Short-term patency of iliofemoral to tibial bypass with vascular allografts in a minority population: A retrospective analysis of a single center acute care facility.

OBJECTIVE: The aim of this study was to examine the short-term patency rates and associated factors of open lower limb, iliofemoral to tibial bypass using cryopreserved saphenous vein (CSV) in a minority population at an acute care hospital in New York City. METHODS: A retrospective analysis of patients undergoing infra-inguinal bypass from iliofemoral vessels to tibial arteries with CSV between March 2020-April 2022 at an acute care facility (Harlem Hospital Center, Harlem, New York) was performed. Data including patient demographics, comorbidities, type of operation, follow-up surveillance, and salvage procedures were collected. Results were presented in patency line graphs and a life table. Target limb revascularization (TLR) and amputation free survival (AFS) were also calculated. RESULTS: Eleven bypass procedures were included in the analysis. Patients were followed for a mean of 10.8 months. Cumulative primary patency rates at 1, 6, and 12 months were 72.7%, 54.5%, and 40.9%, respectively. TLR was 36.4% and the AFS was 66.67% at the mean 10.8-month follow-up. CONCLUSIONS: The patency rates of minority patients undergoing bypass with CSV were analyzed with creation of a life table and calculation of patency rates, TLR and AFS. The short-term primary patency rates and post-operative outcomes were found to be comparable to larger studies in non-minority cohorts. These results suggest that larger studies as well as prospective analyses and randomized controlled trials in this patient cohort and demographic are needed, as well as optimal selection of patients to determine true clinical implications.

Orbital cholesterol granuloma: Case report and literature review.

Cholesterol granuloma is a chronic foreign-body inflammatory response that is often seen in the middle ear, mastoid antrum, and petrous apex. However, it can also occur in other anatomical locations, including the orbit. A 34-year-old male presented with painless nonaxial proptosis of the left eye, and imaging revealed a well-defined intraorbital extraconal lesion consistent with an orbital cholesterol granuloma. The pathogenesis of this rare cystic condition is unknown, but trauma and inadequate airflow through pneumatized temporal bone air cells have been proposed as potential triggers. Treatment involves total excision of the granuloma with careful removal of residual tissue adherent to the bone and the periosteum to minimize the risk of recurrence. Cholesterol granulomas usually have a good prognosis.

An Infected, Noncoronary, Bare Metal Stent Presenting as a Right Groin Abscess.

Bare metal stent infections complicating peripheral endovascular stenting are rare but can be associated with devastating morbidities. The current standard of care necessitates explantation and extra-anatomical bypass of the affected limb. We report the case of a patient presenting with a right groin abscess with draining sinuses secondary to an infected common femoral and right external iliac artery bare metal stent. In addition, a portion of the stent was explanted into the subcutaneous tissues instead of where it was placed intravascularly one year prior. The patient was not an ideal candidate for explantation and bypass due to significant medical comorbidities and underwent local debridement and long-term antibiotic management instead. His postoperative course was uncomplicated, and he had a successful outcome with management utilizing antibiotics and debridement. We aim to highlight the importance of recognizing bare metal stent infections along with their deceptive cutaneous manifestations in order to prevent the development of significant morbidity and mortality.

Recurrent solitary fibrous tumor of eyelid: A rare entity.

Orbital and adnexal solitary fibrous tumors (SFT) are rare entities. The clinico-radiological and histologic features overlap with those of other spindle cell variants, and hence the use of immunohistochemical stains helps in making an accurate diagnosis. Furthermore, a thorough surgical resection is imperative to prevent tumor recurrences. We report a rare case of SFT arising primarily from the eyelid with multiple recurrences.

Case presentation of delayed superficial femoral artery pseudoaneurysm causing an acute deep vein thrombosis.

