A system and methods using tracheal sound intensity variations to screen patients suspected of obstructive sleep apnea during wakefulness. The system includes a mechanism positioning the patient and a sound input device attached to a recording device to receive breathing sound signals. A signal conditioning component amplifies and filters the breathing sound signals, and an analog to digital component digitizes the signals. A detecting component detects onsets of respiratory phases, and a separating component separates inspiratory sound signals and expiratory sound signals from the breathing sound signals. A segmenting component segments the inspiratory and expiratory phase signals into a short duration of overlapping windows, and a collection characteristic extraction component obtains characteristics from each window. A calculation component performs statistical analysis to reduce the number of significant characteristics and classify the patient as OSA or non-OSA and predicts severity of the OSA as one of mild, moderate and severe.