Supplemental Table 1

<b>Supplemental Table 1:</b> Identification of conduction abnormalitites in all participants for free breathing and apneas (end-inspiratory and end-expiratory) during normoxia, hypoxia following twenty minutes, and hypoxia following five hours. Conduction abnormalities were identified from a standard Lead II trace. ECG assessment was carried out by a cardiologist who was blinded to group and condition. All conduction abnormalities associated with voluntary apnea occurred immediately preceding or following apneic break-point.