Kazuyuki Suzuki

Estimation of Lifetime Parameters From Incomplete Field Data

When automobile failures occur within the automotive warranty period, a manufacturer can develop a record of mileages to failure from owners requests for repair. When no failures occur during the warranty period the owner naturally will not report mileages, and it may be inferred that “no record of failures” means “no failures.” By using a follow-up survey or postal reply cards, data can be acquired to include a partial record of nonfailures. A method of estimating lifetime parameters is proposed for analyzing this kind of data. Assuming a Weibull and an exponential lifetime distribution under the random censoring model, I derive a consistent estimator that can be applied to any censoring distribution.

Nonparametric Estimation of Lifetime Distributions from a Record of Failures and Follow-Ups

Abstract This article deals with the estimation problem of the survival function of an industrial product in which the real operating time is different from its actual calendar time. In an observational study of the product, sometimes only the time until failure is observable from the repair requests made by the owner, but nonfailure times themselves are not. The generalized maximum likelihood estimator of the survival function is presented, and its consistency, asymptotic normality, and variance are given. Operating times of construction machines and lifetimes of Channing House men are used to illustrate the method.

PROSTATIC CANCER IN A PATIENT ON LONG-TERM HEMODIALYSIS

Isoji Sasagawa, MD, Department of Urology, Yamagata University, School of Medicine, 2-2-2 Iidanishi., Yamagata-shi, Yamagata 990-23 (Japan) Dear Sir, Since Matas et al. [1] first described nine cancers among uremic patients, various neoplasms have been reported to occur in patients on hemodialysis [2, 3]. Recently, a possible relationship between cancer and hemodialysis has been emphasized [4]. However, the literature dealing with prostatic cancer in hemodialysis patients is scanty [5]. Herein we report a case of prostatic cancer on long-term hemodialysis. A 61-year-old Japanese male was admitted to our hospital with a 2-month history of lower abdominal and left leg pain. His previous history revealed gout at the age of 49 years, and hemodialysis had been started 68 months ago due to the end-stage renal failure derived from gouty kidney. Physical examination disclosed lymphadenopathies of the left inguinal areas. The penis, epididymides, spermatic cords and testes were normal, but the prostate was enlarged with hard consistency. A hemogram revealed leukocytes of 6,800/mm3 (normal 4,000–9,000), hemoglobin 9.3 g/dl (normal 14.0–18.0), erythrocytes 351×104/mm3 (normal 430–570 × 104), hematocrit 32% (normal 40–54) and platelet count 267,000/mm3 (normal 130,000–340,000). Serum sodium was 130 mEq/1 (normal 135–146), potassium 4.4 mEq/1 (normal 3.2–4.5), chloride 95 mEq/1 (normal 96–110), calcium 7.8 mg/dl (normal 8.8–10.2) and phosphorus 4.3 mg/dl (normal 2.9– 4.7). Blood urea nitrogen was 56 mg/dl (normal 9–25), serum creatinine 9.3 mg/dl (normal 0.5– 1.5), uric acid 4.7 mg/dl (normal 2.0–7.6) and alkaline phosphatase 201 IU/1 (normal 30–115). Serum prostatic acid phosphatase (PAP), γ-semi-noprotein (γ-SM) and prostatic specific antigen (PSA) were elevated at 1,300 ng/ml (normal less than 3.0), 45 ng/ml (normal less than 4.0) and 598 ng/ml (normal less than 3.6), respectively.

Liposarcoma of the renal capsule

We report a case of liposarcoma of the renal capsule. The literature is reviewed, and diagnosis and management are discussed.

Clinical and pathological studies of renal cell carcinoma and acquired cystic disease of the kidney in chronic dialysis patients.

