Journal Club: Localised hypothermia treatment of the petrous inner ear by a trans-ear canal cooling device

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Today's journal article

Krishnan PS, Yepes MF, King CS, Rajguru SM. Development and Evaluation of a Novel Transcanal Catheter for Delivery of Hypothermia to the Inner Ear. 

Why I picked this article

A brief period of mild hypothermia, or cooling of the body temperature, can be used as an intervention to protect the brain and neurons under stress. It protects neurons by lowering metabolism and reducing inflammation, thereby preserving some neuronal viability under extreme stress, such as traumatic brain injury or hypoxia. Therapeutic use of mild hypothermia to improve patient outcomes has been investigated and implemented for brain disorders. Similarly, for the inner ear pathologies, animal models showed that a mild hypothermia can help protect the inner ear in injury models by reducing inflammation and oxidative stress. 

The question is then how to apply an ideal, controlled amount of hypothermia specifically to the target organ, in this case, the inner ear. Prior approaches cooled the cochlea from the promontory or mastoid, which is harder to standardise. This research tests a simple, noninvasive device that sits in the ear canal and aims to cool both the cochlea (hearing) and the vestibular organs (balance) without getting in a surgeon’s way.

Some of the research findings

Samples: 
  • Human cadaver heads were used in this research.
    • Human cadaveric temporal bones were processed - mastoidectomy was performed to show the facial recess, and the round window niche was drilled. 
    • Semicircular canals were outlined by drilling the mastoid bone posterior and superior aspects. 
    • Cadaveric heads were placed in an aluminium container with meal beads to keep the temperature at 38°C ±3°C. 
  • Thermometers were placed on:
    • approximately 3 cm into the nasopharynx (tracked whole-head temperature)
    • 1 cm into the round and oval window
    • all three semicircular canals
Hypothermia cooling device: 
  • a custom saline-filled cooling catheter with a small balloon tip positioned in the external ear canal next to the tympanic membrane (= eardrum).
    • the catheter: medical grade nylon (PEBAX), flexible
    • the balloon element - polyurethane, soft & allows for low-pressure inflation
    • ~0.4 psi (20 mmHg) used to inflate the balloon
    • The balloon sits immediately lateral to the tympanic membrane. 
  • 15 ml water (5°C) was used. 
  • A 30-minute cooling sequence with continuous temperature logging.
Key results: 
  • Temperatures at the cochlear and vestibular sites fell by approximately 4–6 °C during the 30-minute protocol.
    • The temperature at the round and oval windows both changed 4–6 °C on average, while the systemic body temperature (nasopharynx measurement) did not change. 
    • This suggests that a localised cooling without whole-head hypothermia was achieved. 
  • Computerised modelling reproduced the measured inner-ear temperature reductions, supporting the mechanism and parameter choices.
Researchers suggest that one of the utilities of this hypothermia device is cochlear implant surgery to minimise the damage to the auditory neurons. In this regard, the catheter sits in the ear canal, so it does not obstruct the operative field during the cochlear implant surgery. 
From Figure 3. The temperature changes measured at the nasopharynx, the round window and the oval window, over 30 min with the hypothermic cooling device. Krishnan et al. (2025)

Haruna's takeaway

At the University of Auckland, there is a world-leading team led by Prof. Bennet, Prof. Gunn and A/Prof Davidson who utilise sheep as the large animal model to test various methodologies, including hypothermia, for protecting premature babies' brains. So I was very familiar with medical hypothermia, and very interested in seeing this research title, of doing it for the cochlea, especially because the inner ear is so small and hard to access. The insertion of the probe into the ear canal seemed to achieve cooling in the cadaveric tissue, but I wonder if that might impact the other areas surrounding the ear canal, as the area is fully vascularised and innervated. I wonder if there is literature on the benefit/side-effect of cooling (even as a whole head) with other inner ear diseases, after blast injury/ accidental noise exposure, maybe during an attack of vertigo? 

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This is Haruna's 78/100 of the 100-day challenge to post a science blog article every day! I love inner ear biology & cochlear physiology.