Combining electromyographic and electrical impedance data sets through machine learning: A study in D2-mdx and wild-type mice

INTRODUCTION/AIMS

Needle impedance-electromyography (iEMG) assesses the active and passive electrical properties of muscles concurrently by using a novel needle with six electrodes, two for EMG and four for electrical impedance myography (EIM). Here, we assessed an approach for combining multifrequency EMG and EIM data via machine learning (ML) to discriminate D2-mdx muscular dystrophy and wild-type (WT) mouse skeletal muscle.

METHODS

iEMG data were obtained from quadriceps of D2-mdx mice, a muscular dystrophy model, and WT animals. EIM data were collected with the animals under deep anesthesia and EMG data collected under light anesthesia, allowing for limited spontaneous movement. Fourier transformation was performed on the EMG data to provide power spectra that were sampled across the frequency range using three different approaches. Random forest-based, nested ML was applied to the EIM and EMG data sets separately and then together to assess healthy versus disease category classification using a nested cross-validation procedure.

RESULTS

Data from 20 D2-mdx and 20 WT limbs were analyzed. EIM data fared better than EMG data in differentiating healthy from disease mice with 93.1% versus 75.6% accuracy, respectively. Combining EIM and EMG data sets yielded similar performance as EIM data alone with 92.2% accuracy.

DISCUSSION

We have demonstrated an ML-based approach for combining EIM and EMG data obtained with an iEMG needle. While EIM-EMG in combination fared no better than EIM alone with this data set, the approach used here demonstrates a novel method of combining the two techniques to characterize the full electrical properties of skeletal muscle.

High CD4+:CD8+ ratios with herpes zoster infections in patients with multiple sclerosis on dimethyl fumarate

BACKGROUND

Dimethyl fumarate (DMF) depletes CD8+ and CD4+ T cells, and cases of herpes zoster (HZ) in patients with multiple sclerosis (MS) on DMF have been documented.

OBJECTIVES

To evaluate lymphocyte subsets in patients with MS who developed HZ on DMF (Tecfidera) compared to matched controls who did not develop HZ.

METHODS

We used linear mixed-effects models to test for differences in white blood cell count, lymphocyte percentage, absolute lymphocyte count, CD3+ percentage, absolute CD3+ count, CD4+ percentage, absolute CD4+ count, CD8+ percentage, absolute CD8+ count, and CD4+:CD8+ ratio over time in HZ and non-HZ groups.

RESULTS

Eighteen patients developed HZ while on DMF. The linear mixed-effects model for CD4+:CD8+ ratio showed a significant difference between the HZ and non-HZ groups (p = 0.033). CD4+:CD8+ ratio decreased over time in the HZ group and increased over time in the non-HZ group.

CONCLUSION

Patients with MS who develop HZ while on DMF have high CD4+:CD8+ ratios, suggesting an imbalance of CD4+ and CD8+ cells that may put a patient at risk for developing HZ while on DMF. This result emphasizes the need for lymphocyte subset monitoring (including CD4+:CD8+ ratios) on DMF, as well as vaccination prior to DMF initiation.

Surface Electrical Impedance Myography Detects Skeletal Muscle Atrophy in Aged Wildtype Zebrafish and Aged gpr27 Knockout Zebrafish

Throughout a vertebrate organism's lifespan, skeletal muscle mass and function progressively decline. This age-related condition is termed sarcopenia. In humans, sarcopenia is associated with risk of falling, cardiovascular disease, and all-cause mortality. As the world population ages, projected to reach 2 billion older adults worldwide in 2050, the economic burden on the healthcare system is also projected to increase considerably. Currently, there are no pharmacological treatments for sarcopenia, and given the long-term nature of aging studies, high-throughput chemical screens are impractical in mammalian models. Zebrafish is a promising, up-and-coming vertebrate model in the field of sarcopenia that could fill this gap. Here, we developed a surface electrical impedance myography (sEIM) platform to assess skeletal muscle health, quantitatively and noninvasively, in adult zebrafish (young, aged, and genetic mutant animals). In aged zebrafish (~85% lifespan) as compared to young zebrafish (~20% lifespan), sEIM parameters (2 kHz phase angle, 2 kHz reactance, and 2 kHz resistance) robustly detected muscle atrophy (p < 0.000001, q = 0.000002; p = 0.000004, q = 0.000006; p = 0.000867, q = 0.000683, respectively). Moreover, these same measurements exhibited strong correlations with an established morphometric parameter of muscle atrophy (myofiber cross-sectional area), as determined by histological-based morphometric analysis (r = 0.831, p = 2 × 10-12; r = 0.6959, p = 2 × 10-8; and r = 0.7220; p = 4 × 10-9, respectively). Finally, the genetic deletion of gpr27, an orphan G-protein coupled receptor (GPCR), exacerbated the atrophy of skeletal muscle in aged animals, as evidenced by both sEIM and histology. In conclusion, the data here show that surface EIM techniques can effectively discriminate between healthy young and sarcopenic aged muscle as well as the advanced atrophied muscle in the gpr27 KO animals. Moreover, these studies show how EIM values correlate with cell size across the animals, making it potentially possible to utilize sEIM as a "virtual biopsy" in zebrafish to noninvasively assess myofiber atrophy, a valuable measure for muscle and gerontology research.

