Michael Huang - Academia.edu (original) (raw)

Papers by Michael Huang

Transportation Research Record: Journal of the Transportation Research Board, 2011

A network analysis of spot-market broker operations in supply chain management is presented with ... more A network analysis of spot-market broker operations in supply chain management is presented with a case study of a brokerage firm. By modeling the connections between brokers and vendors, users can define metrics that correlate the strategies to select the vendors with profitability, which identifies new operating policies. Profitability is affected not only by the number of interactions between brokers and vendors but also by the quality of those interactions. The quality of interactions is quantified. The extent to which this approach can yield operating policy guidelines and serve as a tool to evaluate broker performance is demonstrated.

Transportation Research Part E: Logistics and Transportation Review, 2012

In humanitarian relief operations, vehicle routing and supply allocation decisions are critically... more In humanitarian relief operations, vehicle routing and supply allocation decisions are critically important. Similar routing and allocation decisions are studied for commercial settings where efficiency, in terms of minimizing cost, is the primary objective. Humanitarian relief is complicated by the presence of multiple objectives beyond minimizing cost. Routing and allocation decisions should result in quick and sufficient distribution of relief supplies, with a focus on equitable service to all aid recipients. However, quantifying such goals can be challenging. In this paper, we define and formulate performance metrics in relief distribution. We focus on efficacy (i.e., the extent to which the goals of quick and sufficient distribution are met) and equity (i.e., the extent to which all recipients receive comparable service). We explore how efficiency, efficacy, and equity influence the structure of vehicle routes and the distribution of resources. We identify trends and routing principles for humanitarian relief based on the analytical properties of the resulting problems and a series of computational tests.

Dynamic Random Access Memory (DRAM) is used as the main form of storage in main memory. DRAM is s... more Dynamic Random Access Memory (DRAM) is used as the main form of storage in main memory. DRAM is susceptible to cosmic radiation, alpha particles, voltage variations and aging. All of these factors might cause bit faults, word faults, and even entire chip faults. As more main memory is needed on desktops, servers and supercomputers, the chances of finding faults on DRAM will also increase. Redundant Array of Independent Memories (RAIM) is an approach to protect DRAM. By adding additional parity channels to the main memory, RAIM is able to protect main memory against the failure of an entire channel, which makes the main memory a lot more robust compared to memory systems with only Error-Correcting Code (ECC) protection. In this paper, we examine the impact on performance and energy that RAIM schemes have on a system, while also proposing a new type of RAIM implementation that reduces onand off-chip traffic and energy consumption. Compared to contemporary RAIM implementations, our pro...

BMC Infectious Diseases, 2019

Background: Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice for anti-Pneumocystis j... more Background: Trimethoprim-sulfamethoxazole (TMP-SMX) is the drug of choice for anti-Pneumocystis jirovecii pneumonia (PcP) prophylaxis in kidney transplant recipients (KTR). Post-transplant management balances preventing PcP with managing TMP-SMX-related adverse effects. TMP-SMX dose reduction addresses adverse effects but its implications to incident PcP are unclear. Methods: We performed a retrospective review of all patients transplanted between 2011 and 2015 prescribed daily single strength TMP-SMX for twelve months post-transplantation as PcP prophylaxis. Actual TMP-SMX dose and duration, adverse effects, number of dose reductions and reasons, and PcP events were captured. Multivariate logistic regression analyses for risk factors associated with dose reduction were performed. Results: Of 438 KTR, 233 (53%) maintained daily TMP-SMX and 205 (47%) sustained ≥1 dose reduction, with the point prevalence of a reduced dose regimen being between 18 and 25%. Median duration for daily TMP-SMX was 8.45/12 months, contributing 4137 patient-months daily TMP-SMX and 1110 patient-months with a reduced dose. PcP did not occur in any patients. There were 84 documented dose reductions for hyperkalemia and 102 for leukopenia, with 12 and 7 patients requiring TMP-SMX cessation. In multivariate analysis, a living donor transplant protected against hyperkalemia (Odds Ratio 0.46, 95% CI 0.26-0.83, p < 0.01) while acute rejection risked leukopenia (Odds Ratio 3.31, 95% CI 1.39-7.90, p = 0.006). Conclusions: TMP-SMX dose reduction is frequent in the first post-transplant year but PcP does not occur. To limit the need for TMP-SMX dose reduction due to adverse effects, a clinical trial comparing daily to thrice weekly single strength TMP-SMX in de-novo KTR is justified.

