Edema-induced intestinal dysfunction is mediated by STAT3 activation.

Increased signal transducer and activator of transcription 3 (STAT3) activation has been shown to be associated with intestinal dysfunction. The purpose of this study was to investigate the role of STAT3 in edema-induced intestinal dysfunction. Intestinal edema was induced in male Sprague-Dawley rats by a combination of mesenteric venous hypertension and fluid resuscitation (RESUS + VH). Resuscitation fluid alone (RESUS), venous hypertension alone (VH), and sham-operated rats (CONTROL) were used as controls. Edema development, STAT3 DNA binding activity, nuclear translocation, and phosphorylation were measured in rat distal small intestinal muscularis. A significant amount of edema development was measured in the RESUS + VH rats compared with CONTROL and VH from 30 min to 6 h after surgery. Edema developed in the RESUS group at 30 min postsurgery but resolved before 2 h postsurgery. A significant increase in STAT3 DNA binding activity was observed from 30 min to 6 h after surgery in the edematous RESUS + VH group compared with nonedematous CONTROL. In addition, a significant increase in STAT3 nuclear translocation and phosphorylation was measured in the RESUS + VH group 2 and 6 h after surgery. No significant increases in STAT3 activation were observed in either the RESUS or VH groups compared with CONTROL. Rats in both the RESUS + VH and CONTROL groups were pretreated with AG490 (5 mg/kg, i.p.) to block STAT3 activation. Signal transducer and activator of transcription 3 inhibition attenuated edema-induced decrease in intestinal contractile activity and myosin light chain phosphorylation. We conclude from these data that edema-induced decreases in intestinal contractile activity are mediated, at least in part, by STAT3 activation.

Pulmonary air embolization inhibits lung lymph flow by increasing lymphatic outflow pressure.

BACKGROUND: Air embolization of the pulmonary vascular tree increases pulmonary microvascular filtration and induces pulmonary edema formation. Flow from cannulated pulmonary lymphatic vessels increases significantly following air embolization. However, in the intact animal, lymph flows into the venous system and the magnitude of lymph flow is directly affected by systemic venous pressure. We hypothesized that pulmonary air embolization would lead to systemic venous hypertension and that this increase in lymphatic outflow pressure would prevent an increase in pulmonary lymph flow. METHODS AND RESULTS: Pulmonary air embolization was induced in dogs under general anesthesia. Flow from cannulated pulmonary lymphatic vessels was recorded for lymphatic outflow pressure set equal to atmospheric pressure (Q(LA)) and for outflow pressure set equal to systemic venous pressure (Q(LV)) both before and after embolization. Air embolization resulted in significant increases in systemic venous pressure from 6.4 +/- 0.3 to 12.4 +/- 1.2 mm Hg and in QLA from 48 +/- 9 to 175 +/- 29 microL . min(1). However, embolization did not increase Q(LV) (10 +/- 2 vs. 3 +/- 3 microl . min(1)). CONCLUSIONS: Pulmonary air embolization impedes pulmonary lymph flow by increasing systemic venous pressure and, thereby, contributes to pulmonary edema formation.

Impact of acute myocardial edema on left ventricular function.

Studies of the impact of myocardial edema on left ventricular (LV) systolic function show conflicting results. We sought to evaluate the impact of increased myocardial water content (MWC) on LV systolic and diastolic function. Anesthetized dogs (n = 12) were instrumented with myocardial ultrasonic crystals and an LV micromanometer. Systolic function was measured by preload recruitable stroke work (PRSW) and dP/dt(max). Diastolic function was measured by -dP/dt(max) and the isovolumic relaxation constant tau (t). Myocardial water content (MWC) was determined using microgravimetry. In six dogs (coronary sinus hypertension, CSH group) we produced myocardial edema by inflating a coronary sinus balloon for 2 h (30-40 mm Hg). In six other dogs (Plegisol, PLEG group) cardiopulmonary bypass (CPB) was initiated (12.3 +/- 0.8 min), the aorta was cross-clamped (117 +/- 19 s), and 700 mL 4 degrees C crystalloid, hyperkalemic cardioplegic solution (Plegisol) was administered into the aortic root (62 +/- 4 mm Hg). After declamping and reperfusion (7.2 +/- 1.0 min), the dogs were separated from CPB. Myocardial function parameters and MWC were measured for 2 h after edema generation. In the CSH group, MWC significantly increased from 75.9 +/- 0.3% to 77.6 +/- 0.3% (p < .05). In the PLEG group, MWC increased from 75.8 +/- 0.3% to 77.7 +/- 0.3% (p < .05). PRSW and dP/dt(max) did not decrease in either group. Diastolic parameters did not change significantly. We conclude that acute myocardial edema without myocardial injury does not impair LV function.