Electrical impedance dermography differentiates squamous cell carcinoma in situ from inflamed seborrheic keratoses

There are no currently available low-cost, noninvasive methods for discerning the depth of squamous cell carcinoma (SCC) invasion or distinguishing SCC from its benign mimics, such as inflamed seborrheic keratosis (SK). We studied 35 subjects with subsequently confirmed SCC or SK. Subjects underwent electrical impedance dermography measurements at six frequencies to assess the electrical properties of the lesion. Averaged greatest intrasession reproducibility values were 0.630 for invasive SCC at 128 kHz, 0.444 for SCC in situ at 16 kHz, and 0.460 for SK at 128 kHz. Electrical impedance dermography modeling revealed significant differences between SCC and inflamed SK in normal skin (P < 0.001) and also between invasive SCC and SCC in situ (P < 0.001), invasive SCC and inflamed SK (P < 0.001), and SCC in situ and inflamed SK (P < 0.001). A diagnostic algorithm classified SCC in situ from inflamed SK with an accuracy of 0.958, a sensitivity of 94.6%, and a specificity of 96.9%; it also classified SCC in situ from normal skin with an accuracy of 0.796, a sensitivity of 90.2%, and a specificity of 51.2%. This study provides preliminary data and a methodology that can be used in future studies to further advance the value of electrical impedance dermography and inform biopsy decision making in patients with lesions suspicious of SCC.

Electrical Impedance Myography Correlates with Functional Measures of Disease Progression in D2-mdx Mice and Boys with Duchenne Muscular Dystrophy

BACKGROUND

Sensitive, objective, and longitudinal outcome measures applicable to both pre-clinical and clinical interventions are needed to assess muscle health in Duchenne muscular dystrophy (DMD). Electrical impedance myography (EIM) has the potential to non-invasively measure disease progression in mice and boys with DMD.

OBJECTIVE

We sought to evaluate how electrical impedance values (i.e., phase, reactance, and resistance) correlate to established measures of disease in both D2-mdx and wild type (WT) mice and boys with and without DMD.

METHODS

Histological, functional, and EIM data collected from previous studies of WT and D2-mdx mice at 6, 13, 21 and 43 weeks of age were reanalyzed. In parallel, previously collected functional outcome measures and EIM values were reanalyzed from boys with and without DMD at four different age groups from 2 to 14 years old.

RESULTS

In mice, disease progression as detected by histological, functional, and EIM measures, was appreciable over this time period and grip strength best correlated to longitudinal phase and reactance impedance values. In boys, disease progression quantified through commonly utilized functional outcome measures was significant and longitudinal phase demonstrated the strongest correlation with functional outcome measures.

CONCLUSION

Similar changes in EIM values, specifically in longitudinal reactance and phase, were found to show significant correlations to functional measures in both mice and boys. Thus, EIM demonstrates applicability in both pre-clinical and clinical settings and can be used as a safe, non-invasive, and longitudinal proxy biomarker to assess muscle health in DMD.

0609 Sleep Stabilization in Prehypertensive/Hypertensive Patients

Introduction

Variable sleep/wake patterns have been linked to increased cardiometabolic risk. The current project investigates the effects of using sleep hygiene interventions to stabilize sleep timing in prehypertensive/hypertensive patients. Growing evidence supports the importance of regularizing sleep timing in improving cardiovascular health, and we believe that using sleep hygiene techniques to stabilize sleep may reduce these risks.

