Patient and Operative Factors Predict Risk of Discretionary Prolonged Postoperative Mechanical Ventilation in a Broad Surgical Cohort.

BACKGROUND: Patients undergoing surgery with general anesthesia and endotracheal intubation are ideally extubated upon case completion, as prolonged postoperative mechanical ventilation (PPMV) has been associated with poor outcomes. However, some patients require PPMV for surgical reasons, such as airway compromise, while others remain intubated at the discretion of the anesthesia provider. Incidence and risk factors for discretionary PPMV (DPPMV) have been described in individual surgical subspecialties and intensive care unit (ICU) populations, but are relatively understudied in a broad surgical cohort. The present study seeks to fill this gap and identify the perioperative risk factors that predict DPPMV. METHODS: After obtaining institutional review board (IRB) exemption, existing electronic health record databases at our large referral center were retrospectively queried for adult surgeries performed between January 2018 and December 2020 with general anesthesia, endotracheal intubation, and by surgical services that do not routinely leave patients intubated for surgical reasons. Patients who arrived to the ICU intubated after surgery were identified as experiencing DPPMV. Selection of candidate risk factors was performed with LASSO-regularized logistic regression, and surviving variables were used to generate a multivariable logistic regression model of DPPMV risk. RESULTS: A total of 32,915 cases met inclusion criteria, of which 415 (1.26%) experienced DPPMV. Compared to extubated patients, those with DPPMV were more likely to have undergone emergency surgery (42.9% versus 3.4%; P < .001), surgery during an existing ICU stay (30.8% versus 2.8%; P < 0.001), and have 20 of the 31 elixhauser comorbidities ( P < .05 for each comparison), among other differences. A risk model with 12 variables, including American Society of Anesthesiologists (ASA) physical classification status, emergency surgery designation, four Elixhauser comorbidities, surgery during an existing ICU stay, surgery duration, estimated number of intraoperative handoffs, and vasopressor, sodium bicarbonate, and albuterol administration, yielded an area under the receiver operating characteristic curve of 0.97 (95% confidence interval, 0.96-0.97) for prediction of DPPMV. CONCLUSIONS: DPPMV was uncommon in this broad surgical cohort but could be accurately predicted using readily available patient-specific and operative factors. These results may be useful for preoperative risk stratification, postoperative resource allocation, and clinical trial planning.

Engaging the next generation of physician-informaticians through early exposure to the field: successes and challenges associated with starting a novel clinical informatics interest group.

Clinical informatics remains underappreciated among medical students in part due to a lack of integration into undergraduate medical education (UME). New developments in the study and practice of medicine are traditionally introduced via formal integration into undergraduate medical curricula. While this path has certain advantages, curricular changes are slow and may fail to showcase the breadth of clinical informatics activities. Less formal and more flexible approaches can circumvent these drawbacks. Interest groups (IGs), which are organized through the Association of American Medical College Careers in Medicine (CiM) program, exemplify the informal approach. CiM IGs are student-led groups that provide exposure to different specialty options, acting as an adjunct to the traditional medical curriculum. While the primary purpose of these groups is to assist students applying to residency programs, we took a novel approach of using an IG to increase student exposure to an area of medicine that had not yet been formally integrated at our institution. IGs provide unique advantages to formal integration into a curriculum as they can be more easily setup and can quickly respond to student interests. Furthermore, IGs can act synergistically with UME, acting as proving grounds for ideas that can lead to new courses. We believe that the lessons and takeaways from our experience can act as a guide for those interested in starting similar organizations at their own schools.

Resting State Functional Connectivity Is Decreased Globally Across the C9orf72 Mutation Spectrum.

