Effect of nitrous oxide (N2O) on the structure and function of nitrogen-oxide reducing microbial communities.

Nitrous oxide (N2O) is a potent greenhouse gas that can be produced by nitrifying and denitrifying bacteria. Yet the effects of N2O on microbial communities is not well understood. We used batch tests to explore the effects of N2O on mixed denitrifying communities. Batch tests were carried out with acetate as the electron donor and with the following electron acceptors: nitrate (NO3-), nitrite (NO2-), N2O, NO3- + N2O, and NO2- + N2O. Activated sludge from a municipal wastewater treatment plant was used as the inoculum. The bacteria grew readily with N2O as the sole acceptor. When N2O was provided along with NO3- or NO2-, it was used concurrently and resulted in higher growth rates than the same acceptors without added N2O. The microbial communities resulting from N2O addition were significantly different at the genus level from those with just NO3- or NO2-. Tests with N2O as the sole added acceptor revealed a reduced diversity. Analysis of inferred gene content using PICRUSt2 indicated a greater abundance of genera with a complete denitrification pathway when growing on N2O or NO2-, relative to all other tests. This suggests that specific N2O reduction rates are high, and that N2O alone selects for a low-diversity, fully denitrifying community. When N2O is present with NO2- or NO3-, the microbial communities were more diverse and did not select exclusively for full denitrifiers. N2O alone appears to select for a "generalist" community with full denitrification pathways and lower diversity. In terms of denitrification genes, the combination of acceptors with N2O appeared to increase the number of microbes carrying nirK, while fully denitrifying bacteria appear more likely to carry nirS. Lastly, all the taxa in NO2- and N2O samples were predicted to harbor nosZ. This suggests the potential for reduced N2O emissions in denitrifying systems.

Kinetics of nitrous oxide (N2O) formation and reduction by Paracoccus pantotrophus.

Nitrous oxide (N2O) is a powerful greenhouse gas emitted from wastewater treatment, as well as natural systems, as a result of biological nitrification and denitrification. While denitrifying bacteria can be a significant source of N2O, they can also reduce N2O to N2. More information on the kinetics of N2O formation and reduction by denitrifying bacteria is needed to predict and quantify their impact on N2O emissions. In this study, kinetic parameters were determined for Paracoccus pantotrophus, a common denitrifying bacterium. Parameters included the maximum specific reduction rates, [Formula: see text], growth rates, [Formula: see text], and yields, Y, for reduction of NO3- (nitrate) to nitrite (NO2-), NO2- to N2O, and N2O to N2, with acetate as the electron donor. The [Formula: see text] values were 2.9 gN gCOD-1 d-1 for NO3- to NO2-, 1.4 gN gCOD-1 d-1 for NO2- to N2O, and 5.3 gN gCOD-1 d-1 for N2O to N2. The [Formula: see text] values were 2.7, 0.93, and 1.5 d-1, respectively. When N2O and NO3- were added concurrently, the apparent (extant) kinetics, [Formula: see text], assuming reduction to N2, were 6.3 gCOD gCOD-1 d-1, compared to 5.4 gCOD gCOD-1 d-1 for NO3- as the sole added acceptor. The [Formula: see text] was 1.6 d-1, compared to 2.5 d-1 for NO3- alone. These results suggest that NO3- and N2O were reduced concurrently. Based on this research, denitrifying bacteria like P. pantotrophus may serve as a significant sink for N2O. With careful design and operation, treatment plants can use denitrifying bacteria to minimize N2O emissions.

Intraoperative transesophageal echocardiography and epiaortic ultrasound for assessment of atherosclerosis of the thoracic aorta.

