual demise in hearing ability known as sensorineural hearing loss. As the body matures, two processes lead to reduced hearing of certain frequencies. The first is degeneration of a part of the inner ear that contains micropscopic blood vessels, while the second process is the decline in sensitive hair cells inside the cochlea (a snail-shell like structure in the inner ear) that gradually become damaged or die due to increases in free radicals that damage certain cells in the body. The body is unable to regrow these hair cells (these are really nerve endings that detect sound) which leads to the categorization of agerelated hearing loss as a permanent one.

ear mechanisms

What Are The Typical Symptoms Of Age-Related Hearing Loss?

The level of hearing loss will vary between individuals. Some will be able to make simple adjustments in their lifestyle to counteract its affects, while in the case of other individuals the deterioration in hearing ability will require the intervention of modern healthcare.

Symptoms and signs can include:

  • Certain sounds seem too loud
  • Difficulty following a group conversation
  • Difficulty hearing in noisy areas
  • Hard to tell high-pitched sounds (such as “s” or “th”) from one another
  • Increased difficulty in understanding women and children
  • Problems hearing when there is background noise
  • Voices that sound mumbled or slurred

What Is The Recommended Course of Action?

If you suspect that you or someone you care for might be experiencing the telltale signs of hearing loss, it should be investigated by your family doctor, local ENT unit or hearing center. Although the most common causes are linked to aging, other causes should also be investigated to be  ruled out.

These may include:

  • Acoustic neuroma
  • Certain infections such as meningitis, mumps, scarlet fever and measles
  • Use of certain medicines
  • Genetic conditions
  • Skull fractures
  • Traumatic noisy events

To eliminate and diagnose the precise cause(s), a hearing test will need to be performed. A basic test can be conducted at your family doctor’s practice, though it is likely that you may also need to book a physical audiometry test at your local ENT or hearing center.

Equipped with the result, your healthcare advisor will be able to recommend the most suitable solution from using ALDs (Assistive Listening Devices such as Hearing Aids) or adapting certain communication techniques. In the case of severe hearing loss, learning sign language and even cochlear implants may form part of the recommended options.

Hearing loss does not have to undermine your quality of life. It can and should be managed.

 

About the Author:

HearingDirectMelanie Lewis is a trained hearing aid audiologist. She works for Hearing Direct, the UK’s biggest supplier of deaf and hard of hearing aids from hearing aid accessories such as batteries to ALDs (Assistive Listening Devices).

 

* The MarkeTrak VIII survey included 80,000 members of the National Family Opinion (NFO) panel. Of these, 14,623 hearing impaired individuals were identified.

Guest Post by Tom Rokins: How To Look After Your Hearing

Foreword:

Hearing loss can occur at any age for any number of reasons. It most typically occurs between the ages of 49 to 55. It may, or may not, surprise you to learn that people often do not realize they have developed a hearing loss, as it can be a subtle and gradual change. Our guest post this week, by Tom Rokins with Boots Hearingcare, details several easy methods of care and prevention.

-Plural Team

 

HOW TO LOOK AFTER YOUR HEARING

As you know, your ears are pretty important to living a high quality life – they are the things which hear everything going on around you, help you keep balance and help you get around in life.

ear

Think about what things would be like if you suddenly lost your hearing tomorrow; it wouldn’t be a very enjoyable experience.

That’s why you should want to take as much care of those precious aural organs as possible. Thankfully, they’re not too difficult to look after – a bit of TLC and common sense should work wonders to keep your ears working better and for longer.

Keep Loud Music to a Minimum

Everyone’s hearing can be affected negatively by loud music, but some people are more sensitive to this damage than others. Think back to the last gig you went to, or the last time you spent all night clubbing – when you got home, you almost definitely experienced a ringing in your ears, a bit like tinnitus.

That is temporary hearing damage. Sadly, the more you expose yourself to these noisy environments, the more the hearing damage increases. This degeneration is usually slow and subtle – you don’t notice it until it’s too late.

60/60 rule

It’s worth keeping in mind the “60/60” rule – if you listen to an MP3 player at 60% volume, keep it limited to 60 minutes a day or less. Noise-cancelling headphones can be of use; because they eliminate pesky background noise, you can hear better at a lower volume.

If you’re in the club or at a gig, make sure to keep a reasonable distance from the speakers and regularly step outside for a break. If your ears are hurting or ringing, or you have to shout to be heard by someone two meters (~7 ft.) away, the music is too loud.

Drugs That Can Harm Your Hearing

Some drugs can, believe it or not, damage your ears; these are called ototoxic drugs, and they can cause tinnitus and balance problems as well as hearing loss.

Some of these can actually cause permanent deafness, but it is incredibly unlikely that you will be prescribed one of those unless it is completely necessary, a life or death situation. Others will have a temporary effect, and should clear up once the drugs are out of your system.

Some cancer drugs can cause permanent hearing loss, such as Cisplatin. If you’re on a smaller dosage you should be fine, but higher ones could lead to deafness. Aminoglycoside antibiotics, used in treating potentially fatal diseases, can also cause hearing loss, but are becoming less common.

Aspirin and other salicylates can cause tinnitus, loss of hearing and even vertigo when taken in large doses, but these effects are reversible once you stop taking the drug. Quinine, the anti-malarial drug, can have similar results.

Ear Wax and Its Effects on the Ear

Maybe you think of ear wax as a nuisance. You’d be wrong – it protects the inside of your ears, trapping particles of dust, sweat, dirt and the like to prevent infections. It slowly works its way out, taking the rubbish with it.

Too much ear wax can cause itchiness, discomfort, or even slightly diminished hearing. Do not, under any circumstances, start rooting around in there with a cotton bud – this can push the wax further in or even do damage to your ear drum.

Instead, go and get an appointment with your doctor. Once it’s been cleared out, if you are still experiencing problems hearing, you should visit a trained audiologist.

About the author:

Boots HearingcareTom Rokins wrote this article on behalf of Boots Hearingcare, the hearing aid specialists in the UK. If you need any advice on looking after your hearing or even want a free hearing test- get in touch.