A repeat expansion mutation in the C9orf72 gene causes amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), or symptoms of both, and has been associated with gray and white matter changes in brain MRI scans. We used graph theory to examine the network properties of brain function at rest in a population of mixed-phenotype C9orf72 mutation carriers (C9+). Twenty-five C9+ subjects (pre-symptomatic, or diagnosed with ALS, behavioral variant FTD (bvFTD), or both ALS and FTD) and twenty-six healthy controls underwent resting state fMRI. When comparing all C9+ subjects with healthy controls, both global and connection-specific decreases in resting state connectivity were observed, with no substantial reorganization of network hubs. However, when analyzing subgroups of the symptomatic C9+ patients, those with bvFTD (with and without comorbid ALS) show remarkable reorganization of hubs compared to patients with ALS alone (without bvFTD), indicating that subcortical regions become more connected in the network relative to other regions. Additionally, network connectivity measures of the right hippocampus and bilateral thalami increased with increasing scores on the Frontal Behavioral Inventory, indicative of worsening behavioral impairment. These results indicate that while C9orf72 mutation carriers across the ALS-FTD spectrum have global decreased resting state brain connectivity, phenotype-specific effects can also be observed at more local network levels.

Preoperative High, as well as Low, Platelet Counts Correlate With Adverse Outcomes After Elective Total Hip Arthroplasty.

BACKGROUND: Preoperative laboratory studies are often obtained as part of the workup for surgeries such as total hip arthroplasty (THA). An increasing need exists to be able to identify patients at risk for adverse outcomes. Thus, metrics that correlate with postoperative adverse events and readmissions are increasingly important to optimize patient care. The implications of varying abnormal platelet counts, especially on the high end of the spectrum, have yet to be assessed in large, multicenter patient populations. This study aims to risk stratify THA patients with varying preoperative platelet counts to address these questions. The purposes of this study were to (1) evaluate cutoffs for normal versus abnormal platelet counts for patients undergoing THA by using postoperative complications data and (2) assess the correlation of such values with readmission data using the National Surgical Quality Improvement Program database. METHODS: Patients who underwent elective primary THA were identified in the 2011 to 2015 National Surgical Quality Improvement Program database. Risk of 30-day perioperative complications was calculated as a function of preoperative platelet counts. Based on the risk criteria, patients were categorized into the following three groups: normal platelet counts, abnormally low platelet counts, and abnormally high platelet counts. Multivariate analyses were performed to compare 30-day postoperative complications, readmissions, surgical time, and length of hospital stay between these populations. RESULTS: The current study identified 86,845 THA patients. Using the relative risk threshold of 1.5, platelets counts were divided into abnormally low (≤142,000/mL) and abnormally high (≥417,000/mL) categories. Higher rates of any, major, and minor adverse events and hospital readmission were associated with both the abnormally low and high platelet cohorts. CONCLUSION: This study suggests that preoperative high, as well as low, platelet counts are correlated with perioperative complications after THA, including hospital readmissions. Patients with these laboratory findings warrant further attention with possible preoperative and postoperative optimization.

High, As Well As Low, Preoperative Platelet Counts Correlate With Adverse Outcomes After Elective Posterior Lumbar Surgery.

STUDY DESIGN: Retrospective cohort study of prospectively collected data. OBJECTIVE: Assess correlation between preoperative platelet counts and postoperative adverse events after elective posterior lumbar surgery procedures. SUMMARY OF BACKGROUND DATA: Preoperative low platelet counts have been correlated with adverse outcomes after posterior lumbar surgery. Nonetheless, the effect of varying platelet counts has not been studied in detail for a large patient population, especially on the high end of the platelet spectrum. METHODS: Patients who underwent elective posterior lumbar surgery were identified in the 2011 to 2016 National Surgical Quality Improvement Program database. Preoperative platelet counts were considered relative to 30-day perioperative adverse outcomes. Patients were classified into platelet categories based on determining upper and lower bounds on when the adverse outcomes crossed a relative risk of 1.5. Univariate and multivariate analyses compared 30-day postoperative complications, readmissions, operative time, and hospital length of stay between those with low, normal, and high platelet counts. RESULTS: In total, 137,709 posterior lumbar surgery patients were identified. Using the relative risk threshold of 1.5 for the occurrence of any adverse event, patients were divided into abnormally low (≤140,000/mL) and abnormally high (≥447,000/mL) platelet cohorts. The abnormally low and high platelet groups were associated with higher rates of any, major, minor adverse events, transfusion, and longer hospital length of stay. Furthermore, the abnormally low platelet counts were associated with a higher risk of readmissions. CONCLUSION: The data-based cut-offs for abnormally high and low platelet counts closely mirrored those found in literature. Based on these definitions, abnormally high and low preoperative platelet counts were associated with adverse outcomes after elective posterior lumbar surgery. These findings facilitate risk stratification and suggest targeted consideration for patients with high, as well as low, preoperative platelet counts. LEVEL OF EVIDENCE: 3.

