Considerations in determining sample size for pilot studies

There is little published guidance concerning how large a pilot study should be. General guidelines, for example using 10% of the sample required for a full study, may be inadequate for aims such as assessment of the adequacy of instrumentation or providing statistical estimates for a larger study. This article illustrates how confidence intervals constructed around a desired or anticipated value can help determine the sample size needed. Samples ranging in size from 10 to 40 per group are evaluated for their adequacy in providing estimates precise enough to meet a variety of possible aims. General sample size guidelines by type of aim are offered.     

Association of oxidative stress and PON1 with LDL and HDL particle size in middle-aged subjects

BACKGROUND: Alterations in plasma lipoprotein subclass distributions affect atherosclerosis risk. Smaller, denser low-density lipoprotein (LDL) particles (sdLDL) are more susceptible to oxidation. In contrast, most of the protective effects of high-density lipoproteins (HDL) are attributable to larger particles. This study investigates the connection between LDL and HDL particle heterogeneity and oxidative stress, antioxidative defence (AOD) and paraoxonase (PON1) status in a healthy middle-aged Serbian population. MATERIALS AND METHODS: LDL and HDL particle sizes and subclass distributions were measured by gradient gel electrophoresis in 104 men and 103 women, aged 53 +/- 9.4 years. PON1 activities and PON1(Q192R) phenotypes were determined with paraoxon and diazoxon as substrates. The oxidative stress/AOD status was estimated by measuring malondialdehyde (MDA) and superoxide-anion (O2*(-)) levels and superoxide-dismutase (SOD) activity. RESULTS: Subjects with sdLDL had significantly higher MDA (P < 0.001) and O2*(-)(P < 0.05) levels and greater diazoxonase (DZOase) activity (P < 0.05) compared to subjects with larger LDL particles. A high MDA concentration was a significant predictor of the sdLDL phenotype (P < 0.005). Increased levels of and MDA were associated with smaller HDL(3) subclass abundance. Reduced HDL particle size was associated with lower DZOase activity (P < 0.01). CONCLUSIONS: Even in the absence of symptoms of atherosclerosis, sdLDL particles are associated with increased oxidative stress, which may stimulate a compensatory rise in PON1 DZOase activity. Elevated oxidative stress may significantly affect HDL subclass distribution, resulting in the accumulation of smaller, denser HDL particles with diminished antioxidative capacity.     

500例国人正常脾脏大小的CT评价

本文分析了５００例正常脾脏大小的ＣＴ表现。其中男性３４７例，女性１５３例，年龄从５￣８２岁，平均４３岁，脾脏各径线、肋单元及脾指数分别为：（１）前后径７．３￣１３ｃｍ；（２）横径２．３￣４．７ｃｍ；（３）上下径６￣１３ｃｍ；（４）肋单元４￣８；（５）脾指数１０９．９￣６０５．４。笔者认为ＣＴ判断脾脏大小较为准确，应用径线测量及计算脾指数的方法并结合年龄与性别因素能够作出准确合理的综合评价。     

Pacemakers and implantable cardioverter defibrillators: device longevity is more important than smaller size: the patient's viewpoint

The size of pacemakers and implantable cardioverter defibrillators (ICDs) has been diminishing progressively. If two devices are otherwise identical in components, features and technology, the one with a larger battery should have a longer service life. Therefore, patients who receive smaller devices may require more frequent surgery to replace the devices. It is uncertain whether this tradeoff for smaller size is desired by patients. We surveyed 156 patients to determine whether patients prefer a larger, longer-lasting device, or a smaller device that is less noticeable but requires more frequent surgery. The effects of subgroups were evaluated; these included body habitus, age, gender, and patients seen at time of pulse generator replacement (PGR), initial implant, or follow-up. Among 156 patients surveyed, 151 expressed a preference. Of these, 90.1% preferred the larger device and 9.9% the smaller device (P <0.0001). Among thin patients, 79.5% preferred a larger device. Ninety percent of males and 89.2% of females selected the larger device. Among younger patients (< or =72 years), 89.6% preferred the larger device, as did 90.5% of older patients (>72 years). Of patients undergoing PGR or initial implants, 95% favored the larger device, as did 86% of patients presenting for follow-up. The vast majority of patients prefer a larger device to reduce the number of potential replacement operations. This preference crosses the spectrum of those with a previously implanted device, those undergoing initial implants, those returning for routine follow-up, and patients of various ages, gender, and habitus.     

