A method for assessing change in arterial volume of a limb segment of a mammal carried out by a diagnostic system, said method comprising: determining amplitudes of component pulse waves of detected volume pulse waves of a limb segment detected during a baseline period to determine a baseline arterial volume of the limb segment; determining amplitudes of component pulse waves of detected volume pulse waves of the limb segment detected during a time period after a stimulus has been applied to the mammal to induce a period of change in the arterial volume of the limb segment; and determining relative change in arterial volume of the limb segment during the time period after stimulus relative to the arterial volume of the limb segment during the baseline period from the amplitudes of the component pulse waves of the detected volume pulse waves during the baseline and after the stimulus; characterised in that determining relative change in arterial volume of the limb comprises: calculating an average pulse wave amplitude during the baseline period; generating a curve fit of pulse wave amplitudes during the after-stimulus period; calculating a maximum of the fitted curve; determining a time between beginning of the after-stimulus period and the time of the maximum of the fitted curve; and determining a relative amplitude change from the baseline to the maximum of the fitted curve; and determining relative change in arterial volume from the relative amplitude change from the baseline to the maximum of the fitted curve and the average pulse wave amplitude during the baseline period, wherein the method further comprises providing one or more processed data by a processor of the diagnostic system to a doctor or clinical researcher as indicators of arterial stiffness, these data including 1) relative % change in arterial volume of a limb segment after a stimulus; 2) computed relative maximum % change in the radius of the artery after the stimulus; 3) time to maximum change in arterial volume; 4) area under the curve; and 5) pulse wave characteristics. determining amplitudes of component pulse waves of detected volume pulse waves of a limb segment detected during a baseline period to determine a baseline arterial volume of the limb segment; determining amplitudes of component pulse waves of detected volume pulse waves of the limb segment detected during a time period after a stimulus has been applied to the mammal to induce a period of change in the arterial volume of the limb segment; and determining relative change in arterial volume of the limb segment during the time period after stimulus relative to the arterial volume of the limb segment during the baseline period from the amplitudes of the component pulse waves of the detected volume pulse waves during the baseline and after the stimulus; characterised in that determining relative change in arterial volume of the limb comprises: calculating an average pulse wave amplitude during the baseline period; generating a curve fit of pulse wave amplitudes during the after-stimulus period; calculating a maximum of the fitted curve; determining a time between beginning of the after-stimulus period and the time of the maximum of the fitted curve; and determining a relative amplitude change from the baseline to the maximum of the fitted curve; and determining relative change in arterial volume from the relative amplitude change from the baseline to the maximum of the fitted curve and the average pulse wave amplitude during the baseline period, wherein the method further comprises providing one or more processed data by a processor of the diagnostic system to a doctor or clinical researcher as indicators of arterial stiffness, these data including 1) relative % change in arterial volume of a limb segment after a stimulus; 2) computed relative maximum % change in the radius of the artery after the stimulus; 3) time to maximum change in arterial volume; 4) area under the curve; and 5) pulse wave characteristics. calculating an average pulse wave amplitude during the baseline period; generating a curve fit of pulse wave amplitudes during the after-stimulus period; calculating a maximum of the fitted curve; determining a time between beginning of the after-stimulus period and the time of the maximum of the fitted curve; and determining a relative amplitude change from the baseline to the maximum of the fitted curve; and determining relative change in arterial volume from the relative amplitude change from the baseline to the maximum of the fitted curve and the average pulse wave amplitude during the baseline period, wherein the method further comprises providing one or more processed data by a processor of the diagnostic system to a doctor or clinical researcher as indicators of arterial stiffness, these data including 1) relative % change in arterial volume of a limb segment after a stimulus; 2) computed relative maximum % change in the radius of the artery after the stimulus; 3) time to maximum change in arterial volume; 4) area under the curve; and 5) pulse wave characteristics.