Perfusion threshold

Fig. 3.8. Graph demonstrating that the perfusion threshold for mismatch tissue to be salvaged from infarction declines with time. These patients all had major reperfusion on follow-up imaging and tissue with severe hypoperfusion (mean transit time 15-s delay) was able to be salvaged from infarction within 3 h, but at 6 h, the threshold for salvage declined to only 3 s delay in mean transit time (Butcher et al. 2003)...

Butcher K, Parsons M, Baird T, Barber A, Donnan G, Desmond P, Tress B, Davis S (2003) Perfusion thresholds in acute stroke thrombolysis. Stroke 34 2159-2164... 

Baron JC (2001). Perfusion thresholds in human cerebral ischemia historical perspective and therapeutic implications. Cerebrovascular Diseases 11 2-8... 

Acidosis occurs during cardiac arrest because of decreased blood flow and inadequate ventilation. Chest compressions generate only about 20% to 30% of normal cardiac output, leading to inadequate organ perfusion, tissue hypoxia, and metabolic acidosis. Furthermore, the lack of ventilation causes retention of carbon dioxide, leading to respiratory acidosis. The combined acidosis reduces myocardial contractility and may cause arrhythmias because of a lower fibrillation threshold. 

Subcutaneous administration of -hexanc at 143 mg/kg/day for 30 days has been reported to decrease the threshold for ventricular fibrillation in perfused hearts from male Wistar rats (Khedun et al. 1996). Myocardial magnesium and potassium levels were reduced in treated rats. When these levels were corrected by supplementation, the ventricular fibrillation potential was still reduced. Histological alterations (disordered myocardial Z-bands) were also observed in exposed rats. 

Nordstrom CH. 2003. Assessment of critical thresholds for cerebral perfusion pressure performing bedside monitoring of cerebral energy metabolism. Neurosurg Focus... 

Figure 20.2 The apparent hydraulic conductivity (Kapp) in fibrosarcomas at different perfusion pressures. The curve labeled with 1-D was obtained during one-dimensional perfusion of tumor slices. The curve labeled with 3-D was obtained during direct infusion into a tumor chunk via a 23G needle. The perfusion pressure varied between 20 cmH20 and 163 cmH20. The threshold pressures in 1-D and 3-D experiments are indicated by arrow-head and arrow, respectively. The symbols and error bars represent mean and SD, respectively. The number of tumors for each data point was six in 1-D experiments and three or four in 3-D experiments. Reprinted with permission (Zhang et al., 2000).

Review of literature. Cerebrovasc Dis 1 2-15 Hossmann K-A (1994) Viability thresholds and the penumbra of focal ischemia. Ann Neurol 36 557-565 Hossmann KA, Hoehn-Berlage M (1995) Diffusion and perfusion MR imaging of cerebral ischemia. Cerebrovasc Brain Metab Rev 7 187-217... 

Fig. 7.2. Relationship between relative (rADC) and cerebral blood flow (CBF). ADC drops to below normal at CBF values around 15-24 ml/min/100 g, as shown in a pixel-wise comparison between diffusion and perfusion imaging in acute stroke patients. A lower threshold (15 ml/min/100 g) was found for patients imaged earlier (up to 4 h ) compared to the value (24 ml/min/100 g) of those patients imaged between 4.5 and 6.5 h ( ).The data show that the ADC threshold increases with time. [Reproduced with permission from Lin et al. (2003)]...

Shih LC, Saver JL, Alger JR et al. (2003). Perfusion-weighted magnetic resonance imaging thresholds identifying core, irreversibly infarcted tissue. Stroke 34 1425-1430... 

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