No evidence of NO-induced damage in potential donor organs after brain death.

Brain death induces multiple-organ dysfunction, with undesirable consequences for organ transplantation. However, the mechanisms are not completely clear. In the hearts, lungs, livers, and kidneys of rats, we investigated whether brain death leads to changes in nitric oxide (NO) production or to the formation of nitrotyrosine (the footprint of peroxynitrite, formed from NO and superoxide) or to lipid peroxidation products. To produce a rat model of brain death, we inflated a subdurally placed balloon catheter. We used the Griess reaction to assay plasma nitrite and nitrate. Proteolytic digestion followed by high-performance liquid chromatography (HPLC) with electrochemical detection determined nitrotyrosine formation in the tissues. Tissues were also examined immunohistochemically with anti-nitrotyrosine antibody. We used a thiobarbituric acid method to assay lipid peroxidation. An intense, transient hemodynamic activation occurred at the onset of brain death (heart rate, 496 beats/min; mean arterial pressure (AP), 181 mm Hg; dP/dt(max), 11,500 mm Hg/sec). A constant hypotensive phase (mean AP, 50 mm Hg; dP/dt(max), 2,674 mm Hg/sec) followed. Plasma concentration of nitrite plus nitrate remained unchanged 2 hours after brain death (32.8 +/- 1.5 vs 31.3 +/- 2.2 micromol/liter at zero time). Neither HPLC nor immunohistochemistry detected significant nitrotyrosine formation in the tissues. We detected no increase in lipid peroxidation products.Our results indicate that changes in the generation of reactive nitrogen and active oxygen species do not play an important role in post-brain-death organ dysfunction, at least not at the early stage.

Consequences of static and pulsatile pressure on transmembrane exchanges during in vitro microdialysis: implication for studies in cardiac physiology.

Microdialysis is an established technique for measuring the kinetics of various neurotransmitters within the extracellular space in the field of neurochemistry. Recently, its use has been extended to sampling in other tissues, including liver, kidney and the heart. A persistent problem in cardiac microdialysis concerns two parameters related to myocardial function: pressure and frequency (heart rate). The aim of the study is to evaluate the consequences of pressure and frequency on transmembrane exchanges. Linear flexible microdialysis probes (membrane length: 12 mm, outside diameter: 390 microns, MWCO 50,000 Daltons) were designed in our laboratory. The probes, perfused at 2 microL/min with sterile water, were placed in a system filled with a glucose solution (2 g/L) and able to generate either static: 0 to 400 mmHg (0 to 53.31 kPa) or pulsatile pressure: 0-100; 0-200; 0-300 mmHg (0-13.32; 0-26.65; 0-39.98 kPa) at different frequencies: 1, 2 and 3 Hz. At 2 mu litre min-1 perfusion rate, the pressure inside the probe is estimated to be 80 mmHg (10.66 kPa). Under static pressure conditions, the glucose recovery rate can be expressed as an exponential function, and the outflow rate can be expressed as a linear function of the external pressure level. Under dynamic conditions, the external mean pressure must be accounted for. When external mean pressure exceeds 80 mmHg (10.66 kPa) (pressure generated by the flow rate of perfusion inside the probe), the recovery rate increases with frequency. Conversely, if the outer mean pressure is lower than 80 mmHg (10.66 kPa), the recovery rate decreases with frequency. Theoretical and experimental modelling results in a nomogram that can be used to estimate in vivo recovery. In conclusion, mass transfer across a microdialysis membrane is dependent on the direction of the transmembrane pressure gradient and increases with heart rate. These findings must be taken into account when in vivo recovery rates during cardiac microdialysis are determined.

Increase in myocardial interstitial adenosine and net lactate production in brain-dead pigs: an in vivo microdialysis study.