Effects of primary and secondary intra-abdominal hypertension on mesenteric lymph flow: implications for the abdominal compartment syndrome.

Intra-abdominal hypertension leading to abdominal compartment syndrome complicates trauma resuscitation. The purpose of this study was to determine the effect of primary (1 degrees) and secondary (2 degrees) intra-abdominal hypertension (IAH) on hemodynamics, intestinal fluid balance, and mesenteric lymph flow. Anesthetized dogs were instrumented with vascular catheters, intra-abdominal manometer, and mesenteric lymphatic fistulae. 1 degrees IAH was created by infusing 0.9% saline into the peritoneal cavity to increase abdominal pressure. 2 degrees IAH was created by elevating the inferior vena cava (IVC) pressure between 20 and 25 mmHg and crystalloid resuscitation to create intestinal edema to induce IAH. At baseline and at 30-min intervals, hemodynamics, lymph flow (QL), IVC, and intra-abdominal pressures were measured. Tissue water was determined using microgravimetry to assess gut edema. Results are reported as mean +/- SEM, with n = 7-8 dogs per group. 1 degrees IAH significantly increased CVP and decreased QL. 1 degrees IAH stopped mesenteric QL, thus transvascular fluid flux necessarily exceeded QL, contributing to gut edema formation. 2 degrees IAH significantly increased CVP and QL. 2 degrees IAH increased QL despite elevated IAP. Interstitial protein washdown maintained the plasma-to-interstitial oncotic gradient, thus increased transvascular fluid flux was due principally to increased capillary pressure. Transvascular fluid flux exceeded QL as manifested by increasing gut tissue water as QL plateaued. Modest elevations in IAP significantly affect mesenteric QL and the development of gut edema. The principle of early abdominal decompression to reduce mesenteric/IVC venous hypertension and capillary pressure is supported by these data.

Resuscitation-induced intestinal edema decreases the stiffness and residual stress of the intestine.

We have shown that acute edema impairs intestinal transit and we wanted to know whether this could be from changes in the physical characteristics of the intestine. Our hypothesis was that acute edema will change the physical characteristics of the intestine, which were measured by standardized engineering measures of elastic modulus, to determine stiffness and opening angle, and to determine residual stress. Rats were randomized to sham, mild edema (80 mL/ kg of normal saline resuscitation), and severe edema groups (80 mL/kg of normal saline resuscitation with intestinal venous hypertension). Segments of distal ileum were hung to a fixed point in a tissue bath and to a tensiometer and were stretched in increments of 1 mm, recording the new length and the corresponding force from the tensiometer to determine elastic modulus. Next, two transverse cuts were made yielding a 1- to 2-mm-thick ring-shaped segment of tissue and were then cut radially to open the ring. The opening angle was measured. Acute intestinal edema led to a decrease in transit, elastic modulus, and opening angle of the intestine in the absence of ischemic injury. Acute intestinal edema leads to a significant loss in stiffness and residual stress and is a plausible explanation for how acute edema impairs intestinal transit.

Cost of a ventilator-associated pneumonia in a shock trauma intensive care unit.