Kidney international, 2016

Transplant tourism, a form of transplant commercialization, has resulted in serious short-term ad... more Transplant tourism, a form of transplant commercialization, has resulted in serious short-term adverse outcomes that explain reduced short-term kidney allograft survival. However, the nature of longer-term outcomes in commercial kidney transplant recipients is less clear. To study this further, we identified 69 Canadian commercial transplant recipients of 72 kidney allografts transplanted during 1998 to 2013 who reported to our transplant center for follow-up care. Their outcomes to 8 years post-transplant were compared with 702 domestic living donor and 827 deceased donor transplant recipients during this period using Kaplan-Meier survival plots and multivariate Cox regression analysis. Among many complications, notable specific events included hepatitis B or C seroconversion (7 patients), active hepatitis and/or fulminant hepatic failure (4 patients), pulmonary tuberculosis (2 patients), and a type A dissecting aortic aneurysm. Commercial transplantation was independently associat...

Canadian journal of kidney health and disease, 2016

Studies have shown that erythropoietin-stimulating agents (ESAs) protect mice against the develop... more Studies have shown that erythropoietin-stimulating agents (ESAs) protect mice against the development of diabetes through direct effects on pancreatic ß cells. However, the effect of ESAs on the incidence of diabetes in humans has not been well studied. It is unknown whether exposure to ESAs is associated with a reduced incidence of new-onset diabetes after transplant (NODAT). The objective of this study is to examine the relationship between ESA exposure post-renal transplant and the development of NODAT. We performed a single center, retrospective cohort analysis. We compared patients who received a first live or deceased donor renal allograft, with any exposure to an ESA vs. those without such exposure and who developed NODAT and who did not. Patients with a prior history of diabetes mellitus or multi-organ transplant, including a second renal transplant were excluded. NODAT was defined based on the 2008 Canadian Diabetes Association criteria. Multivariate logistic regression ana...

Transplantation Proceedings, 2005

Dietary salt is an important contributor to hypertension in the general population. While its rol... more Dietary salt is an important contributor to hypertension in the general population. While its role in cyclosporine-induced hypertension is minimal, its role in tacrolimus-based immunosuppression has not been defined. We measured the 24-hour urine sodium excretion as an estimate of intake in a group of stable renal transplant recipients on tacrolimus (N ϭ 143) who had serum creatinine fluctuations Ͻ20% during the preceding 3 months. Average clinic-measured blood pressure (BP) from before and after the 24-hour urine collection was computed. Patients with recent changes in antihypertensive medications were excluded. Average systolic BP was 126 Ϯ 14 and diastolic BP 76 Ϯ 7 mm Hg. Urine sodium was 162.6 Ϯ 70 mmol/d (range 50 to 351), and the sodium/creatinine ratio was 15.4 Ϯ 6.4. There was no correlation between urine sodium excretion and either systolic or diastolic BP (R ϭ 0.07 and R ϭ 0.05, P ϭ NS) or the sodium/creatinine and systolic/diastolic BP (R ϭ 0.13, R ϭ 0.11, P ϭ NS). By multiple linear regression only weight and urine protein were independently associated with both systolic BP (P Ͻ .0001 for each) and diastolic BP (P Ͻ .05 for each). In conclusion, there is no appreciable influence of dietary salt intake on BP under tacrolimus-based immunosuppression. Restricting dietary salt intake in these patients cannot be recommended at the current time.

