Optimising perioperative care for hip and knee arthroplasty in South Africa: a Delphi consensus study.

BACKGROUND: A structured approach to perioperative patient management based on an enhanced recovery pathway protocol facilitates early recovery and reduces morbidity in high income countries. However, in low- and middle-income countries (LMICs), the feasibility of implementing enhanced recovery pathways and its influence on patient outcomes is scarcely investigated. To inform similar practice in LMICs for total hip and knee arthroplasty, it is necessary to identify potential factors for inclusion in such a programme, appropriate for LMICs. METHODS: Applying a Delphi method, 33 stakeholders (13 arthroplasty surgeons, 12 anaesthetists and 8 physiotherapists) from 10 state hospitals representing 4 South African provinces identified and prioritised i) risk factors associated with poor outcomes, ii) perioperative interventions to improve outcomes and iii) patient and clinical outcomes necessary to benchmark practice for patients scheduled for primary elective unilateral total hip and knee arthroplasty. RESULTS: Thirty of the thirty-three stakeholders completed the 3 months Delphi study. The first round yielded i) 36 suggestions to preoperative risk factors, ii) 14 (preoperative), 18 (intraoperative) and 23 (postoperative) suggestions to best practices for perioperative interventions to improve outcomes and iii) 25 suggestions to important postsurgical outcomes. These items were prioritised by the group in the consecutive rounds and consensus was reached for the top ten priorities for each category. CONCLUSION: The consensus derived risk factors, perioperative interventions and important outcomes will inform the development of a structured, perioperative multidisciplinary enhanced patient care protocol for total hip and knee arthroplasty. It is anticipated that this study will provide the construct necessary for developing pragmatic enhanced care pathways aimed at improving patient outcomes after arthroplasty in LMICs.

Mortality in the vertebroplasty population.

BACKGROUND AND PURPOSE: Vertebroplasty is an effective treatment for painful compression fractures refractory to conservative management. Because there are limited data regarding the survival characteristics of this patient population, we compared the survival of a treated with an untreated vertebral fracture cohort to determine whether vertebroplasty affects mortality rates. MATERIALS AND METHODS: The survival of a treated cohort, comprising 524 vertebroplasty recipients with refractory osteoporotic vertebral compression fractures, was compared with a separate historical cohort of 589 subjects with fractures not treated by vertebroplasty who were identified from the Rochester Epidemiology Project. Mortality was compared between cohorts by using Cox proportional hazards models adjusting for age, sex, and Charlson indices of comorbidity. Mortality was also correlated with pre-, peri-, and postprocedural clinical metrics (eg, cement volume use, RDQ score, analog pain scales, frequency of narcotic use, and improvement in mobility) within the treated cohort. RESULTS: Vertebroplasty recipients demonstrated 77% of the survival expected for individuals of similar age, ethnicity, and sex within the US population. Compared with individuals with both symptomatic and asymptomatic untreated vertebral fractures, vertebroplasty recipients retained a 17% greater mortality risk. However, compared with symptomatic untreated vertebral fractures, vertebroplasty recipients had no increased mortality following adjustment for differences in age, sex, and comorbidity (HR, 1.02; 95% CI, 0.82-1.25). In addition, no clinical metrics used to assess the efficacy of vertebroplasty were predictive of survival. CONCLUSIONS: Vertebroplasty recipients have mortality rates similar to those of individuals with untreated symptomatic fractures but have worse mortality compared with those with asymptomatic vertebral fractures.

Cerebral venous sinus density on noncontrast CT correlates with hematocrit.

BACKGROUND AND PURPOSE: A positive correlation between HCT and CT attenuation of intravascular blood has long been assumed but has never been established by using substantial patient numbers and modern CT equipment. The purpose of this study was to determine whether apparent increased attenuation on CT in cerebral venous sinuses can be attributed to hemoconcentration alone and to assess whether sinus thrombosis can be differentiated from hemoconcentrated blood based on attenuation values alone. MATERIALS AND METHODS: We measured HUs in a region of interest within the confluence of dural venous sinuses in 166 unenhanced head CTs and correlated these data with HCT and HGB values in male and female patients aged 2 to 100 years. We then compared these data with similar measurements in 8 patients with recent venous sinus thrombosis. Two-tailed t test and linear regression analyses were performed to evaluate HGB and HCT between groups and with measured CT attenuation of intravascular blood, respectively. RESULTS: A statistically significant relationship was noted between both HCT and HGB with CT attenuation. Seven of 8 patients with sinus thrombosis had attenuation values >70, but none of the normal subjects had HUs >70. CONCLUSIONS: Hemoconcentration correlates with CT attenuation in cerebral venous sinuses. Our findings suggest that comparing the ratio of HUs to HCT may be useful in gauging concern for sinus thrombosis.

