Spacecraft sample collection and subsurface excavation of asteroid (101955) Bennu.

Carbonaceous asteroids, such as (101955) Bennu, preserve material from the early Solar System, including volatile compounds and organic molecules. We report spacecraft imaging and spectral data collected during and after retrieval of a sample from Bennu's surface. The sampling event mobilized rocks and dust into a debris plume, excavating a 9-meter-long elliptical crater. This exposed material is darker, spectrally redder, and more abundant in fine particulates than the original surface. The bulk density of the displaced subsurface material was 500 to 700 kilograms per cubic meter, which is about half that of the whole asteroid. Particulates that landed on instrument optics spectrally resemble aqueously altered carbonaceous meteorites. The spacecraft stored 250 ± 101 grams of material, which will be delivered to Earth in 2023.

Pebbles and sand on asteroid (162173) Ryugu: In situ observation and particles returned to Earth.

The Hayabusa2 spacecraft investigated the C-type (carbonaceous) asteroid (162173) Ryugu. The mission performed two landing operations to collect samples of surface and subsurface material, the latter exposed by an artificial impact. We present images of the second touchdown site, finding that ejecta from the impact crater was present at the sample location. Surface pebbles at both landing sites show morphological variations ranging from rugged to smooth, similar to Ryugu's boulders, and shapes from quasi-spherical to flattened. The samples were returned to Earth on 6 December 2020. We describe the morphology of >5 grams of returned pebbles and sand. Their diverse color, shape, and structure are consistent with the observed materials of Ryugu; we conclude that they are a representative sample of the asteroid.

Sample collection from asteroid (162173) Ryugu by Hayabusa2: Implications for surface evolution.

The near-Earth asteroid (162173) Ryugu is thought to be a primitive carbonaceous object that contains hydrated minerals and organic molecules. We report sample collection from Ryugu's surface by the Hayabusa2 spacecraft on 21 February 2019. Touchdown images and global observations of surface colors are used to investigate the stratigraphy of the surface around the sample location and across Ryugu. Latitudinal color variations suggest the reddening of exposed surface material by solar heating and/or space weathering. Immediately after touchdown, Hayabusa2's thrusters disturbed dark, fine grains that originate from the redder materials. The stratigraphic relationship between identified craters and the redder material indicates that surface reddening occurred over a short period of time. We suggest that Ryugu previously experienced an orbital excursion near the Sun.

An artificial impact on the asteroid (162173) Ryugu formed a crater in the gravity-dominated regime.

The Hayabusa2 spacecraft investigated the small asteroid Ryugu, which has a rubble-pile structure. We describe an impact experiment on Ryugu using Hayabusa2's Small Carry-on Impactor. The impact produced an artificial crater with a diameter >10 meters, which has a semicircular shape, an elevated rim, and a central pit. Images of the impact and resulting ejecta were recorded by the Deployable CAMera 3 for >8 minutes, showing the growth of an ejecta curtain (the outer edge of the ejecta) and deposition of ejecta onto the surface. The ejecta curtain was asymmetric and heterogeneous and it never fully detached from the surface. The crater formed in the gravity-dominated regime; in other words, crater growth was limited by gravity not surface strength. We discuss implications for Ryugu's surface age.

[Valve-sparing aortic root replacement for young female patients with Marfan syndrome].

Annuloaortic ectasia is frequently related with Marfan syndrome, and Bentall procedure or aortic root replacement with valved conduit has been the conventional standard operation for this disease. Recently, some institutes have adopted valve-sparing aortic root replacement (VSARR) instead of Bentall procedure. Young female patients with Marfan syndrome who wishes for childbearing seem to be a group of good candidates of this type of operation, because it let them free from morbidities after artificial valve implantation. Valve-sparing operation should be taken into consideration when the size of Valsalva sinus reaches 45 mm for patients with Marfan syndrome and when it reaches 40 mm for patients with past histories or family histories of aortic dissection or aortic rupture. Since pregnancy is one of the most serious risk factors for aortic events, Valsalva sinus of 40 mm or larger could be the new standard for surgical indication if VSARR is applicable.

The surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy.

The near-Earth asteroid 162173 Ryugu, the target of the Hayabusa2 sample-return mission, is thought to be a primitive carbonaceous object. We report reflectance spectra of Ryugu's surface acquired with the Near-Infrared Spectrometer (NIRS3) on Hayabusa2, to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micrometers was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, which is consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Hayabusa2 arrives at the carbonaceous asteroid 162173 Ryugu-A spinning top-shaped rubble pile.

