Spatiotemporal characterization of an experimental model of muscle pain in humans based on short-wave diathermy

BACKGROUND

Commonly used models for eliciting muscle pain involve the injection of algesic substances or the induction of delayed onset muscle soreness. The former require invasive procedures, and the time frame for pain induction and subsidence in the latter can be inconvenient. This study presents a detailed spatiotemporal characterization of a new experimental model of muscle pain based on short-wave diathermy (SWD), developed to overcome the limitations of existing models.

METHODS

The shoulder was selected as target site and the effects of the model were tested in two sessions to assess its reliability. Pain intensity profiles were recorded during the application of SWD, and changes in pressure pain threshold (PPT) in the infraspinatus muscle, together with pain intensity, duration, and quality were assessed 30 min after induction.

RESULTS

SWD-induced pain intensity scores averaged 4 points on a visual analogue scale, whereas PPT showed a consistent decrease of about 25% relative to baseline values. Pain was localized in the shoulder area, and was described as continuous, dull, well-delimited, heavy, and bearable. Pain lasted for an average of 145 min without requiring reinduction and was reliably elicited in both experimental sessions.

CONCLUSION

SWD can be used to elicit experimental muscle pain in a non-invasive, long-lasting, and reliable way and allows for repeated within- and between-session testing in the shoulder.

SIGNIFICANCE STATEMENT

SWD produces deep heating in muscles by converting electromagnetic energy to thermal energy. It was previously shown that it can be used to elicit experimental pain in the forearm muscles, and the present study demonstrates that this can be reliably generalized to other body sites, such as the shoulder. Furthermore, SWD application is non-invasive and presents a convenient time frame for pain induction and subsidence, thus overcoming limitations associated with traditional muscle pain models.

Mass Spectrometry-Based Evaluation of the Bland-Altman Approach: Review, Discussion, and Proposal

Reliable quantification in biological systems of endogenous low- and high-molecular substances, drugs and their metabolites, is of particular importance in diagnosis and therapy, and in basic and clinical research. The analytical characteristics of analytical approaches have many differences, including in core features such as accuracy, precision, specificity, and limits of detection (LOD) and quantitation (LOQ). Several different mathematic approaches were developed and used for the comparison of two analytical methods applied to the same chemical compound in the same biological sample. Generally, comparisons of results obtained by two analytical methods yields different quantitative results. Yet, which mathematical approach gives the most reliable results? Which mathematical approach is best suited to demonstrate agreement between the methods, or the superiority of an analytical method A over analytical method B? The simplest and most frequently used method of comparison is the linear regression analysis of data observed by method A (y) and the data observed by method B (x): y = α + βx. In 1986, Bland and Altman indicated that linear regression analysis, notably the use of the correlation coefficient, is inappropriate for method-comparison. Instead, Bland and Altman have suggested an alternative approach, which is generally known as the Bland-Altman approach. Originally, this method of comparison was applied in medicine, for instance, to measure blood pressure by two devices. The Bland-Altman approach was rapidly adapted in analytical chemistry and in clinical chemistry. To date, the approach suggested by Bland-Altman approach is one of the most widely used mathematical approaches for method-comparison. With about 37,000 citations, the original paper published in the journal The Lancet in 1986 is among the most frequently cited scientific papers in this area to date. Nevertheless, the Bland-Altman approach has not been really set on a quantitative basis. No criteria have been proposed thus far, in which the Bland-Altman approach can form the basis on which analytical agreement or the better analytical method can be demonstrated. In this article, the Bland-Altman approach is re-valuated from a quantitative bioanalytical perspective, and an attempt is made to propose acceptance criteria. For this purpose, different analytical methods were compared with Gold Standard analytical methods based on mass spectrometry (MS) and tandem mass spectrometry (MS/MS), i.e., GC-MS, GC-MS/MS, LC-MS and LC-MS/MS. Other chromatographic and non-chromatographic methods were also considered. The results for several different endogenous substances, including nitrate, anandamide, homoarginine, creatinine and malondialdehyde in human plasma, serum and urine are discussed. In addition to the Bland-Altman approach, linear regression analysis and the Oldham-Eksborg method-comparison approaches were used and compared. Special emphasis was given to the relation of difference and mean in the Bland-Altman approach. Currently available guidelines for method validation were also considered. Acceptance criteria for method agreement were proposed, including the slope and correlation coefficient in linear regression, and the coefficient of variation for the percentage difference in the Bland-Altman and Oldham-Eksborg approaches.

Reproducibility of volume analysis of dynamic susceptibility contrast perfusion-weighted imaging in untreated glioblastomas

PURPOSE

Despite a high variability, the hotspot method is widely used to calculate the cerebral blood volume (CBV) of glioblastomas on DSC-MRI. Our aim was to investigate inter- and intra-observer reproducibility of parameters calculated with the hotspot or a volume method and that of an original parameter assessing the fraction of pixels in the tumour volume displaying rCBV > 2: %rCBV > 2.

METHODS

Twenty-seven consecutive patients with untreated glioblastoma (age: 63, women: 11) were retrospectively included. Three observers calculated the maximum tumour CBV value (rCBVmax) normalized with a reference ROI in the contralateral white matter (CBVWM) with (i) the hotspot method and (ii) with a volume method following tumour segmentation on 3D contrast-enhanced T1-WI. From this volume method, %rCBV > 2 was also assessed. After 8-12 weeks, one observer repeated all delineations. Intraclass (ICC) and Lin's (LCC) correlation coefficients were used to determine reproducibility.

RESULTS

Inter-observer reproducibility of rCBVmax was fair with the hotspot and good with the volume method (ICC = 0.46 vs 0.65, p > 0.05). For CBVWM, it was fair with the hotspot and excellent with the volume method (0.53 vs 0.84, p < 0.05). Reproducibility of one pairwise combination of observers was significantly better for both rCBVmax and CBVWM (LCC = 0.33 vs 0.75; 0.52 vs 0.89, p < 0.05). %rCBV > 2 showed excellent inter- and intra-observer reproducibility (ICC = 0.94 and 0.91).

CONCLUSION

Calculated in glioblastomas with a volume method, rCBVmax and CBVWM yielded good to excellent reproducibility but only fair with the hotspot method. Overall, the volume analysis offers a highly reproducible parameter, %rCBV > 2, that could be promising during the follow-up of such heterogeneous tumours.

Validated Simple HPLC-UV Method for Mycophenolic Acid (MPA) Monitoring in Human Plasma. Internal Standardization: Is It Necessary?

The aim of the work was to prepare a simple but reliable HPLC-UV method for the routine monitoring of mycophenolic acid (MPA). Sample preparation was based on plasma protein precipitation with acetonitrile. The isocratic separation of MPA and internal standard (IS) fenbufen was made on Supelcosil LC-CN column (150 × 4.6 mm, 5 µm) using a mobile phase: CH₃CN:H₂O:0.5M KH₂PO₄:H₃PO₄ (260:700:40:0.4, v/v). UV detection was set at 305 nm. The calibration covered the MPA concentration range: 0.1–40 µg/mL. The precision was satisfactory with RSD of 0.97–7.06% for intra-assay and of 1.92–5.15% for inter-assay. The inaccuracy was found between −5.72% and +2.96% (+15.40% at LLOQ) and between −8.82% and +5.31% (+19.00% at LLOQ) for intra- and inter-assay, respectively, fulfilling acceptance criteria. After a two-year period of successful application, the presented method has been retrospectively calibrated using the raw data disregarding the IS in the calculations. The validation and stability parameters were similar for both calculation methods. MPA concentrations were recalculated and compared in 1187 consecutive routine therapeutic drug monitoring (TDM) trough plasma samples from mycophenolate-treated patients. A high agreement (r² = 0.9931, p < 0.0001) of the results was found. A Bland–Altman test revealed a mean bias of −0.011 μg/mL (95% CI: −0.017; −0.005) comprising −0.14% (95% Cl: −0.39; +0.11), whereas the Passing–Bablok regression was y = 0.986x + 0.014. The presented method can be recommended as an attractive analytical tool for medical (hospital) laboratories equipped with solely basic HPLC apparatus. The procedure can be further simplified by disapplying an internal standard while maintaining appropriate precision and accuracy of measurements.

