Cerebral hemodynamics at altitude: effects of hyperventilation and acclimatization on cerebral blood flow and oxygenation.

OBJECTIVE: Alterations in cerebral blood flow (CBF) and cerebral oxygenation are implicated in altitude-associated diseases. We assessed the dynamic changes in CBF and peripheral and cerebral oxygenation engendered by ascent to altitude with partial acclimatization and hyperventilation using a combination of near-infrared spectroscopy, transcranial Doppler ultrasound, and diffuse correlation spectroscopy. METHODS: Peripheral (Spo2) and cerebral (Scto2) oxygenation, end-tidal carbon dioxide (ETCO2), and cerebral hemodynamics were studied in 12 subjects using transcranial Doppler and diffuse correlation spectroscopy (DCS) at 75 m and then 2 days and 7 days after ascending to 4559 m above sea level. After obtaining baseline measurements, subjects hyperventilated to reduce baseline ETCO2 by 50%, and a further set of measurements were obtained. RESULTS: Cerebral oxygenation and peripheral oxygenation showed a divergent response, with cerebral oxygenation decreasing at day 2 and decreasing further at day 7 at altitude, whereas peripheral oxygenation decreased on day 2 before partially rebounding on day 7. Cerebral oxygenation decreased after hyperventilation at sea level (Scto2 from 68.8% to 63.5%; P<.001), increased after hyperventilation after 2 days at altitude (Scto2 from 65.6% to 69.9%; P=.001), and did not change after hyperventilation after 7 days at altitude (Scto2 from 62.2% to 63.3%; P=.35). CONCLUSIONS: An intensification of the normal cerebral hypocapnic vasoconstrictive response occurred after partial acclimatization in the setting of divergent peripheral and cerebral oxygenation. This may help explain why hyperventilation fails to improve cerebral oxygenation after partial acclimatization as it does after initial ascent. The use of DCS is feasible at altitude and provides a direct measure of CBF indices with high temporal resolution.

Risk stratification by pre-operative cardiopulmonary exercise testing improves outcomes following elective abdominal aortic aneurysm surgery: a cohort study.

BACKGROUND: In 2009, the NHS evidence adoption center and National Institute for Health and Care Excellence (NICE) published a review of the use of endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms (AAAs). They recommended the development of a risk-assessment tool to help identify AAA patients with greater or lesser risk of operative mortality and to contribute to mortality prediction.A low anaerobic threshold (AT), which is a reliable, objective measure of pre-operative cardiorespiratory fitness, as determined by pre-operative cardiopulmonary exercise testing (CPET) is associated with poor surgical outcomes for major abdominal surgery. We aimed to assess the impact of a CPET-based risk-stratification strategy upon perioperative mortality, length of stay and non-operative costs for elective (open and endovascular) infra-renal AAA patients. METHODS: A retrospective cohort study was undertaken. Pre-operative CPET-based selection for elective surgical intervention was introduced in 2007. An anonymized cohort of 230 consecutive infra-renal AAA patients (2007 to 2011) was studied. A historical control group of 128 consecutive infra-renal AAA patients (2003 to 2007) was identified for comparison.Comparative analysis of demographic and outcome data for CPET-pass (AT ≥ 11 ml/kg/min), CPET-fail (AT < 11 ml/kg/min) and CPET-submaximal (no AT generated) subgroups with control subjects was performed. Primary outcomes included 30-day mortality, survival and length of stay (LOS); secondary outcomes were non-operative inpatient costs. RESULTS: Of 230 subjects, 188 underwent CPET: CPET-pass n = 131, CPET-fail n = 35 and CPET-submaximal n = 22. When compared to the controls, CPET-pass patients exhibited reduced median total LOS (10 vs 13 days for open surgery, n = 74, P < 0.01 and 4 vs 6 days for EVAR, n = 29, P < 0.05), intensive therapy unit requirement (3 vs 4 days for open repair only, P < 0.001), non-operative costs (£5,387 vs £9,634 for open repair, P < 0.001) and perioperative mortality (2.7% vs 12.6% (odds ratio: 0.19) for open repair only, P < 0.05). CPET-stratified (open/endovascular) patients exhibited a mid-term survival benefit (P < 0.05). CONCLUSION: In this retrospective cohort study, a pre-operative AT > 11 ml/kg/min was associated with reduced perioperative mortality (open cases only), LOS, survival and inpatient costs (open and endovascular repair) for elective infra-renal AAA surgery.

Tissue engineering small-diameter vascular grafts: preparation of a biocompatible porcine ureteric scaffold.

This study aimed to investigate a biocompatible, biomechanically functional, small-diameter (<6 mm) scaffold for tissue engineering a vascular graft using acellular porcine ureters. Porcine ureters were decellularized and sterilized using sequential treatment with hypotonic Tris buffer, sodium dodecyl sulphate 0.1% w/v (plus proteinase inhibitors), nuclease solution (RNase and DNase), and peracetic acid. The scaffold was compared with fresh ureter according to histology, immunocytochemistry, quantitative determination of alpha-galactosyl (alpha-Gal), and biochemistry. The biomechanical properties of the scaffold were compared with those of fresh ureters and human saphenous vein. The biocompatibility of decellularized ureters was assessed using in vitro contact and extract cytotoxicity tests. The in vivo biocompatibility was investigated using a mouse model. The histioarchitecture of the acellular ureteric scaffolds was preserved with some loss of basement membrane proteins while showing no evidence of cellularity. There was no evidence of residual alpha-Gal epitope present in acellular ureter. The ultimate tensile strength, compliance, and burst pressures of the acellular ureters were not compromised, compared with fresh tissues (p > 0.05), and the results compared favorably with fresh human saphenous vein samples (p > 0.05). The decellularized scaffolds were shown to be biocompatible with porcine smooth muscle and endothelial cells in vitro. One month after subcutaneous implantation in mice, explants were analyzed immunohistochemically using anti-CD3, Factor VIII, F4/80 (macrophage), and alpha-smooth muscle actin antibodies. The fresh tissue controls had a significantly thicker capsule (of inflammatory cells and fibrous tissue) than decellularized implants (p < 0.05). Decellularized explants were infiltrated with a combination of fibroblast-like cells and macrophages, indicating a healthy repair process. This study has demonstrated the potential of acellular porcine ureteric scaffolds in tissue engineering small-diameter living vascular grafts.

Late lumbar hemorrhage after open repair of abdominal aortic aneurysm: computed tomographic appearance resembling type II endoleak.

Development of endoleak after conventional open repair of abdominal aortic aneurysm is less well documented compared with endovascular stenting. We present a case report of a 65-year-old man who had sudden onset of back pain with central abdominal tenderness 34 days after successful open repair of an abdominal aortic aneurysm. Urgent laparotomy revealed the presence of a noninfective intrasac hemorrhage, due to recanalization of the lumbar arteries. These were successfully suture ligated. Delayed lumbar hemorrhage should be an important differential diagnosis by frontline medical personnel in patients with recent open aneurysm repair. The recent literature on other causes and management strategies is also reviewed.