The Hayabusa2 spacecraft arrived at the near-Earth carbonaceous asteroid 162173 Ryugu in 2018. We present Hayabusa2 observations of Ryugu's shape, mass, and geomorphology. Ryugu has an oblate "spinning top" shape, with a prominent circular equatorial ridge. Its bulk density, 1.19 ± 0.02 grams per cubic centimeter, indicates a high-porosity (>50%) interior. Large surface boulders suggest a rubble-pile structure. Surface slope analysis shows Ryugu's shape may have been produced from having once spun at twice the current rate. Coupled with the observed global material homogeneity, this suggests that Ryugu was reshaped by centrifugally induced deformation during a period of rapid rotation. From these remote-sensing investigations, we identified a suitable sample collection site on the equatorial ridge.

The geomorphology, color, and thermal properties of Ryugu: Implications for parent-body processes.

The near-Earth carbonaceous asteroid 162173 Ryugu is thought to have been produced from a parent body that contained water ice and organic molecules. The Hayabusa2 spacecraft has obtained global multicolor images of Ryugu. Geomorphological features present include a circum-equatorial ridge, east-west dichotomy, high boulder abundances across the entire surface, and impact craters. Age estimates from the craters indicate a resurfacing age of [Formula: see text] years for the top 1-meter layer. Ryugu is among the darkest known bodies in the Solar System. The high abundance and spectral properties of boulders are consistent with moderately dehydrated materials, analogous to thermally metamorphosed meteorites found on Earth. The general uniformity in color across Ryugu's surface supports partial dehydration due to internal heating of the asteroid's parent body.

Images from the surface of asteroid Ryugu show rocks similar to carbonaceous chondrite meteorites.

The near-Earth asteroid (162173) Ryugu is a 900-m-diameter dark object expected to contain primordial material from the solar nebula. The Mobile Asteroid Surface Scout (MASCOT) landed on Ryugu's surface on 3 October 2018. We present images from the MASCOT camera (MASCam) taken during the descent and while on the surface. The surface is covered by decimeter- to meter-sized rocks, with no deposits of fine-grained material. Rocks appear either bright, with smooth faces and sharp edges, or dark, with a cauliflower-like, crumbly surface. Close-up images of a rock of the latter type reveal a dark matrix with small, bright, spectrally different inclusions, implying that it did not experience extensive aqueous alteration. The inclusions appear similar to those in carbonaceous chondrite meteorites.

[Posterior mediastinal hemangioma successfully resected with cardiopulmonary bypass; report of a case].

Mediastinal hemangioma is a rare tumor. We report a case of a 62-year-old woman with a posterior mediastinal hemangioma. She had a history of right breast cancer and a follow-up chest radiography revealed a mass located in the left posterior mediastinum. The size was about 80 mm in diameter. The tumor surrounded the descending thoracic aorta and involved intercostal arteries. Complete excision could be achieved by decompressing the descending aorta with the aid of partial cardiopulmonary bypass and the aortic cross-clamp. Histologically, the tumor was diagnosed as a benign hemangioma. It was reported that hemangioma would reccur after subtotal excision. To employ cardiopulmonary bypass was a very effective approach for the purpose of complete excision in our case.

Mortality and cerebral outcome in patients who underwent aortic arch operations using deep hypothermic circulatory arrest with retrograde cerebral perfusion: no relation of early death, stroke, and delirium to the duration of circulatory arrest.