Micro-CT scan with virtual dissection of left ventricle is a non-destructive, reproducible alternative to dissection and weighing for left ventricular size

Micro-CT scan images enhanced by iodine staining provide high-resolution visualisation of soft tissues in laboratory mice. We have compared Micro-CT scan-derived left ventricular (LV) mass with dissection and weighing. Ex-vivo micro-CT scan images of the mouse hearts were obtained following staining by iodine. The LV was segmented and its volume was assessed using a semi-automated method by Drishti software. The left ventricle was then dissected in the laboratory and its actual weight was measured and compared against the estimated results. LV mass was calculated multiplying its estimated volume and myocardial specific gravity. Thirty-five iodine-stained post-natal mouse hearts were studied. Mice were of either sex and 68 to 352 days old (median age 202 days with interquartile range 103 to 245 days) at the time of sacrifice. Samples were from 20 genetically diverse strains. Median mouse body weight was 29 g with interquartile range 24 to 34 g. Left Ventricular weights ranged from 40.0 to 116.7 mg. The segmented LV mass estimated from micro-CT scan and directly measured dissected LV mass were strongly correlated (R² = 0. 97). Segmented LV mass derived from Micro-CT images was very similar to the physically dissected LV mass (mean difference = 0.09 mg; 95% confidence interval − 3.29 mg to 3.1 mg). Micro-CT scanning provides a non-destructive, efficient and accurate visualisation tool for anatomical analysis of animal heart models of human cardiovascular conditions. Iodine-stained soft tissue imaging empowers researchers to perform qualitative and quantitative assessment of the cardiac structures with preservation of the samples for future histological analysis.

High-Throughput Multiparallel Enteropathogen Detection via Nano-Liter qPCR

Quantitative molecular diagnostic methods can effectively detect pathogen-specific nucleic acid sequences, but costs associated with multi-pathogen panels hinder their widespread use in research trials. Nano-liter qPCR (nL-qPCR) is a miniaturized tool for quantification of multiple targets in large numbers of samples based on assay parallelization on a single chip, with potentially significant cost-savings due to rapid throughput and reduced reagent volumes. We evaluated a suite of novel and published assays to detect 17 enteric pathogens using a commercially available nL-qPCR technology. Amplification efficiencies ranged from 88 to 98% (mean 91%) and were reproducible across four operators at two separate facilities. When applied to fecal material, assays were sensitive and selective (99.8% of DNA amplified were genes from the target organism). Due to nanofluidic volumes, detection limits were 1-2 orders of magnitude less sensitive for nL-qPCR than an enteric TaqMan Array Card (TAC). However, higher detection limits do not hinder detection of diarrhea-causing pathogen concentrations. Compared to TAC, nL-qPCR displayed 99% (95% CI 0.98, 0.99) negative percent agreement and 62% (95% CI 0.59, 0.65) overall positive percent agreement for presence of pathogens across diarrheal and non-diarrheal fecal samples. Positive percent agreement was 89% among samples with concentrations above the nL-qPCR detection limits. nL-qPCR assays showed an underestimation bias of 0.34 log₁₀ copies/gram of stool [IQR -0.40, -0.28] compared with TAC. With 12 times higher throughput for a sixth of the per-sample cost of the enteric TAC, the nL-qPCR chip is a viable alternative for enteropathogen quantification for studies where other technologies are cost-prohibitive.

Reliability of the conditioned pain modulation paradigm across three anatomical sites

Background and aims Conditioned Pain Modulation (CPM) is a measure of pain inhibition-facilitation in humans that may elucidate pain mechanisms and potentially serve as a diagnostic test. In laboratory settings, the difference between two pain measures [painful test stimulus (TS) without and with the conditioning stimulus (CS) application] reflects the CPM magnitude. Before the CPM test can be used as a diagnostic tool, its reliability on the same day (intra-session) and across multiple days (inter-session) needs to be known. Furthermore, it is important to determine the most reliable anatomical sites for both the TS and the CS. This study aimed to measure the intra-session and inter-session reliability of the CPM test paradigm in healthy subjects with the TS (pressure pain threshold-PPT) applied to three test sites: the face, hand, and dorsum of the foot, and the CS (cold pressor test-CPT) applied to the contralateral hand. Methods Sixty healthy participants aged 18-65 were tested by the same examiner on 3 separate days, with an interval of 2-7 days. On each day, testing was comprised of two identical experimental sessions in which the PPT test was performed on each of the three dominant anatomical sites in randomized order followed by the CPM test (repeating the PPT with CPT on the non-dominant hand). CPM magnitude was calculated as the percent change in PPT. The Intraclass Correlation Coefficient (ICC), Coefficient of Variation (CV), and Bland-Altman analyses were used to assess reliability. Results PPT relative reliability ranged from good to excellent at all three sites; the hand showed an intra-session ICC of 0.90 (0.84, 0.94) before CPT and ICC of 0.89 (0.83, 0.92) during CPT. The PPT absolute reliability was also high, showing a low bias and small variability when performed on all three sites; for example, CV of the hand intra-session was 8.0 before CPT and 8.1 during CPT. The relative reliability of the CPM test, although only fair, was most reliable when performed during the intra-session visits on the hand; ICC of 0.57 (0.37, 0.71) vs. 0.20 (0.03, 0.39) for the face, and 0.22 (0.01, 0.46) for the foot. The inter-session reliability was lower in all three anatomical sites, with the best reliability on the hand with an ICC of 0.40 (0.23, 0.55). The pattern of absolute reliability of CPM was similar to the relative reliability findings, with the reliability best on the hand, showing lower intra-session and inter-session variability (CV% = 43.5 and 51.5, vs. 70.1 and 73.1 for the face, and 75.9 and 78.9 for the foot). The CPM test was more reliable in women than in men, and in older vs. younger participants. Discussion The CPM test was most reliable when the TS was applied to the dominant hand and CS performed on the contralateral hand. These data indicate that using the CS and TS in the same but contralateral dermatome in CPM testing may create the most reliable results.

