Medial-olivocochlear (MOC) reflex responses in young adult cardiopulmonary bypass patients

Cardiopulmonary bypass surgery is performed in patients who need revascularization in coronary diseases. The aim of this study is to compare the medial-olivocochlear reflex (MOC) responses of patients who underwent cardiopulmonary bypass surgery before and after surgery and to determine their level of influence. In this study, 40 individuals who had coronary artery bypass (CAB) surgery and 40 did not have any cardiovascular disease participated in this study. Preoperative and postoperative tympanometry, pure tone audiometry, transient otoacoustic emission (TEOAE), and emission tests in suppression were performed on patients who had CAB surgery. The results before and after surgery were statistically analyzed. Preoperative TEOAE values of the patients in the coronary bypass group were found to be statistically significantly lower than those in the control group (p=0.001; p<0.01). The decrease in the postoperative TEOAE measurement of the cases compared to the preoperative values was statistically significant (p=0.001; p<0.01). Preoperative suppressed TEOAE values of the cases in the case group were found to be statistically significantly lower than those in the control group (p=0.001; p<0.01). The change in the post-surgical value of the 1k Hz suppressed TEOAE measurement of the cases was not statistically significant compared to the pre-surgery, but it was found to be significant in all other frequencies (p=0.001; p<0.01). According to pure tone audiometry results, the preop and postop values of the cases in the case group were found to be statistically significantly higher than the cases in the control group (p=0.001; p<0.01). In the postoperative results of the cases compared to preop, the change was found to be significant at 8000 Hz in the right ear and at 500, 1000, 2000 and 4000 Hz in the left ear. The stria vascularis part of the cochlea has a high degree of microvascular structure. Increased permeability in the endothelium disrupts the electrolyte balance in the endolymph. As a result, the signal transmission between hair cells is disrupted. The basilar membrane response is inhibited by the activation of MOC fibers that synapse on outer hair cells(OHCs) in order to reduce the intensity of sounds. We think that the cochlear damage in our patients may be caused by the involvement of the vascular endothelial wall resulting from coronary bypass. In addition, antioxidants and inhibitors can cause hearing loss due to oxidative stress. Our patients in our study are exposed to oxidative stress due to bypass surgery and may cause hearing loss. OHC's are more susceptible to ischemia than inner hair cells. Vascular endothelial damage as a result of cardiopulmonary bypass causes ischemia and causes OHC loss. Our results support the cochlear damage that may occur after ischemia. Due to the increase in coronary diseases, there is a need for revascularization. Although some complications develop in the cochlea and auditory pathways as a result of cardiopulmonary bypass surgery, it has an important place in the health system as an alternative and safe method, which is being used by more and more centers. MOC fibers, which protect the auditory system from acoustic traumas, strengthen frequency selectivity and increase understanding in noise, are significantly affected by cardiopulmonary bypass surgery.