부산대학교 도서관

This study examined the temporal change in cardiac baroreflex response following severe traumatic brain injury (TBI) with or without additional hypotensive/hypoxemic insults. Rats were randomly assigned into three groups - sham craniotomy only, 10% PBBI only, and PBBI combined with hypoxemia/hemorrhagic shock (PHH). The PHH group received 30-min hypoxemia (fraction of inspired oxygen = 0.1) and then 30-min hemorrhagic hypotension (mean arterial pressure = 40mmHg) following PBBI. To assess the baroreflex function, phenylephrine was injected via femoral vein catheter with a sequential dosing regimen of 2, 1, 0.5, 5, 10 lg/kg. Systolic blood pressure (SBP) and electrocardiogram were recorded. Twenty minutes after the last dose of phenylephrine, the dosing regimen was repeated. This phenylephrine pressor test was performed on the injury day (day 0), and again on 1 and 5 days postinjury. A linear regression line of heart period (R-R interval from the electrocardiogram) against SBP was plotted for each test, in which the slope of the line was taken as an index of baroreflex sensitivity (BRS). Additionally, heart rate was derived from the electrocardiogram recordings. In PBBI and PHH group, BRS was higher than that in the sham group at all time points. While BRS remained steady in the sham control group (ranged 0.26 ± 0.08 - 0.36 ± 0.11 ms/mmHg) throughout the experiment, it exhibited a gradual increase in the PBBI group with the peak (0.65 ± 0.15 ms/ mmHg) occurring at day 5 post-injury. In contrast, a decreasing trend was observed in the PHH group, in which an acute increase in BRS (0.59 ± 0.1ms/mmHg) was detected on day 0. The differences in heart rate were not significant between groups, yet PHH trended lower acutely following injury and at 5 days post-injury, indicating bradycardia. Persistent disturbance of cardiovascular responses induced by TBI and the additional insults may potentially result in reduced perfusion of the vital organs and consequently worsen the clinical outcomes. [ABSTRACT FROM AUTHOR]