Reproducibility of ultrasound measurement of pancreatic size with new advanced high-resolution dynamic image scanners

The reproducibility of ultrasound measurements of the pancreas was investigated in 10 healthy volunteers. All subjects underwent three different evaluations, each consisting of three ultrasound examinations, at 8:00 after overnight fasting, at 12:00 after a solid, standard meal, and at 14:00. The longitudinal and anteroposterior (AP) diameters of the head, body, and tail, as well as the total areas of the gland, were measured in longitudinal and axial scans. Significant differences were observed in the head and body longitudinal diameters measured at 12:00 and in the tail AP diameter at 14:00. We conclude that ultrasonography of the pancreas should be performed in the morning with patients in the fasting state. In these conditions, the reliability of ultrasound measurements of the gland appears to be the highest. © 1993 John Wiley & Sons, Inc.     

Sonographic assessment and grading of spleen size.

Ultrasonography was used to evaluate spleen size in patients with various clinical conditions including those of the liver, blood, collagen, or autoimmune disease. To express spleen size, a spleen index (SI), the product of the transverse diameter and its perpendicular diameter measured on the maximum cross-sectional image of the spleen, was used. SI correlated well with the volumes of resected spleens. Splenomegaly was present in high percentages of patients with liver, blood, collagen, and autoimmune disease, even though a majority of these spleens were not large enough to palpate. By grading the SI, characteristic distributions of SI were obtained for patients with different types of diseases. Obtaining and grading the SI by the use of ultrasound appears to be a significant supplemental aid for evaluating spleen size, especially in patients whose spleens are not palpable.     

Calculating effect size for continuous variables: D537--a robust, quantile-based approach

The calculation of effect size is an important step in measuring the potential real-life significance of the effect of an intervention. In the case of continuous data, Cohen's d is frequently used. This scales the difference between the means of two groups, or the mean difference between pairs of measurements, by dividing by the standard deviation. However, outlying values, especially in small studies, can influence the size of d. This article presents D537, a robust formula for d that is based on rank statistics. The median is used as a measure of difference, while the scaling factor is the range between the 30th and 70th percentiles of the distribution; a range that is equal to one standard deviation when the data are normally distributed. When data are normally distributed, the value of D537 is equal to that of Cohen's d. As D537 is based on the 30th, 50th and 70th percentiles, it is robust to outliers.     

急性心肌梗死早期ST段预测梗死面积的意义

目的 :探讨急性心肌梗死 (AMI)早期ST段与最终梗死面积之间的关系及溶栓治疗在其中的作用。方法 :分析 84例急性心肌梗死患者 (其中溶栓组n =31,对照组n =5 3)入院时和入院后 1周的 12 -导联体表心电图 ,用Aldrich公式预测梗死面积和SelvesterQRS积分系统计算最终梗死面积。结果 :溶栓组的最终梗死面积比早期预测梗死面积明显减小 (P <0 .0 5 ) ,其中有 15例 (48.39% )减少≥ 2 0 % ;而对照组的最终梗死面积与早期预测面积无明显差异 ,只有 7例 (13.2 1% )减少≥ 2 0 %。结论 :体表心电图抬高的ST段可用于早期预测梗死面积 ,作为评估溶栓治疗效果的一项无创、简便的方法。     

近场射流宽度在评价三尖瓣返流中的应用探讨

本文观察了39例三尖瓣返流患者的彩色返流束，根据返流束是否偏心分为中心返流组（A组）和偏心返流组（B组），并把两组返流束大小参数同多普勒法计算的每搏返流流率进行相关分析。结果发现，近场射流宽度与三尖瓣返流流率间在A、B两组均呈良好相关（r＝0.75，和0.71，P＜0.05），返流束长度及面积在A组与运流流率间呈中度相关（r＝0.58，和0.54，P＜0.05），而在B组则无明显相关（P＞0.05）。结论：（1）近场射流宽度可以较准确地评价三尖瓣返流程度;（2）在偏心三尖瓣返流时彩色返流束长度和面积低估返流程度。     