Transplantation Research, 2016

Background: Tacrolimus is available as twice-daily Prograf® (Tac-BID) and the once-daily formulat... more Background: Tacrolimus is available as twice-daily Prograf® (Tac-BID) and the once-daily formulation, Advagraf® (Tac-OD). Although therapeutically equivalent, some transplant recipients require dose adjustments to achieve similar tacrolimus trough concentrations [Tac C 0 ] after conversion between formulations. Tacrolimus is primarily metabolized by cytochrome P450 3A5 (CYP3A5). We sought to determine whether genetic polymorphisms in the CYP3A5 enzyme; CYP3A5 *1/*1 and CYP3A5 *1/*3 (expressers) compared to CYP3A5 *3/*3 (non-expressers) could account for discrepancies in dose requirements following conversion from Tac-BID to Tac-OD. Methods: A cohort of 60 renal transplant recipients (RTR) from our larger conversion study of 496 patients underwent additional testing for CY3A5 genetic polymorphisms. Analysis included demographics, tac dosing and [Tac C 0 ] pre-and post-conversion and dosing changes relative to CYP3A5 genotypes. CYP3A5 genetic polymorphisms were identified through analysis of genomic DNA. Results: Conversion from tac bid to tac OD in this cohort required a mean (SD) dose increase from 3.1 (1.0) mg/day to 3.8 (1.3) mg/day (p = 0.007), to achieve similar [Tac C 0 ]. The *1/*3 expresser group required a greater percentage dose adjustment (56.7 %) in converting from Tac-BID to Tac-OD as compared to the *3/*3 non-expresser group (26.6 %). Similar findings were observed with the both expresser groups combined (*1/*1 &*1/*3). The expressers were significantly more highly represented in the East Asian cohort. Conclusions: The CYP3A5 expresser polymorphism necessitates an increase in dosing upon conversion from Tac-BID to Tac-OD, with the expresser genotypes contributing significantly to this finding. Given the variability in frequency of CYP3A5 genotypes in various ethnic groups, future studies should account for both isoenzyme polymorphism and ethnicity in optimizing dosing requirements. Trial registration: Clinical trials.gov identifier: NCT01884480

Clinical kidney journal, 2012

Ethnicity is an important determinant of post-renal transplant outcomes. Limited data are availab... more Ethnicity is an important determinant of post-renal transplant outcomes. Limited data are available on cardiovascular risk differences in kidney transplant recipients (KTR) based on ethnicity. A group of 129 clinically stable age-matched KTR [43 South Asian (SA), 86 Caucasian]) were assessed for plasma total and high-molecular-weight (HMW) adiponectin, cystatin C, apolipoproteins A1 and B, C-reactive protein, uric acid, urine albumin-to-creatinine ratio, estimated glomerular filtration rate (eGFR) and transplant-specific plus traditional Framingham risk factors. SA and Caucasians were compared by t-tests, Wilcoxon rank-sum or chi-square testing. Accounting for the matched design, multivariable linear regression was performed to determine predictors of adiponectin concentrations. SA did not differ from Caucasians in background cardiac disease or cardioprotective medication use or risk factors other than smoking (26 versus 56%, P = 0.001). Total adiponectin (9.5 ± 3.5 versus 12.9 ± 6....

Clinical kidney journal, 2013

BACKGROUND: Limited comparative data are available on the outcomes between extended-release and s... more BACKGROUND: Limited comparative data are available on the outcomes between extended-release and standard-release tacrolimus when used de novo in kidney transplant recipients (KTRs). METHODS: We identified KTRs transplanted at our institution during 2009-10 routinely prescribed extended-release tacrolimus and compared them with those transplanted during 2008-09 prescribed standard-release tacrolimus. Graft function (eGFR by MDRD-7 equation) at 12 months post-transplant (primary outcome); new-onset diabetes and other cardiovascular risk factors, BK viremia incidence, acute rejection, and graft survival to 12 months (secondary outcomes) were compared by intent-to-treat analysis. Time-to-steady-state concentration and number of dose adjustments required to attain steady state were recorded. RESULTS: There were no important demographic differences between the extended-release (N = 106) and standard-release (N = 95) cohorts. The estimated glomerular filtration rate (eGFR) at 12 months was...