In the present report, we have described the case of a significantly delayed presentation of a pseudoaneurysm (PSA) and subsequent mass effect causing an acute deep vein thrombosis (DVT). The patient had presented with a mass in the right groin and edema of the right lower extremity prompting further imaging studies. The imaging studies demonstrated a superficial femoral artery PSA and an acute femoral vein DVT. Our patient had no history of recent trauma or femoral access procedures performed in the last ≥5 years. Surgical repair of the PSA was performed, and the DVT was managed with anticoagulation therapy.

Surgical resection of orbital primitive neuroectodermal tumor without adjuvant chemotherapy.

Primitive neuroectodermal tumor (PNET) of the orbit is a very rare entity. We report a case of a 10-year-old boy having progressive protrusion of the eyeball, restricted ocular motility, ptosis, and ocular pain for 2 months. On examination, a fixed, nontender, firm, hyperemic, nonpulsatile globular mass was palpated in the superomedial quadrant of the orbit. Computed tomography scans of the orbit depicted a well-defined, soft tissue density lesion within the orbit without evidence of any bone defect or erosion. Surgical resection of the encapsulated lesion through anterior orbitotomy followed by histopathology and immunohistochemistry examination confirmed the diagnoses of PNET. The patient has been on regular follow-up for 2 years and has shown no sign of recurrence.

A glued technique of external dacryocystorhinostomy.

PURPOSE: Fibrin glue was used for anastomosis of lacrimal sac and nasal mucosal flaps and was compared with the conventional suture technique in external dacryocystorhinostomy. METHODS: A prospective interventional randomized control study in which 50 consecutive patients of primary acquired nasolacrimal duct obstruction (PANDO) were equally allocated into two groups. The case group underwent glued technique of external dacryocystorhinostomy (Ext DCR) in which fibrin glue was used for the apposition of the anterior lacrimal sac and nasal mucosal flaps. In the control group, conventional technique of Ext DCR was used to suture the flaps. Functional success was assessed by improvement in epiphora and fluorescein dye disappearance test (FDDT), whereas anatomical success was assessed by lacrimal irrigation and endoscopic view of the osteotomy site. RESULTS: The anatomical success in both the groups was 92%, whereas the functional success was 92% in the case group and 88% in the control group. The difference in the success rates between the two groups was statistically non-significant. CONCLUSION: Glued technique of Ext DCR is a simple and easy alternative to suturing of the flaps. Though the final outcome was comparable in both the groups, glue can be especially useful in uncooperative cases, in cases of excessive bleeding, or in situations where the flaps are very thin or have become friable.

Reinforcement Learning Based Optimal Tracking Control Under Unmeasurable Disturbances With Application to HVAC Systems.

This paper presents the design of an optimal controller for solving tracking problems subject to unmeasurable disturbances and unknown system dynamics using reinforcement learning (RL). Many existing RL control methods take disturbance into account by directly measuring it and manipulating it for exploration during the learning process, thereby preventing any disturbance induced bias in the control estimates. However, in most practical scenarios, disturbance is neither measurable nor manipulable. The main contribution of this article is the introduction of a combination of a bias compensation mechanism and the integral action in the Q-learning framework to remove the need to measure or manipulate the disturbance, while preventing disturbance induced bias in the optimal control estimates. A bias compensated Q-learning scheme is presented that learns the disturbance induced bias terms separately from the optimal control parameters and ensures the convergence of the control parameters to the optimal solution even in the presence of unmeasurable disturbances. Both state feedback and output feedback algorithms are developed based on policy iteration (PI) and value iteration (VI) that guarantee the convergence of the tracking error to zero. The feasibility of the design is validated on a practical optimal control application of a heating, ventilating, and air conditioning (HVAC) zone controller.

Adaptive Dynamic Programming for Model-Free Global Stabilization of Control Constrained Continuous-Time Systems.

