A medical system comprising: means (40, 42, 44, 46; 86) for measuring a plurality of impedance values of a path within a patient over time, wherein the path includes at least one blood vessel or cardiac chamber of the patient, and wherein the impedance values vary as a function of blood pressure within the at least one vessel or chamber; the means for measuring the plurality of impedance values comprising an electrical sensing module coupled to a plurality of electrodes arranged to sense cardiac activity of the patient; means (102, 104) for detecting a cardioelectrogram and an impedance waveform from the sensed cardiac activity; an impedance parameter module for determining a plurality of values of an impedance parameter over time based on the measured impedance values, wherein each of the impedance parameter values is determined based on a respective sub-plurality of the impedance values; a comparison module for comparing at least one of the impedance parameter values to at least one prior impedance parameter value; and means for identifying a change in a cardiovascular parameter related to the blood pressure based on the comparison; characterized in that the impedance parameter module is configured to: identify an R-wave for a current cardiac cycle from the EGM identify a maximum impedance and a minimum impedance for the current cardiac cycle from the impedance waveform, determine a first time interval between the R-wave and the minimum impedance, determine a second time interval between the R-wave and the maximum impedance, and determine a ratio of the first time interval and the second time interval, and wherein the comparison module is configured to compare the ratio of the current cardiac cycle to a ratio of a prior cardiac cycle. means (40, 42, 44, 46; 86) for measuring a plurality of impedance values of a path within a patient over time, wherein the path includes at least one blood vessel or cardiac chamber of the patient, and wherein the impedance values vary as a function of blood pressure within the at least one vessel or chamber; the means for measuring the plurality of impedance values comprising an electrical sensing module coupled to a plurality of electrodes arranged to sense cardiac activity of the patient; means (102, 104) for detecting a cardioelectrogram and an impedance waveform from the sensed cardiac activity; an impedance parameter module for determining a plurality of values of an impedance parameter over time based on the measured impedance values, wherein each of the impedance parameter values is determined based on a respective sub-plurality of the impedance values; a comparison module for comparing at least one of the impedance parameter values to at least one prior impedance parameter value; and means for identifying a change in a cardiovascular parameter related to the blood pressure based on the comparison; characterized in that the impedance parameter module is configured to: identify an R-wave for a current cardiac cycle from the EGM identify a maximum impedance and a minimum impedance for the current cardiac cycle from the impedance waveform, determine a first time interval between the R-wave and the minimum impedance, determine a second time interval between the R-wave and the maximum impedance, and determine a ratio of the first time interval and the second time interval, and wherein the comparison module is configured to compare the ratio of the current cardiac cycle to a ratio of a prior cardiac cycle. identify an R-wave for a current cardiac cycle from the EGM identify a maximum impedance and a minimum impedance for the current cardiac cycle from the impedance waveform, determine a first time interval between the R-wave and the minimum impedance, determine a second time interval between the R-wave and the maximum impedance, and determine a ratio of the first time interval and the second time interval, and wherein the comparison module is configured to compare the ratio of the current cardiac cycle to a ratio of a prior cardiac cycle.