## 4 Discussion
An original study noted that analyzing a group of patients being treated for obstructive sleep apnea with PAP therapy, at one and 13 weeks after treatment, those who presented treatment emergent central sleep apnea in the first week were 3.5% but they resolved it by the thirteenth week. TECSA persisted in only a quarter of the affected patients, who had the highest rates of dropping out therapy. This means that in many cases treatment emergent apnea is a condition that resolves spontaneously and when TECSA persists there is a need to change therapy [35]. A study conducted by [PERSON] et al. noticed an unsolicited resolution of central sleep apnea activity with CPAP in 86% of sample in 2-3 months, defining TECSA as a transient disorder and self-limited [36]. The pathophysiological mechanisms leading to the development of TECSA are not yet fully understood. Certainly, there are two factors that conceptually underlie the development of this pathology: low apnea threshold and high loop gain (LG). LG can be defined as a feedback mechanism consisting of the controller gain, that is the change in ventilation induced by a change in PaCO2 level and the plant gain, the ability of the lungs and respiratory muscles to increase ventilation. A high loop gain means increased response to small chemical stimuli leading to ventilatory instability [18]. According to [PERSON] et al. in ventilatory control, controller gain stands for chemoreflex sensitivity, plant gain is the measurement of variation in blood gases and the delay gain is defined by circulatory delay and blending gases between blood and various tissues. Another important factor to evaluate is that LG is not a fixed value but tends to change continuously in an unstable situation as in the case of an OSA patient with obstructed breathing. This can occur as a result of many variables: blood gas change, lung volume, negative intra-thoracic pressure, respiratory muscle activity, and airway resistance [37]. Men are more likely to develop central treatment apnea than women because they have statistically a higher loop gain [31]. Apnoeic threshold (AT) is the individual's PaCO2 value below which a central apnea will occur, meaning that if the PaCO2 level falls below this threshold, spontaneous respiratory activity will stop [38]. Arousals from sleep is determined by a neuromechanical drive associated with ventilatory effort that immediately precedes arousal from sleep. When breathing decreases during an apnoeic event, the carbon dioxide associated with respiratory- efforts increases. Subjects with a higher threshold are better able to tolerate increases in respiratory drive [32]. A low AT threshold is one of the pathophysiological mechanisms of OSAs. In patients with obstructive sleep apnea, electroencephalographic micro-wakings are often observed on polysomnography. These patients are characterized by an instability of the respiratory system and control due to a low AT threshold, leading to frequent transitions from sleep to arousal and vice versa. When ventilation increases, subsequent ventilatory overshoot may cause the PaCO2 level to fall below AT, resulting in the onset of central apnea [18]. There is a correlation between central sleep apnea and OSA as far as some patients being treated for obstructive sleep apnea. Continuous positive airway pressure increase lung volume and improve CO2 damping (reducing plant gain) [33]. The prevalence of treatment emergent central sleep apnea development associated with C-PAP use is highly variable in the literature, this ranges from 5% to 20% [21]. In accordance with this [PERSON] et al. defined the emergence of central apnea using CPAP therapy really variable but older patients and higher AHI seem to be two risk factors that increase the probability to develop TECSA [35]. TECSA has also been associated with surgery, occasionally described after the surgical treatment of OSAS, in particular with tracheostomy and maxillomandibular advancement [39]. CPAP and oral appliances can intermittently decrease PaCO2 level to a value below the AT.