我々は, 1984年4月から1992年1月までに長期透析患者1,352名において発生した27例の腎細胞癌 (RCC) を経験した. その発見率は約50人に1人 (2.0%) でcontrol群と比較すると約29倍の高率であった. この27例のRCCおよびcontrol群のRCCに対し臨床・病理学的検討を加えるとともに, 対象とした261例の透析患者をHD群とCAPD群, ACDK群と非ACDK群に分類し平均年齢, 透析期間, 原疾患等の比較検討を行った. Control群に選定した当院の検診受診者29,657名より発生した21例のRCCは全例単発であり, 組織学的細胞型が全て単一で, 摘出腎に認められた嚢胞は, その上皮が単層で, 増殖・癒合傾向を示さなかった. これに対し長期透析群より発生したRCC例では, 癌が両側・多発性に発生し, 複数の組織学的細胞型が混在する傾向を示した. さらに, 摘出腎に嚢胞が多数認められ, 嚢胞上皮は重層化し, 異形成や過形成性変化を92%の症例で認めた. これらの変化は前癌状態である可能性が示唆された.またACDKを “超音波検査法にて一側腎に2個以上の嚢胞を認めるとき” と定義したところHD例の60.9%, CAPD例の50.7%にACDKを合併し, 透析導入前の患者においても約7.8%にACDKを認めた. ACDKは男性で若年者, 透析期間が長く, 慢性糸球体腎炎および腎硬化症を原疾患にもつ群より高率に発生し, 糖尿病性腎症の群からの発生は有意に低かった. 本検討より長期透析患者に発生したRCCおよび摘出腎に認められた嚢胞上皮は特徴的な病理組織学的所見を呈し, また, ACDKは透析の方法によらずに発生し, さらに, 透析前の患者にも出現することから, 嚢胞発生には慢性腎不全がいかなる状態で存続していたかが重要である可能性が示唆された. 我々は, 長期透析患者の腎に嚢胞が一つでも確認されれば, これを癌発生の危険因子と捉え厳重に経過観察していく必要があると考えている.

Significance of Levels of Circulating IgA-Class Immune Complex in Discriminant Analysis of Patients with IgA Nephropathy before Renal Biopsy

Discriminant analysis of clinical markers including circulating IgA-class immune complex (IgA-CIC) before renal biopsy in patients with IgA nephropathy is described. Fifty-six patients with IgA nephropathy (IgA nephropathy group) and 54 patients with other primary chronic glomerulonephritis (non-IgA nephropathy group) were examined. Discriminant analysis was applied to separate these two groups by using 21 clinical markers including levels of IgA-CIC. The levels of IgA-CIC in sera were measured by a solid-phase anti-C3 Facb enzyme immunoassay (EIA). Among these clinical markers, the levels of serum IgA, IgA-CIC and creatinine, and the degree of microhematuria in the IgA nephropathy group were significantly higher than those in the non-IgA nephropathy group. Contributions of IgA and IgA-CIC to the classification were very high and both had almost the same effect. The correct classification rate was 80.00% using five clinical markers: serum IgA, microhematuria, IgA-CIC, serum creatinine, and blood urea nitrogen. It was shown that the levels of serum IgA and IgA-CIC were major markers for the clinical diagnosis of patients with IgA nephropathy. It was concluded that discriminant analysis before renal biopsy was useful for the diagnosis of IgA nephropathy.

Changes in Urinary Methylguanidine in Cases with End-Stage Renal Disease

Methylguanidine (MG), one of the most detrimental uremic toxins, is a product of creatinine oxidation. Although the amount of MG output depends on the concentration of creatinine, it is thought that the participation of active oxygen in the process of MG production markedly boosts its productivity1. In patients with end-stage renal disease (ESRD), the level of MG output may depend on the formation of active oxygen, since such patients have an increased amount of ceratinine which is a precursor of MG2–6. In fact, some patients who have more than 10 mg/dl of plasma creatinine (P-CR) respond well to conservative therapy and do not require hemodialysis treatment.

Application of Markovian Decision Theory to the Problem of Highway Maintenance

In this paper a maintenance problem of a road-type construction, which we call “road”, is discussed. A road is assumed to be inspected periodically, and its state being the degree of its deterioration is observed. The road is partitioned into several blocks whose states determine the state of the whole road. A block is a fixed length of a road where a maintenance activity can be performed. After each observation, an action is taken for the maintenance of the road. The maintenance cost may have some economy of scale when consecutive blocks are to be repaired. The problem is to find an optimal maintenance policy for the road, and it is formulated using Markovian deterioration models. A couple of properties on the optimal policy are investigated, and it is shown that an optimal policy for our maintenance problem is a simple structured control limit policy.