BACKGROUND: Brain death-related cardiovascular dysfunction has been documented; however, its mechanisms remain poorly understood. We investigated changes in myocardial function and metabolism in brain-dead and control pigs. METHODS: Heart rate, systolic (SAP) and mean (MAP) arterial pressure, left ventricular (LV) dP/dtmax, rate-pressure product, cardiac output (CO), left anterior descending coronary artery blood flow, lactate metabolism, and interstitial myocardial purine metabolite concentrations, monitored by cardiac microdialysis, were studied. A volume expansion protocol was performed at the end of the study. RESULTS: After brain death, a transient increase in heart rate (from 90 [67-120] to 158 [120-200] beats/min) (median, with range in brackets), MAP (82 [74-103] to 117 [85-142] mmHg), LV dP/dtmax (1750 [1100-2100] to 5150 [4000-62,000] mmHg x sec(-1), rate-pressure product (9100 [7700-9700] beats mmHg/min to 22,750 [20,000-26,000] beats mmHg/min), CO (2.2 [2.0-4.0] to 3.3 [3.0-6.0] L/min), and a limited increase in left anterior descending coronary artery blood flow (40 [30-60] to 72 [50-85] ml/min) were observed. Net myocardial lactate production occurred (27 [4-40] to -22 [-28, -11] mg/L, P<0.05) and persisted for 2 hr. A 6-7-fold increase in adenosine dialysate concentration was observed after brain death induction (2.9 [1.0-5.8] to 15.8 [7.0-50.7] micromol/L), followed by a slow decline. Volume expansion significantly increased MAP, CO, and LV dP/dtmax in control animals, but decreased LV dP/dtmax and slightly increased CO in brain-dead animals. A significant increase in adenosine concentration was observed in both groups, with higher levels (P<0.05) in brain-dead animals. CONCLUSIONS: Brain death increased oxygen demand in the presence of a limited increase in coronary blood flow, resulting in net myocardial lactate production and increased interstitial adenosine concentration consistent with an imbalance between myocardial oxygen demand and supply. This may have contributed to the early impairment of cardiac function in brain-dead animals revealed by rapid volume infusion.

[Protective effect of labetalol on cardiovascular consequences of brain death in the swine]. / Effet protecteur du labétalol contre les conséquences cardiovasculaires de la mort cérébrale chez le porc.

OBJECTIVE: Assessment of the preventive effect on cardiovascular changes following experimental brain death (BD) in the pig by pretreatment with labetalol, an alpha and beta adrenoreceptor blocking agent. STUDY DESIGN: Experimental study. ANIMALS: Ten 25-35 kg domestic pigs allocated either in the control group (n = 5) or the labetalol group (n = 5). METHODS: BD was achieved in anaesthetized animals by the rapid inflation of a Foley catheter inserted into the sub-dural space. In the labetalol group, the agent (total: 10 +/- 3 mg.kg-1) was administered immediately before BD and thereafter over a 20-min period, in order to maintain haemodynamic parameters at control values. The following haemodynamic data were recorded over a 3 hour period after BD: heart rate (HR), dP/dtmax, mean arterial pressure (MAP), pulmonary capillary wedge pressure (PCWP), cardiac output (CO) and left anterior descending coronary artery blood flow (CBF). Afterwards, a dynamic loading test with 500 mL of dextran over 20 min was performed. RESULTS: In the control group, BD elicited a significant increase in HR (from de 96 +/- 9 to 176 +/- 11 b.min-1), dP/dtmax (from 1,960 +/- 123 to 4,904 +/- 930 mmHg.s-1), MAP (from 88 +/- 5 to 119 +/- 11 mmHg), CO (from 2.4 +/- 0.2 to 3.6 +/- 0.7 L.min-1) and CBF (from 45 +/- 6 to 73 +/- 7 mL.min-1) respectively. Apart from a slight increase in HR and a significant increase in CBF (from 34 +/- 4 to 55 +/- 6 mL.min-1), no other modifications occurred in the labetalol group. Following volume expansion, the labetalol group animals experienced a significant increase in CO (from 2.3 +/- 0.3 to 3.7 +/- 0.2 L.min-1), dP/dtmax (from 1,400 +/- 91 to 2,100 +/- 212 mmHg.s-1) and MAP (from 55 +/- 5 to 70 +/- 5 mmHg). In the opposite, a significant decrease in dP/dtmax (from 1,645 +/- 450 to 628 +/- 152 mmHg.s-1) occurred in the control group. CONCLUSION: The protective effect of labetalol confirms the role played by the activation of the cardiac sympathetic nervous system in the cardiocirculatory changes following BD.