This article addresses the problem of global stabilization of continuous-time linear systems subject to control constraints using a model-free approach. We propose a gain-scheduled low-gain feedback scheme that prevents saturation from occurring and achieves global stabilization. The framework of parameterized algebraic Riccati equations (AREs) is employed to design the low-gain feedback control laws. An adaptive dynamic programming (ADP) method is presented to find the solution of the parameterized ARE without requiring the knowledge of the system dynamics. In particular, we present an iterative ADP algorithm that searches for an appropriate value of the low-gain parameter and iteratively solves the parameterized ADP Bellman equation. We present both state feedback and output feedback algorithms. The closed-loop stability and the convergence of the algorithm to the nominal solution of the parameterized ARE are shown. The simulation results validate the effectiveness of the proposed scheme.

A prospective study on epidemiology of dacryocystitis at a tertiary eye care center in Northern India.

AIM: The aim of this study is to study the prevalence, incidence, and the epidemiological characteristics of the patients of acquired dacryocystitis at a tertiary eye care center of Northern India. MATERIALS AND METHODS: It was a prospective, cross-sectional study carried out over a period of 2 years (July 2016-July 2018). The prevalence, incidence, and the epidemiological characteristics of acquired dacryocystitis were studied and analyzed. Chi-square test was used to test the qualitative distribution. RESULTS: A total of 212 cases were included in the study. The prevalence rate of dacryocystitis was 19.5 cases per 10,000 patients, and the incidence rate was 15 cases per 10,000 patients. Chronic dacryocystitis (183; 86.30%) was more commonly encountered clinical type than acute dacryocystitis. Majority of cases (204; 96.23%) were due to the primary acquired nasolacrimal duct (NLD) obstruction, whereas eight cases (3.78%) were due to the secondary acquired NLD obstruction. Females were more commonly affected (156; 73.58%). The mean age was 44.44 ± 18.95 (range: 12-86) years. Majority of the patients 108 (50.94%) belonged to 3rd-6th decades of life. The disease was more prevalent in people belonging to lower-middle socioeconomic class (92; 43.40%) living in rural areas (130; 61.32%) and the majority of them were housewives (125; 59%). CONCLUSIONS: The incidence and prevalence of acquired dacryocystitis were 15 and 19.5 cases per 10,000 patients. It was much more common in females of lower socioeconomic status and is seen commonly in the 3rd to 6th decades of life.

Favorable prognosis with nonsurgical management of type III acute odontoid fractures: a consecutive series of 212 patients.

BACKGROUND CONTEXT: The recommended primary treatment for type III odontoid fractures (OFx) is external immobilization, except for patients having major displacement of the odontoid fragment. The bony fusion rate of type III OFx has been reported to be >85%. High compliance to treatment recommendations is favorable only if the treatment leads to a good outcome. PURPOSE: The primary aim of this study was to determine the long-term outcome after conservative and surgical treatment of type III OFx and to reaffirm that primary external immobilization is the best treatment for most type III fractures. STUDY DESIGN/SETTING: Retrospective study based on a prospective database. PATIENT SAMPLE: Two hundred twelve consecutive patients with type III OFx treated at Oslo University Hospital over an 8-year period (2009-2017). OUTCOME MEASURES: Long-term rates of bony fusion, crossover from primary conservative treatment to surgical fixation, new onset spinal cord injury (SCI), severe persistent neck pain (visual analogue scale - VAS), and persistent disability measured with Neck Disability index (NDI). METHODS: The present study was based on data extracted from our quality control database for acute cervical spine fractures from a general population. During the years 2018 to 2019 long-term follow-up of alive patients was performed (median follow-up time was 38.0 months; range 3.0-108.0 months). The follow-up included neurological examination, radiological examination and scoring of bony fusion status, crossover from primary conservative treatment to surgical fixation, new onset SCI, neck pain, and Neck Disability Index (NDI score). RESULTS: In this consecutive series of 212 patients with type III acute OFx, median patient age was 72 years, 56% had severe preinjury comorbidities (ASA score ≥3) and 22% lived dependently. Severe comorbidities and dependent living were significantly associated with increasing age (p<.001). The trauma mechanism was fall injury in 82%. The median age of patients injured by falls was significantly higher than in patients with a nonfall injury (p<.001). At the time of diagnosis, 4% had an OFx related SCI. Primary treatment was external immobilization alone in 95.3% and open surgical fixation in 4.7%. Patients treated with primary external immobilization alone presented with significantly less translation of the odontoid fragment (p<.001) and less angulation of the odontoid fragment (p=.025) than patients treated with primary surgery. Subsequent crossover to surgical fixation was performed in 5.4%. At long-term follow-up, 95.7% of patients had bony fusion of the OFx, 80.5% had minimal/no neck pain, and none developed new onset SCI. There was no significant difference in long-term follow-up VAS (p=.444) or NDI (p=.562) between the primary external immobilization group and the primary surgical group. CONCLUSION: This study reaffirms that nonsurgical treatment remains the preferable option in the majority of patients with type III OFx.