Abnormally High, as Well as Low, Preoperative Platelet Counts Correlate With Adverse Outcomes and Readmissions After Elective Total Knee Arthroplasty.

BACKGROUND: Laboratory studies are routinely performed as a part of the preoperative workup for a total knee arthroplasty (TKA). The ramifications of abnormal preoperative platelet counts remain uncharacterized in large, multicenter patient populations. METHODS: Patients who underwent elective primary TKA were identified in the 2011-2015 National Surgical Quality Improvement Program database. Risk of 30-day postoperative complications was calculated as a function of preoperative platelet counts. Patients were characterized as having a normal platelet count, abnormally low platelet count, and abnormally high platelet count based on relative risk calculations. Univariate and multivariate analyses were performed to associate abnormal platelet counts with patient demographics, operative variables, 30-day postoperative complications, and readmissions. RESULTS: In total, 140,073 patients who underwent elective TKA were identified. Using the relative risk threshold of 1.5 for any adverse event, abnormally low and abnormally high platelet count thresholds were set at ≤116,000/mL and ≥492,000/mL, respectively. Multivariate analyses revealed low platelet counts to be associated with higher rates of any, major, and minor adverse events and longer length of stay. Analogously, high platelet counts were associated with higher rates of any and minor adverse events and longer length of stay. CONCLUSION: The present study employed a large patient sample size and showed that elective TKA patients with abnormally high, as well as low, platelet counts are at increased risk of postoperative adverse outcomes. Focused attention needs to be paid to TKA patients with preoperative abnormal platelet counts for optimization and postoperative care. LEVEL OF EVIDENCE: Level III, retrospective comparative study.

Loss of functional connectivity is an early imaging marker in primary lateral sclerosis.

OBJECTIVE: The clinical diagnosis of primary lateral sclerosis can only be made after upper motor neuron symptoms have progressed for several years without developing lower motor neuron signs. The goal of the study was to identify neuroimaging changes that occur early in primary lateral sclerosis, prior to clinical diagnosis. METHODS: MRI scans were obtained on 13 patients with adult-onset progressive spasticity for five years or less who were followed longitudinally to confirm a clinical diagnosis of primary lateral sclerosis. Resting state functional MRI, diffusion tensor imaging, and anatomical images were obtained. These "pre-PLS" patients were compared to 18 patients with longstanding, established primary lateral sclerosis and 28 controls. RESULTS: Pre-PLS patients had a marked reduction in seed-based resting-state motor network connectivity compared to the controls and patients with longstanding disease. White matter regions with reduced fractional anisotropy were similar in the two patient groups compared to the controls. Patients with longstanding disease had cortical thinning of the precentral gyrus. A slight thinning of the right precentral gyrus was detected in initial pre-PLS patients' scans. Follow-up scans in eight pre-PLS patients 1-2 years later showed increasing motor connectivity, thinning of the precentral gyrus, and no change in diffusion measures of the corticospinal tract or callosal motor region. CONCLUSIONS: Loss of motor functional connectivity is an early imaging marker in primary lateral sclerosis. This differs from literature descriptions of amyotrophic lateral sclerosis, warranting further studies to test whether resting-state functional MRI can differentiate between amyotrophic lateral sclerosis and primary lateral sclerosis at early disease stages.