Methods

As part of a larger study, fifty-three participants (55.5 ± 1.4 years; 51% male) completed sleep diaries during 3 study periods. The first period (S1) was a baseline control, the second period (S2) was a 4-week wait-list control condition, and the third period (S3) was an 8-week randomly assigned intervention that used sleep hygiene approaches and scheduling to stabilize sleep timing or stabilize and lengthen sleep. Currently, we are still blind to condition; however, because both conditions involve sleep stabilization, an analysis using linear mixed models was used to assess change in the variability of total sleep time (SDTST), wake up time (SDWUT), and fall asleep time (SDFAT) across the 3 study periods.

Results

There was a significant decrease in SDTST variability (standard deviation) at post-intervention (S3) compared to S2 (p&lt;0.01) and S1 (p&lt;0.01). There was also a significant decrease in SDWUT variability at post-intervention (S3) compared to S2 (p&lt;0.01) and S1 (p&lt;0.01). There was a trend towards a significantly decreased SDFAT at S3 compared to S2 (p=0.057), but there was a significant decrease in SDFAT variability during S3 compared to S1 (p&lt;0.01).

Conclusion

These data suggest that we were able to utilize sleep hygiene interventions to decrease the variability in total sleep time, wake-up time and fall asleep time. When we unblind we will report on if we were able to increase and lengthen the sleep period for those in the sleep extension condition.

Support (If Any)

NIH (R01HL125379 to Dr. Janet Mullington), Harvard Catalyst, Harvard Clinical and Translational Science Center (UL1TR001102)

Improved ALS clinical trials through frequent at-home self-assessment: a proof of concept study

OBJECTIVE

To determine the potential for improving amyotrophic lateral sclerosis (ALS) clinical trials by having patients or caregivers perform frequent self-assessments at home.

METHODS AND PARTICIPANTS

We enrolled ALS patients into a nonblinded, longitudinal 9-month study in which patients and caregivers obtained daily data using several different instruments, including a slow-vital capacity device, a hand grip dynamometer, an electrical impedance myography-based fitness device, an activity tracker, a speech app, and the ALS functional rating scale-revised. Questions as to acceptability were asked at two time points.

RESULTS

A total of 113 individuals enrolled, with 61 (43 men, 18 women, mean age 60.1 ± 9.9 years) collecting a minimum of 7 days data and being included in the analysis. Daily measurements resulted in more accurate assessments of the slope of progression of the disease, resulting in smaller sample size estimates for a hypothetical clinical trial. For example, by performing daily slow-vital capacity measurements, calculated sample size was reduced to 182 subjects/study arm from 882/arm for monthly measurements. Similarly, performing the ALS functional rating scale weekly rather than monthly led to a calculated sample size of 73/arm as compared to 274/arm. Participants generally found the procedures acceptable and, for many, improved their sense of control of their disease.

INTERPRETATION

Frequent at-home measurements using standard tools holds the prospect of tracking progression and reducing sample size requirements for clinical trials in ALS while also being acceptable to the patients. Future studies in this and other neurological disorders should consider adopting this approach to data collection.

A Serious Flaw in Nutrition Epidemiology: A Meta-Analysis Study

Background Many researchers have studied the relationship between diet and health. Specifically, there are papers showing an association between the consumption of sugar sweetened beverages and Type 2 diabetes. Many meta-analyses use individual studies that do not attempt to adjust for multiple testing or multiple modeling. Hence the claims reported in a meta-analysis paper may be unreliable as the base papers do not ensure unbiased statistics. Objective Determine (i) the statistical reliability of 10 papers and (ii) indirectly the reliability of the meta-analysis study. Method We obtained copies of each of the 10 papers used in a metaanalysis paper and counted the numbers of outcomes, predictors, and covariates. We estimate the size of the potential analysis search space available to the authors of these papers; i. e. the number of comparisons and models available. The potential analysis search space is the number of outcomes times the number of predictors times 2 c , where c is the number of covariates. This formula was applied to information found in the abstracts (Space A) as well as the text (Space T) of each base paper. Results The median and range of the number of comparisons possible across the base papers are 6.5 and (2 12,288), respectively for Space A, and 196,608 and (3072-117,117,952), respectively for Space T. It is noted that the median of 6.5 for Space A may be misleading as each study has 60-165 foods that could be predictors. Conclusion Given that testing is at the 5% level and the number of comparisons is very large, nominal statistical significance is very weak support for a claim. The claims in these papers are not statistically supported and hence are unreliable so the meta-analysis paper is also unreliable.