A pilot study of the use of pain questionnaires in vertebroplasty research.

SUMMARY: Administration of comprehensive outcomes measures in elderly patients presenting for vertebroplasty is considered difficult. We administered a battery of 11 outcomes questionnaires with a total of 82 questions, both in person before vertebroplasty and by telephone after vertebroplasty in 20 consecutive patients (mean age, 74.5 years; 80% women). Initial and follow-up interviews required an average of 17.4 +/- 0.36 minutes (range, 14-21 minutes) and 27.2 +/- 0.73 minutes (range, 16-33 minutes), respectively.

Baseline pain and disability in the Investigational Vertebroplasty Efficacy and Safety Trial.

BACKGROUND AND PURPOSE: Multiple case series of vertebroplasty outcomes have been published, though no large, placebo controlled trial has yet been performed. Our aim was to report baseline characteristics for the Investigational Vertebroplasty Efficacy and Safety Trial (INVEST), a randomized blinded controlled study of vertebroplasty. MATERIALS AND METHODS: We compared baseline demographics, pain scores, and scores on the modified Roland-Morris Disability Scale (RMDS), a back pain-specific metric, between 2 groups. One group included subjects enrolled at the lead INVEST site (n = 27 to date). The second group consisted of eligible patients seen concurrently at the lead INVEST site, who declined enrollment (n = 70). Comparisons were made by using 2-sample t tests. RESULTS: Mean ages were similar between groups, averaging approximately 74 years among study participants and 77 years among nonenrolled eligible patients (P = .17). Approximately 75% of subjects were female in both groups. RMDS scores of enrolled patients at the lead site (18.0 +/- 4.2) were not statistically different from those of eligible nonenrolled patients at the lead site (18.6 +/- 3.6, P = .49). Pain scores in the enrolled subjects were measured as "average intensity over the prior 24 hours" with mean scores of 7.6 +/- 2.1 among enrolled patients at the lead site. Pain scores in eligible nonenrolled patients were measured as "pain at rest," with mean score of 3.4 +/- 3.3, and "pain with activity," with mean score of 8.5 +/- 2.0. CONCLUSIONS: Patient demographics among subjects enrolled in the INVEST are similar to those in a cohort of eligible nonenrolled patients. Back pain-specific disability was similar between subjects enrolled in the INVEST study and eligible nonenrolled patients at the lead site.

Urinary tract infections in the potential vertebroplasty patient: incidence, significance, and management.

SUMMARY: Percutaneous vertebroplasty has been deferred due to potential complications from urinary tract infections (UTIs). Our aim was to help sort out the types of treatment needed for percutaneous vertebroplasty patients and the length delay for performing the procedure. We searched for information regarding the ramifications of infection from the literature and devised a plan of treatment for the various infectious problems that may occur in patients undergoing percutaneous vertebroplasty. We devised a plan of action for the screening, testing, diagnosis and treatment of patients with a potential UTI who are presenting for a percutaneous vertebroplasty.

Efficacy of percutaneous vertebroplasty for multiple synchronous and metachronous vertebral compression fractures.

BACKGROUND AND PURPOSE: Limited data exists regarding the efficacy of percutaneous vertebroplasty for multiple synchronous and metachronous vertebral compression fractures. The purpose of this study was to evaluate whether the number of vertebral levels treated during percutaneous vertebroplasty procedures or the number of separate vertebroplasty procedures performed on a given patient affect clinical outcomes. MATERIALS AND METHODS: We defined 3 patient populations in our retrospective study. Group 1 included 328 patients who underwent 1 single-level vertebroplasty procedure. Group 2 included 226 patients who underwent a single procedure in which 2 or more vertebral levels were treated. Group 3 included 101 patients who underwent 2 or more separate vertebroplasty procedures. Follow-up was performed between 1 week and 2 years postoperatively. Clinical outcomes were assessed through analysis of quantitative measurements of pre- and postoperative levels of pain with and without activity (0-10) as well as mobility improvement. The Kruskal-Wallis rank sum test was used to evaluate the differences among groups. Univariate and chi(2) analyses were performed to show the proportion of underlying diseases in each group. RESULTS: Mean pain improvement with/without activity at 2-year follow-up was 5.8/3, 4.9/3.7, and 5.4/3.1 in groups 1, 2, and 3, respectively; and mean mobility improvement in 2-year follow-up was 0.67, 0.63, and 0.65 for groups 1, 2, and 3, respectively. CONCLUSIONS: There was no significant difference in pain relief and mobility improvement in patients treated for multiple synchronous or metachronous vertebral compression fractures in comparison with those treated for solitary isolated fractures.