2015 ACC Health Policy Statement on Cardiovascular Team-Based Care and the Role of Advanced Practice Providers.

The mission of the American College of Cardiology is "to transform cardiovascular care and improve heart health." Cardiovascular team-based care is a paradigm for practice that can transform care, improve heart health, and help meet the demands of the future. One strategic goal of the College is to help members successfully transition their clinical practices to the future, with all its complexity, challenges, and opportunities. The ACC's strategic plan is aligned with the triple aim of improved care, improved population health, and lower costs per capita. The traditional understanding of quality, access, and cost is that you cannot improve one component without diminishing the others. With cardiovascular team-based care, it is possible to achieve the triple aim of improving quality, access, and cost simultaneously to also improve cardiovascular health. Striving to serve the best interests of patients is the true north of our guiding principles. Cardiovascular team-based care is a model that can improve care coordination and communication and allow each team member to focus more on the quality of care. In addition, the cardiovascular team-based care model increases access to cardiovascular care and allows expansion of services to populations and geographic areas that are currently underserved. This document will increase awareness of the important components of cardiovascular team-based care and create an opportunity for more discussion about the most creative and effective means of implementing it. We hope that this document will stimulate further discussions and activities within the ACC and beyond about team-based care. We have identified areas that need improvement, specifically in APP education and state regulation. The document encourages the exploration of collaborative care models that should enable team members to optimize their education, training, experience, and talent. Improved team leadership, coordination, collaboration, engagement, and efficiency will enable the delivery of higher-value care to the betterment of our patients and society.

Managing the acute coronary syndrome patient: Evidence based recommendations for anti-platelet therapy.

Acute coronary syndrome (ACS) is best managed by a multidisciplinary team in which primary care physicians, physician assistants, nurse practitioners, and pharmacists play a key role. This article summarizes recent updates to American College of Cardiology Foundation/American Heart Association guidelines for the management of unstable angina (UA)/non ST-segment elevation ACS (NSTE-ACS) and ST-segment elevation myocardial infarction (STEMI), focusing on antiplatelet therapy. Dual antiplatelet therapy comprising aspirin plus a P2Y12 inhibitor (clopidogrel, prasugrel, or ticagrelor) is recommended for patients with NSTE-ACS, and those with STEMI both during and after reperfusion. The guidelines provide recommendations regarding the utilization of P2Y12 inhibitors in specific circumstances and are discussed in this review. Health care teams with a key role in post-ACS care need to be familiar with the latest guidelines and support patients with education on risk reduction and the benefits of long-term medication adherence.

Oscillatory vagal maneuvers produce ventricular entrainment in patients with atrial fibrillation.

BACKGROUND: Atrial fibrillation (AF) is the most common sustained dysrhythmia and appears to be an independent predictor of sudden cardiac death. The irregular ventricular rhythm contains both linear and non-linear patterns; however, it remains unclear whether vagally mediated effects are present within these patterns. OBJECTIVE: We sought to determine if (1) power spectral analysis of heart rate can detect changes in vagal activity in patients with AF and (2) if the vagus modulates ventricular response during AF. METHODS: Time and frequency domain parameters of heart rate variability (HRV) were calculated during forced vagal oscillations at 0.125 and 0.25 Hz imposed by neck suction and deep breathing in five AF patients. RESULTS: There was a significant increase in SDRRI during deep breathing/neck suction combined compared to baseline (p=0.01) and deep breathing (p=0.03). Neck suction significantly increased SDRRI compared to baseline (p=0.03). Deep breathing/neck suction significantly increased spectral power compared to baseline (p=0.02) and deep breathing (p=0.03). Neck suction significantly increased spectral power compared to baseline (p=0.03). Deep breathing did not significantly increase HRV compared to baseline (p>0.20). In addition, SDRRI and spectral power were significantly correlated during deep breathing (r=0.91, p=0.03) and deep breathing/neck suction combined (r=0.92, p=0.02). INTERPRETATION: These data suggest that (1) power spectral analysis can detect vagal influences on heart rate in AF patients, and (2) oscillatory vagal maneuvers produce ventricular entrainment during AF.

