There were significant increase in chronic (after 6 weeks) versus acute phase of threshold (0.8 ± 0.4 V so với 1.6 ± 0.7V; p < 0.001), but no difference in acute and chronic phase of sensing (8.4 ± 2.3 mA so với 8.5 ± 2.0mA; p = 0.52) and resistance (629 ± 139 ohms so với 688 ± 333 ohms; p = 0.6).