Percutaneous vertebroplasty for painful compression fractures in a small cohort of patients with a decreased expectation-related placebo effect due to dementia.

BACKGROUND AND PURPOSE: Although abundant literature has reported success with vertebroplasty for the treatment of painful compression fractures, none has accounted for a potential expectation-related placebo effect. We report the results of vertebroplasty for painful vertebral body compression fractures in a small cohort of patients with dementia with the assumption that this patient subgroup is subjected to a decreased placebo effect. MATERIALS AND METHODS: All patients with objective evidence of dementia (N = 10) who had undergone vertebroplasty at our institution were identified from a comprehensive prospectively constructed vertebroplasty data base. The patients' pain at rest and activity, mobility, and pain-medication use were analyzed at 2 hours postprocedure, 1 week, 1 month, 6 months, and 1 year. RESULTS: Pain with activity decreased or resolved in 80%-100% of patients at each time point, whereas pain at rest decreased or resolved in 78%-100% of all patients at each time point. Improved mobility was reported in 80%-100% of patients at all time points. Pain medication was decreased or stopped in 67% of patients at 1 week and in 100% of patients at 6 months and 1 year. CONCLUSION: Treatment of painful compression fractures in patients with dementia demonstrates a high rate of success regarding pain relief and mobility. This study offers additional evidence that vertebroplasty has true benefit.

Significance and targeting of small, central clefts in severe fractures treated with vertebroplasty.

We report a small cohort of patients with severe osteoporotic fractures treated with vertebroplasty. We note a high prevalence of small, central, intraosseous clefts in these severe fractures. Rather than filling the small amount of residual bone marrow around the periphery of these severe fractures, as suggested by previous authors, we suggest central needle placement to fill these central clefts.

Vertebroplasty in multiple myeloma: outcomes in a large patient series.

BACKGROUND AND PURPOSE: Despite the literature supporting the efficacy of vertebroplasty for treatment of osteoporotic vertebral compression fractures, few reports exist documenting its use in the treatment of compression fractures in multiple myeloma patients. Accordingly, we sought to characterize the imaging characteristics, clinical course, and outcomes in myeloma patients treated with vertebroplasty. MATERIALS AND METHODS: We performed a retrospective review of clinical outcome data from 67 multiple myeloma patients treated with vertebroplasty since October 2000. Quantitative outcome data including the Roland Morris Disability Questionnaire (RDQ) and Visual Analog Scales for pain and qualitative outcome data (self-reported pain, mobility, and narcotic use) were collected preoperatively, immediately after vertebroplasty, and at 1 week, 1 month, 6 months, and 1 year after treatment. RESULTS: Significant improvements in all of the outcome measures were observed postoperatively and throughout the duration of follow-up. Quantitative outcome measures (RDQ, analog pain scale 0-10, with rest and activity) improved by 11.0 (48%; P < .0001), 2.7 (25%; P < .001), and 5.3 (48%; P < .0001) points, respectively, with persistent improvement at 1 year (P < .01; P < .03; P < .001). Eighty-two percent and 89% of patients experienced a significant improvement in subjective rest pain and activity pain, respectively. Subjective scores achieved durable improvements, with 65% of patients requiring fewer narcotics after vertebroplasty and 70% having improved mobility. CONCLUSION: Vertebroplasty provides significant and durable pain relief for patients with intractable spinal pain secondary to compression fractures resulting from multiple myeloma.

Balloon-assisted coiling of intracranial aneurysms: evaluation of local thrombus formation and symptomatic thromboembolic complications.