Activation of AMP-activated protein kinase by 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside in the muscle microcirculation increases nitric oxide synthesis and microvascular perfusion.

OBJECTIVE: To investigate the effects of activation of the AMP-activated protein kinase (AMPK) on muscle perfusion and to elucidate the mechanisms involved. METHODS AND RESULTS: In a combined approach, we studied the vasoactive actions of AMPK activator by 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR) on rat cremaster muscle resistance arteries ( approximately 100 mum) ex vivo and on microvascular perfusion in the rat hindlimb in vivo. In isolated resistance arteries, AICAR increased Thr172 phosphorylation of AMPK in arteriolar endothelium, which was predominantly located in microvascular endothelium. AICAR induced vasodilation (19+/-4% at 2 mmol/L, P<0.01), which was abolished by endothelium removal, inhibition of NO synthase (with N-nitro-L-arginine), or AMPK (with compound C). Smooth muscle sensitivity to NO, determined by studying the effects of the NO donor S-nitroso-N-acetylpenicillamine (SNAP), was not affected by AICAR except at the highest dose. AICAR increased endothelial nitric oxide synthase activity, as indicated by Ser1177 phosphorylation. In vivo, infusion of AICAR markedly increased muscle microvascular blood volume (approximately 60%, P<0.05), as was evidenced by contrast-enhanced ultrasound, without effects on blood pressure, femoral blood flow, or hind leg glucose uptake. CONCLUSIONS: Activation of AMPK by AICAR activates endothelial nitric oxide synthase in arteriolar endothelium by increasing its Ser1177 phosphorylation, which leads to vasodilation of resistance arteries and recruitment of microvascular perfusion in muscle.

Decreased microvascular vasomotion and myogenic response in rat skeletal muscle in association with acute insulin resistance.

In addition to increased glucose uptake, insulin action is associated with increased total and microvascular blood flow, and vasomotion in skeletal muscle. The aim of this study was to determine the effect of acute insulin resistance caused by the peripheral vasoconstrictor alpha-methylserotonin (alphaMT) on microvascular vasomotion in muscle. Heart rate (HR), mean arterial pressure (MAP), femoral blood flow (FBF), whole body glucose infusion (GIR) and hindleg glucose uptake (HGU) were determined during control and hyperinsulinaemic euglycaemic clamp conditions in anaesthetized rats receiving alphaMT infusion. Changes in muscle microvascular perfusion were measured by laser Doppler flowmetry (LDF) and vasomotion was assessed by applying wavelet analysis to the LDF signal. Insulin increased GIR and HGU. Five frequency bands corresponding to cardiac, respiratory, myogenic, neurogenic and endothelial activities were detected in the LDF signal. Insulin infusion alone increased FBF (1.18 +/- 0.10 to 1.78 +/- 0.12 ml min(-1), P < 0.05), LDF signal strength (by 16% compared to baseline) and the relative amplitude of the myogenic component of vasomotion (0.89 +/- 0.09 to 1.18 +/- 0.06, P < 0.05). When infused alone alphaMT decreased LDF signal strength and the myogenic component of vasomotion by 23% and 27% respectively compared to baseline, but did not affect HGU or FBF. Infusion of alphaMT during the insulin clamp decreased the stimulatory effects of insulin on GIR, HGU, FBF and LDF signal and blocked the myogenic component of vasomotion. These data suggest that insulin action to recruit microvascular flow may in part involve action on the vascular smooth muscle to increase vasomotion in skeletal muscle to thereby enhance perfusion and glucose uptake. These processes are impaired with this model of alphaMT-induced acute insulin resistance.