Transplantation, 2008

The effect of unilateral nephrectomy on the cardiovascular risk profile of living kidney donors h... more The effect of unilateral nephrectomy on the cardiovascular risk profile of living kidney donors has not been prospectively studied. We performed an observational cohort study of 58 living donors to 6 months postdonation for changes in 24-hr ambulatory blood pressure profiles, renal function, urine protein excretion, body mass index, glucose tolerance, and fasting lipid profiles. The 24-hr systolic blood pressure average and night-day ratio were unchanged from pre-to postdonation (118.9Ϯ11 vs. 118.1Ϯ14 mm Hg, Pϭ0.77; 0.87Ϯ0.07 vs. 0.87Ϯ0.09, Pϭ0.68, respectively). Estimated glomerular filtration rate declined from 91.9Ϯ16 to 61.6Ϯ12 mL/min/1.73 m 2 (PϽ0.0001). Protein excretion, body mass index, glucose, and lipids were unchanged. No significant differences were noted between dippers and nondippers either pre-or postdonation. In summary, living kidney donation in the short term is safe. We suggest further observation of individuals with lower glomerular filtration rate for possible increased cardiovascular risk factors in the future.

Transplantation, 2007

C-reactive protein (CRP) is a strong predictor of cardiovascular disease, all-cause mortality, an... more C-reactive protein (CRP) is a strong predictor of cardiovascular disease, all-cause mortality, and renal allograft loss. Little is known about the effects of immunosuppressive and cardiovascular risk-modifying drugs on CRP in renal transplant recipients.

Transplantation Proceedings, 2004

Survival after kidney transplantation is better than on the waiting list, even in the elderly. Ho... more Survival after kidney transplantation is better than on the waiting list, even in the elderly. However, the effects of a prolonged waiting time for an organ on death with graft function have not been critically examined in this patient group. We conducted a single-center retrospective analysis of our cadaveric renal transplant experience in patients older than 60 years who received a kidney between January 1, 1990 and December 31, 2003. Besides waiting time, the effects of recipient age, gender, and diabetes were also examined. Cox proportional hazards analysis using patient death as a time-dependent outcome was used to estimate the hazard ratio of death posttransplantation. Using Kaplan-Meier survival methodology, patients with waiting times Յ5 years had significantly better survival times posttransplantation compared with those with waiting times Ͼ5 years (6.2 vs 2.8 years; P Ͻ .001). Each year of waiting was associated with hazard ratio 1.16 (95% confidence interval [CI], 1.06-1.27) for death. Prolonged waiting time on dialysis is deleterious to patient survival in recipients older than 60 years at transplantation. Early transplantation thus should be strongly encouraged in this group of patients.

Transplantation, 2006

Background. There are few data directly comparing the effects of two-hour postingestion monitored... more Background. There are few data directly comparing the effects of two-hour postingestion monitored cyclosporine (C2-CsA) vs. trough-monitored tacrolimus (C0-Tac) on renal function and cardiovascular risk factors. Methods. We studied 378 (202 C2-CsA vs. 176 C0-Tac) incident kidney transplant recipients in Toronto, Canada, from August 1, 2000 and December 31, 2003. Outcomes included changes in estimated glomerular filtration rate (eGFR at 1 and 6 months by modification of diet in renal disease four-variable equation), mean arterial pressure (MAP), total cholesterol (TC), and new-onset diabetes mellitus (NODM) at six months posttransplant. The independent effect of treatment/monitoring strategies on continuous outcomes and time-to-NODM was modeled using linear and Cox regression, respectively. Results. Mean eGFR was 59.5 vs. 62.9 ml/min at one month and 50.6 vs. 61.2 ml/min at six months for C2-CsA vs. C0-Tac, respectively. Multiple linear regression revealed the slope of eGFR to be 0.93 ml/min/month lower in C2-CsA patients. This was equivalent to an adjusted average eGFR difference of 4.64 ml/min between months one and six posttransplant. There was no significant difference in average MAP and TC. In a stepwise multivariable Cox model and a propensity score analysis, there was no significant association between the type of treatment/monitoring strategy and time-to-NODM. Conclusions. There was a greater decline in eGFR for patients on C2-CsA (vs. C0-Tac) between one and six months posttransplant. However, MAP, TC, and the risk of NODM were comparable in both treatment/monitoring groups. The long-term impact of short-term reductions in eGFR as a function of the type of treatment/monitoring strategy requires further study.