BACKGROUND: Nosocomial pneumonia and especially ventilator-associated pneumonia (VAP) are costly complications for the hospitalized patient. Nosocomial pneumonia has been estimated to cost $5,000 per episode, but the specific cost for a VAP has not been well estimated. As part of a successful performance improvement program in decreasing VAP from 10 VAPs/100 ICU admissions to 2.5 VAPs/100 ICU admissions, we examined the costs associated with VAP. METHODS: From January 1, 2002, through September 30, 2003, Shock Trauma Intensive Care Unit patients and charts were reviewed concurrently by an infection control practitioner for development of VAP as defined by National Nosocomial Infection Surveillance (NNIS) guidelines. Costs were obtained from the hospital's cost accounting software Transition Systems version 3.1.01 (TSI). All patients requiring greater than one day of mechanical ventilation were evaluated. Seventy patients with VAP and 70 patients without VAP were matched according to age and Injury Severity Score. Differences were compared using Kruskal-Wallis and two sample T-tests. Significance was considered for p < 0.05. RESULTS: The ICU cost difference was significant (p < 0.05) between the case-controlled patients with VAP ($82,195) and those without VAP ($25,037). There was also a significant increase in ICU length of stay (21.6 versus 6.4 days) and the number of ventilator days (17.7 versus 5.8; both, p < 0.05). Mortality was not different in the case-controlled population. A substantial portion of the increased cost of a VAP was from the increase in ICU length of stay ($1,861/day). Pharmacy, respiratory and "other" also accounted for the increases when cost distribution was analyzed. This translates into a cost avoidance of approximately $428,685 per 100 admissions to the ICU. CONCLUSIONS: Ventilator-associated pneumonia not only leads to a significant increase in ventilator days and ICU length of stay, but adds substantially to hospital costs. In our ICU, an episode of VAP costs $57,000 per occurrence.

Mild hypothermia impairs left ventricular diastolic but not systolic function.

Hypothermia is a component of myocardial protection during cardiopulmonary bypass (CPB) and cardioplegic arrest (CA). Patients in the early post CPB period often show mild hypothermia and cardiac dysfunction. We sought to investigate the impact of hypothermia on left ventricular (LV) function. Anesthetized dogs (n = 12) were instrumented with myocardial ultrasonic crystals and LV micromanometer. Systolic function was measured by preload recruitable stroke work (PRSW). Diastolic function was measured by -dP/dt(max) and tau. In six dogs (Norm group), body temperature was maintained at baseline levels. In another six dogs (Hypo group), body temperature dropped gradually over the time course of the experiment. The body temperature in the Hypo group decreased from 37.0 +/- 0.3 degrees C to 35.2 +/- 1.0 degrees C. -dP/dt(max) decreased and tau increased significantly with hypothermia but were stable in the Norm group. Both tau and -dP/dt(max) showed a linear relationship to the body temperature (r =.91 and r = .93, respectively). PRSW did not change and cardiac output decreased with hypothermia. Thus, even mild hypothermia impairs LV diastolic but not systolic function. Cardiac output is temperature sensitive and therefore rewarming of patients post-CPB has priority.

Abdominal compartment syndrome: the cause or effect of postinjury multiple organ failure.

Abdominal compartment syndrome (ACS) has emerged to be a significant problem in patients who develop postinjury multiple organ failure (MOF). Current laboratory research suggests that ACS could be a second hit for the development of MOF. Recent studies demonstrate that ACS is an independent predictor of MOF and that the prevention of ACS decreases the incidence of MOF. The Trauma Research Centers at the University of Colorado and the University of Texas-Houston Medical School are focused on defining the role of the gut in postinjury MOF. Because ACS is a plausible modifiable risk factor, our interest has been to 1) describe the epidemiology of ACS, 2) build prediction models, 3) provide strategies for prevention and treatment of ACS, and 4) develop relevant laboratory models. This review summarizes our findings.

Improved myocardial function using a Na+/H+ exchanger inhibitor during cardioplegic arrest and cardiopulmonary bypass.

