Development of a monitor for tidal volume using ECG to eliminate

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Lead-I and -III electrocardiograms were measured, A/D converted, and then processed by a note-type personal computer. The maximum and minimum values in the QRS complex were detected, and using Einthoven's delta, they were converted into the values in an orthogonal lead system. Then the difference between the maximum and minimum values was calculated. Finally, the angle of a vector was obtained which consisted of the lead-I difference and the difference in the lead orthogonal to the lead-I.The angles obrained at the interval of heart beat were interpolated by a cubic spline function to yield a continuous curve. The difference between a local maxsimum and minimum in the curve gave the estimate for a relative value of tidal volume. These data processings were done on a real-time basis. Simultaneously with the electrocardiograms, respiratory flow was measured, and inspiratory flow was integrated to produce tidal volume. The crrelation coefficient between the measured and estimated tidal volume was large. The coefficient was influenced by prefiltering, deep breath, position of the subject, and abnormal dederto-cardiograms. Experiments suggested that obstructive sleep apnea could be detected by this method.