OBJECTIVE: Our goal was to investigate factors for mortality and cerebral outcome in patients with aneurysm of the aortic arch. METHODS: From 1993 to 1996, 148 patients with aortic arch aneurysm underwent operations involving deep hypothermic circulatory arrest with retrograde cerebral perfusion. Age was 63.9 +/- 11.6 years (mean +/- standard deviation) and 52 patients were older than 70 years. Twenty-eight had acute aortic dissection. Twelve had ruptured aneurysms. Fourteen had redo operations. Seventy had aortic dissection. The aneurysms were caused by atherosclerosis in 123 patients and by other causes in 25. Median sternotomy was used in 92 and left thoracotomy in 56. Twenty-eight patients underwent replacement of the ascending aorta to the proximal arch, 62 had total arch replacement, 38 had distal arch replacement, 12 had simultaneous replacement of the distal arch and the descending aorta or thoracoabdominal aorta, and 8 had patch repair. RESULTS: Fifteen (10.1%) early deaths occurred. New stroke occurred in six (4.0%) patients and transient delirium in 37 (25.0%). The duration of deep hypothermic circulatory arrest plus retrograde cerebral perfusion was 49 +/- 17 minutes, and it was more than 60 minutes in 36 patients. Patients awoke 7.5 +/- 8.2 hours after the operation. Logistic regression analysis demonstrated that risk factors for mortality were ruptured aneurysm, chronic obstructive pulmonary disease, arterial cannulation in the ascending aorta, and stroke. Risks for stroke were ruptured aneurysm and replacement of the distal arch. Risks for delirium were age older than 70 years and atherosclerotic aneurysm. Duration of circulatory arrest plus cerebral perfusion did not correlate with length of time before the patient regained consciousness. No difference was found in mortality, stroke, and delirium between patients with and those without more than 60 minutes of circulatory arrest and cerebral perfusion. CONCLUSION: Prolonged (> 60 minutes) deep hypothermic circulatory arrest with retrograde cerebral perfusion was not a risk factor for mortality and stroke in patients who underwent surgery for aneurysms of the aortic arch. However, the prevalence of transient delirium necessitates further investigations.

Feasibility study of a mechanical suturing device for less invasive mitral operations.

BACKGROUND: Because of smaller incisions and limited exposure, less invasive operations on the mitral valve can be arduous and time-consuming. This study examined the feasibility of a mechanical suturing device to facilitate less invasive mitral replacement. METHODS: Five mongrel dogs underwent limited left thoracotomy. After conventional cardiopulmonary bypass and cardioplegia, the mitral valve was exposed through a left atriotomy. After excision of the anterior leaflet, subannular sutures were placed using a mechanical suturing device. This device simultaneously passes two ends of a pledgeted 2-0 braided suture through the valvular annulus, then mechanically grasps both needles on the atrial aspect. Hence, a mattress suture is accomplished one-handed in a single continuous motion. This procedure was repeated around the entire annulus. A mechanical valve was seated and the sutures were tied and cut. RESULTS: All mechanical valves were implanted successfully. In the 4 animals in which it was attempted, cardiopulmonary bypass was successfully weaned. No evidence of perivalvular leak was observed by echocardiography. CONCLUSIONS: These data establish the feasibility of a mechanical suturing device for operations on the mitral valve. The device is easily mastered, maintains precise spacing between sutures, and permits rapid placement of mattress sutures. We predict widespread application for both less invasive and conventional valve operations.

Elephant trunk procedure for surgical treatment of aortic dissection.

BACKGROUND: In surgical intervention for aortic dissection, a highly radical operation can be performed by distal anastomosis with a true lumen resulting in thrombotic closure of the dissecting lumen. In this anastomosis, the elephant trunk procedure, in which a graft is inserted into the distal true lumen, prevents blood flow leakage into the dissecting lumen at the anastomosis site and also strengthens this area. METHODS: We performed this procedure in 15 patients (8 men and 7 women). Acute aortic dissection was observed in 9 patients and chronic dissection in 6. Stanford type A dissection was diagnosed in 10 patients and type B in 5. RESULTS: Graft replacement of the ascending aorta and total aortic arch was performed in 10 patients and descending aortic replacement in 5. A graft with a diameter of 16 to 24 mm was inserted into the true lumen of the descending aorta, and the false lumen was closed. Subsequently, distal anastomosis was performed on the true lumen. There were two hospital deaths. Postoperative digital subtraction angiography showed good results in living patients, and computed tomographic scanning showed thrombotic closure in the dissecting lumen of the descending aorta. CONCLUSIONS: The elephant trunk procedure is useful for closing the false lumen of the distal aorta.

Surgical strategies in managing organ malperfusion as a complication of aortic dissection.