BACKGROUND AND PURPOSE: Remodeling balloons are used to assist in endovascular coiling of aneurysms. We evaluated our experience with balloon-assisted coiling (BAC) in an attempt to determine whether this technique increased the rate of thrombus formation or symptomatic thromboembolic complications. MATERIALS AND METHODS: In 3 years, we treated 221 patients with intracranial aneurysms. Statistical analysis was performed to assess whether BAC increased the rate of thrombus formation or symptomatic thromboembolic complications. Patient demographics, aneurysm size, location, neck width, antiplatelet therapy, and rupture status were evaluated. RESULTS: We detected no statistically significant difference in rates of thrombus formation (14% versus 9% with and without BAC, respectively, P=0.35) or symptomatic thromboembolic events (7% versus 5% with and without BAC, respectively, P=0.76), though our power to detect small differences was limited. There was also no correlation with age, sex, rupture status, aneurysm size, or location. There was a significant increase in the rates of thrombus formation (6% versus 16%, P=0.02) and symptomatic thromboembolic complications (3% versus 10%, P=0.04) in aneurysms that were classified as narrow- or wide-necked, respectively. The use of clopidogrel was associated with a decrease in the rate of complications (P=0.01). CONCLUSION: In this series, we detected no significant increase in the rates of either intraprocedural thrombus formation or symptomatic thromboembolic events in patients treated with BAC. Larger studies are required to confirm our observations. Wide-necked aneurysms were independently associated with increased rates of thrombus formation and symptomatic thromboembolic complications, whereas the use of clopidogrel was protective (P=0.01).

Endovascular treatment of epistaxis in patients with hereditary hemorrhagic telangiectasia.

BACKGROUND AND PURPOSE: The treatment of epistaxis in patients with hereditary hemorrhagic telangiectasia can be very challenging. The purpose of our study was to evaluate our experience with endovascular epistaxis embolization in patients with hemorrhagic hereditary telangiectasia and to compare this with our experience in patients treated for idiopathic epistaxis. MATERIALS AND METHODS: Over a 6-year period, we treated 22 patients with epistaxis by using endovascular embolization. Twelve of 22 patients had hereditary hemorrhagic telangiectasia; 10 patients had idiopathic epistaxis. The angiographic findings, efficacy of treatment, and complications for both groups were compared. RESULTS: Patients with hereditary hemorrhagic telangiectasia had angiographic abnormalities in 92% of cases compared with only 30% in the idiopathic epistaxis group. Compared with a group of 10 patients treated for other causes of epistaxis, those with hereditary hemorrhagic telangiectasia required significantly more re-embolization treatments or additional surgical procedures because of continued or recurrent bleeding episodes after embolization (P=.03). Complications were rare; a single patient in the idiopathic epistaxis group had a self-limited groin hematoma and postembolization facial pain. CONCLUSION: Endovascular embolization of epistaxis is a safe procedure that can be useful for patients with severe acute epistaxis or chronic persistent bleeding. Patients who undergo endovascular embolization for epistaxis related to hereditary hemorrhagic telangiectasia require repeat embolization and subsequent surgical procedures more often than those with idiopathic epistaxis.

In vitro antiproliferative activity of the farnesyltransferase inhibitor R115777 in hematopoietic progenitors from patients with myelofibrosis with myeloid metaplasia.

R115777 is an orally bioavailable farnesyltransferase inhibitor (FTI) that has displayed encouraging activity in patients with acute myeloid leukemia. To determine whether R115777 might exert similar activity in myelofibrosis with myeloid metaplasia (MMM), we evaluated its effects on circulating myeloid progenitor cells from patients with MMM (n=25) using in vitro colony-forming assays. The median R115777 concentrations that inhibited colony formation by 50% were 34 and 2.7 nM for myeloid and megakaryocytic colonies from MMM patients, respectively. Progenitors from normal controls and patients with other myeloproliferative disorders demonstrated similar sensitivity. Since the ras polypeptides are one putative target of FTIs, the potential role of ras effectors was examined by incubating parallel progenitor assays with the phosphatidyl-inositol-3 (PI-3) kinase inhibitor LY294002 and the mitogen-activated protein kinase 1 inhibitor PD98059. MMM progenitor colonies (n=7) were highly sensitive to LY294002 but not to PD98059, implying that the PI-3 kinase pathway may be critical for survival and proliferation of these cells. In addition to indicating that MMM progenitors are sensitive to clinically achievable R115777 concentrations in vitro, these results provide a potential explanation for the thrombocytopenia observed with R115777 during the treatment of other hematologic malignancies.