Interleukin-6 attenuates insulin-mediated increases in endothelial cell signaling but augments skeletal muscle insulin action via differential effects on tumor necrosis factor-alpha expression.

OBJECTIVE: The cytokine interleukin-6 (IL-6) stimulates AMP-activated protein kinase (AMPK) and insulin signaling in skeletal muscle, both of which result in the activation of endothelial nitric oxide synthase (eNOS). We hypothesized that IL-6 promotes endothelial cell signaling and capillary recruitment in vivo, contributing to increased glucose uptake. RESEARCH DESIGN AND METHODS: The effect of IL-6 with and without insulin on AMPK, insulin, and eNOS signaling in and nitric oxide (NO) release from human aortic endothelial cells (HAECs) was examined. The physiological significance of these in vitro signaling events was assessed by measuring capillary recruitment in rats during control and euglycemic-hyperinsulinemic clamps with or without IL-6 infusion. RESULTS: IL-6 blunted increases in insulin signaling, eNOS phosphorylation (Ser1177), and NO production and reduced phosphorylation of AMPK in HAEC in vitro and capillary recruitment in vivo. In contrast, IL-6 increased Akt phosphorylation (Ser473) in hindlimb skeletal muscle and enhanced whole-body glucose disappearance and glucose uptake during the clamp. The differences in endothelial cell and skeletal muscle signaling were mediated by the cell-specific, additive effects of IL-6 and insulin because this treatment markedly increased tumor necrosis factor (TNF)-alpha protein expression in HAECs without any effect on TNF-alpha in skeletal muscle. When HAECs were incubated with a TNF-alpha-neutralizing antibody, the negative effects of IL-6 on eNOS signaling were abolished. CONCLUSIONS: In the presence of insulin, IL-6 contributes to aberrant endothelial cell signaling because of increased TNF-alpha expression.

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle.

Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.

Contrast-enhanced ultrasound measurement of microvascular perfusion relevant to nutrient and hormone delivery in skeletal muscle: a model study in vitro.

Contrast-enhanced ultrasound (CEU) has been used to measure muscle microvascular perfusion in vivo in response to exercise and insulin. In the present study we address whether CEU measurement of capillary volume is influenced by bulk flow and if measured capillary filling rate allows discrimination of different flow pattern changes within muscle. Three in vitro models were used: (i) bulk flow rate was varied within a single length of capillary tubing; (ii) at constant bulk flow, capillary volume was increased 3-fold by joining lengths of capillary in series, and compared to a single length; and (iii) at constant bulk flow, capillary volume was increased by sharing flow between a number of lengths of identical capillaries in parallel. The contrast medium for CEU was gas-filled albumin microbubbles. Pulsing interval (time) versus acoustic-intensity curves were constructed and from these, capillary volume and capillary filling rate were calculated. CEU estimates of capillary volume were not affected by changes in bulk flow. Furthermore, as CEU estimates of capillary volume increased, measures of capillary filling rate decreased, regardless of whether capillaries were connected in series or parallel. Therefore, CEU can detect a change in filling rate of the microvascular volume under measurement, but it can not be used to discriminate between different flow patterns within muscle that might account for capillary recruitment in vivo.

Local nitric oxide synthase inhibition reduces skeletal muscle glucose uptake but not capillary blood flow during in situ muscle contraction in rats.