Between December 1978 and March 1994, 48 of 312 patients who underwent surgery for aortic dissection were diagnosed with major vascular complications. There were 18 patients with type A dissection and 30 patients with type B. In 23 patients with acute dissection, the site of vascular obstruction was the abdominal aorta in 12 patients, brachiocephalic artery in 7, iliac artery in 4, left common carotid artery in 3 and thoracic aorta in 2. In 26 patients with chronic dissection, the site of vascular obstruction was the abdominal aorta in 13 patients, brachiocephalic artery in 10, renal artery in 5, iliac artery in 4, superior mesenteric artery in 2, left common carotid artery in 2 and celiac artery in 1. Fifteen patients underwent proximal repair of the aorta during the acute stage, including the ascending aorta in 6 patients, from ascending aorta to arch in 7, arch to descending aorta in 1, thoracoabdominal aorta in 1, and entry closure in 1. In the acute stage, eight patients had palliative surgery, including aortic fenestration in four patients, axillo-femoral bypass in two, cross-over bypass to the iliac or femoral artery in one, bypass to superior mesenteric artery in one, bypass to the renal artery in one, and ileum resection in one. During the chronic phase, seven patients with type B dissection, who had malperfused unilateral renal artery, underwent proximal aortic repair.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term results of patch repair for saccular aneurysms of the transverse aortic arch.

OBJECTIVE: Long-term results of patch repair in patients with a saccular aneurysm of the aortic arch were investigated. PATIENTS: From December 1984, 43 patients with a saccular aneurysm of the arch underwent patch repair. Indications for patch repair were determined as orifice diameter of aneurysm being less than 1/3 of the total circumference of the aorta. METHOD: Midsternotomy was used in 38 patients, and left thoracotomy in five. Selective cerebral perfusion was used in 28 patients, deep hypothermic circulatory arrest with retrograde cerebral perfusion in eight during the last 3 years, and partial cardiopulmonary bypass in seven. RESULTS: There were five (11.6%) early deaths, and causes were respiratory failure in two patients, low cardiac output in two, and gastrointestinal bleeding in one. Stroke was found in three patients (6.9%). During follow-up, seven patients died, two due to rupture of a residual or pseudoaneurysm, one due to reoperation of pseudoaneurysm, one due to stroke, two due to respiratory failure, and one due to unknown cause. Postoperative survival, including early death, was 69.3% at 5 years and 43.3% at 9 years. Aortic reoperation was done in three patients with a pseudoaneurysm formation and two survived. Freedom from reoperation was 91.7% at 5 years and 38.2% at 9 years. Event free ratio was 79.3 +/- 9.8% at 5 years and 37.6 +/- 18.6% at 9 years. CONCLUSION: Because of a high incidence of pseudoaneurysm or residual aneurysms after patch repair for a saccular aneurysm of the aortic arch, strict criteria for the patch repair should be applied or graft replacement of the aorta is recommended.

Surgery for aortic dissection with intimal tear in the transverse aortic arch.

OBJECTIVES: This study reports surgical experience of 72 cases of aortic dissection with intimal tear in the transverse aortic arch. METHODS: Of 325 patients with aortic dissection, 72 (22.2%) had a tear in the arch, including 27 with acute dissection and 45 with chronic dissection. Mean age at surgery was 60.8 +/- 14.1 years. The dissection was localized from the ascending aorta to the arch in 30 patients and extensive from the ascending aorta to the descending aorta in 42. Surgeries consisted of total arch replacement in 50 patients, hemiarch replacement in 20, and extra-anatomical bypass in 1. In the initial series, cardiopulmonary bypass for brain protection during arch procedures was selective cerebral perfusion (61 patients), but since July 1993 deep hypothermic circulatory arrest with retrograde cerebral perfusion was exclusively utilized (8 patients). RESULTS: Hospital mortality was 9.7%, 11.1% of the patients who had acute dissection and 8.8% with chronic dissection. There has been no mortality since February 1993. The mean follow-up period was 51 +/- 37 months, and there were 3 late deaths. The 5 and 10 year survival rate was 85.3 +/- 4.8 in all patients, 84.3 +/- 8.9% with acute dissection, and 85.5 +/- 5.7% with chronic dissection. The 5 and 10 year survival was 79.8 +/- 7.1 with extensive dissection, and 93.5 +/- 6.5% with localized dissection. During follow-up, 6 patients underwent subsequent aortic surgeries. The freedom from reoperation at 5 years and at 10 years was 91.4 +/- 4.8% and 65.6 +/- 14.4%, respectively. In patients with acute dissection it was 92.3 +/- 7.4% and 61.5 +/- 25.6% at 5 years and 10 years, while with chronic dissection it was 87.0 +/- 7.0% and 44.0 +/- 17.3% at 5 years and 10 years, respectively (n.s.). The freedom from subsequent reoperation for the aorta in all patients was 91.4 +/- 4.8% at 5 years and 10 years was 65.6 +/- 14.4%. With acute dissection it was 92.3 +/- 7.4% at 5 years and 61.5 +/- 25.6% at 10 years, while that with chronic dissection it was 91.3 +/- 5.9% and 65.7 +/- 16.8% at 5 years and 10 years respectively (n.s.). The freedom from all reoperations with extensive dissection at 5 years and 10 years was 86.6% +/- 7.2% and 34.2 +/- 17.3%, respectively, moreover, the freedom from reoperations with localized dissection at 5 and at 10 years was 90.0 +/- 9.5% (n.s.). However, the freedom from subsequent aorta reoperation with extensive dissection at 5 years and 10 years was 86.6 +/- 7.2% and 56.0 +/- 16.0%, respectively, while with localized dissection it was 100% at 10 years (P < 0.01). CONCLUSION: Early and late surgical result for arch dissection was satisfactory with a surgical principle of resecting the aortic segment that contains the initial intimal tear and graft replacement.

