Processing device for use in monitoring of peripheral arterial perfusion of a subject, said processing device comprising: - an input for receiving first detection data of a tissue region of a subject, said first detection data being acquired over time by detecting radiation reflected from and/or transmitted through tissue of the subject, and for receiving second detection data of a skin region of a subject, said second detection data being acquired over time by detecting radiation received from said skin region in response to coherent light being emitted towards said skin region, - a PPG unit for deriving a photoplethysmography, PPG, signal from said first detection data, - a flow unit for deriving, from said second detection data, a flow signal indicative of a flow of light scattering particles within the skin region, and - an evaluation unit for evaluating said PPG signal and said flow signal to obtain information on the peripheral arterial perfusion, characterized in that the evaluation unit is adapted to determine a state of low vascular compliance and/or a state of low cardiac output based on a combined evaluation of said PPG signal and said flow signal; wherein said evaluation unit is configured to evaluate a PPG ratio of the AC component to the DC component of the PPG signal and a speckle ratio of the AC component to the DC component of the flow signal; wherein said evaluation unit is configured to determine a state of non-compliant blood vessels and a high peripheral perfusion if the speckle ratio exceeds a second speckle threshold and if the PPG ratio exceeds a second PPG threshold and to determine a state of compliant blood vessels if the speckle ratio is below a second speckle threshold and if the PPG ratio exceeds the second PPG threshold. - an input for receiving first detection data of a tissue region of a subject, said first detection data being acquired over time by detecting radiation reflected from and/or transmitted through tissue of the subject, and for receiving second detection data of a skin region of a subject, said second detection data being acquired over time by detecting radiation received from said skin region in response to coherent light being emitted towards said skin region, - a PPG unit for deriving a photoplethysmography, PPG, signal from said first detection data, - a flow unit for deriving, from said second detection data, a flow signal indicative of a flow of light scattering particles within the skin region, and - an evaluation unit for evaluating said PPG signal and said flow signal to obtain information on the peripheral arterial perfusion, characterized in that the evaluation unit is adapted to determine a state of low vascular compliance and/or a state of low cardiac output based on a combined evaluation of said PPG signal and said flow signal; wherein said evaluation unit is configured to evaluate a PPG ratio of the AC component to the DC component of the PPG signal and a speckle ratio of the AC component to the DC component of the flow signal; wherein said evaluation unit is configured to determine a state of non-compliant blood vessels and a high peripheral perfusion if the speckle ratio exceeds a second speckle threshold and if the PPG ratio exceeds a second PPG threshold and to determine a state of compliant blood vessels if the speckle ratio is below a second speckle threshold and if the PPG ratio exceeds the second PPG threshold. characterized in that the evaluation unit is adapted to determine a state of low vascular compliance and/or a state of low cardiac output based on a combined evaluation of said PPG signal and said flow signal; wherein said evaluation unit is configured to evaluate a PPG ratio of the AC component to the DC component of the PPG signal and a speckle ratio of the AC component to the DC component of the flow signal; wherein said evaluation unit is configured to determine a state of non-compliant blood vessels and a high peripheral perfusion if the speckle ratio exceeds a second speckle threshold and if the PPG ratio exceeds a second PPG threshold and to determine a state of compliant blood vessels if the speckle ratio is below a second speckle threshold and if the PPG ratio exceeds the second PPG threshold.