Fast-track thrombolysis protocol for acute limb ischemia.

OBJECTIVE: Catheter-directed thrombolysis in the treatment of acute lower extremity arterial occlusions often requires several interventional sessions to generate successful outcomes. It is typically an expensive procedure, necessitating extended hospital length of stay (LOS) that may be associated with an increase in both local and systemic hemorrhagic complications. Five years ago, we created the fast-track thrombolysis protocol for arteries (FTTP-A) to deal with these concerns. The goal of our protocol is to re-establish patency during the first session of thrombolysis, thus decreasing costs and complications associated with prolonged periods of thrombolytic exposure. METHODS: A retrospective study of 42 patients who were treated for acute limb ischemia at our institution by FTTP-A from January 2014 to February 2019 was performed. FTTP-A includes periadventitial lidocaine injection at the arterial puncture site under ultrasound guidance, contrast arteriography of the entire targeted segment, pharmacomechanical rheolytic thrombectomy of the occluded arterial segment, tissue plasminogen activator infusion along the occluded segment, balloon maceration of the thrombus, and (if deemed necessary) placement of a stent in an area of significant (≥30%) stenosis that is refractory to balloon angioplasty and thrombolysis. After the stenosis or thrombus is cleared, patients are prescribed an oral anticoagulant agent. RESULTS: Primary FTTP-A (50 total interventions) was performed in 42 patients. The median age of patients was 67.2 ± 12.2 years (range, 41-98 years), and 54.8% were male; 59.5% of the procedures were performed on the left lower extremity. Initial arterial access was obtained through the common femoral artery in 39 of 42 cases (92.9%); in the remaining 3 cases, it was obtained in a left bypass access site, a right femoral-popliteal graft, and a right femoral-femoral graft. The mean operative time was 148.9 ± 62.9 minutes (range, 83-313 minutes), and the mean volume of tissue plasminogen activator infused was 9.7 ± 4.0 mg (range, 2-20 mg). The median cost including medications and interventional tools was $4673.19 per procedure. The mean postoperative LOS was 3.1 ± 4.5 days (range, 1-25 days). Median postoperative LOS was 1 day. Mean postoperative follow-up was 27 ± 19.2 months (range, 0-62 months). Single-session FTTP-A was successful in 81% (n = 34/42) of patients; the remaining 8 patients (19%) required a single additional session. Of the 42 patients, 34 (81%) required arterial stenting. Periprocedural complications consisted of one patient with hematuria, which resolved, and one patient with thrombocytopenia, which resolved. No patients experienced rethrombosis within 30 days of FTTP-A. During the 5-year study period, there was no significant local or systemic hemorrhage, limb loss, or mortality related to this protocol. CONCLUSIONS: FTTP-A appears to be a safe, efficacious, and cost-effective procedure in the resolution of acute lower extremity arterial occlusions.

Management and long-term outcome of type II acute odontoid fractures: a population-based consecutive series of 282 patients.

