Carbon monoxide (CO) poisoning is one of the most common types of fatal poisonings worldwide. Acute exposure to high levels of CO as well as chronic exposure to low levels of CO and excessive noise can lead to high frequency hearing loss. In this study, twelve guinea pigs were randomly divided into two groups: (1) exposed to noise and (2) exposed to noise plus CO. Auditory brainstem responses (ABRs) were measured prior to the experiment and immediately, 5, 10 and 15 days post exposures. There was a significant difference between the ABR thresholds before and immediately after exposure to noise at frequencies of 4, 8, and 16 kHz and the most threshold shift was observed at 8 kHz. There was also a significant difference between the ABR thresholds before and immediately after exposure to noise and CO at frequencies of 2, 4, 8, and 16 kHz which demonstrated a temporary hearing loss after exposure to noise and CO and the major impact of CO on developing noise induced hearing loss occurred at 8 kHz. No significant difference was observed between the ABR thresholds recorded before conducting the experiments and the ones obtained 5, 10 and 15 days after simultaneous exposure to noise and CO at none of frequencies. Simultaneous exposure to noise and CO contributes to transient hearing loss in guinea pigs with the most evident temporary shift at 8 kHz. The methods were accepted in the Ethics Committee of Iran University of Medical Science (registration No. CTRI/2016/01/017170) on January 18, 2016.

<p>The aim of this review study was to overview articles available from 2019 to 2021 to answer the question: "Is the COVID-19 associated with sudden vestibular abnormalities among people with COVID-19 infection or improved peopleof the COVID-19?" Articles included in this review were searched through the PubMed, Scopus, and Google Scholar databases from 2019 to 2021. We have utilized the search terms vertigo, dizziness, vestibular neuritis, and C0VID-19. According to the 33 available articles, the total number of patients was 363. The 95 patients (26.1%) reported dizziness, vertigo, and imbalance during the COVID-19 infection or after of the recovery. The 12 patients (12.6%) showed the vestibular neuritis, 2 patients (2.1%) indicated the cerebellitis, 2 patients (2.1%) demonstrated the benign paroxysmal positional vertigo, 2 patients observed (about 1%) with the labyrinthitis, and 1 patient (about 1%) depicted the intra-labyrinthine hemorrhage. Several studies have been reported the relationship between the COVID-19 and the vestibular system. Although more comprehensive studies are needed to investigate this matter but the evidence suggests that the COVID-19 is a neuroinvasive virus, and it is the most likely hypothesis for the cause of sudden vestibular abnormalities in the infected patients.</p>