OBJECTIVES: This study sought to determine the role of transesophageal echocardiography (TEE) and epiaortic ultrasound in the detection of atherosclerosis of the ascending aorta in patients undergoing cardiac surgery. BACKGROUND: Atherosclerosis of the ascending aorta is a major risk factor for perioperative stroke and systemic embolism in patients undergoing cardiac surgery. METHODS: Forty-four patients underwent prospective evaluation of the ascending aorta with two ultrasound techniques-epiaortic ultrasound and biplane TEE-and by palpation. The severity of atherosclerosis was graded on a four-point scale as normal, mild, moderate or severe. RESULTS: A comparison of results with biplane TEE and those with epiaortic ultrasound yielded a kappa value of 0.12 (95% confidence interval 0 to 0.25), indicating poor correlation between the two. Compared with epiaortic ultrasound, biplane TEE significantly underestimated the severity of ascending aortic atherosclerosis, and this underestimation was more marked in the distal ascending aorta (p < 0.0001). When compared with epiaortic ultrasound and biplane TEE, palpation of the ascending aorta significantly underestimated the presence and severity of atherosclerosis (p < 0.0001 for both). CONCLUSIONS: Epiaortic ultrasound is more accurate than TEE for identification of atherosclerosis of the ascending aorta, but both ultrasound techniques are superior to palpation. Epiaortic ultrasound and TEE provide complementary information regarding thoracic aortic atherosclerosis. Modification of surgical technique on the basis of results of intraoperative epiaortic ultrasound and TEE in elderly patients undergoing cardiac procedures may prevent atheroembolic complications.

Cross-linking surface immunoglobulin increases the stiffness of lymphocytes.

Cross-linking surface immunoglobulin (sIg) on B-lymphocytes causes a substantial increase in the mechanical stiffness of the cells. This has been demonstrated using a new method for measuring cellular deformability. The method is based on a device, the "Cell Poker", which we use to determine the force required slightly to indent or compress a cell adherent to a rigid substrate in culture. Cross-linking of sIg by bivalent anti-sIg antibodies is necessary to elicit the increase in stiffness; binding of monovalent Fab fragments is insufficient. The increase in stiffness is partially reversed by cytochalasin D and by completion of the capping of the cross-linked sIg. The modulation of cellular deformability and the induction of cellular dynamic processes such as capping are similar in their requirements for cross-linking sIg and in their sensitivity to cytochalasins. This suggests that both kinds of responses stem from similar cellular processes and structures. These results emphasize the mechanical capability of lymphocytes and suggest that the physiological functions of these cells are likely to employ this capability.

Ventriculoarterial coupling with intra-aortic balloon pump in acute ischemic heart failure.

PURPOSE: We analyzed the mechanism of effects of intra-aortic balloon pumping using the pressure-volume relationship and ventriculoarterial coupling in the normal and failing hearts. MATERIALS: In 12 anesthetized Holstein calves (weight, 94 +/- 8 kg), the ventricular end-systolic and arterial elastances, pressure-volume area, and external work were analyzed during steady-state contractions with traditional hemodynamic parameters with intra-aortic balloon pumping-off and -on (1:1 synchronous ratio). An acute ischemic heart failure was induced by injecting 10 microm microspheres (4.2 +/- 1.8 x 10(7). 100g left ventricular weight-1) into the left main coronary artery; all measurements were repeated. RESULTS: Intra-aortic balloon pumping did not change hemodynamic parameters in the control. However, during heart failure, intra-aortic balloon pumping decreased the arterial elastance from 3.6 +/- 1.3 mm Hg to 2.9 +/- 1.2 mm Hg. mL-1 while not affecting the ventricular end-systolic elastance, this resulted in an improvement of the ventriculoarterial coupling ratio from 3.1 +/- 0.8 to 2.3 +/- 0.8. Intra-aortic balloon pumping decreased not only end-systolic pressure (from 69 +/- 16 mm Hg to 64 +/- 19 mm Hg) but end-diastolic volume and pressure (from 139 +/- 38 mL to 137 +/- 37 mL and from 13. 9 mm Hg to 12.8 mm Hg, respectively) with the leftward shift of the pressure-volume loop. Pressure-volume area decreased (from 914 +/- 284 mm Hg to 849 +/- 278 mm Hg. mL) although stroke volume increased (from 21 +/- 6 mL to 24 +/- 6 mL). CONCLUSION: Reduction of the arterial elastance with intra-aortic balloon pumping improved the ventriculoarterial coupling ratio and increased stroke volume. Leftward shift of the pressure-volume loop resulted in the reduction of pressure-volume area, which suggests the conservation of the myocardial oxygen consumption.

Reoperations on the aortic root and ascending aorta.