A High-Throughput Method for the Analysis of Erythrocyte Fatty Acids and the Omega-3 Index

Omega-3 long-chain polyunsaturated fatty acids (n-3 LCPUFA) have several health benefits. In particular, low n-3 LCPUFA status is associated with cardiovascular disease (CVD) and led to the development of the omega-3 index that is the proportion of eicosapentaenoic acid and docosahexaenoic acid in the erythrocyte membranes, as a marker of CVD risk. Most methods used to measure the omega-3 index are laborious and time consuming. Therefore, the aim of this study was to develop a high-throughput method for the extraction and measurement of erythrocyte fatty acids and the omega-3 index. For sample extraction and quantification, two methods were used; a single-step extraction, degradation, and derivatization method by Lepage and Roy, followed by gas chromatography flame ionization detection (GC-FID), which is commonly used and a high-throughput method using an automated methyl tert-butyl ether extraction followed by electrospray ionization mass spectrometry. Both methods were first applied to the analysis of known concentrations of synthetic phospholipid (PL) mixtures to determine recovery and precision prior to their application in the analysis of human erythrocytes. The range of recoveries over five synthetic PL mixtures were 86.4-108.9% and the coefficient of variation was <10% (within-run) and ≤15.2% (between-run). Both methods showed high correlation (R = 0.993) for the omega-3 index and there was no systematic bias in the detection of omega-3 index using either method. The new high-throughput method described here offers considerable advantages in terms of simplicity and throughput compared to the GC-FID method and provides additional information on molecular PL concentrations.

Comparing Assessments of Physical Functional Independence in Older Adults With Mobility Limitations

OBJECTIVES

The aims of the study were (1) to assess the agreement and correlation between self-reported functional independence and observations of family caregivers in a heterogeneous population of community-dwelling older adults with disabilities and (2) to determine how self-reports and caregiver reports correlate with evaluator rated functional independence over time.

DESIGN

Data were drawn from a larger, randomized controlled trial examining the effects of a caregiver-inclusive intervention on outcomes of care recipients and their family caregivers. Functional independence measures were obtained using a self-report version of the Functional Independence Measure (care recipient self-reported Functional Independence Measure, caregiver self-reported Functional Independence Measure) and the Functional Autonomy Measurement System (evaluator perspective). They were administered at baseline (preintervention) and after the intervention at 6, 22, and 58 wks.

RESULTS

Bivariate correlation analyses of 90 dyads consisting of older care recipients and their family caregivers reported moderate to very strong correlations between the three functional independence measures across all time points (rS = 0.45-0.91, P < 0.01). Bland-Altman analyses revealed a small systematic bias between care recipient and caregiver assessments of functional independence, with participants reporting higher scores across all time points (mean difference = 2.00-2.97).

CONCLUSIONS

There is substantial consistency among the self-assessed, caregiver-assessed, and evaluator assessed functional independence of older adults. Caregivers may be used as proxies for community-dwelling older adults without severe cognitive impairments with functional limitations.

TO CLAIM CME CREDITS

Complete the self-assessment activity and evaluation online at http://www.physiatry.org/JournalCME CME OBJECTIVES: After reviewing this article, readers will be able to: (1) Describe the strength of association between self-reported functional independence and observations of family caregivers in a heterogeneous population of community-dwelling older adults with disabilities over time; (2) Describe the level of agreement between self-reported functional independence and observations of family caregivers over time; and (3) Describe the associations among self-reported, caregiver reported and evaluator rated functional independence over time.

LEVEL

Advanced ACCREDITATION: The Association of Academic Physiatrists is accredited by the Accreditation Council for Continuing Medical Education to provide continuing medical education for physicians.The Association of Academic Physiatrists designates this Journal-based CME activity for a maximum of 1.0 AMA PRA Category 1 Credit(s)™. Physicians should only claim credit commensurate with the extent of their participation in the activity.

Highly wearable cuff-less blood pressure and heart rate monitoring with single-arm electrocardiogram and photoplethysmogram signals

Background

Long-term continuous systolic blood pressure (SBP) and heart rate (HR) monitors are of tremendous value to medical (cardiovascular, circulatory and cerebrovascular management), wellness (emotional and stress tracking) and fitness (performance monitoring) applications, but face several major impediments, such as poor wearability, lack of widely accepted robust SBP models and insufficient proofing of the generalization ability of calibrated models.

Methods

This paper proposes a wearable cuff-less electrocardiography (ECG) and photoplethysmogram (PPG)-based SBP and HR monitoring system and many efforts are made focusing on above challenges. Firstly, both ECG/PPG sensors are integrated into a single-arm band to provide a super wearability. A highly convenient but challenging single-lead configuration is proposed for weak single-arm-ECG acquisition, instead of placing the electrodes on the chest, or two wrists. Secondly, to identify heartbeats and estimate HR from the motion artifacts-sensitive weak arm-ECG, a machine learning-enabled framework is applied. Then ECG-PPG heartbeat pairs are determined for pulse transit time (PTT) measurement. Thirdly, a PTT&HR-SBP model is applied for SBP estimation, which is also compared with many PTT-SBP models to demonstrate the necessity to introduce HR information in model establishment. Fourthly, the fitted SBP models are further evaluated on the unseen data to illustrate the generalization ability. A customized hardware prototype was established and a dataset collected from ten volunteers was acquired to evaluate the proof-of-concept system.

Results

The semi-customized prototype successfully acquired from the left upper arm the PPG signal, and the weak ECG signal, the amplitude of which is only around 10% of that of the chest-ECG. The HR estimation has a mean absolute error (MAE) and a root mean square error (RMSE) of only 0.21 and 1.20 beats per min, respectively. Through the comparative analysis, the PTT&HR-SBP models significantly outperform the PTT-SBP models. The testing performance is 1.63 ± 4.44, 3.68, 4.71 mmHg in terms of mean error ± standard deviation, MAE and RMSE, respectively, indicating a good generalization ability on the unseen fresh data.

Conclusions

The proposed proof-of-concept system is highly wearable, and its robustness is thoroughly evaluated on different modeling strategies and also the unseen data, which are expected to contribute to long-term pervasive hypertension, heart health and fitness management.

A Comparison of the Immunochemical Methods, PETINIA and EMIT, With That of HPLC-UV for the Routine Monitoring of Mycophenolic Acid in Heart Transplant Patients

BACKGROUND

The aim of this study was to evaluate particle enhanced turbidimetric inhibition immunoassay (PETINIA) recently developed for mycophenolic acid (MPA) determination in plasma and to compare it with a reference high-performance liquid chromatography (HPLC) method, using samples from heart transplant recipients. The results are presented in the context of PETINIA being compared with enzyme multiplied immunoassay technique (EMIT).

METHODS

PETINIA evaluation was performed using 194 routine trough plasma samples at steady state. EMIT was evaluated using 677 samples from 61 steady-state 12-hour profiles obtained from 35 heart transplant patients. Evaluation was undertaken on a Dimension EXL 200 analyzer (PETINIA) and on a Viva-E analyzer (EMIT).

RESULTS

The mean MPA concentration measured by PETINIA was significantly higher than that measured by high-performance liquid chromatography combined with UV detector (2.36 ± 1.30 mcg/mL versus 1.82 ± 1.23 mcg/mL, respectively, P < 0.0001). Bland-Altman analysis revealed a mean bias of 0.54 mcg/mL [95% confidence interval (CI), 0.49-0.59] comprising 33.48% (95% CI, 30.34-36.61). Passing-Bablok regression was: y = 1.100x + 0.38 (95% CI for slope: 1.044-1.154 and for intercept: 0.30-0.47). Regardless of a significant observed correlation (r = 0.9230, P < 0.0001), the statistical analyses showed a significant difference between PETINIA and the reference chromatographic method. The mean MPA concentration measured by EMIT was significantly higher than that measured by HPLC (7.48 ± 8.34 mcg/mL versus 5.57 ± 6.61 mcg/mL, respectively, P < 0.0001) with a mean bias of 1.91 mcg/mL (95% CI, 1.75-2.07) comprising 35.91% (95% CI, 34.37-37.45). The significant difference between EMIT and HPLC was confirmed by Passing-Bablok regression: y = 1.300x + 0.24 (95% CI for slope: 1.279-1.324 and for intercept: 0.18-0.29). The analysis of the determinations, grouped by sampling time, revealed positive bias between EMIT and HPLC ranging from 24.54% to 42.77% and inversely proportional to MPA concentrations with r = 0.9122 (P < 0.001).