Abstract A55: Assessing the applicability of leventhal's common sense model of illness representation to explain african american prostate cancer survivors' disease experiences and disease Management Strategies

Background: Culture has a major influence on many aspects of health in general, and cancer prevention and control in particular. Culture influences the receptiveness of consensus and evidence-based risk reduction strategies across the continuum of care. Culture also provides men with templates for interacting with clinicians and the health care system. Over the past two decades, medical and public health practitioners have devoted a great deal of attention to understanding how African American culture influences the multi-level processes that create or maintain prostate cancer treatment disparities. The current study adds to this growing body of literature by exploring the usefulness of Leventhal's Common Sense Model (CSM) of Illness Representation to explain the content and structure of African American prostate cancer survivors' narratives of their disease process and disease management strategies. Narrative structure was evaluated using the five illness representation domains of the CSM (i.e., cause, control/cure, consequences, identity, and, timeline). Narrative content was explored using investigator created sub-themes representing each illness representation domain. Methods: A purposive sample of prostate cancer survivors was recruited via cancer registries, word-of-mouth and newspaper advertisements in New York and Georgia from 2013 to 2014. Survivors were eligible to participate if they were diagnosed with localized prostate cancer (T1 or T2), able to speak and understand English, and self-identified as African American. Each participant completed a semi-structured, in-depth interview with a graduate trained interviewer. All men provided written informed consent and received a $50 incentive for their participation. Each interview was audiotape recorded, transcribed verbatim by a professional transcriptionist and entered into MAXQDA12 software for data management and analysis. All transcribed interviews were coded independently by a three-member team until a minimum of 80% coding agreement was reached. Results: A total of 15 men completed in-depth interviews. All interviews lasted between 30 - 90 minutes. With regard to narrative structure, survivors provided descriptions characterizing all five of the illness representation domains. More survivors provided descriptions relating to causes and consequences, while fewer provided descriptions related to the timeline domain. With regard to coping, many interviewees reported that it was challenging to simultaneously develop a treatment care plan while managing their emotions. Most descriptions of the consequences centered around concerns men had related to treatment rather than having the disease. Several interviewees expressed concerns about limitations placed on their personal and social relationships as a result of treatment complications. With regard to emotional coping, men reported a variety of adaptive and maladaptive strategies including acceptance, avoidance, humor, religion, and shared decision-making with family members and significant others. Despite these concerns, most men were grateful to be alive and were optimistic about their prognosis. Conclusion: The results of this research suggest that the CSM can be used to explain African American prostate cancer survivors' experiences with treatment care planning and coping. Future research should elucidate culturally acceptable strategies to help men simultaneously develop treatment plans and deal with the emotional aspect of having this disease. Future research should also focus on identifying similarities and differences between African American and White survivors using the CSM to determine if unique or one-size-fits all interventions are sufficient.

Citation Format: Jarrett Johnson, Sarbesh Pandeya, Ahmed Kabore, Levi Ross. Assessing the applicability of leventhal's common sense model of illness representation to explain african american prostate cancer survivors' disease experiences and disease Management Strategies. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr A55.

Abstract A54: Examining sociodemographic differences in unmet treatment information needs among localized prostate cancer survivors