甲状腺癌实时超声造影增强特征与肿瘤大小的关系

目的探讨甲状腺癌实时CEUS增强特征与结节大小的关系。方法将68例经手术病理证实的甲状腺癌患者按肿瘤最大直径分为<10 mm1、0~20 mm、>20 mm 3组,分析各组肿瘤的绝对始增时间、相对始增时间、增强的均匀性、有无灌注缺损、增强顺序、增强强度及增强时病灶边界。结果甲状腺癌增强多晚于周围甲状腺实质,以不均匀、向心性增强为主,且增强时病灶边界多数不清或欠清,3组间差异均无统计学意义(P>0.05)。直径<10 mm及10~20 mm甲状腺癌以低增强为主;直径>20 mm的甲状腺癌以高增强为主。随着肿瘤直径增大,其内出现灌注缺损的概率增加,在3组中分别为28.57%(6/21)、54.29%(19/35)和75.00%(9/12),差异有统计学意义(P<0.05)。结论甲状腺癌CEUS增强特征与肿瘤大小有一定关系;实时CEUS可为临床提供更多有价值的信息。     

超声对胆管癌术前分期探讨肿瘤大小,回声与壁浸润关系

为了解胆管癌肿瘤大小、回声与壁浸润程度的关系，本文对６４例胆管肿瘤进行了回顾性分析。超声测量肿瘤厚径、长径与壁浸润的手术病理结果相比较：以厚径１．５ｃｍ为界，≤１．５ｃｍ肿瘤３１例，与管壁浸润的三个程度Ｓ１（未侵及浆膜）、Ｓ２（侵及浆膜）、Ｓ３（侵及浆膜外）的关系分别为２５．８％（８例）、４８．４％（１９例）、２５．８％（８例）；肿瘤厚径＞１．５ｃｍ２４例，分别为１２．１％（４）、３６．４％（１２）、５１．５％（１７）。肿瘤长径≤３ｃｍＳ１、Ｓ２、Ｓ３的比例分别为２１．６％（８／３７）、４６％（１７／３７）、３２．４％（１２／３７）；＞３ｃｍ的肿瘤分别为１４．８％（４／２７）、３７％（１０／２７）、４８．２％（１３／２７）。结果显示，胆管肿瘤壁浸润的程度与肿瘤的大小无关。对肿瘤回声观察，可见弱回声肿瘤壁浸润程度的超声诊断率较高（８６％）；强回声肿瘤最低（４４％）；肿瘤的回声直接影响壁浸润程度的判断     

急性心肌梗死溶栓血管再通早晚与梗死面积的关系

目的：观察经静脉溶栓治疗急性心肌梗死（AMI）患者，梗死相关血管（IRA）再通早晚与其心肌梗死面积之关系。方法；选取经溶栓后IRA再灌流患者71例，发病2～3周行99mTC－MIBI心肌断层显像测定AMI梗死范围指数，二维超声测定在室射血分数（LVEF）。结果：1）57例距发病≤6hIRA再通患者的梗死范围指数低于14例＞6h组（0．326±0．075比0．373±0．071，P＜0．05）；2）梗死范围指数与LVEF中度相关（r＝0．5139，P＜0．001）。结论：AMI患者静脉溶栓治疗IRA早开通比晚开通者的心梗范围缩小，心功能得到更好保护。     

Difference in Cryptococcus neoformans cellular and capsule size in sequential pulmonary and meningeal infection: a postmortem study

Cryptococcus neoformans is an encapsulated yeast that primarily causes a life-threatening meningoencephalitis in immunosuppressed individuals especially those with HIV/AIDS. Its main virulence factor is its polysaccharide capsule which interferes with complement-mediated phagocytosis. C. neoformans infections ensue following inhalation of small desiccated less encapsulated propagules leading to pulmonary pneumonia or colonization of the host's respiratory tract. Numerous murine experimental studies have shown major discrepancies in cryptococcal cell and capsule enlargement between the lung and brain. In this report, we describe a nonmurine experimental model of the striking variability between cryptococcal cell and capsule size diameters in histology sections of postmortem lung and brain in a fatal cryptococcal infection in a heart transplant recipient.     

