1. Intermittent perfusion protects the brain during deep hypothermic circulatory arrest1 
Stephen M Langley, Paul J Chai, MD, Sara E Miller, PhD, James R Mault, MD, James J Jaggers, MD, Steven S Tsui, MD, Andrew J Lodge, MD, Ann Lefurgey, PhD, Ross M Ungerleider, MD 
The Annals of Thoracic Surgery 
Volume 68, Issue 1, Pages 4-12 (July 1999)
DOI: /S (99)

2. Fig 1
Experimental protocol and data collection sequence. After anesthesia and instrumentation was accomplished, baseline (pre-CPB) measurements were obtained. Animals were placed on CPB and perfusion cooled to 18°C over 20 minutes. Data were obtained at 18°C immediately before the experimental period. Animals were then assigned to one of the following three group periods: (1) 60 minute CPB at 18°C (n = 5); (2) 60 minutes uninterrupted deep hypothermic circulatory arrest (DHCA) at 18°C (n = 5); or (3) 60 minutes of DHCA at 18°C with intermittent perfusion for 1 minute every 15 minutes (n = 5). Upon completion of the experimental period CPB was reinstituted, animals were warmed to 37°C, and weaned off CPB. Postbypass measurements were made after stabilization for 30 minutes.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

3. Fig 2
Percent recovery of CMRO2. When postbypass CMRO2 is expressed as a percent of prebypass values, control animals experienced full recovery of cerebral metabolism. In animals subjected to a continuous 60-minute period of UI-DHCA, recovery of cerebral metabolism was markedly impaired. When a 60-minute period of DHCA was interrupted with reperfusion for 1 minute every 15 minutes (I-DHCA), recovery was significantly greater than the UI-DHCA group and not significantly different from the control animals. ∗Significantly greater than UI-DHCA value (p < 0.05).
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

4. Fig 3
Cerebral capillary or small arteriole after 60 minutes of CPB at 37°C with no ischemia. This transversely sectioned blood vessel is a capillary or small arteriole. Endothelial layer (E); mitochondria (M) in endothelial cell; basal lamina (B). Where the endothelial cells meet, junctional complexes (J) are seen. At the 7 o’clock position, a small cellular projection (CP) is seen lying within the basal lamina. This is probably a smooth muscle projection, which would suggest the vessel was a small arteriole rather than a capillary. The three areas of lucency (L) seen superiorly are probably due to incomplete perfusion fixation. The vessel and surrounding neuropil are within normal limits.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

5. Fig 4
Section of the cerebral vascular endothelial cell seen in Figure 3 at higher magnification. Mitochondria (M) and short cisternae of rough endoplasmic reticulum (RER) are seen within the cytoplasm of a vascular endothelial cell. A junctional complex (J) can be seen separating contiguous endothelial cells. The basement membrane (B) surrounds the vessel and beyond this is a complete covering of astrocytic foot processes (AsP).
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

6. Fig 5
Transverse section through a small cerebral arteriole after 60 minutes of DHCA without reperfusion (alpha-stat cooling). The vessel is surrounded by edema fluid within astrocyte foot processes (AsP). Astrocyte mitochondria (M); the endothelial cell nucleus (N) is conspicuous and lobulated; junctional complex (J); basal lamina (B). There is considerable vacuolation (Va) of the cytoplasm in the cells of the surrounding neuropil.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

7. Fig 6
Transverse section through a cerebral arteriole after 60 minutes of DHCA with 60 minutes of reperfusion (alpha-stat cooling). The vessel is collapsed. Marked perivascular edema of the astrocyte foot plates (Asp) surrounds the vessel. Large vacuoles (Va) are present in the neuropil. Numerous synapses (Sy) can be identified. On the outside of the endothelial cell, the nucleus of a smooth muscle cell (SM) is prominently situated. Basal lamina (B); endothelial cell nucleus (N); mitochondria (M). A junctional complex (J) is clearly visible. The overall impression is that the edema is less after a period of reperfusion than immediately after the arrest period.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

8. Fig 7
Transverse section through a capillary or small arteriole after 60 minutes of DHCA without reperfusion (pH-stat cooling). Gross swelling of the astrocyte foot processes (AsP) results in the large pale area that surrounds the vessel. Astrocyte mitochondria (M). The vascular endothelial cell (E) is only thickened where the lobulated nucleus (N) occupies the cytoplasm—a cellular process (CP) of either a pericyte or a smooth muscle cell appears to cap this nucleus. The basement membrane (B) demarcates the vascular and extravascular elements. Within the vessel lumen, a red blood cell (RBC) is clearly visible. In the neuropil, a large glial cell is prominent (G) and a considerable amount of vacuolation (Va) is visible. Synaptic connections (Sy) are frequently seen.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )

9. Fig 8
Transverse section through a small arteriole or capillary after 60 minutes of DHCA and intermittent perfusion for 2 minutes every 20 minutes. The vessel wall is formed by thin endothelial cells (E), whose only site of thickening is where the nucleus is located (N). Mitochondria (M) are visible in the cytoplasm, and typical junctional complexes (J) can be seen between contiguous endothelial cells. The darker part of the junctional complexes situated towards the luminal end are the zonulae occludentes or tight junctions. The cellular process (CP) of either a pericyte or a smooth muscle cell can be seen outside the endothelial layer in three separate positions. The surrounding neuropil is extremely well fixed. There is no evidence of swelling of the astrocyte foot processes or vacuoles within the cytoplasm of the glial or neural tissue. Two synapses are particularly well visualized (Sy). The overall impression is of well-fixed, normal-looking cerebral vascular endothelium and surrounding neuropil.
The Annals of Thoracic Surgery  , 4-12DOI: ( /S (99) )