CONCLUSIONS

The new immunochemical PETINIA method was associated with significantly higher MPA concentrations in routine therapeutic drug monitoring samples from heart transplant patients. The magnitude of the MPA overestimation was similar to that observed by use of the EMIT method.

Using BD Vacutainer CD4 Stabilization Tubes for Absolute Cluster of Differentiation Type 4 Cell Count Measurement on BD FacsCount and Partec Cyflow Cytometers: A Method Comparison Study from Zimbabwe

Background

Blood collected in conventional EDTA tubes requires laboratory analysis within 48 hours to provide valid CD4 cell count results. This restricts access to HIV care for patients from rural areas in resource-constraint settings due to sample transportation problems. Stabilization Tubes with extended storage duration have been developed but not yet evaluated comprehensively.

Objective

To investigate stability of absolute CD4 cell count measurement of samples in BD Vacutainer CD4 Stabilization Tubes over the course of 30 days.

Methods

This was a laboratory-based method comparison study conducted at a rural district hospital in Beitbridge, Zimbabwe. Whole peripheral blood from 88 HIV positive adults was drawn into BD Vacutainer CD4 Stabilization Tubes and re-tested 1, 2, 3, 5, 7, 14 and 30 days after collection on BD FacsCount and Partec Cyflow cytometers in parallel. Absolute CD4 cell levels were compared to results from paired samples in EDTA tubes analysed on BD FacsCount at the day of sample collection (references methodology). Bland-Altman analysis based on ratios of the median CD4 counts was used, with acceptable variation ranges for Limits of Agreements of +/-20%.

Results

Differences in ratios of the medians remained below 10% until day 21 on BD FacsCount and until day 5 on Partec Cyflow. Variations of Limits of Agreement were beyond 20% after day 1 on both cytometers. Specimen quality decreased steadily after day 5, with only 68% and 40% of samples yielding results on BD FacsCount and Partec Cyflow at day 21, respectively.

Conclusions

We do not recommend the use of BD Vacutainer CD4 Stabilization Tubes for absolute CD4 cell count measurement on BD FacsCount or Partec Cyflow due to large variation of results and decay of specimen quality. Alternative technologies for enhanced CD4 testing in settings with limited laboratory and sample transportation capacity still need to be developed.

Comparison of Hevylite™ IgA and IgG assay with conventional techniques for the diagnosis and follow-up of plasma cell dyscrasia

Background

Heavy/light chain assay allows the characterization and quantification of immunoglobulin light chains bound to heavy chains for each Ig’k and Ig’λ immunoglobulin class, discriminating between the involved/uninvolved isotypes in plasma cell dyscrasia. The Ig’k/Ig’λ ratio (heavy/light chain ratio) enables to monitor the trend of monoclonal component during therapy and disease evolution.

Objective

In this study, we evaluate the impact of the heavy/light chain assay in monitoring multiple myeloma patients in comparison with conventional techniques.

Methods

Serum samples of 28 patients with IgG or IgA monoclonal component were collected for a mean of 109 days and analyzed. The heavy/light chain assay was compared with classical immunoglobulin quantification (Ig’Tot), serum immunofixation electrophoresis, serum protein electrophoresis, and serum-free light chains quantification. Serum samples from 30 healthy patients were used as control (polyclonal).

Results

Heavy/light chain ratio and serum immunofixation electrophoresis were comparable in 86% of the cases, and free light chain ratio and heavy/light chain ratio in 71.8%. Heavy/light chain assay and Ig’Tot measurements showed a concentration-dependent agreement in monoclonal patients. The heavy/light chain assay was able to quantify the monoclonal component migrating in SPE β region: this occurred in 10% of our IgG and 50% of our IgA patients.

Conclusions

The concordance scores indicate that heavy/light chain and Ig’Tot assays show differences at high monoclonal component values. The heavy/light chain ratio, serum immunofixation electrophoresis, and free light chain ratio showed partial concordance. Our study confirmed that, in the context of heavy/light chain assay, heavy/light chain Ig’k and Ig’λ absolute values and heavy/light chain ratio are both important tools to monitor the presence of monoclonal component that are difficult to be identified in SPE.

A deconvolution method for deriving the transit time spectrum for ultrasound propagation through cancellous bone replica models

The acceptance of broadband ultrasound attenuation for the assessment of osteoporosis suffers from a limited understanding of ultrasound wave propagation through cancellous bone. It has recently been proposed that the ultrasound wave propagation can be described by a concept of parallel sonic rays. This concept approximates the detected transmission signal to be the superposition of all sonic rays that travel directly from transmitting to receiving transducer. The transit time of each ray is defined by the proportion of bone and marrow propagated. An ultrasound transit time spectrum describes the proportion of sonic rays having a particular transit time, effectively describing lateral inhomogeneity of transit times over the surface of the receiving ultrasound transducer. The aim of this study was to provide a proof of concept that a transit time spectrum may be derived from digital deconvolution of input and output ultrasound signals. We have applied the active-set method deconvolution algorithm to determine the ultrasound transit time spectra in the three orthogonal directions of four cancellous bone replica samples and have compared experimental data with the prediction from the computer simulation. The agreement between experimental and predicted ultrasound transit time spectrum analyses derived from Bland–Altman analysis ranged from 92% to 99%, thereby supporting the concept of parallel sonic rays for ultrasound propagation in cancellous bone. In addition to further validation of the parallel sonic ray concept, this technique offers the opportunity to consider quantitative characterisation of the material and structural properties of cancellous bone, not previously available utilising ultrasound.

Experimental and computer simulation validation of ultrasound phase interference created by lateral inhomogeneity of transit time in replica bone: marrow composite models

The measurement of broadband ultrasound attenuation in cancellous bone for the assessment of osteoporosis follows a parabolic-type dependence with bone volume fraction, having minima values corresponding to both entire bone and entire marrow. Langton has recently proposed that the primary attenuation mechanism is phase interference due to variations in propagation transit time through the test sample as detected over the phase-sensitive surface of the receive ultrasound transducer. This fundamentally simple concept assumes that the propagation may be considered as an array of parallel ‘sonic rays’. The transit time of each ray is defined by the proportion of bone and marrow propagated, being a minimum (tmin) solely through bone and a maximum (tmax) solely through marrow, from which a transit time spectrum, may be defined describing the proportion of sonic rays having a particular transit time.

The aim of this study was to test the hypothesis that there is a dependence of phase interference upon the lateral inhomogeneity of transit time by comparing experimental measurements and computer simulation predictions of ultrasound propagation through a range of relatively simplistic solid:liquid models.

From qualitative and quantitative comparison of the experimental and computer simulation results, there is an extremely high degree of agreement of 94.2%–99.0% between the two approaches. This combined experimental and computer simulation study has successfully demonstrated that lateral inhomogeneity of transit time has significant potential for phase interference to occur if a phase-sensitive receive ultrasound transducer is implemented as in most commercial ultrasound bone analysis devices.