A comparison of left atrial size by two-dimensional transthoracic echocardiography and magnetic endocardial catheter mapping

This study sought to validate the accuracy of magnetic electroanatomic mapping (MEAM) for determining cardiac chamber size in a clinically relevant situation. The authors chose to compare LA size measured by MEAM to that assessed by two-dimensional guided M-mode echocardiography. The study included 37 patients with drug refractory paroxysmal atrial fibrillation who underwent two-dimensional echocardiography and a detailed MEAM of the LA. The entire LA was mapped with a mean of 132 +/- 50 points with attention to identifying the mitral annulus and posterior wall of the LA. The MEAM measurement of LA size was taken as the distance from the anterior wall of the LA to the posterior wall in a plane parallel to the mitral valve annulus at atrial end-diastole. LA dimension determined by M-mode echocardiography was assessed in a plane parallel to the mitral valve annulus in the parasternal long-axis view during atrial end-diastole. LA size assessed by M-mode echocardiography was 41.2 +/- 5.0 versus 40.9 +/- 4.5 mm as assessed by MEAM, with good correlation (r = 0.87, P < 0.001). Only three patients had a difference in LA size that was > 0.3 cm between the two measurement techniques. Thus, it appears that LA anteroposterior dimension as determined by electroanatomic mapping is similar to that determined by two-dimensional guided M-mode echocardiography. MEAM appears to be an accurate method by which LA size can be assessed in patients with drug refractory atrial fibrillation undergoing left atrial ablation procedures.     

The Effect of Electrode Design on the Efficiency of Delivery of Radiofrequency Energy to Cardiac Tissue In Vitro

Four types of electrodes were studied with respect to efficiency of delivery of radiofrequency energy (HFE) and characteristics of the lesions produced in dog ventricular muscle in vitro. An imbeddable needle electrode was found to be the most efficient of the four types studied, with a lesion volume/energy-delivered ratio of 1.10 mm³joule at an optimum power level of 2.8 watts and power density at the electrode surface of 0.45 watt/mm². Lesion volume was linearly related to energy delivered at all power levels used below a power density of 0.64 watt/mm², at and above which tissue impedance increased abruptly. The electrode catheter typically used for RFE ablations was the least efficient at 0.15 mm^3/joule and a power density at the electrode surface of 0.50 watt/mm² at 6.27 watts. Masking 2/3 of the electrode surface with electrically insulating epoxy caused the RFE current to be directed into the tissue, resulting in a threefold increase in efficiency (0.46 mm³/joule) at less than half the power (2.79 watts). A flat, thermally insulated electrode with larger (10 mm²) contact area approached the efficiency of the imbedded electrode with a ratio of 0.69 mm³/joule at a low power density of 0.19 watt/mm² and 1.85 watt power level. Characteristics of an "ideal" electrode for RFE lesion production in cardiac tissue are discussed.     

Throwing kinematics and elbow varus torque relative to ball size in junior baseball players

[Purpose] The purpose of this study was to investigate changes in the shoulder and elbow joint angles, upper limb angular velocities, and elbow varus torque when throwing balls of two different sizes. [Participants and Methods] The pitching motion of 26 junior baseball players was analyzed using an optical motion capture system. The balls used were a standard baseball and a small ball of equal weight. Shoulder external rotation/abduction and elbow flexion were measured. The maximum values of shoulder joint internal rotation, elbow joint extension, wrist flexion angular velocity, and elbow joint varus torque were also evaluated. The ball velocity was determined as an index of pitching performance. [Results] The shoulder external rotation and elbow flexion angles were higher when pitching with a small ball. The joint angular velocity was also significantly higher when pitching with a small ball for all items examined. The ball speed was significantly higher with the small ball. The maximum varus torque of the elbow joint divided by the ball velocity was significantly lower for the small ball. [Conclusion] For a junior baseball player with a small hand length, using a small ball enables pitching with low stress on the elbow joint.