BACKGROUND CONTEXT: The surgical fixation rate of type II odontoid fracture (OFx) in the elderly (≥65 years) is much lower than expected if the treatment adheres to current general treatment recommendations. Outcome data after conservative treatment for elderly patients with these fractures are sparse. PURPOSE: The main aim of this study was to determine the long-term outcome after conservative and surgical treatments of type II OFx (all age-groups) to evaluate whether nonoperative treatment yields an acceptable outcome. STUDY DESIGN/SETTING: Retrospective study based on a prospective database. PATIENT SAMPLE: Two hundred eighty-two consecutive patients with type II OFx treated at Oslo University Hospital over an 8-year period. OUTCOME MEASURES: Long-term rates of bony fusion, fibrous union, pseudarthrosis, crossover from primary conservative treatment to surgical fixation, new-onset spinal cord injury (SCI), and neck pain were the outcome measures used. METHODS: The present study was based on data extracted from our quality control database for acute cervical spine fractures. All ages were included. In addition, long-term follow-up of alive patients was performed during the years 2018-2019. The follow-up included neurological examination, radiological examination, and scoring of bony fusion status, crossover from primary conservative treatment to surgical fixation, new-onset SCI, neck pain, and Neck Disability Index (NDI score). Data are described by counts, percentages, medians, means, ranges and standard deviations where appropriate. For statistical analyses the Mann-Whitney U test, Wilcoxon signed-rank test, and t tests were used. RESULTS: During the eight-year study period, we registered 282 consecutive patients with type II OFx; 54% were males, patient age ranged from 15 to 101 years, 84% were ≥65 years of age (WHO definition of elderly), and 51% were ≥80 years of age. Severe comorbidities (American Society of Anesthesiologists, ASA ≥3) were seen in 67%, whereas nonindependent living was registered in 32%. Severe comorbidities and nonindependent living were significantly associated with increasing age (p<.001). SCI secondary to the OFx was seen in 5.3%. Primary treatment of the OFx was conservative (external immobilization alone) in 193 patients (68.4%), open surgical fixation in 87 patients (30.9%), and no treatment in two critically injured patients. At the time of long-term follow-up, 125 patients had died, nine patients declined the invitation to follow-up, and five patients did not respond. Thus, 143 patients were available for follow-up with a median follow-up time of 39 months (range 5-115 months). At long-term follow-up, the fusion status was bony fusion in 39.2% of patients, fibrous union in 57.3%, and pseudarthrosis in 3.5%. The proportion of bony fusion was significantly higher in the primary surgical fixation group (p=.005). No patients had new-onset SCI presenting after the start of primary treatment. The proportion of crossover from primary external immobilization to surgery was 14.4%, whereas proportion of revision surgery in the primary surgical group was 9.5%. There was no significant difference between the primary surgical fixation group and the primary conservative treatment group at long-term follow-up with respect to the proportion of pseudarthrosis and degree of neck pain. CONCLUSIONS: Primary conservative treatment of elderly patients with type II OFx appears to be safe and should be regarded a viable treatment option.

Direct Sciatic Nerve Electrical Stimulation for Complex Regional Pain Syndrome Type 1.