Background: Prostate cancer is the most commonly diagnosed cancer among men living in the United States. All men diagnosed with prostate cancer must undergo the complex process of treatment decision-making. Men have to be exposed to a range of issues related to treatment care planning and aftercare before they can make an informed treatment choice. The literature suggests that many men make prostate cancer treatment decisions before having all of their information needs satisfied. Patients who do not satisfy all of their information needs before undergoing treatment will have unmet needs. Men with unmet needs are more susceptible to making ill-informed choices and selecting treatment options that are poorly aligned with their preferences. Objectives: To quantify levels of unmet treatment information needs and to explore sociodemographic correlates of unmet needs among a sample of localized prostate cancer survivors. Methodology: From 2013 to 2014, sixty-three prostate cancer survivors completed self-administered surveys on a touch-screen computer. All participants were 40 years or older, self-identified as African American or White, was treated for or actively monitoring localized prostate cancer (Stage T1 or T2), and lived or worked in Western New York or Georgia. The survey collected information on sociodemographic variables, information seeking behavior, and treatment information needs. Unmet treatment information needs were classified as details or issues that survivors deemed important to know but did not explore before making their treatment decision. Each of the 20 treatment information need items was rated as “0 = unimportant” or “1= important”. An unmet needs composite scale was created which ranged from 0 - 20 (α = 0.895). Univariate statistics (frequencies, means and standard deviations) were computed to describe the study sample. Bivariate (T-test, ANOVA and Chi-square) and multivariate statistics were computed to examine associations between study variables. Significance levels for all statistical procedures was set at p ≤ 0.05. Results: Most participants were White (58.7%), college graduates (54.0%), not working (58.7%), married (78.4%) and had annual household incomes of $45,000+ (49.2%). A majority of participants (57.0%) reported at least one unmet information need (range = 0 – 19 unmet needs, mean = 2.83). African Americans reported more unmet needs than Whites (3.64African American vs. 2.50Whites). Results from multiple linear regression analysis indicated that race (β = -2.14, p = 0.05), income (β = -4.60, p = 0.01), and insurance status (β = 6.73, p = 0.01) were significant predictors of unmet information need (F(9,41) = 2.34; p = 0.03). African Americans were less likely to get information they wanted about “How different treatment options work (χ2 = 0.02)” and “How much time is required to complete treatment (χ2 = 0.04).” Conclusions: These results suggest that many prostate cancer patients do not receive all of the information they deem important for treatment decision-making. Treatment information seeking behavior appears to be an emerging area of disparity for African Americans and men with lower income. Patient centered interventions need to be developed and implemented to reduce unmet treatment information needs within these medically underserved populations.

Citation Format: Jarrett Johnson, Sarbesh Pandeya, Ahmed Kabore, Stuart H. Tedders, Levi Ross. Examining sociodemographic differences in unmet treatment information needs among localized prostate cancer survivors. [abstract]. In: Proceedings of the Ninth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2016 Sep 25-28; Fort Lauderdale, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(2 Suppl):Abstract nr A54.

Georgia's collaborative approach to expanding mosquito surveillance in response to Zika virus: a case study

Zika virus (ZIKV) was declared an international public health emergency by the World Health Organization on February 1, 2016. Due to the known and estimated range of the ZIKV mosquito vectors, southern and central US states faced increased risk of ZIKV transmission. With the state of Georgia hosting the world's busiest international airport, a climate that supports the ZIKV vectors, and limited surveillance (13 counties) and response capacity, the Department of Public Health (DPH) was challenged to respond and prevent ZIKV transmission. This case study describes and evaluates the state's surveillance capacity before and after the declaration of ZIKV as a public health emergency.

METHOD

We analyzed surveillance data from the DPH to compare the geographical distribution of counties conducting surveillance, total number, and overall percentage of mosquito species trapped in 2015 to 2016. Counties conducting surveillance before and after the identification of the ZIKV risk were mapped using ArcMap 10.4.1. Using SAS (version 9.2) (SAS Institute, Inc, Cary, NC), we performed the independent 2 sample t test to test for differences in prevalence in both years, and a χ² analysis to test for differences between numbers of species across the 13 counties. In addition, weighted frequency counts of mosquitoes were used to test (χ²) an association between major mosquito vector species and 7 urban counties. Lastly, using data from 2012-2016, a time-trend analysis was conducted to evaluate temporal trends in species prevalence.

RESULTS

From 2015 to 2016, surveillance increased from 13 to 57 (338% increase) counties geographically dispersed across Georgia. A total of 76,052 mosquitoes were trapped and identified in 2015 compared to 144,731 (90.3% increase) in 2016. Significant differences between species (P<.001) and significant associations (P<.0001) between 7 urban counties and major mosquito vectors were found. Significant differences in prevalence were found between several species and year highlighting species-year temporal trends.

CONCLUSIONS

The DPH collaborative response to ZIKV allowed a rapid increase in its surveillance footprint. Existing and new partnerships were developed with the military and local health departments to expand and share data. This additional surveillance data allowed DPH to make sound public health decisions regarding mosquito-borne disease risks and close gaps in data related to vector distribution.