Flow cytometric lymphocyte subset analysis using material from frozen whole blood

Multicenter immune monitoring programs commonly rely on storing and shipping cryopreserved peripheral blood mononuclear cells (PBMC), isolated from whole blood before freezing. However, under many conditions in the field, facilities to separate PBMC are absent. Here, we investigate the feasibility of using whole blood (WB) frozen at -80°C as a source of viable lymphocytes for use in immunological studies. We compare the percentage of CD4 and CD8 T lymphocytes and their subsets from frozen WB with results from cryopreserved PBMC in five random healthy blood donors (three female, two male). We report that CD4 and CD8 values in lymphocytes from WB frozen up to 120 days were very similar to those of PBMC frozen up to 10 days. These data suggest that within the limits of parameters investigated in this study, contrary to our original assumptions, whole blood frozen at -80°C may in fact be an appropriate source of viable lymphocytes for T cell enumeration assays in immunological and epidemiological studies.

Evaluation of normalization strategies for qPCR quantitation of intracellular viral DNA: the example of Vaccinia virus

Quantitation of intracellular viral genomes is critical in both clinical and fundamental virology. Quantitative real time PCR (qPCR) is currently the gold standard to detect and monitor virus infections, due to its high sensitivity and reproducibility. The reliability of qPCR data depends primarily on the technical process. Normalization, which corrects inter-sample variations related to both pre-analytical and qPCR steps, is a key point of an accurate quantitation. Total DNA input and qPCR-measured standards were evaluated to normalize intracellular Vaccinia virus (VACV) genomes. Three qPCR assays targeting either a single-copy chromosomic gene, a repeated chromosomic DNA sequence, or a mitochondrial DNA sequence were compared. qPCR-measured standards, unlike total DNA input, allowed for accurate normalization of VACV genome, regardless of the cell number. Among PCR-measured standards, chromosomic DNA and mitochondrial DNA were equivalent to normalize VACV DNA and multi-copy standards displayed lower limits of quantitation than single-copy standards. The combination of two qPCR-measured standards slightly improved the reliability of the normalization. Using one or two multi-copy standards must be favored for relative quantitation of intracellular VACV DNA. This concept could be applied to other DNA viruses.

A reliable and safe method of collecting blood samples from implantable central venous catheters for determination of plasma gentamicin concentrations

STUDY OBJECTIVE

To evaluate the extent of agreement between plasma gentamicin concentrations determined from samples collected by using implantable subcutaneous central venous catheters (ports) with the push-pull method and those collected by finger lancet punctures in children with febrile neutropenia.

DESIGN

Prospective, randomized study.

SETTING

University-affiliated, tertiary care hospital.

PATIENTS

Sixty-two children with cancer who had single- or double-lumen ports and who received gentamicin for treatment of febrile neutropenia between February 2008 and October 2009.

INTERVENTION

One blood sample was collected from the port by using the push-pull method at the same time one blood sample was collected by finger lancet puncture for determination of plasma gentamicin concentrations.

MEASUREMENTS AND MAIN RESULTS

Forty-four pairs of samples were available for assessment of agreement, and 43 were available for pharmacokinetic analysis. Agreement between plasma gentamicin concentrations determined from blood samples from ports and finger lancet punctures was assessed by the intraclass correlation coefficient (ICC), Bland-Altman analysis, and comparison of simulated dosage adjustments. Changes in port patency were monitored for 1 week after port sampling. Differences in simulated dosage adjustments calculated by using either the port or finger lancet puncture samples that differed by greater than 20% were considered clinically significant. Agreement between the 44 finger lancet puncture and port sample pairs was excellent (ICC 0.991, 95% confidence interval 0.984-0.995). Port plasma gentamicin concentrations were 4.7% lower than those concentrations determined in blood from finger lancet punctures. The observed limits of agreement ranged from -20.5% to 11%. Differences in dosage adjustments calculated by using port and finger lancet puncture plasma gentamicin concentrations were not clinically significant in 38 (88%) of 43 cases. No changes in port patency were observed in the week after port sampling.

CONCLUSION

The push-pull method of blood sampling is a reliable and safe option for determining plasma gentamicin concentrations in children with ports.

Development and validation of an expedited 10 g protein counter (EP-10) for dietary protein intake quantification

OBJECTIVE

Precise protein quantification is essential in clinical dietetics, particularly in the management of renal, burn, and malnourished patients. The expedited 10 g protein counter (EP-10) was developed to expedite the estimation of dietary protein for nutritional assessment and recommendation. The main objective of this study was to compare the validity and efficacy of the EP-10 with the American Dietetic Association's "Exchange List for Meal Planning" (ADA-7 g) in quantifying dietary protein intake, against computerized nutrient analysis (CNA).

DESIGN

Protein intake of 197 food records kept by healthy adult subjects in Singapore was determined thrice using 3 different methods: (1) EP-10, (2) ADA-7 g, and (3) CNA using SERVE program (Version 4.0). Assessments using the EP-10 and ADA-7 g were performed by 2 assessors in a blind crossover manner while a third assessor performed the CNA. All assessors were blind to each other's results. Time taken to assess a subsample (n = 165) using the EP-10 and ADA-7 g was also recorded.

RESULTS

Mean difference in protein intake quantification when compared with the CNA was statistically nonsignificant for the EP-10 (1.4 ± 16.3 g, P = .239) and statistically significant for the ADA-7 g (-2.2 ± 15.6 g, P = .046). Both the EP-10 and ADA-7 g had clinically acceptable agreement with the CNA, as determined via Bland-Altman plots, although it was found that EP-10 had a tendency to overestimate with protein intakes above 150 g. The EP-10 required significantly less time for protein intake quantification than the ADA-7 g (mean time of 65 ± 36 seconds vs. 111 ± 40 seconds, P < .001).

CONCLUSION

The EP-10 and ADA-7 g are valid clinical tools for protein intake quantification in an Asian context, with EP-10 being more time efficient. However, a dietician's discretion is needed when the EP-10 is used on protein intakes above 150 g.

The Bland-Altman method should not be used in regression cross-validation studies

The purpose of this study was to demonstrate the bias in the Bland-Altman (BA) limits of agreement method when it is used to validate regression models. Data from 1,158 men were used to develop three regression equations to estimate maximum oxygen uptake (R2 = .40, .61, and .82, respectively). The equations were evaluated in a cross-validation sample of 581 men. The BA means and differences were correlated (p < .001) in the cross-validation sample for each model (r = .55, .39, and .26, respectively), thus demonstrating bias. The BA method is inappropriate for validation of regression models. Validation of regression equations is properly conducted by plotting the residuals against the estimated values and examining the magnitude of the estimation error.

Incurred sample reanalysis: different evaluation approaches on data obtained for spironolactone and its active metabolite canrenone

Background: The inherent reproducibility of a bioanalytical approach is usually sustained through incurred sample reanalysis (ISR). Questions relating to the number of ISRs, the right moment for performing reanalysis, the way of performing an appropriate statistical refinement of experimental data and actions to be taken in the case of failure are frequently raised. Results: Data resulting from ISR following a bioequivalence study for spironolactone formulations are discussed. Reanalysis of samples was carried out twice: immediately after the end of the study and after a period that overcame the long-term stability study achieved during method validation. The Bland–Altman approach was used to assess experimental results. ISR was successful over the short reanalysis period for both compounds. Data produced through reanalysis after the long-term period indicated a systematic positive bias for the metabolite canrenone (although results supported reproducibility). The results obtained for spironolactone were affected by a strong negative systematic bias and failed to support reproducibility. The explanation deals with the continuous conversion of spironolactone to canrenone in plasma samples. However, reproducibility of the method may be sustained by comparing original and repeated differences between concentration values in samples by means of a paired t-test, Wilcoxon sign rank-sum test and linear regression. Conclusions: Different statistical approaches for making data comparisons are discussed and may be successfully applied during reanalysis of samples from a bioequivalence study. Results of the evaluations may differ in accordance with the statistical procedure being applied, thus a definitive conclusion requires consideration of all specific experimental circumstances arising during production of the processed data.