BACKGROUND: Reoperations on the aortic root and the ascending aorta are being performed with increasing frequency and remain a challenging problem. METHODS: Eighty-one patients (age range, 14 to 78 years) underwent reoperations on the aortic root or the ascending aorta during a 14.5-year interval ending October 1996. The previous operations were aortic valve procedure (28%), coronary artery bypass grafting (25%), aortic root replacement (24%), ascending aortic replacement (19%), and miscellaneous (5%). Twenty-two patients (27%) had had two or more previous operations. The principal indications for reoperation were true or false aneurysm (35%), acute or chronic dissection (28%), and malfunction of an aortic valve substitute (27%). The reoperations performed were aortic root replacement (composite graft, allograft, or autograft) in 48 patients and graft replacement of the ascending aorta in 33 patients. Concomitant procedures included aortic arch replacement in 43 patients (55%) and coronary artery bypass grafting in 33 patients (41%). RESULTS: The 30-day mortality rate was 8.6% (7 patients). It was 8.3% for aortic root replacement and 9.1% for ascending aorta replacement (p > 0.05). Using stepwise multivariate logistic regression analysis of 23 variables, preoperative functional class III/IV (p = 0.047) and duration of cardiopulmonary bypass (p = 0.007) were significant independent predictors of early death. The mean duration of follow-up was 3.6 years. The 1-year, 5-year, and 10-year survival rates were 89%, 81%, and 69%, respectively. Freedom from reoperation on the heart or ascending aorta was 98%, 92%, and 69%, respectively. Reoperation for false aneurysm (p = 0.050) and the presence of coexisting coronary artery disease requiring bypass grafting (p = 0.010) were the only significant predictors of late mortality. CONCLUSIONS: Reoperations on the aortic root and the ascending aorta can be accomplished with acceptable early mortality and satisfactory long-term results. More frequent resection of the aneurysmal or dissected segments of the ascending aorta and aortic root at the initial operation may reduce the need for subsequent reoperation.

Pierce-Donachy pediatric VAD: progress in development.

BACKGROUND: Despite the successful use of ventricular assist devices in adults over the past 15 years, relatively little has been done to develop similar devices for pediatric patients. Consequently, no such device is currently available. A review of clinical data suggests that the majority of patients in need of a pediatric ventricular assist device, either for postcardiotomy cardiogenic shock or as a bridge to cardiac transplantation, are neonates weighing 3 to 5 kg. Attempts to "scale down" an adult blood pump to make an appropriate device for these patients have been difficult due to the lack of sufficiently small, commercially available valves and the tendency for thrombus to develop in these small pumps. METHODS: We report on progress in the development of the Pierce-Donachy pediatric ventricular assist device, which incorporates 10-mm-diameter bileaflet valve prototypes. Particle image velocimetry is used to quantify the velocity field inside the pump. RESULTS AND CONCLUSIONS: Particle image velocimetry velocity maps demonstrate the complexity of the flow patterns in these pumps and suggest that improved flow patterns may result from the use of valves with improved hemodynamic performance. Animal tests to determine whether improved flow patterns and better "washing" of the pump's blood-contacting surfaces will reduce thrombus formation are underway.

Thrombosis of mitral valve bioprostheses in patients requiring circulatory assistance.

Two patients with new mitral valve bioprostheses required implantation of Bio-Medicus centrifugal pumps (Bio-Medicus, Minneapolis, MN) for circulatory support and had evidence of prosthetic valve thrombosis 1 and 4 days later. Both patients died of thromboembolic complications despite surgical removal of the thrombus. Thrombosis is a rare early complication of bioprosthetic valves and in these cases was probably related to low transvalvular flow due to the use of circulatory assist devices. We discuss possible strategies for avoiding and managing this catastrophic complication.

Hypothermic bypass and circulatory arrest for operations on the descending thoracic and thoracoabdominal aorta.