Predictive factors for postoperative cerebral complications in patients with thoracic aortic aneurysm.

OBJECTIVE: Perioperative factors affecting the outcomes of postoperative brain function in patients with thoracic aortic aneurysm were demonstrated. PATIENTS AND METHODS: From December 1977 to September 1994, 745 patients with thoracic aortic aneurysm underwent 846 operations. The mean age at surgery was 57.1 +/- 14.2 years old. Four hundred seventy-four patients had true aneurysm and 372 had aortic dissection. Two hundred forty-four patients underwent repair in the ascending aorta, 189 arch repair, 242 repair in the descending aorta. 79 replacement of the thoracoabdominal aorta, and 92 extra-anatomical bypass or thrombo-exclusion of the aorta. Conventional cardiopulmonary bypass was used in 297 patients, partial cardiopulmonary bypass through femoral access in 167, selective cerebral perfusion in 253, deep hypothermic circulatory arrest and retrograde cerebral perfusion in 50, temporary shunt in 29, and no circulatory support was applied in 50. Postoperative cerebral complications were divided into permanent cerebral dysfunction. RESULTS: The early mortality rate was 15.5% (131 patients). Incremental risk factors for hospital mortality were non-preexisting cardiac lesions, ruptured aneurysm, postoperative cerebral complications, sepsis, bleeding, low output syndrome and renal failure. Cerebral complications occurred in 81 patients (9.6%), involving 47 permanent and 34 transient sequelae. The early mortality rate in patients with postoperative brain damage was 42.0%. The etiologies of the brain damage diagnosed by computed tomography were embolism in 41 patients, cerebral hypoperfusion in 16 and unknown in 24. Incremental risk factors for postoperative cerebral complications were: operation early in the series advanced age at surgery, preoperative renal failure, aortic arch lesions, atherosclerotic aneurysm, aortic arch procedures and clamping of the aortic arch. CONCLUSIONS: Although there was an increased incidence of advanced age and complex lesions in patients with aortic aneurysm, an improvement in surgical results has recently been achieved using advanced diagnostic and surgical techniques.

Repair for aneurysms of the entire descending thoracic aorta or thoracoabdominal aorta using a deep hypothermia.

OBJECTIVE: Replacement of the entire descending aorta or of the thoracoabdominal aorta still has a significant risk for postoperative paraplegia. Surgical strategies using a deep hypothermia to protect the spinal cord or viscera are discussed. METHODS: From April 1994, 25 patients underwent graft replacement of the entire descending aorta (13 patients) or thoracoabdominal aorta (12 patients) using a deep hypothermia. Five patients had atherosclerotic aneurysms and 20 had aortic dissection. There were 20 males and 5 females, whose age ranged from 26 to 72 years old, 47 years old in average. Surgery consisted with proximal anastomosis using deep hypothermia (18 degrees C) with retrograde cerebral perfusion by elevating central venous pressure to 20 mmHg, reconstruction of the intercostal arteries, and distal open anastomosis, while perfusing the brain and heart. Proximal open anastomosis was used with retrograde cerebral perfusion technique in 18 patients. Averaged number of reconstructed intercostal arteries was 2.1 for each patient. RESULTS: No early mortality was found and one patient died of respiratory failure 6 months after surgery. One patient had a postoperative stroke and one had a delayed onset of paraplegia 2 days after operation. The cause of paraplegia was secondary hypoxemia and hypotension due to pneumonia. CONCLUSION: Utilization of the deep hypothermia in surgery for aneurysms of the entire descending aorta or of the thoracoabdominal aorta provided an adequate protection of the spinal cord as well as the abdominal viscera, eliminated clamp injury or cerebral embolization of debris or thrombi, and afforded excellent surgical exposures.