Agreement between the Heidelberg Retina Tomograph (HRT) stereometric parameters estimated using HRT-I and HRT-II

PURPOSE

To assess agreement between Heidelberg Retina Tomograph (HRT)-I and HRT-II stereometric parameters and to determine whether parabolic error correction (PEC) to the topographies improves agreement.

METHODS

University of California San Diego Diagnostic Innovations in Glaucoma Study participants with two HRT-II examinations (n = 380) or one HRT-I and one HRT-II examinations (n = 344) acquired on the same day were included. From the group of 380 eyes, 200 eyes were randomly selected to estimate the repeatability coefficients of HRT-II rim area and volume, cup area and volume, and mean retinal nerve fiber layer (RNFL) thickness parameters (HRT-II control group), and the remaining 180 eyes were used to assess agreement between two HRT-II examinations (HRT-II study group). Agreement between stereometric parameters of HRT-I and HRT-II examinations (HRT-I vs. HRT-II study group) were assessed with (1) no PEC, (2) HRT PEC, and (3) a modified PEC. Bland-Altman plots were used to assess agreement using estimates of bias and clinical limits of agreement (CLA) based on repeatability coefficients.

RESULTS

In the HRT-II study group, agreement between stereometric parameters was good, with no statistically significant biases. For all parameters, differences were within the CLA in 94% of participants. In the HRT-I vs. HRT-II study group, there was a small statistically significant bias between the stereometric parameters, but all differences were within CLA for ≥95% of participants. In both study groups, PEC did not improve agreement.

CONCLUSIONS

Agreement between HRT-I and HRT-II stereometric parameters was good, and PEC did not improve agreement. These results suggest that HRT-I and HRT-II examinations can be used interchangeably to detect changes in stereometric parameters over time.

Imatinib assay by HPLC with photodiode-array UV detection in plasma from patients with chronic myeloid leukemia: Comparison with LC-MS/MS

BACKGROUND

Imatinib, a competitive inhibitor of BCR-ABL tyrosine kinase, is now the first-line treatment for chronic myelogenous leukemia (CML). Therapeutic drug monitoring targeting trough plasma levels of about 1000ng/mL may help to optimize the therapeutic effect.

METHODS

We developed a high-performance liquid chromatography (HPLC) method with UV/Diode Array Detection (DAD) for trough imatinib concentration determination in human plasma. Imatinib trough levels were measured in plasma from 65 CML patients using our method and LC-MS/MS as the reference method. Results with these two methods were compared using Deming regression, chi-square test, and sign test.

RESULTS

The calibration curve was prepared in blank human plasma. HPLC-UV/DAD calibration curves were linear from 80 to 4000ng/mL, and the limit of quantification was set at 80ng/mL. The between-day variation was 6.1% with greater than 96% recovery after direct plasma deproteinization and greater than 98% recovery from the column. No significant differences in imatinib plasma levels were found between HPLC-UV/DAD and LC-MS/MS.

CONCLUSIONS

This HPLC-UV/DAD method was sufficiently specific and sensitive for imatinib TDM, with no evidence of interference. Our rapid inexpensive HPLC-UV/DAD method that requires only widely available equipment performs well for plasma imatinib assays.

Measurement error for ultrasound fetal biometry performed by paramedics in rural Bangladesh

OBJECTIVES

To document the accuracy and precision of sonographic fetal biometry performed by nine paramedics from rural Bangladesh.

METHODS

Paramedics underwent intensive training (6 weeks) including hands-on practice then underwent a series of standardization exercises. Measurements of each fetus were taken by a highly-trained medical doctor (study supervisor) and the nine paramedics. Crown-rump length (CRL) in fetuses of less than 10 weeks' gestation, and biparietal diameter (BPD), occipitofrontal diameter, head and abdominal circumference (AC) and femur diaphysis length (FL) were measured twice using standard procedures by each paramedic and the medical doctor for each fetus, with at least 20 min between them. Precision was quantified using variance components analysis; the intraobserver error for each of the paramedics was calculated by comparing repeat measurements taken on the same participant, and the measurements obtained by each individual paramedic were also compared with those taken by the others (interobserver error). Accuracy was estimated by comparing the mean of the two measures taken by each paramedic to those taken by the study supervisor using paired t-tests. Bland-Altman plots were used to visually assess the relationship between precision of repeat measurements (intraobserver error) and fetal size.

RESULTS

A total of 180 women, at 7 to 31 weeks' gestation, participated in the study. Intraobserver error of the measurements obtained by the paramedics, expressed as the mean SD, ranged from 0.97 mm for BPD in the first trimester to 7.25 mm for AC in the third trimester, and was larger than the interobserver error (i.e. accounting for a greater proportion of total variance) for most measurements. Interobserver error ranged from 0.00 mm for FL to 3.36 mm for AC, both in the third trimester. For all measurements except CRL, intraobserver error increased with increasing fetal size. The measurements obtained by the paramedics did show some statistically significant differences from those obtained by the study supervisor, but these were relatively small in magnitude.

CONCLUSIONS

Both inter- and intraobserver measurement errors were within the range reported in the literature for studies conducted by technical staff and medical doctors. With intense training, paramedics with no prior exposure to ultrasonography can provide accurate and precise measures of fetal biometry.

Incurred sample reanalysis: enhancing the Bland–Altman approach with tolerance intervals

This article describes the need for incurred sample reanalysis and suggests that the combination of a Bland–Altman plot and tolerance intervals can provide a visual evaluation of method performance. It also shows how the proposed combination is a tool that may be of value in determining minimum sample size. An example dataset is worked through in its entirety so that a reader unfamiliar with the topic can gain sufficient information to analyze their own data. Related topics include the generation of 66.7% tolerance factors, comparison of mean-normalized and log differences and the use of probability plots to evaluate error distributions. The suggestions presented in this article are meant to be a continuation of the ongoing incurred sample reanalysis discussion and, as such, further comment is invited.

A novel online Food Recall Checklist for use in an undergraduate student population: a comparison with diet diaries

BACKGROUND

University students are commonly overlooked when diet of populations is measured and there is a lack of comprehensive dietary assessment in whole university student populations. To measure diet of undergraduate students, a new online 121-item Food Recall Checklist (FoRC) was designed as an alternative to a non-weighed record (food diary). This article reports the comparison between the new dietary assessment method (FoRC) and the food diary as a measure of energy (kJ), fat (g), Non-Starch Polysaccharide (NSP) (g), fruit and vegetables (g), breakfast cereal (g) and bread (g) and alcohol (units) intake.

METHODS

Fifty-three students at the University of Aberdeen completed four days of FoRC then four days food diary. Median agreement and correlation between the two methods was assessed for foods and nutrients using the Spearman's rank correlation co-efficient and the Wilcoxon signed ranks test. Agreement between FoRC and food diary was assessed using the Bland-Altman method.