INTRODUCTION: We have demonstrated that a component of post-cardiopulmonary bypass (CPB)/cardioplegic arrest (CPA) myocardial dysfunction is related to myocardial edema. Myocardial ischemia/reperfusion that occurs with CPB/CPA activates the Na(+)/H(+) exchanger to normalize intracellular pH, with intracellular Na(+) (and water) accumulation. We hypothesized that Na(+)/H(+) exchanger inhibition with a selective inhibitor (EMD 87580) would decrease myocardial edema and improve myocardial performance after CPB/CPA. METHODS: Anesthetized dogs (n = 14) were instrumented with myocardial ultrasonic crystals, and left ventricular (LV) micromanometer, to study myocardial function. Myocardial tissue water (MWC) was determined using microgravimetry. Treated animals (n = 5) received EMD 87580 (5 mg/kg IV pretreatment and 10 mol/L cardioplegia); control animals (n = 9) received a saline vehicle. After baseline, hypothermic CPB/CPA was initiated for 2 h, followed by reperfusion/rewarming for 45 min and separation from CPB. Myocardial function parameters and MWC were measured at 30 min, 60 min, and 120 min after CPB. RESULTS: Preload recruitable stroke work did not decrease from baseline in EMD 87580-treated animals, and was significantly greater in EMD 87580-treated animals than control animals at 120 min after CPB. At a similar LV end-diastolic volume, the maximal rate of rise of LV pressure (dp/dtMAX) was significantly decreased from baseline at all time points in control animals, and unchanged in EMD 87580-treated animals. MWC increased with CPB/CPA in both groups, with no difference between groups. There was no difference in - dp/dtMAX or slope of the end-diastolic pressure-volume relationship. CONCLUSION: Na(+)/H(+) exchanger inhibition improves systolic but not diastolic function after CPB/CPA. This is not due to a reduction in MWC.

Sodium/hydrogen-exchanger inhibition during cardioplegic arrest and cardiopulmonary bypass: an experimental study.

OBJECTIVE: We sought to determine whether pretreatment with a sodium/hydrogen-exchange inhibitor (EMD 96 785) improves myocardial performance and reduces myocardial edema after cardioplegic arrest and cardiopulmonary bypass. METHODS: Anesthetized dogs (n = 13) were instrumented with vascular catheters, myocardial ultrasonic crystals, and left ventricular micromanometers to measure preload recruitable stroke work, maximum rate of pressure rise (positive and negative), and left ventricular end-diastolic volume and pressure. Cardiac output was measured by means of thermodilution. Myocardial tissue water content was determined from sequential biopsy. After baseline measurements, hypothermic (28 degrees C) cardiopulmonary bypass was initiated. Cardioplegic arrest (4 degrees C Bretschneider crystalloid cardioplegic solution) was maintained for 2 hours, followed by reperfusion-rewarming and separation from cardiopulmonary bypass. Preload recruitable stroke work and myocardial tissue water content were measured at 30, 60, and 120 minutes after bypass. EMD 96 785 (3 mg/kg) was given 15 minutes before bypass, and 2 micromol was given in the cardioplegic solution. Control animals received the same volume of saline vehicle. Arterial-coronary sinus lactate difference was similar in both animals receiving EMD 96 785 and control animals, suggesting equivalent myocardial ischemia in each group. RESULTS: Myocardial tissue water content increased from baseline in both animals receiving EMD 96 785 and control animals with cardiopulmonary bypass and cardioplegic arrest but was statistically lower in animals receiving EMD 96 785 compared with control animals (range, 1.0%-1.5% lower in animals receiving EMD 96 785). Preload recruitable stroke work decreased from baseline (97 +/- 2 mm Hg) at 30 (59 +/- 6 mm Hg) and 60 (72 +/- 9 mm Hg) minutes after cardiopulmonary bypass and cardioplegic arrest in control animals; preload recruitable stroke work did not decrease from baseline (98 +/- 2 mm Hg) in animals receiving EMD 96 785 and was statistically greater at 30 (88 +/- 5 mm Hg) and 60 (99 +/- 4 mm Hg) minutes after bypass and arrest compared with control animals. CONCLUSIONS: Sodium/hydrogen-exchanger inhibition decreases myocardial edema immediately after cardiopulmonary bypass and cardioplegic arrest and improves preload recruitable stroke work. Sodium/hydrogen-exchange inhibition during cardiac procedures with cardiopulmonary bypass and cardioplegic arrest may be a useful adjunct to improve myocardial performance in the immediate postbypass or arrest period.

The antioxidant N-acetylcysteine preserves myocardial function and diminishes oxidative stress after cardioplegic arrest.