Doppler ultrasonographic identification of the critical segmental artery for spinal cord protection.

OBJECTIVE: The purpose of this study is to evaluate the possibility of identifying critical segmental arteries (CSAs) based on Doppler ultrasonographic hemodynamics. METHODS: In 18 mongrel dogs, the descending aorta was scanned directly with a 5-MHz linear probe through left thoracotomies and the flow velocities in segmental arteries were measured by pulsed Doppler. The aorta was cross-clamped between Th13 and L1, and flow velocity changes were recorded. According to flow increases, segmental arteries were divided into three groups: arteries with the largest flow increase (L-arteries), arteries with the smallest increase (S-arteries) and other arteries (O-arteries). Animals were divided into three groups. One aortic segment including an L-artery or an S-artery was perfused via a temporary shunt during 30-min aortic cross-clamping distal to the left subclavian artery (Group L or Group S) and neurological outcomes were compared with those of animals without shunting (Group N) after 24 and 48 h. RESULTS: L-arteries had significantly larger flow increases than S- and O-arteries (74.3+/-33.8, 20.4+/-9.8 and 33.3+/-17.8 cm/s, P<0.01). In Group N, five of the six animals were completely paraplegic (Tarlov Grade 0) and the other was Grade 1. In Group S, four animals were Grade 4 and two were Grade 0 after 24h. However, two animals showed delayed paraplegia. Therefore, four animals were Grade 0 and two were Grade 4 after 48 h. All animals in Group L were neurologically normal (Grade 4) at both after 24h (vs. Group N, P=0.0013) and 48 h (vs. Group N, P=0.0013; vs. Group S, P=0.019). CONCLUSIONS: Flow responses to aortic cross-clamping differed among segmental arteries and selective perfusion of L-arteries completely prevented paraplegia. Therefore, L-arteries were considered to be CSAs. Hemodynamic measurement of segmental arterial flow using Doppler ultrasonography could be clinically useful for spinal cord protection during thoracoabdominal aortic surgery.

Arterial blood gas management in retrograde cerebral perfusion: the importance of carbon dioxide.

OBJECTIVES: Many interventional physiological assessments for retrograde cerebral perfusion (RCP) have been explored. However, the appropriate arterial gas management of carbon dioxide (CO2) remains controversial. The aim of this study is to determine whether alpha-stat or pH-stat could be used for effective brain protection under RCP in terms of cortical cerebral blood flow (CBF), cerebral metabolic rate for oxygen (CMRO2), and distribution of regional cerebral blood flow. METHODS: Fifteen anesthetized dogs (25.1+/-1.1 kg) on cardiopulmonary bypass (CPB) were cooled to 18 degrees C under alpha-stat management and had RCP for 90 min under: (1), alpha-stat; (2), pH-stat; or (3), deep hypothermic (18 degrees C) antegrade CPB (antegrade). RCP flow was regulated for a sagittal sinus pressure of around 25 mmHg. CBF was monitored by a laser tissue flowmeter. Serial analyses of blood gas were made. The regional cerebral blood flow was measured with colored microspheres before discontinuation of RCP. CBF and CMRO2 were evaluated as the percentage of the baseline level (%CBF, %CMRO2). RESULTS: The oxygen content of arterial inflow and oxygen extraction was not significantly different between the RCP groups. The %CBF and %CMRO2 were significantly higher for pH-stat RCP than for alpha-stat RCP. The regional cerebral blood flow, measured with colored microspheres, tended to be higher for pH-stat RCP than for alpha-stat RCP, at every site in the brain. Irrespective of CO2 management, regional differences were not significant among any site in the brain. CONCLUSIONS: CO2 management is crucial for brain protection under deep hypothermic RCP. This study revealed that pH-stat was considered to be better than alpha-stat in terms of CBF and oxygen metabolism in the brain. The regional blood flow distribution was considered to be unchanged irrespective of CO2 management.