RESULTS

The mean time taken to complete FoRC for one day was 7.4 minutes. Intakes of fat (g and % food energy), NSP and bread were similar between FoRC and the food diary. Median energy intake was 8185 kJ in the food diary and 8007 kJ in FoRC. However, FoRC recorded significantly lower intakes of energy and alcohol and significantly higher intakes of fruit and vegetables and breakfast cereal compared with the food diary. There was considerable variation in agreement between methods at the individual level. For all variables except alcohol and percentage energy from fat, correlation co-efficients were statistically significant and greater than 0.5.

CONCLUSION

At the group level, four days of FoRC showed good median agreement with the food diary and there was high correlation between methods for most foods and nutrients. This suggests that this novel method of assessing diet can provide a useful alternative for assessing group mean intakes but that individual intakes may need to be interpreted with care.

Reliability and validity of an activity monitor (IDEEA) in the determination of temporal-spatial gait parameters in individuals with cerebral palsy

This study evaluated within- and between-session reliability and validity of temporal-spatial gait parameters derived from the intelligent device for energy expenditure and activity (IDEEA) activity monitor (Minisun, Fresno, CA) in subjects with cerebral palsy, using three-dimensional gait analysis (3-DGA) as the criterion standard. Twenty-five subjects with cerebral palsy (mean age 14.1 years, range 8-23) and 30 control subjects (mean age 14.2 years, range 7-24) completed two 3-DGA, 1 week apart with simultaneous IDEEA data collection. The IDEEA had lower within-session reliability than the 3-DGA for both groups, indicated by greater measurement errors and wider repeatability values for all temporal-spatial parameters. Between-session reliability of 3-DGA was high for both groups with intra-class correlation coefficients (ICC) >0.80. The IDEEA monitor showed high between-session reliability for control subjects (ICC 0.71-0.89), but lower reliability in subjects with cerebral palsy, particularly for walking velocity and stride length (ICC 0.53 and 0.62, respectively). Validity comparison between IDEEA and 3-DGA measures using Bland Altman 95% limits of agreement showed a measurement bias, with the IDEEA over-estimating step and stride length and underestimating cadence in both subject groups compared to 3-DGA. The 95% limits of agreement were smaller in controls (step +/-0.20 m; stride +/-0.27 m; walking velocity +/-0.28 m/s) than in subjects with cerebral palsy (step +/-0.36 m; stride +/-0.37 m; velocity +/-0.58 m/s). Modifications may be necessary to improve the reliability and validity of the IDEEA in children, particularly for use in neurological conditions.

Tympanic membrane versus temporal artery temperatures of adult perianesthesia patients

Reaching preoperative temperature stability is a critical discharge criterion afer anesthesia and surgery. Although numerous methods of measuring temperature exist, tympanic membrane (TM) thermometers have replaced oral thermometers in most perianesthesia units. With reliability of tympanic temperature readings being questioned in numerous reports and by many practitioners, the temporal artery (TA) thermometer has gained popularity among perianesthesia nurses for its noninvasive approach and ease of operation. A prospective study was undertaken to determine the ability of the TA thermometer to substitute for the TM thermometer in adult perianesthesia patients.

How to use linear regression and correlation in quantitative method comparison studies

Linear regression methods try to determine the best linear relationship between data points while correlation coefficients assess the association (as opposed to agreement) between the two methods. Linear regression and correlation play an important part in the interpretation of quantitative method comparison studies. Their major strength is that they are widely known and as a result both are employed in the vast majority of method comparison studies. While previously performed by hand, the availability of statistical packages means that regression analysis is usually performed by software packages including MS Excel, with or without the software programe Analyze-it as well as by other software packages. Such techniques need to be employed in a way that compares the agreement between the two methods examined and more importantly, because we are dealing with individual patients, whether the degree of agreement is clinically acceptable. Despite their use for many years, there is a lot of ignorance about the validity as well as the pros and cons of linear regression and correlation techniques. This review article describes the types of linear regression and regression (parametric and non-parametric methods) and the necessary general and specific requirements. The selection of the type of regression depends on where one has been trained, the tradition of the laboratory and the availability of adequate software.

Bymixer system can measure O2 uptake and CO2 elimination in the anesthesia circle circuit

BACKGROUND

The ability to measure carbon dioxide elimination (Vco(2)), oxygen uptake (Vo(2)), and R (respiratory exchange ratio, Vco(2)/Vo(2)) during anesthesia may help the non-invasive detection of critical events (e.g., abrupt decrease in cardiac output) and metabolic upset (e.g., onset of anaerobic metabolism).

METHODS

We have developed a new clinical bymixer (inline mixing chamber) that can measure mixed inspired and expired gas fractions in the anesthesia circle circuit. The addition of a standard anesthesia gas analyzer and flowmeter, and a new airway temperature and humidity sensor, allow determinations of Vco(2) and Vo(2) at the airway opening of the circle circuit. Over a range of tidal volume and frequency, Vco(2) and Vo(2) were compared to reference values generated by the combustion of metered liquid ethanol in a new metabolic lung simulator.

RESULTS

By linear regression, bymixer-flow measurements of Vco(2) (slope = 1.02, Y-intercept = -5.31, coefficient of determination, R(2) = 0.998) and Vo(2) (slope = 1.05, Y-intercept = -4.34, R(2) = 0.993) correlated closely to the reference values generated by the metabolic lung simulator. Limits of agreement analysis generated percent errors (mean +/- 1.96 SD) of -1.2 +/- 7.2% for Vco(2) and 2.5 +/- 9.8% for Vo(2).

CONCLUSIONS

The new clinical bymixer is compact, lightweight, disposable, inexpensive, and has a fast and adjustable response time (time constant about 14 sec). Anesthesia circle circuit integrity is maintained. Bymixer-flow measurements of Vco(2) and Vo(2) are accurate and may add to clinical monitoring under anesthesia and surgery.

Importance and Interpretation of Fast-Response Airway Hygrometry During Ventilation of Anesthetized Patients

BACKGROUND

Measurement of oxygen uptake (Vo2) should help detect non-steady state critical events and metabolic derangement during anesthesia. Vo2 requires measurement of respiratory relative humidity (RH) and temperature (T). We have developed a fast response T and humidity sensor (HS), which uses tiny wet and dry thermometers to determine RH by psychrometry, where low RH causes evaporation to decrease wet T below dry T. In laboratory bench studies, we determined that >/=5 l/min gas flow through the HS is required for valid psychrometry function. This study demonstrates that monitoring of flow through the HS enhances the accuracy of RH measurement and interpretation.

METHODS

Phase One: Laboratory bench validation; We designed a special bench setup for the validation of metabolic gas exchange compared to precise ethanol combustion. Phase 2: Clinical study; During mechanical ventilation of 6 anesthetized surgical patients, airway flow was used to successfully select valid wet T and dry T during inspiration and expiration, from which respective RH's were calculated using principles of psychrometry.

RESULTS

The average (+/-SD) percent error for airway Vco2 (compared to the stoichiometric value) was -1.84 +/- 2.69% (Table 2). The average (+/-SD) percent error for airway Vo2 was 0.91 +/- 3.10%. Average RQ was 0.649 +/- 0.017. For all patients, average inspired RH was 36.1 +/- 11.8% (range of 17-52%), which differed significantly from expiration (103 +/- 9%). Among the 6-8 consecutive breaths for each patient, average standard deviations of expired RH were only 0.6%.