OBJECTIVE: Oxidative stress contributes to myocardial ischemia-reperfusion injury. We hypothesized that administration of the antioxidant N-acetylcysteine would have beneficial effects on myocardial function after cardiopulmonary bypass and cardioplegic arrest. METHODS: Anesthetized dogs (n = 18) were instrumented with myocardial ultrasonic crystals and a left ventricular micromanometer. Systolic function was measured by preload recruitable stroke work. Myocardial tissue water was determined by microgravimetry. Treated animals received 100 mg.kg(-1) N-acetylcysteine 10 minutes before initiation of cardiopulmonary bypass followed by 20 mg.kg(-1).h(-1) continuous infusion until 1 hour after cardiopulmonary bypass. After baseline, cardiopulmonary bypass and 2-hour crystalloid cardioplegic arrest was initiated, then reperfusion/rewarming for 40 minutes and separation from cardiopulmonary bypass. Myocardial function parameters and myocardial tissue water were measured at 30, 60, and 120 minutes after cardiopulmonary bypass. Oxidative stress was measured by 8-isoprostane concentrations in the coronary sinus plasma. RESULTS: Preload recruitable stroke work did not decrease from baseline in the N-acetylcysteine group and was significantly greater in N-acetylcysteine group compared with controls at 30 (104% +/- 9% vs 80% +/- 4%; P <.05) and 120 minutes (98% +/- 7% vs 79% +/- 4%; P <.05) after cardiopulmonary bypass. Concentrations of 8-isoprostane in the coronary sinus plasma of the control dogs were significantly higher 30 minutes after cardiopulmonary bypass compared with baseline but were unchanged in the N-acetylcysteine group. Myocardial edema resolution was significantly greater in the N-acetylcysteine group at 30 minutes after cardiopulmonary bypass compared with control (-2.5% +/- 0.7% vs -0.3% +/- 0.5% myocardial tissue water; P <.05). CONCLUSIONS: Administration of the antioxidant N-acetylcysteine preserves systolic function and enhances myocardial edema resolution after cardiopulmonary bypass/cardioplegic arrest. Furthermore, oxidative stress was significantly reduced in the treated animals. Therefore, our findings support the hypothesis that oxidative stress is the main cause for myocardial dysfunction after ischemia-reperfusion.

Lessons learned from the evacuation of an urban teaching hospital.

HYPOTHESIS: Valuable lessons can be learned from the emergent evacuation of a large urban teaching hospital because of flooding. DESIGN: Case report. SETTING: Four hundred fifty-bed adult and 150-bed children's tertiary referral teaching hospital. CASE SUMMARY: Massive rainfall from tropical storm Allison caused extensive flooding. Emergency power came on at 1:40 AM. Complete power loss occurred at 3:30 AM. The decision to begin evacuation of patients was made at approximately 10:30 AM. All 575 patients were either discharged from the hospital (169 patients) or evacuated (406 patients) to 29 other facilities by both ambulance and helicopter by 3 PM the next day. Six deaths occurred, none of which could be attributed to the conditions created by the flooding. CONCLUSIONS: The lessons learned from this experience included the following: (1) flooding will occur in a flood plain; (2) electrical power outages are not necessarily temporary-begin evacuation; (3) appoint a triage officer from those available; (4) have a reliable in-house communication system not dependent on telephone lines or electricity; (5) have a reliable telephone system for contacting outside facilities; (6) have flashlights available on all units; (7) have battery-operated exit signs and stairway lights; (8) maximize use of volunteers when they are available and fresh; (9) maintain a paper record of all patient transfers; (10) coordinate loading of ambulances and helicopters for patient transfer; and (11) reassign staff as necessary to care for transferred patients. Emergent evacuation of a large, tertiary hospital requires extensive effort from both the hospital staff and the community.

Myocardial performance after cardiopulmonary bypass and cardioplegic arrest: impact of na+/h+ exchanger inhibition.

This study was designed to determine if pretreatment with a sodium/hydrogen exchange inhibitor (EMD 96 785) improves myocardial performance and reduces myocardial edema after cardioplegic arrest (CPA) and cardiopulmonary bypass (CPB). Anesthetized canines (n = 18) were instrumented with vascular catheters, myocardial ultrasonic crystals, and left ventricle (LV) micromanometer to measure preload recruitable stroke work (PRSW), +dP/dt(max), and cardiac output. Serial myocardial tissue water content (MWC) was determined from sequential biopsy. After baseline measurements, hypothermic (28 degrees C) cardiopulmonary bypass was initiated. CPA was maintained for 2 h, followed by reperfusion/rewarming and separation from CPB. PRSW and myocardial tissue water were measured at 30, 60, and 120 min after CPB. EMD 96 785 (3 mg/kg) was given 15 min prior to CPB. Controls received the same volume of saline vehicle. It was found that MWC increased from baseline in both EMD 96 785 and controls with CPB/CPA. PRSW decreased from baseline at 30 and 60 min post CPB/CPA in controls; PRSW did not decrease from baseline with EMD 96 785, and was statistically greater at 30 and 60 min post CPB/CPA compared to controls. Thus, Na(+)/H(+) exchanger inhibition with EMD 96 785 (3 mg/kg) pretreatment improves post-CPB/CPA myocardial performance without reducing myocardial edema. Na(+)/H(+) exchanger inhibition during cardiac procedures using CPB/CPA may be a useful adjunct to improve immediate post-CPB/CPA myocardial performance.

