An adaptive bio-signal feature combining apparatus (200; 800) comprising: a feature extractor (210; 810) configured to extract first feature values and second feature values from a bio-signal of an object, wherein the bio-signal comprises a photoplethysmogram, PPG, signal; a stable interval determiner (220; 820) configured to determine at least one stable interval in the bio-signal ; a statistical variable calculator (230; 830) configured to calculate a statistical variable value of a first feature and a statistical variable value of a second feature for each of the at least one stable interval based on the first and second feature values extracted from the at least one stable interval , wherein the first feature indicates a cardiac output and the second feature indicates a total peripheral vascular resistance, and wherein the statistical variable comprises a mean, a variance, a standard deviation, or a mean absolute deviation; and a feature combiner (240; 840) configured to calculate an integrated combining coefficient that is used to combine the first feature and the second feature, based on the statistical variable value of the first feature and the statistical variable value of the second feature, wherein the feature combiner (240; 840) is further configured to calculate a combining coefficient of each stable interval based on the statistical variable values of the first and second features which are calculated for each stable interval, and wherein the feature combiner (240; 840) calculates the integrated combining coefficient by combining the combining coefficients calculated for each stable interval, wherein the feature extractor (210; 810), the stable interval determiner (220; 820), the statistical variable calculator (230; 830), and the feature combiner (240; 840) are included in one or more processors. a feature extractor (210; 810) configured to extract first feature values and second feature values from a bio-signal of an object, wherein the bio-signal comprises a photoplethysmogram, PPG, signal; a stable interval determiner (220; 820) configured to determine at least one stable interval in the bio-signal ; a statistical variable calculator (230; 830) configured to calculate a statistical variable value of a first feature and a statistical variable value of a second feature for each of the at least one stable interval based on the first and second feature values extracted from the at least one stable interval , wherein the first feature indicates a cardiac output and the second feature indicates a total peripheral vascular resistance, and wherein the statistical variable comprises a mean, a variance, a standard deviation, or a mean absolute deviation; and a feature combiner (240; 840) configured to calculate an integrated combining coefficient that is used to combine the first feature and the second feature, based on the statistical variable value of the first feature and the statistical variable value of the second feature, wherein the feature combiner (240; 840) is further configured to calculate a combining coefficient of each stable interval based on the statistical variable values of the first and second features which are calculated for each stable interval, and wherein the feature combiner (240; 840) calculates the integrated combining coefficient by combining the combining coefficients calculated for each stable interval, wherein the feature extractor (210; 810), the stable interval determiner (220; 820), the statistical variable calculator (230; 830), and the feature combiner (240; 840) are included in one or more processors. <EOS>