Bioelectrical impedance analysis (BIA) is a non-invasive technique to measure the fluid content of various tissues. Based on Ohmâ s law, tissue impedance is determined by passing a current through the tissue and measuring the voltage. The total impedance is composed of multiple parameters:​ the resistance, and reactance, or magnitude and phase angle, all of which may vary based on tissue composition. For example, an increase in fluid volume will result in a lower resistance, while a lower phase angle has shown to be associated with a lower muscle mass and increased mortality in heart failure patients. We demonstrate that BIA measurements of the neck are able to detect changes in the fluid content, from before to after sleep, as well as differentiate patients who show worsening in sleep apnea severity subject to fluid overloading. Furthermore, we propose a design for a portable device to measure BIA in a clinical setting.