BACKGROUND: Hypothermic cardiopulmonary bypass with intervals of circulatory arrest is a useful adjunct during operations on the descending thoracic aorta and distal aortic arch when severe aortic disease precludes placement of clamps on the aorta. Hypothermia also has a marked protective effect on spinal cord function during periods of aortic occlusion. METHODS: Fifty-one patients (age range, 22 to 79 years) with descending thoracic or thoracoabdominal aortic disease had resection and graft replacement of the diseased aortic segments using hypothermic cardiopulmonary bypass and intervals of circulatory arrest in situations where the location, extent, or severity of disease precluded placement of clamps on the proximal aorta (8 patients) or (in 43 patients) when extensive thoracic (11) or thoracoabdominal (32) aortic disease was present and the risk for development of spinal cord ischemic injury and renal failure was judged to be increased. Patent intercostal (below T-6) and upper lumbar arteries were attached to the graft whenever possible. RESULTS: Thirty-day mortality was 9.8% (5 patients). Paraplegia occurred in 2 and paraparesis in 1 of the 46 30-day survivors (6.5%). Among the 27 operative survivors with thoracoabdominal aneurysms, paraplegia occurred in 1 of 12 with Crawford type I (8%), 0 of 10 with type II, and 1 of 5 with type III aneurysms (20%). Paraplegia occurred in none of the 12 patients with aortic dissection and in 2 of the 15 patients with degenerative aneurysms. Renal failure requiring dialysis occurred in 1 (2.2%) of the 46 30-day survivors. CONCLUSIONS: Hypothermic circulatory arrest is a valuable adjunct for the treatment of complex aortic disease involving the aortic arch and thoracoabdominal aorta. In patients with thoracoabdominal aneurysms, its use has been associated with a low incidence of renal failure and an incidence of paraplegia/paraparesis in traditionally high-risk subsets (type I and II aneurysms, aortic dissection), which may be less than that observed with other surgical techniques.

Strategy for the reduction of stroke incidence in cardiac surgical patients.

Atherosclerosis of the ascending aorta (AAA) and severe carotid artery disease are risk factors for stroke in cardiac surgical patients. Twelve hundred of a consecutive series of 1,334 patients 50 years of age or older having a cardiac operation were screened for the presence of AAA by intraoperative ultrasonographic scanning and for the presence of carotid artery occlusive disease (791 of 798 patients > or = 65 years of age and younger symptomatic patients) by carotid duplex scanning. Coronary artery disease was present in 88% of the patients. Patients with moderate or severe AAA (n = 231; 19.3% of the total) were treated by ascending aortic replacement (n = 27) or by modified, less extensive techniques (n = 168) to avoid the atherosclerotic areas. Thirty-three patients had combined carotid endarterectomy and cardiac operation. Thirty-day mortality and stroke rates for the 1,200 patients were 4.0% and 1.6%, respectively. The stroke rate was low (1.1%) among the 969 patients with no or mild AAA. It was zero among 27 patients with moderate or severe AAA who had ascending aortic replacement and among the 33 patients who had carotid endarterectomy. The stroke rates were higher for 111 patients with moderate or severe ascending aortic disease who had only minor interventions (6.3%) and for 16 patients with severe carotid artery disease who did not have carotid endarterectomy (18.7%). Screening for AAA and carotid artery disease and aggressive surgical treatment of moderate or severe AAA and severe or symptomatic carotid artery disease appears to reduce the frequency of stroke in older cardiac surgical patients.

An electrically powered total artificial heart. Over 1 year survival in the calf.

An electric motor driven orthotopic artificial heart was implanted in a 110 kg female Holstein calf as part of a series of 12 such implants intended to demonstrate the in vivo durability and compatibility of the device. The device uses pusher plates set into motion by a reversing brushless DC motor and roller screw to alternately eject two cylindrical sac type blood pumps. The pumps use Bjork-Shiley Delrindisc convexo-concave or monostrut valves. The left pump provides an 88-90 ml dynamic stroke volume. Woven Dacron grafts and polyurethane coated Dacron/Lycra cuffs are used to attach the device to the major arteries and atria, respectively. A polyurethane conduit and anchoring skin button bring motor wires percutaneously to an extracorporeal controller. The controller provides balanced cardiac output sensitive to atrial or aortic pressures, without operator intervention. The system is hermetically sealed and uses a simple compliance sac to maintain thoracic pressure between the pumps. The calf recovered uneventfully from surgery and thrived thereafter. She was killed on the 388th post-operative day because of worsening cardiac insufficiency. The previous three operative survivors in this series lived 131, 134, and 204 days. These results indicate the device's good potential for durability and body compatibility.

Cell poking. Determination of the elastic area compressibility modulus of the erythrocyte membrane.