Cardiac risk factors and the use of cardioprotective medications in patients with chronic renal insufficiency

Cardiovascular disease (CVD) is a major cause of morbidity and mortality among patients with chronic renal insufficiency (CRI). beta-Adrenergic blockers, acetylsalicylic acid (ASA), angiotensin-converting enzyme (ACE) inhibitors, and 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) all reduce CVD mortality, but little is known about the extent to which these medications are used in patients with CRI. This study, a prospective cross-sectional study of consecutive patients seen by nephrologists in four Canadian centers for follow-up of progressive CRI in 1999, was performed to investigate the prevalence of coronary risk factors and use of cardioprotective medications among patients with CRI. Patients had creatinine clearances of 75 mL/min or less but were not on dialysis therapy. Three hundred four consecutive patients meeting the inclusion criteria were enrolled. Mean age was 60.8 +/- 15.7 years, mean creatinine clearance was 30.3 +/- 18 mL/min, and the case mix of kidney diseases was similar to that in the Canadian Organ Replacement Registry data. One hundred seventeen of 304 patients (38.5%) had a history of previous CVD, and the prevalence of CVD was greater in patients with more severe CRI. Two hundred forty-three patients (79.9%) had a history of hypertension, 132 patients (43.4%) had hyperlipidemia, 114 patients (37.5%) had diabetes mellitus, and 71 patients (27.3%) were smokers. Thirty-five percent of the patients with CVD had blood pressures greater than 140/90 mm Hg; 103 patients (33.9%) were administered beta-blockers; 196 patients (64.5%), ACE inhibitors or angiotensin-receptor blockers; 83 patients (27.3%), ASA; and 56 patients (18.4%), statins. Patients with diabetes were not more likely than those without diabetes to be prescribed cardioprotective medications. CVD is common in the predialysis population, and its prevalence increases with more severe kidney failure. Despite this, the use of cardioprotective medications is relatively low, and many patients had suboptimal blood pressure control. Given the high burden of disease in these patients, beta-blockers and ACE inhibitors should be used to control hypertension and/or for cardioprotection, and the increased use of ASA and statins should be considered.

The relationship between cardiac output and access flow during hemodialysis

Satisfactory hemodialysis access flow (Qa) is necessary for dialysis adequacy. However, high access flows are postulated to increase cardiac output (CO). The relationship between Qa and CO is not well defined. The purpose of this study was to observe the relationship between Qa and CO and to evaluate the effect of blood volume change (BVdelta) on Qa and CO during hemodialysis (HD). Measurements of Qa and CO (ultrasound dilution; Transonics Monitor, Ithaca, NY) were performed sequentially at baseline in 18 patients (13 forearm arteriovenous fistulae, 5 Gore-Tex grafts) and after an intervention involving either HD with attempted zero BVdelta (mean: -0.4%; range: -2.6 to 1.6%) or a significant BVdelta (mean: -7.3%; range: -3.1 to -11.9%). Measurement of BVdelta was done by hematocrit dilution (Crit-Line Monitor, In-Line Diagnostics, Riverdale, UT). The volume ultrafiltered (V(UF)) and the mean arterial pressure (MAP) were recorded at baseline and after intervention. In five patients with fistulae, CO was measured after manual occlusion of the fistula for 1 min. At baseline, mean (+/-SD) Qa was 1455+/-600 ml/min, and CO was 6.8+/-1.8 L/min. The relationship between Qa and CO was strong, Qa = 0.20 CO + 0.06 (r = 0.62; p = 0.01); this was not significantly altered with either intervention. Access flow was not changed with either zero BVdelta or significant BVdelta. Cardiac output was not altered when there was no BVdelta; however, CO did decrease by 1.2+/-0.6 L/min (p<0.001) after BVdelta reduction. The Qa/CO ratio was unchanged after zero BVdelta but was increased after BVdelta (p = 0.004). There were no correlations with MAP change or V(UF). There were no differences in Qa, CO, or Qa/CO by access type. The mean Qa/CO was 21+/-6%. Three patients had Qa/CO <15%, and they all had access stenoses. Cardiac output did not decrease after transient (1 min) occlusion of the fistula. In conclusion, there is a strong relationship between Qa and CO. With BVdelta, the Qa is maintained while the CO falls and the Qa/CO increases, perhaps by reflex vasoconstriction of the systemic circulation. Longitudinal studies are required to determine which is the dependent variable. A low Qa/CO may indicate access dysfunction.