BACKGROUND
Cardiorespiratory (apnea) monitors are prescribed for infants at risk of prolonged, pathophysiological cessation of breathing. Most commercially available apnea monitors detect infants' respiration by measuring transthoracic impedance. Although all of these devices use AC excitation to measure the transthoracic impedance, the frequency of excitation varies from one manufacturer to another. To date, the effect of excitation frequency on transthoracic impedance measurements has not been well documented.