Blood lactic acid levels after artificial heart implantation.

The aim of this study is to investigate blood lactic acid levels after the placement of the AbioCor implantable replacement heart to determine whether circulatory support with the AbioCor device results in adequate tissue perfusion. Tissue perfusion may not be adequate during cardiac surgery, especially with the use of cardiopulmonary bypass (CPB). Inadequate perfusion is usually associated with anaerobic metabolism, metabolic acidosis, and lactate accumulation. Ten calves had implantation of the AbioCor by means of a right thoracotomy. Standard cardiopulmonary bypass was performed during surgery. Lactic acid levels and blood gas analyses were measured. All animals were monitored for pressures in the aorta, pulmonary artery, and left and right atria. The output of the AbioCor was calculated based on beat rate and stroke volume. All animals were rapidly weaned off cardiopulmonary bypass to full AbioCor support and had normal hemodynamics with normal filling pressures. The lactic acid levels were elevated after surgery, peaked at 8 to 12 hours, and then gradually decreased to the normal range 24 hours after surgery. There was a positive relationship between lactate levels, oxygen consumption, and extraction rate, that is, the lactic acid levels were higher in the presence of increased oxygen consumption and increased oxygen extraction rate. There was a negative relationship between lactate levels and oxygen delivery, and arterial and venous oxygen content, that is, the lactic acid levels were higher when oxygen delivery and arterial and venous oxygen contents were low. The pathophysiology of lactic acidosis is uncertain, but is most likely due to inadequate perfusion during cardiopulmonary bypass, and lactate washout after adequate perfusion has been established. The return to aerobic metabolism with clearance of lactate demonstrates that the AbioCor is able to provide complete circulatory support with normal tissue perfusion.

A phase II trial of pirfenidone (5-methyl-1-phenyl-2-[1H]-pyridone), a novel anti-fibrosing agent, in myelofibrosis with myeloid metaplasia.

The anti-fibrotic and cytokine modulatory properties of pirfenidone suggest its usefulness in the treatment of myelofibrosis with myeloid metaplasia (MMM). In a prospective study, 28 patients with MMM were treated with oral pirfenidone. Twelve patients completed 1 year of therapy; 13 were withdrawn because of disease progression and three because of drug intolerance. Only one patient experienced a clinically relevant benefit with respect to anaemia and splenomegaly. The overall lack of clinical benefit correlated with no significant improvement in the bone marrow morphological features of the disease. We conclude that pirfenidone has no significant clinical or biological activity in MMM.

Current status of the AbioCor implantable replacement heart.

BACKGROUND: The AbioCor implantable replacement heart (IRH) has been developed as an alternative to transplant (ie, destination therapy). We report our experience with the AbioCor IRH in a bovine model at the University of Louisville. METHODS: Male Holstein cows were used (85 to 115 kg). The internal controller, battery, and secondary transcutaneous energy transfer coil were implanted in the right flank. After cardiopulmonary bypass, the thoracic unit was implanted orthotopically. After removal of air and weaning from cardiopulmonary bypass, the AbioCor was connected to internal components and energy transfer through transcutaneous energy transfer coils was achieved. RESULTS: Nineteen animals underwent implantation of the AbioCor IRH for a proposed 30-day duration. There were 6 deaths, none related to device malfunction. All animals demonstrated normal hemodynamics with normal pressures in the aorta, pulmonary artery, left atrium, and right atrium. There was no significant hemolysis and all animals demonstrated normal end organ function. The internal battery allowed for brief periods of untethered mobility. CONCLUSIONS: The AbioCor IRH has resulted in normal hemodynamics and normal end organ function without evidence of hemolysis in a bovine model.

Radiation therapy for symptomatic hepatomegaly in myelofibrosis with myeloid metaplasia.