OBJECTIVE: Foot and leg pain in complex regional pain syndrome (CRPS) presents a challenge even with neuromodulation techniques such as spinal cord stimulation (SCS). We report our experience with a novo technique of direct sciatic nerve electrical stimulation (DISNES) for intractable foot and leg pain in CRPS I. MATERIALS AND METHODS: Following Research Ethics Board (REB) approval, data were gathered for 16 patients (10 women and 6 men, age 26-61 years) who had been subjected to ipsilateral DISNES. All 16 patients had failed conventional medical management. As well, seven subjects were previously treated with SCS for CRPS I pain. These subjects reported pain relief in the thigh and leg, however the SCS was unable to alleviate the disabling foot pain despite varied and multiple programming techniques. The remaining nine subjects were treated primarily with DISNES. Evaluation was done using visual analog scale (VAS), Oswestry Disability Index version 2 (ODI), and quality of life (EQ-5D and SF-36) scores done both pre-DISNES and at two follow-ups. RESULTS: VAS scores decreased by 59% at follow-up (F/U) 1 (P = 0.00001) and 46% F/U 2. ODI improving by 40% F/U 1 (P = 0.0038) and 37% F/U 2. SF-36 scores improved by 69% F/U 1 (P = 0.015) and 80% F/U 2. EQ-5D scores improved significantly by F/U 1 (P = 0.00030) but insignificantly at F/U 2 (P = 0.81). There was also a rapid resolution of autonomic features such as edema, hyperemia, and allodynia (within 7-10 days). Three subjects returned to work post-DISNES. CONCLUSION: Our study shows that DISNES helps to control the disabling foot pain in CRPS I, thus improving the quality of life, improving ambulation and decreasing disability. DISNES also alleviates autonomic features and dystonia in CRPS I. Further studies are needed to determine long-term efficacy as this study pool is limited in size and follow-up period.

Pregnancy and parental leave among plastic surgery residents in Canada: a nationwide survey of attitudes and experiences.

SUMMARY: Small surgical residency programs like plastic surgery can be challenging environments to accommodate parental leave. This study aimed to report the experiences, attitudes and perceived support of Canadian plastic surgery residents, recent graduates and staff surgeons with respect to pregnancy and parenting during training. Residents and staff surgeons were invited via email to participate in an online survey. The results presented here explore experiences of pregnancy and parental leave of current plastic surgery residents and staff surgeons. Residents' and staff surgeons' perceptions of program director support, policies, negative comments and the impact of parental leave on the workload of others were also explored. Although the findings suggest that there may be improvements in the support of program directors, there continues to be a negative attitude in surgical culture toward pregnancy during residency. The perceived confusion of respondents with respect to programspecific policies emphasizes the need for open conversations and standardization of parental leave.

Odontoid fractures: impact of age and comorbidities on surgical decision making.

BACKGROUND: Surgical fixation is recommended for type II and III odontoid fractures (OFx) with major translation of the odontoid fragment, regardless of the patient's age, and for all type II OFx in patients aged ≥50 years. The level of compliance with this recommendation is unknown, and our hypothesis is that open surgical fixation is less frequently performed than recommended. We suspect that this discrepancy might be due to the older age and comorbidities among patients with OFx. METHODS: We present a prospective observational cohort study of all patients in the southeastern Norwegian population (3.0 million) diagnosed with a traumatic OFx in the period from 2015 to 2018. RESULTS: Three hundred thirty-six patients with an OFx were diagnosed, resulting in an overall incidence of 2.8/100000 persons/year. The median age of the patients was 80 years, and 45% were females. According to the Anderson and D'Alonzo classification, the OFx were type II in 199 patients (59%) and type III in 137 patients (41%). The primary fracture treatment was rigid collar alone in 79% of patients and open surgical fixation in 21%. In the multivariate analysis, the following parameters were significantly associated with surgery as the primary treatment: independent living, less serious comorbidities prior to the injury, type II OFx and major sagittal translation of the odontoid fragment. Conversion from external immobilization alone to subsequent open surgical fixation was performed in 10% of patients. Significant differences the in conversion rate were not observed between patients with type II and III fractures. The level of compliance with the treatment recommendations for OFx was low. The main deviation was the underuse of primary surgical fixation for type II OFx. The most common reasons listed for choosing primary external immobilization instead of primary surgical fixation were an older age and comorbidities. CONCLUSION: Major comorbidities and an older age appear to be significant factors contributing to physicians' decision to refrain from the surgical fixation of OFx. Hence, comorbidities and age should be considered for inclusion in the decision tree for the choice of treatment for OFx in future guidelines.

Evaluation of wait times for assessment and epilepsy surgery according the geographic area of residence in the province of Saskatchewan, Canada.

