Transvenous Diaphragm Neurostimulation Mitigates Ventilation-associated Brain Injury

Abstract

Rationale: Mechanical ventilation (MV) is associated with hippocampal apoptosis and inflammation, and it is important to study strategies to mitigate them. Objectives: To explore whether temporary transvenous diaphragm neurostimulation (TTDN) in association with MV mitigates hippocampal apoptosis and inflammation after 50 hours of MV. Methods: Normal-lung porcine study comparing apoptotic index, inflammatory markers, and neurological-damage serum markers between never-ventilated subjects, subjects undergoing 50 hours of MV plus either TTDN every other breath or every breath, and subjects undergoing 50 hours of MV (MV group). MV settings in volume control were Vt of 8 ml/kg, and positive end-expiratory pressure of 5 cm H₂O. Measurements and Main Results: Apoptotic indices, microglia percentages, and reactive astrocyte percentages were greater in the MV group in comparison with the other groups (P < 0.05). Transpulmonary pressure at baseline and at study end were both lower in the group receiving TTDN every breath, but lung injury scores and systemic inflammatory markers were not different between the groups. Serum concentrations of four neurological-damage markers were lower in the group receiving TTDN every breath than in the MV group (P < 0.05). Heart rate variability declined significantly in the MV group and increased significantly in both TTDN groups over the course of the experiments. Conclusions: Our study found that mechanical ventilation is associated with hippocampal apoptosis and inflammation, independent of lung injury and systemic inflammation. Also, in a porcine model, TTDN results in neuroprotection after 50 hours, and the degree of neuroprotection increases with greater exposure to TTDN.

Keywords: ICU; apoptosis; brain injuries; mechanical ventilators; post-ICU syndrome.

Figure 1.

Left: Dot plot of the hippocampal apoptotic indices (%) for all groups. Apoptotic indices found were 31.70 (29.79–43.76) for the mechanical ventilation (MV) group, 20.53 (10.85–26.46) for the TTDN50% + MV group, 6.57 (4.94–11.26) for the TTDN100% + MV group, and 0.96 (0.50–1.61) for the never-ventilated (NV) group. Post hoc analysis using Dunn’s multiple comparison test showed statistically significant differences between the MV and NV groups (31.70 vs. 0.96, P < 0.0001), between the MV and TTDN100% + MV groups (31.70 vs. 6.57, P = 0.0041), and between the TTDN50% + MV and NV groups (20.53 vs. 0.96, P = 0.0205). Center and right: Examples of hippocampus slides for all groups, showing terminal deoxynucleotidyl transferase–mediated dUTP nick-end labeling–positive cells (brown). Scale bars, 100 µm. TTDN50% = temporary transvenous diaphragm neurostimulation every other breath; TTDN100% = temporary transvenous diaphragm neurostimulation every breath.

Figure 2.

Left: Dot plot of percentages of IBA-1 (ionizing calcium-binding adaptor molecule-1)–positive hippocampal cells (%) for all groups. IBA-1–positive cell percentages found were 36.17 (30.71–48.27) for the mechanical ventilation (MV) group, 16.70 (10.82–22.42) for the TTDN50% + MV group, 9.80 (7.86–11.19) for the TTDN100% + MV group, and 10.12 (8.93–10.65) for the never-ventilated (NV) group. Post hoc analysis using Dunn’s multiple comparison test showed statistically significant differences between the MV and NV groups (36.17 vs. 10.12, P = 0.0006), and between the MV and TTDN100% + MV groups (36.17 vs. 9.80, P = 0.0002). Center and right: Examples of hippocampus slides for all groups, showing IBA-1–positive cells (brown). Scale bars, 100 µm. TTDN50% = temporary transvenous diaphragm neurostimulation every other breath; TTDN100% = temporary transvenous diaphragm neurostimulation every breath.

Figure 3.

Left: Dot plot of percentages of GFAP (glial fibrillary acid protein)–positive cells (%). GFAP-positive cell percentages found were 25.63 (21.21–28.66) for the mechanical ventilation (MV) group, 11.93 (5.81–15.78) for the TTDN50% + MV group, 10.41 (7.10–11.56) for the TTDN100 + MV group, and 10.69 (9.31–12.85) for the never-ventilated (NV) group. Post hoc analysis using Dunn’s multiple comparison test showed statistically significant differences between the MV and NV groups (25.63 vs. 10.69, P = 0.0037), between the MV and TTDN100% + MV groups (25.63 vs. 10.41, P = 0.0004), and between the MV and TTDN50% + MV group (25.63 vs. 11.93, P = 0.0221). Center and right: Examples of hippocampus slides for all groups, showing GFAP-positive cells (brown). Scale bars, 100 µm. TTDN50% = temporary transvenous diaphragm neurostimulation every other breath; TTDN100% = temporary transvenous diaphragm neurostimulation every breath.

Figure 4.

Dot plot showing GFAP (glial fibrillary acid protein) concentrations in the serum: 0.40 ng/ml (0.28–0.57) for the mechanical ventilation (MV) group, 0.29 ng/ml (0.25–0.32) for the TTDN50% + MV group, 0.04 ng/ml (0.02–0.06) for the TTDN100% + MV group, and 0.15 ng/ml (0.07–0.23) for the never-ventilated (NV) group. Post hoc analysis using Dunn’s multiple comparison test showed statistically significant differences in GFAP serum concentrations between the MV and NV groups (0.40 vs. 0.15, P = 0.0043), between the MV and TTDN100% + MV groups (0.40 vs. 0.04, P < 0.0001), and between the TTDN50% + MV and TTDN100% + MV groups (0.29 vs. 0.04, P = 0.0015). TTDN50% = temporary transvenous diaphragm neurostimulation every other breath; TTDN100% = temporary transvenous diaphragm neurostimulation every breath.

Figure 5.

Dot plot showing UCHL1 (ubiquitin carboxy-terminal hydrolase L1) concentrations in the serum: 96.96 pg/ml (80.65–109.60) for the mechanical ventilation (MV) group, 110.00 pg/ml (97.59–200.40) for the TTDN50% + MV group, 44.68 pg/ml (36.56–58.34) for the TTDN100% + MV group, and 76.57 pg/ml (42.48–90.26) for the never-ventilated (NV) group. Post hoc analysis using Dunn’s multiple comparison test showed statistically significant differences between the MV and TTDN100% + MV groups (96.96 vs. 44.68, P = 0.0325), between the TTDN50% + MV and TTDN100% + MV groups (110.00 vs. 44.68, P = 0.0015), and between the TTDN50% + MV and NV groups (110.00 vs. 76.57, P = 0.0348). TTDN50% = temporary transvenous diaphragm neurostimulation every other breath; TTDN100% = temporary transvenous diaphragm neurostimulation every breath.