Transplantation Journal, 2010

Nephron Clinical Practice, 2007

Background/Aims: Seasonal variation in lipid levels is well described in the general population, ... more Background/Aims: Seasonal variation in lipid levels is well described in the general population, but has not been examined in renal transplant recipients (RTR). We sought to determine whether seasonal differences exist in RTR, a group at high risk for hyperlipidemia. Methods: We reviewed our population of 920 adults, identifying primary allograft recipients with survival ≧1 year, stable function, and ≧1 pair of post-6 months ‘winter’ (December 21 to March 20) plus ‘summer’ (June 21 to September 22) fasting lipid measurements within the same year. Correlations between factors affecting lipids and lipid level change were followed by multiple linear regression analysis. Results: 243 patients contributed 344 pairs. When most recent seasonal pair (n = 243) and all pairs (n = 344) were separately analyzed, no seasonal total cholesterol difference (winter vs. summer) was seen (5.08 vs. 5.05 mmol/l, p = 0.80; 5.11 vs. 5.09 mmol/l, p = 0.81 respectively). Opposing variation was seen between ...

Clinical Transplantation, 2009

Microalbuminuria predicts graft loss and all-cause mortality in renal transplant recipients. In t... more Microalbuminuria predicts graft loss and all-cause mortality in renal transplant recipients. In the general population, it clusters with both traditional cardiovascular risk factors and elevated C-reactive protein (CRP). Our objective was to define the relationship between microalbuminuria and these risk factors in stable renal transplant recipients. We identified 222 stable recipients who were minimum two months post-transplant and provided three urine albumin-to-creatinine ratio (ACR) measurements, excluding those with recent illness and proteinuria. Microalbuminuria was defined as averaged ACR &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; or =2.0 in men and 2.8 mg/mmol in women (Canadian Diabetes Association 2003). Risk factors associated with microalbuminuria were determined by multivariate logistic regression analysis. Averaged ACR correlated to CRP (R = 0.21, p = 0.001). Prevalence of microalbuminuria was 48% (108/222). Patients with microalbuminuria had higher CRP (7.01 +/- 8 vs. 3.21 +/- 3 mg/L, p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.0001) and systolic BP (129 +/- 17 vs. 123 +/- 12 mmHg, p = 0.004). Microalbuminuria was associated with increasing CRP [odds ratio 1.129 per 1 mg/L (95% CI 1.058-1.204), p = 0.0002], SBP [1.248 per 10 mmHg (1.023-1.522), p = 0.029] and smoking [1.938 (1.023-3.672), p = 0.042]. Post-transplant microalbuminuria is prevalent and is associated with elevated CRP, elevated BP, and smoking. Its relationship to these factors suggests it may be an indicator of graft and patient health.

Clinical Transplantation, 2006

Background: The role of dietary cations in hypertension has been evaluated in the general populat... more Background: The role of dietary cations in hypertension has been evaluated in the general population and selected subgroups, but its contribution to blood pressure (BP) elevations in patients with functional renal allografts has not been critically examined. Methods: After counseling based on Dietary Approaches to Stop Hypertension (DASH) guidelines, we measured timed 24-h urine excretion rates of sodium, potassium, calcium, and magnesium as a surrogate for their dietary intake, in 244 stable adult single-organ renal transplant recipients, correlating these with averaged blinded clinicmeasured BP values. Multiple linear regression analysis adjusting for factors affecting BP in transplant recipients was performed. Results: There was no correlation between systolic (SBP) or diastolic pressure (DBP) and 24-h urine excretion rates of each cation. There was no BP difference between patients receiving cyclosporine and tacrolimus (127/77 vs. 129/78 mmHg, p 5 0.38), or in cation excretion except for calcium (2.85 7 2.0 vs. 2.90 7 2.8, p 5 0.002). Protein excretion (po0.0001), age (p 5 0.002), and weight (p 5 0.04) were positively associated with SBP, while only weight (p 5 0.01) was associated with DBP by multivariate analysis. Conclusion: Dietary cation intake is not significantly associated with BP in renal transplant recipients. These data do not support recommendations to alter dietary cation intake as part of the management of post-transplantation hypertension.