OBJECTIVE: To describe the experience with liver irradiation in advanced cases of myelofibrosis with myeloid metaplasia (MMM). METHODS: Over a 20-yr period, 14 patients with MMM were treated with a total of 25 courses of liver, abdominal, or abdominal and pelvic irradiation for symptomatic hepatomegaly with (5 patients) or without (9 patients) ascites. All 14 patients had advanced disease and 11 (79%) had previous splenectomy. The median radiation therapy (RT) dose per course was 150 cGy (range 50-1000) administered at a median of six fractions. Four patients received two to six courses. RESULTS: Twelve of the 14 patients (86%) had a transient (median 3 months) subjective response from RT. However, in only 35% of these was there a transient (median 3 months) decrease in palpable liver size. Four of the five patients with ascites experienced a short-term response from RT. Eight of the 13 patients suitable for evaluation (62%) had treatment-associated cytopenia, often in the form of anemia and/or thrombocytopenia. At last follow-up, 10 patients (71%) had died after a median of 7 months (range 0.1-23) and 4 were alive at 3, 20, 33, and 57 months after RT. CONCLUSIONS: Low-dose abdominal RT for symptomatic hepatomegaly or ascites associated with advanced-stage MMM is myelosuppressive and provides only temporary and mainly subjective and short-lived relief.

Intermediate-term results after partial left ventriculectomy for end-stage dilated cardiomyopathy: is there a survival benefit?

BACKGROUND: The mortality of congestive heart failure remains high despite advances in medical therapy. Partial left ventriculectomy (PLV) has been advocated as a surgical alternative for select patients with dilated cardiomyopathy. METHODS: A prospective clinical trial of PLV for patients with end-stage idiopathic dilated cardiomyopathy was performed. Inclusion criteria were left ventricular end-diastolic diameter (LVEDD) greater than 7 cm, refractory New York Heart Association (NYHA) Class IV symptoms, and severely depressed exercise oxygen consumption. RESULTS: Twenty patients underwent PLV with mean follow-up of 21.1 months. Sixteen were male; mean age was 50.1 years +/- 12.0 years (range 25-67 years). Left ventricle (LV) ejection fraction improved after surgery from 14.1% +/- 4.7% to 24.1% +/- 3.1% (p < 0.05, t-test) and this improvement persisted up to 3 years after operation. LVEDD and NYHA Class also were notably improved. There were two early deaths for an operative mortality of 10% (2 of 20 patients). Nine patients after initial improvement in clinical status and LV function developed worsening congestive heart failure (CHF). Six of the 9 ultimately died of complications secondary to CHF. One-, 2-, and 3-year survival rates were 84%, 64%, and 40%, respectively, by Kaplan-Meier analysis. The other three patients required listing for transplantation because of recurrent NYHA Class IV symptoms. Freedom from death or the need for listing for transplantation at 1, 2, and 3 years was 65%, 53%, and 33%, respectively. The remaining nine patients all had improvement in their NYHA classification. CONCLUSIONS: PLV can be performed with acceptable early and intermediate term mortality; survival compares favorably to reports of similar groups of patients treated with medical therapy alone.

Can a linear electrical analog model of a mechanical valve predict flow by using a pressure gradient?

The objective was to determine whether a previously developed technique for biological aortic valves could predict flow through a mechanical valve. An electrical analog model of the aortic valve that includes compliance, resistance, and inertance parameters, and corresponding second order differential equations was used to predict flow given a pressure gradient, as previously reported. Simulated pressures and flow were recorded by using a pulse duplicator system. The heart rate was varied from 60 to 180 bpm, and the stroke volume was varied from 22 to 67 cc. Resistance, inertance, and compliance parameters of the governing differential equation were estimated by using a least-squares fit to the measured flow at 120 bpm and 50 cc stroke volume. By using these parameter estimates, flow was calculated for other heart rates and stroke volumes. To achieve a better flow prediction, a nonlinear filter (third order polynomial range calibration equation) was applied to the output of the linear model (flow). The mean error, full-scale error, and spectral error in magnitude and phase between measured and predicted flow were compared. Error in mean flow ranged from 3% at medium flow rates to 90% at low flow rates. The maximum and minimum full scale errors were 12% and 5%, respectively. Error in the harmonics of measured and calculated flow ranged from 0% to 55%. Larger errors were usually present at the higher harmonics. The agreement between measured and calculated flow was better at normal and high flows but rather poor at low flows. The nonlinear filter (range calibration equation) was unable to account for the discrepancies between the measured and calculated flow over all flow ranges. It seems that this linear model and nonlinear filter have limited application, and an alternate nonlinear approach may produce better results.