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. 2015 Oct;36(10):2089-102.
doi: 10.1088/0967-3334/36/10/2089. Epub 2015 Aug 19.

Does heart rate variability reflect the systemic inflammatory response in a fetal sheep model of lipopolysaccharide-induced sepsis?

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Does heart rate variability reflect the systemic inflammatory response in a fetal sheep model of lipopolysaccharide-induced sepsis?

Lucien D Durosier et al. Physiol Meas. 2015 Oct.

Abstract

Fetal inflammatory response occurs during chorioamnionitis, a frequent and often subclinical inflammation associated with increased risk for brain injury and life-lasting neurologic deficits. No means of early detection exist. We hypothesized that systemic fetal inflammation without septic shock will be reflected in alterations of fetal heart rate (FHR) variability (fHRV) distinguishing baseline versus inflammatory response states. In chronically instrumented near-term fetal sheep (n = 24), we induced an inflammatory response with lipopolysaccharide (LPS) injected intravenously (n = 14). Ten additional fetuses served as controls. We measured fetal plasma inflammatory cytokine IL-6 at baseline, 1, 3, 6, 24 and 48 h. 44 fHRV measures were determined continuously every 5 min using continuous individualized multi-organ variability analysis (CIMVA). CIMVA creates an fHRV measures matrix across five signal-analytical domains, thus describing complementary properties of fHRV. Using principal component analysis (PCA), a widely used technique for dimensionality reduction, we derived and quantitatively compared the CIMVA fHRV PCA signatures of inflammatory response in LPS and control groups. In the LPS group, IL-6 peaked at 3 h. In parallel, PCA-derived fHRV composite measures revealed a significant difference between LPS and control group at different time points. For the LPS group, a sharp increase compared to baseline levels was observed between 3 h and 6 h, and then abating to baseline levels, thus tracking closely the IL-6 inflammatory profile. This pattern was not observed in the control group. We also show that a preselection of fHRV measures prior to the PCA can potentially increase the difference between LPS and control groups, as early as 1 h post LPS injection. We propose a fHRV composite measure that correlates well with levels of inflammation and tracks well its temporal profile. Our results highlight the potential role of HRV to study and monitor the inflammatory response non-invasively over time.

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Figures

Figure 1
Figure 1
(A) Arterial blood gas and acid-base responses to lipopolysaccharide. Blue, control group (n = 5); red, LPS group (n = 10) at baseline, 1 h, 3 h, 6 h, 24 h, 48 h and 54 h after start of the experiment. Mean ± SD. We found a significant time-LPS interactions for pH (P = 0.03), pO2, pCO2, lactate and BE (all P < 0.001). (B) Cardiovascular responses to lipopolysaccharide. Blue, control group (n = 6); red, LPS group (n = 10); mABP, fetal mean arterial blood pressure in mmHg; FHR, fetal heart rate at baseline in beats per minute (bpm), 1 h, 3 h, 6 h, 24 h, 48 h and 54 h after start of the experiment. Mean ± SD. We found time-LPS interaction for mABP and FHR responses (P = 0.015 and P < 0.001, respectively). This was significant for FHR at 6 h (P = 0.008). (C) Fetal inflammatory response to lipopolysaccharide. Blue, control group (n = 5); red, LPS group (n = 10); Mean ± SD. *, P = 0.001 versus control.
Figure 2
Figure 2
Temporal profile of fHRV composite measure #2, averaged over LPS and control groups. Temporal profile of the averaged PCA-derived composite fHRV measure for both LPS (10 animals) and control (7 animals) groups, using 4 fHRV measures, and 2 subsequent PCA components. The fHRV composite measure is normalized with respect to each animal’s baseline before being averaged across groups. Lightly shaded areas correspond to the confidence intervals around the mean. The number of animals used in the average plot may vary across time due to missing fHRV values (from periods of low quality ECG data). The time periods not shown were not available or had too many missing values. The common baseline value is indicated as a dotted line.
Figure 3
Figure 3
Temporal profile of fetal heart rate, averaged over LPS and control groups. Temporal profile of the fetal heart rate for both LPS (10 animals) and control (7 animals) groups. The fetal heart rate is normalized with respect to each animal’s baseline before being averaged across groups. Lightly shaded areas correspond to the confidence intervals around the mean. The number of animals used in the average plot may vary across time due to missing fHRV values (from periods of low quality ECG data). The time periods not shown were not available or had too many missing values. The common baseline value is indicated as a dotted line.

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