PP018 Cardiac reflex responses measured by impedance cardiography are different between low and high cardiac output...

Pre-eclampsia (PE) has been categorised into subtypes depending on low or high cardiac output (CO) states. Are cardiac reflex responses (CRR) different between these two subtypes?

Impedance cardiography (ICG) measurements of cardiac cycle time intervals (CCTI) before and after orthostatic challenge are evaluated in the clinical phase of PE with low and high CO (LPE and HPE, respectively).

Examinations were performed in 25 LPE (CO⩽7l/min) and 16 HPE (CO⩾9l/min). A third generation ICG device using a four electrode arrangement (NICCOMO, Medis, Germany) was used to measure CCTI in supine position and after moving to upright position. The pre-ejection period (PEP) is the time-interval between ventricular depolarisation and start of aortic flow. The left ventricular ejection time (LVET) is the time-interval between opening and closing of the aortic valve. Systolic time ratio (STR) is PEP/LVET. Diastolic time (DT) is the heart period duration - (PEP+LVET). Time intervals were expressed as a percentage of the heart period duration, i.e. PEPi, LVETi and DTi. Orthostatic-induced changes from supine to upright position (cardiac reflex response or CRR) were evaluated using One-sample Wilcoxon Signed Rank Tests. All CRRs were compared between LPE and HPE using Mann-Whitney U tests. Data are presented as medians (interquartile ranges).

Maternal age was comparable between LPE and HPE [29 (26-34) vs 28 (26-33) years; p=0.55]. This was also true for gestational age [34 (30-38) vs 36 (31-39) weeks; p=0.50], and pre-gestational BMI [24 (22-30) vs 25 (24-32); p=0.21]. Birth weight percentiles were lower in LPE compared to HPE [18 (5-31) vs 44 (18-83); p<0.01]. CRRs within each group are shown in Table 1. CRRs of PEP, PEPi and DT were different between LPE and HPE [p⩽0.04], whereas changes in LVET, LVETi, DTi and STR were not [p⩾0.09]. Reflex-induced changes of diastolic blood pressure and heart rate (HR) were not significantly different between LPE and HPE [p⩾0.41].

Orthostasis does not change PEP in HPE, but induces a significant increase of PEP in LPE. PEP is dependent on HR, preload, afterload and sympathetic activity. There is no difference in the reflex-induced response of HR, DBP (∼afterload), and STR (∼sympathetic activity) between the two groups. This suggests that the orthostatic-induced change in the isovolumetric contraction time in LPE is preload-induced. Our observations suggest that hemodynamic background mechanisms behind LPE and HPE are different, and support the view that these subtypes are two different clinical entities.