CONCLUSION

We conclude that airway flow monitoring enhances the interpretation and accuracy of the fast-response HS measurements during inspiration and expiration, allowing for the determination of Vo2 in patients during anesthesia.

New metabolic lung simulator: development, description, and validation

OBJECTIVE

Indirect calorimetry, the determination of airway carbon dioxide elimination (V(CO2),and oxygen uptake (V(O2)), can be used to non-invasively detect non-steady state perturbations of gas kinetics and mirror tissue metabolism. Validation of monitoring instruments in patients is difficult because there is no standard reference measurement, a wide range of physiologic values is required, and steady state is difficult to achieve and confirm. We present the development, critical details, and validation of a practical bench setup of a metabolic lung simulator, to generate a wide range of accurate, adjustable, and stable reference values of V(CO2) and V(O2), for development, calibration, and validation of indirect calorimetry methodology and clinical monitors.

METHODS

We utilized a metered alcohol combustion system, which allowed safe, precise, and adjustable delivery of ethanol to a specially designed wick system to stoichiometrically generate reference V(CO2) and V(O2). Gas was pumped through a circular circuit between the separate metabolic chamber and mechanical lung, to preserve basic features of mammalian gas kinetics, including a physiologic ventilation waveform and the ability to induce non-steady state changes. Accurate and precise generation of V(CO2) and V(O2) were validated against separate measurements of gas flow and gas fractions in a collection bag.

RESULTS

For volume control ventilation, average error for V(CO2) and V(O2) was -0.16% +/- 1.77 and 1.68% +/- 3.95, respectively. For pressure control ventilation, average error for V(CO2) and V(O2) was 0.90% +/- 2.48% and 4.86% +/- 2.21% respectively. Low values of measured ethanol vapor and carbon monoxide supported complete and pure combustion.

CONCLUSIONS

The comprehensive description details the solutions to many problems, to help future investigations of metabolic gas exchange and contribute to improved patient monitoring during anesthesia and critical care medicine.

Extent of agreement in gentamicin concentration between serum that is drawn peripherally and from central venous catheters

OBJECTIVE

At our institution, patients who receive once-daily dosing of gentamicin have serum concentrations determined 3 and 6 hours after dose administration. Patients with single-lumen central venous catheters have the 3-hour samples drawn peripherally. The objective of this study was to evaluate the extent of agreement between peripheral and central venous catheter serum gentamicin concentrations drawn 3 hours after dose administration.

METHODS

In this prospective, observational study, patients provided both a peripheral and a central blood sample for determination of serum gentamicin concentration. The order of sampling (central venous catheter versus peripheral first) was randomized. Agreement was assessed by determination of the intraclass correlation coefficient and Bland-Altman analysis. The clinically acceptable targets for the lower limit of the intraclass correlation coefficient and Bland-Altman limits of agreement were defined a priori as >0.80 and +/-6%, respectively. Differences between the theoretical dose adjustments using the central venous catheter versus the peripheral sample result were described.

RESULTS

Forty-five pairs of samples were collected: 42 from single-lumen implantable central venous catheters (ports) and 3 from peripherally inserted central venous catheters. The intraclass correlation coefficient was 0.91. However, the Bland-Altman analysis resulted in a mean percentage difference (central venous catheter versus peripheral) of -0.92% and limits of agreement of -27.9% to 26.0%. The gentamicin dose adjustment based on the central venous catheter sample result would have led to clinically significant dose adjustments in 19 (42%) cases, when compared with the peripheral sample result.

CONCLUSIONS

These results indicate a lack of agreement between peripheral and single-lumen central venous catheter samples. In particular, ports are not appropriate sites for monitoring serum gentamicin concentrations.

Comparison of insulin sensitivity assessment indices with euglycemic-hyperinsulinemic clamp data after a dietary and exercise intervention in older adults

Multiple indices to assess insulin sensitivity calculated from mathematical equations based on fasting blood parameters or oral glucose tolerance data have been developed. Although these indices have frequently been validated using euglycemic-hyperinsulinemic clamp data, the utility of each equation in measuring change in insulin sensitivity over time remains uncertain. We examined change in insulin sensitivity in response to a 12-week diet and exercise intervention in 31 older men and women with impaired glucose tolerance using a euglycemic-hyperinsulinemic clamp and 10 commonly used insulin sensitivity equations. Mean glucose disposal as calculated from clamp data was significantly higher after the intervention compared with baseline (5.92 +/- 0.38 vs 5.18 +/- 0.30 mg . kg fat free mass(-1) . min(-1), P = .013). In contrast, none of the examined indices indicated a significant change in insulin sensitivity over time (all P > .3). A limits of agreement approach to compare insulin sensitivity calculated from each equation with the measure of glucose disposal from the clamp indicated overall imperfect agreement between measures (agreement limits ranged from +/-2.48 to +/-4.23 mg . kg fat free mass(-1) . min(-1)) despite significant bivariate correlations between indices and clamp data. The wide variability in the 95% prediction limits of agreement among equations suggests that these equations vary substantially from a euglycemic-hyperinsulinemic clamp in their ability to assess insulin sensitivity. Despite the observed limited agreement using this statistical approach, changes in several calculated indices were significantly correlated with changes in clamp data, suggesting that these indices may have some utility in tracking improvements in insulin sensitivity. Further research is necessary to examine agreement between indices and clamp data in larger, more heterogeneous populations and in response to other interventions where the magnitude of change in insulin sensitivity may be larger.

An enzymatic clinical chemistry laboratory experiment incorporating an introduction to mathematical method comparison techniques

An enzymatic laboratory experiment based on the analysis of serum is described that is suitable for students of clinical chemistry. The experiment incorporates an introduction to mathematical method-comparison techniques in which three different clinical glucose analysis methods are compared using linear regression and Bland-Altman difference plots. The experiment may also be undertaken using simple glucose solutions by general biochemistry students.

Novel, Adjustable, Clinical Bymixer Measures Mixed Expired Gas Concentrations in Anesthesia Circle Circuit

We have introduced a novel, parallel design into a new clinical bymixer (patent pending), named for the bypass of a constant fraction of total flow through a mixing chamber. Over a wide range of tidal volumes (300-1200 mL), frequency (6-20 breaths/min), and PCO(2) (6-50 mm Hg), the bymixer provided accurate measurement of mixed expired gas fractions in the ventilation circuit compared with an expired gas collection in a metabolic lung bench setup (average slope, 1.00; average y intercept, -0.01; average coefficient of determination, R(2) = 0.9988). Simple changes in mixing chamber volume provided adjustable bymixer response times. The fast bymixer response (time constant, 6.4 s) should allow measurements to be updated every 20 s (where 95% response occurs by three time constants). The new clinical bymixer is constructed from standard anesthesia circuit components, attaches easily to the anesthesia machine inspired outlet and expired inlet ports, is simple to clean and sterilize, and has no reservoir to trap condensed water vapor from expired gas. The new clinical bymixer may facilitate indirect calorimetry (CO(2) elimination, VCO(2), and oxygen uptake, VCO(2)) during anesthesia and the noninvasive detection of metabolic upset (e.g., onset of anaerobic metabolism) and critical events (e.g., pulmonary embolism).

IMPLICATIONS

A new clinical bymixer (inline mixing chamber) provides a fast response and accurate measurements of mixed expired gas fractions in the anesthesia circle circuit. A novel parallel design facilitates adjustable response, easy cleaning, and construction from standard airway circuit components. The new clinical bymixer may facilitate widespread introduction of indirect calorimetry during anesthesia.