Cell poking, a new method for measuring mechanical properties of single cells was used to determine the elastic area compressibility modulus of osmotically swollen human erythrocytes. With this method we determined the force required to indent cells attached to a glass coverslip (Petersen, N.O., W. B. McConnaughey , and E. L. Elson , 1982, Proc. Natl. Acad. Sci. USA, 79:5327. Forces on the order of one millidyne and indentations on the order of one micron were detected. An analysis of these data in terms of a simplified mechanical model yielded the elastic area compressibility modulus. This analysis used a variational approach to minimize the isothermal elastic potential energy density function given by E. A. Evans and R. Skalak (Mechanics and Thermodynamics of Biomembranes, 1980, CRC Press, Boca Raton , FL). Measurements on swollen erythrocytes gave a range of values, depending in part on the osmotic conditions, of 17.9 +/- 8.2 to 34.8 +/- 12.0 mdyn /micron for the elastic area compressibility modulus at 25 degrees C. Fractional area expansion greater than 2.6 +/- 0.8% produced rapid cell lysis. These values were not corrected for the reversible movement of water across the cell membrane in response to hydrostatic pressure gradients. Our results agree reasonably with those obtained by Evans et al. (Evans, E.A., R. Waugh , and L. Melnick , 1976, Biophys. J., 16:585-595.) using micropipette aspiration under similar conditions.

Management of the severely atherosclerotic aorta during cardiac operations.

Embolization of atheroma from the ascending aorta is a major cause of stroke following cardiac surgery. We evaluated a protocol for intraoperative detection and treatment of the severely atherosclerotic ascending aorta which included epiaortic ultrasonographic scanning and resection and graft replacement of the involved segment using hypothermic ischemic arrest. During an 81-month interval, 47 patients 50 years of age and older (mean age 71 years) who underwent coronary artery bypass grafting had resection and graft replacement of the ascending aorta. This represented approximately 2% of the patients in this age group who had cardiac operations during this interval. Nineteen patients (40%) required additional procedures. The 30-day mortality rate was 4.3% (2 patients). Both patients died of myocardial failure. None of the 45 surviving patients sustained a perioperative stroke. There have been no strokes or transient ischemic events in the follow-up period, which extends to 72 months (mean 21 months). While this technique for management of the severely atherosclerotic aorta could be considered radical, it was associated with lower mortality and stroke rates than those that were observed in patients with moderate or severe atherosclerosis in whom only minor modifications in technique were made to avoid embolization of atheroma. Resection and graft replacement during a period of hypothermic circulatory arrest is currently our preferred method of treatment for the severely atherosclerotic aorta during cardiac surgery.

Hypothermic circulatory arrest for cerebral protection during combined carotid and cardiac surgery in patients with bilateral carotid artery disease.

OBJECTIVE: The authors evaluated the protective effect of hypothermic circulatory arrest for patients with bilateral carotid artery disease who underwent cardiac surgical procedures. SUMMARY BACKGROUND DATA: Severe bilateral carotid artery disease coexisting with cardiac disease that requires surgical treatment is associated with a substantial incidence of stroke after operations that require cardiopulmonary bypass. The optimal method of management of patients with these coexisting conditions is not established clearly. Because hypothermia has a protective effect on neural and myocardial tissue during cardiac operations, a protocol employing profound hypothermia and a period of circulatory arrest was evaluated in a group of patients who underwent combined carotid and cardiac surgery who were considered to be at increased risk for the development of stroke. METHODS: Fifty patients with bilateral carotid artery disease, including 24 patients with high-grade unilateral stenosis and contralateral occlusion and 6 patients with 80% to 99% bilateral stenosis, underwent combined carotid endarterectomy and cardiac surgery (coronary artery bypass grafting in all 50 patients and additional procedures in 8 patients). Profound systemic hypothermia (15 C) was instituted, and the carotid endarterectomy was performed during a period of circulatory arrest that averaged 30 minutes. The cardiac procedure was performed during the periods of cooling and rewarming. RESULTS: The 30-day mortality rate was 6% (3 patients). There were no early postoperative strokes or reversible ischemic neurologic deficits. There have been seven late deaths in the postoperative period, which extends to 54 months. None of these deaths were caused by stroke. There has been one late stroke, which occurred in the distribution of the unoperated carotid artery. CONCLUSIONS: This technique provides adequate protection of the brain and myocardium during combined carotid and cardiac surgical procedures and appears to reduce the frequency of stroke in the high-risk subgroup of patients with bilateral carotid artery disease.