The relationship between lung injury and heart rate variability induced by hemorrhagic shock: a new experimental approach

Heart rate variability (HRV) has been recently used to recognize cardiovascular disorders. The aim of this study was to determine the relationship between lung injury in different severity of hemorrhagic shock and HRV. Male Sprague-Dawley rats were randomly divided into sham group and groups with three different time courses of hemorrhagic shock (HS): Short Time Course (STC, ۳۴.۵±۱.۴min), Moderate Time Course (MTC, ۸۱.۶±۳.۹min) and Long Time Course (LTC, ۱۳۷.۴۲±۱۰.۵min). All experiments were done in conscious animals. HS was induced by blood withdrawing until blood pressure decreased to ۴۰±۵ mmHg, remaining at this level until the end of the compensatory end point. Then, animal were resuscitated by infusion of blood and lactated ringer solution. Hemodynamic was recorded and HRV was analyzed by Power Lab system and Kubios software, respectively. Besides, blood gas parameters, plasma malondialdehyde (MDA) and lung TNF-α and iNOS gene expression were evaluated. All frequency components of HRV increased from the starting point of the blood withdrawal and reached the maximum values at the compensatory end point in all HS groups. Very Low Frequency (VLF) decreased sharply and reached to below basal values after resuscitation in the all HS groups. Interestingly, VLF in the LTC group was lower than that in the other groups. Furthermore, analyzing of blood gas parameters indicated that the metabolic acidosis in the groups of STC and MTC has been compensated, while in the LTC group has not. The changes in gene expression and MDA showed a significant damage in the LTC group. In the present study we indicated an inverse relationship between VLF and the severity of lung injury in severe hemorrhagic shock which may linked to impairment in vascular myogenic function and sympathetic overactivity. Therefore, we suggest that HRV analysis could be valuable for predicting lung injuries in different level of hemorrhagic shock.

کلیدواژه ها:

Conscious rat ، cardiovascular disorders ، resuscitation