[Time-dependent measurement of differential digital plethysmogram in bicycle ergometer exercise]

Time-dependent measurements of differential digital plethysmogram during exercise were made on five male subjects. The results obtained were as follows; Differential digital plethysmogram (delta DPG) was obtained by using biophysical amplifier with the time constant of 0.03 seconds which minimized the fluctuation of the baseline in digital plethysmogram (DPG). A linear relationship was shown in P wave amplitude of both delta DPG and DPG. The decrease in delta DPG-P waves was observed in visual concentrations, mental learning and arithmetic, initial inspiratory phase with tachycardia, maximal inspiratory and/or expiratory breath holding, and head-up tilt at 60 degrees or over. The increase in delta DPG-P waves was obtained at the expiratory phase with bradycardia and in the effect of alcohol intake. During 15 minutes of bicycle ergometer exercise at 750 kpm/min, the P wave amplitude in delta DPG decreased to 77% of the control in the first one minute of exercise, and then gradually increased to 218% at the final stage of exercise (p less than 0.01). Heart rate measured simultaneously increased, as compared from the beginning of exercise. P wave amplitude and heart rate after exercise decreased progressively to the control level. It is suggested that the initial decrease in P wave amplitude of delta DPG couples with the dominant activity of the sympathetic vasoconstrictor, and the final increase in P waves is due to the compound factors of the increased cardiac output and arteriolar vasodilation.