A computer program product for use with a computer comprising at least one processing module, comprising: a computer-usable medium comprising computer readable program code modules embodied in said computer-usable medium, wherein said computer readable program modules comprise: a computer-readable first program code module that causes said computer to process plethysmography signals obtained from a pulse oximeter probe, which is secured to a central source site of a patient, by separating out a pulsatile arterial component signal stream and a venous impedance component signal stream; and a computer-readable second program code module that causes said computer to evaluate said pulsatile arterial component signal stream, said venous impedance signal stream, or both, to determine an occurrence of an air restriction event, an air obstruction event, or a combination thereof, wherein evaluating said pulsatile arterial component signal stream, said venous impedance signal stream, or both, comprises quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time, wherein quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time comprises evaluating changes in an amplitude of a waveform, peak or trough counting, peak-peak timing, peak-trough height, area under a curve, shape of curves, or evaluating changes in positions of peaks, troughs or midpoints from heartbeat to heartbeat or breath to breath. a computer-usable medium comprising computer readable program code modules embodied in said computer-usable medium, wherein said computer readable program modules comprise: a computer-readable first program code module that causes said computer to process plethysmography signals obtained from a pulse oximeter probe, which is secured to a central source site of a patient, by separating out a pulsatile arterial component signal stream and a venous impedance component signal stream; and a computer-readable second program code module that causes said computer to evaluate said pulsatile arterial component signal stream, said venous impedance signal stream, or both, to determine an occurrence of an air restriction event, an air obstruction event, or a combination thereof, wherein evaluating said pulsatile arterial component signal stream, said venous impedance signal stream, or both, comprises quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time, wherein quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time comprises evaluating changes in an amplitude of a waveform, peak or trough counting, peak-peak timing, peak-trough height, area under a curve, shape of curves, or evaluating changes in positions of peaks, troughs or midpoints from heartbeat to heartbeat or breath to breath. a computer-readable first program code module that causes said computer to process plethysmography signals obtained from a pulse oximeter probe, which is secured to a central source site of a patient, by separating out a pulsatile arterial component signal stream and a venous impedance component signal stream; and a computer-readable second program code module that causes said computer to evaluate said pulsatile arterial component signal stream, said venous impedance signal stream, or both, to determine an occurrence of an air restriction event, an air obstruction event, or a combination thereof, wherein evaluating said pulsatile arterial component signal stream, said venous impedance signal stream, or both, comprises quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time, wherein quantifying the pulsatile arterial component signal stream, said venous impedance signal stream, or both, in real time comprises evaluating changes in an amplitude of a waveform, peak or trough counting, peak-peak timing, peak-trough height, area under a curve, shape of curves, or evaluating changes in positions of peaks, troughs or midpoints from heartbeat to heartbeat or breath to breath.