Effect of Mild Hypothermia on the Diaphragmatic Microcirculation and Function in a Murine Cardiopulmonary Resuscitated Model.

OBJECTIVE: Diaphragm dysfunction often occurs in patients with prolonged mechanical ventilation (MV) after resuscitation. Mild hypothermia (MHT) is a classical treatment to improve the outcomes of cardiac arrest (CA), however, the effect of MHT on diaphragm function remains unclear. In the present study, we aim to investigate the effect of MHT on diaphragmatic microcirculation and function using a murine cardiopulmonary resuscitation model.

METHODS: Thirty-two rats were randomly assigned into a resuscitation normothermia group (RNT), an intra-resuscitation hypothermia group (IRH), a post-resuscitation hypothermia group (PRH), or a sham control group. CA was induced by airway occlusion, and resuscitation was implemented by precordial compression and MV. The diaphragmatic microvascular blood flow velocity, diaphragmatic microcirculation flow index (MFI) and perfused vascular density (PVD) were measured. The diaphragm was then removed for in vitro contractile property examination and cross-sectional area measurement. The lipid peroxidation and superoxide dismutase (SOD) levels in the diaphragm were also assayed.

RESULTS: Either early or delayed MHT intervention did not improve the diaphragmatic microvascular blood flow velocity, MFI, and PVD, which were significantly decreased during prolonged MV after resuscitation. Compared with the RNT group, treatment with MHT increased the diaphragm contractility, fiber dimensions, and SOD levels and decreased diaphragm lipid peroxidation. A more significant change in these indices was observed in the IRH group compared with that in the PRH group.

CONCLUSION: MHT preserves the diaphragm contractility and fiber dimensions and decreases oxidative stress but does not improve the microcirculatory blood supply during prolonged MV after resuscitation. Early MHT intervention is more efficient in preventing diaphragm dysfunction than delayed intervention after CA.