OBJECTIVE: We have previously shown in humans that local infusion of a nitric oxide synthase (NOS) inhibitor into the femoral artery attenuates the increase in leg glucose uptake during exercise without influencing total leg blood flow. However, rodent studies examining the effect of NOS inhibition on contraction-stimulated skeletal muscle glucose uptake have yielded contradictory results. This study examined the effect of local infusion of an NOS inhibitor on skeletal muscle glucose uptake (2-deoxyglucose) and capillary blood flow (contrast-enhanced ultrasound) during in situ contractions in rats. RESEARCH DESIGN AND METHODS: Male hooded Wistar rats were anesthetized and one hindleg electrically stimulated to contract (2 Hz, 0.1 ms) for 30 min while the other leg rested. After 10 min, the NOS inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) (arterial concentration of 5 micromol/l) or saline was infused into the epigastric artery of the contracting leg. RESULTS: Local NOS inhibition had no effect on blood pressure, heart rate, or muscle contraction force. Contractions increased (P < 0.05) skeletal muscle NOS activity, and this was prevented by L-NAME infusion. NOS inhibition caused a modest significant (P < 0.05) attenuation of the increase in femoral blood flow during contractions, but importantly there was no effect on capillary recruitment. NOS inhibition attenuated (P < 0.05) the increase in contraction-stimulated skeletal muscle glucose uptake by approximately 35%, without affecting AMP-activated protein kinase (AMPK) activation. CONCLUSIONS: NOS inhibition attenuated increases in skeletal muscle glucose uptake during contraction without influencing capillary recruitment, suggesting that NO is critical for part of the normal increase in skeletal muscle fiber glucose uptake during contraction.

Insulin and contraction increase nutritive blood flow in rat muscle in vivo determined by microdialysis of L-[14C]glucose.

In the present study, a mathematical model using the microdialysis outflow: inflow (O/I) ratio of the novel analogue L-[14C]glucose has been developed which allows the calculation of the nutritive (and non-nutritive) flow in muscle as a proportion of total blood flow. Anaesthetized rats had microdialysis probes carrying L-[14C]glucose inserted through a calf muscle group (tibialis/plantaris/gastrocnemius). The nutritive fraction of total blood flow was determined under basal conditions and in response to contraction (electrical field stimulation), insulin (hyperinsulinaemic euglycaemic clamp with 10 mU min(-1) kg(-1) insulin) or saline control from limb blood flow and the microdialysis O/I ratio of L-[14C]glucose. Both contraction and insulin infusion decreased the O/I ratio of L-[14C]glucose and increased total limb blood flow. Calculations based on mathematical models using L-[14C]glucose O/I and limb blood flow revealed that during basal conditions, the nutritive fraction of total flow was 0.38 +/- 0.06, indicating that basal flow was predominantly non-nutritive. Contraction and insulin increased the nutritive fraction to 0.82 +/- 0.24 (P < 0.05) and 0.52 +/- 0.12 (P < 0.05). Thus the increase in limb blood flow from insulin was fully accommodated by nutritive flow, while contraction increased nutritive flow at the expense of non-nutritive flow. This novel method using microdialysis and the O/I ratio of L-[14C]glucose allows the determination of the nutritive fraction of total flow in muscle as well as the proportion of total flow that may be redistributed in response to contraction and insulin.

Biochemical and genetic analyses provide insight into the structural and mechanistic properties of actin filament disassembly by the Aip1p cofilin complex in Saccharomyces cerevisiae.

Explication of the Aip1p/cofilin/actin filament complex may lead to a more detailed understanding of the mechanisms by which Aip1p and cofilin collaborate to rapidly disassemble filaments. We further characterized the actin-Aip1p interface through a random mutagenic screen of ACT1, identifying a novel Aip1p interaction site on actin. This finding is consistent with our current ternary complex model and offers insights into how Aip1p may disturb intersubunit contacts within an actin filament. In addition, site-directed mutagenesis aimed at interfering with salt bridge interactions at the predicted Aip1p-cofilin interface revealed hyperactive alleles of cof1 and aip1 that support the ternary complex model and suggest that conformational changes in cofilin structure may be transmitted to actin filaments, causing increased destabilization. Furthermore, these data support an active role for Aip1p in promoting actin filament turnover.