PURPOSE: The aim of this study was to determine and compare the waiting times for surgical assessment, neuropsychological testing and epilepsy surgery between people with epilepsy who live in cities with available neurologists vs not. METHODS: We reviewed all cases referred for epilepsy surgery between 2007 and 2017 at the Saskatchewan Epilepsy Program Royal University Hospital (SEP) (n = 98; Saskatchewan, Canada). Mann-Whitney U test was used to compare wait times from first diagnosis of epilepsy to epilepsy surgery between patients who live in cities with neurologists (mainly urban areas) vs cities without neurologists (mainly rural areas). RESULTS: The mean age of patients who enrolled in SEP was 37.8 ± 12.8 years. The median wait time from date of epilepsy diagnosis to referral was 9.5 years in Saskatoon and Regina (cities with available neurologists) and 14 years in other areas of Saskatchewan (small cities and rural areas with no available neurologists) (p = 0.03). The median wait time from date of epilepsy diagnosis to first consult with the epileptologist was 10 years in Saskatoon and Regina and 15.5 years in other areas of Saskatchewan (p = 0.03). The median wait time from date of first diagnosis to epilepsy surgery was 13.2 years in Saskatoon and Regina and 18.2 years in other areas of Saskatchewan (p = 0.05). CONCLUSION: A notable difference was observed in surgical wait times between patients who live in cities with available neurologists compared with people living in rural areas and cities with no neurologists. This suggests that delayed surgical treatment for epilepsy is related with the availability of neurologists.

Reinforcement Learning-Based Linear Quadratic Regulation of Continuous-Time Systems Using Dynamic Output Feedback.

In this paper, we propose a model-free solution to the linear quadratic regulation (LQR) problem of continuous-time systems based on reinforcement learning using dynamic output feedback. The design objective is to learn the optimal control parameters by using only the measurable input-output data, without requiring model information. A state parametrization scheme is presented which reconstructs the system state based on the filtered input and output signals. Based on this parametrization, two new output feedback adaptive dynamic programming Bellman equations are derived for the LQR problem based on policy iteration and value iteration (VI). Unlike the existing output feedback methods for continuous-time systems, the need to apply discrete approximation is obviated. In contrast with the static output feedback controllers, the proposed method can also handle systems that are state feedback stabilizable but not static output feedback stabilizable. An advantage of this scheme is that it stands immune to the exploration bias issue. Moreover, it does not require a discounted cost function and, thus, ensures the closed-loop stability and the optimality of the solution. Compared with earlier output feedback results, the proposed VI method does not require an initially stabilizing policy. We show that the estimates of the control parameters converge to those obtained by solving the LQR algebraic Riccati equation. A comprehensive simulation study is carried out to verify the proposed algorithms.

Output Feedback Q-Learning Control for the Discrete-Time Linear Quadratic Regulator Problem.

Approximate dynamic programming (ADP) and reinforcement learning (RL) have emerged as important tools in the design of optimal and adaptive control systems. Most of the existing RL and ADP methods make use of full-state feedback, a requirement that is often difficult to satisfy in practical applications. As a result, output feedback methods are more desirable as they relax this requirement. In this paper, we present a new output feedback-based Q-learning approach to solving the linear quadratic regulation (LQR) control problem for discrete-time systems. The proposed scheme is completely online in nature and works without requiring the system dynamics information. More specifically, a new representation of the LQR Q-function is developed in terms of the input-output data. Based on this new Q-function representation, output feedback LQR controllers are designed. We present two output feedback iterative Q-learning algorithms based on the policy iteration and the value iteration methods. This scheme has the advantage that it does not incur any excitation noise bias, and therefore, the need of using discounted cost functions is circumvented, which in turn ensures closed-loop stability. It is shown that the proposed algorithms converge to the solution of the LQR Riccati equation. A comprehensive simulation study is carried out, which illustrates the proposed scheme.