Volunteer bias in recruitment, retention, and blood sample donation in a randomised controlled trial involving mothers and their children at six months and two years: a longitudinal analysis.

BACKGROUND: The vulnerability of clinical trials to volunteer bias is under-reported. Volunteer bias is systematic error due to differences between those who choose to participate in studies and those who do not. METHODS AND RESULTS: This paper extends the applications of the concept of volunteer bias by using data from a trial of probiotic supplementation for childhood atopy in healthy dyads to explore 1) differences between a) trial participants and aggregated data from publicly available databases b) participants and non-participants as the trial progressed 2) impact on trial findings of weighting data according to deprivation (Townsend) fifths in the sample and target populations. 1) a) Recruits (n = 454) were less deprived than the target population, matched for area of residence and delivery dates (n = 6,893) (mean [SD] deprivation scores 0.09[4.21] and 0.79[4.08], t = 3.44, df = 511, p<0.001). b) i) As the trial progressed, representation of the most deprived decreased. These participants and smokers were less likely to be retained at 6 months (n = 430[95%]) (OR 0.29,0.13-0.67 and 0.20,0.09-0.46), and 2 years (n = 380[84%]) (aOR 0.68,0.50-0.93 and 0.55,0.28-1.09), and consent to infant blood sample donation (n = 220[48%]) (aOR 0.72,0.57-0.92 and 0.43,0.22-0.83). ii) Mothers interested in probiotics or research or reporting infants' adverse events or rashes were more likely to attend research clinics and consent to skin-prick testing. Mothers participating to help children were more likely to consent to infant blood sample donation. 2) In one trial outcome, atopic eczema, the intervention had a positive effect only in the over-represented, least deprived group. Here, data weighting attenuated risk reduction from 6.9%(0.9-13.1%) to 4.6%(-1.4-+10.5%), and OR from 0.40(0.18-0.91) to 0.56(0.26-1.21). Other findings were unchanged. CONCLUSIONS: Potential for volunteer bias intensified during the trial, due to non-participation of the most deprived and smokers. However, these were not the only predictors of non-participation. Data weighting quantified volunteer bias and modified one important trial outcome. TRIAL REGISTRATION: This randomised, double blind, parallel group, placebo controlled trial is registered with the International Standard Randomised Controlled Trials Register, Number (ISRCTN) 26287422. Registered title: Probiotics in the prevention of atopy in infants and children.

Mechanics of the left ventricular myocardial interstitium: effects of acute and chronic myocardial edema.

Myocardial interstitial edema forms as a result of several disease states and clinical interventions. Acute myocardial interstitial edema is associated with compromised systolic and diastolic cardiac function and increased stiffness of the left ventricular chamber. Formation of chronic myocardial interstitial edema results in deposition of interstitial collagen, which causes interstitial fibrosis. To assess the effect of myocardial interstitial edema on the mechanical properties of the left ventricle and the myocardial interstitium, we induced acute and chronic interstitial edema in dogs. Acute myocardial edema was generated by coronary sinus pressure elevation, while chronic myocardial edema was generated by chronic pulmonary artery banding. The pressure-volume relationships of the left ventricular myocardial interstitium and left ventricular chamber for control animals were compared with acutely and chronically edematous animals. Collagen content of nonedematous and chronically edematous animals was also compared. Generating acute myocardial interstitial edema resulted in decreased left ventricular chamber compliance compared with nonedematous animals. With chronic edema, the primary form of collagen changed from type I to III. Left ventricular chamber compliance in animals made chronically edematous was significantly higher than nonedematous animals. The change in primary collagen type secondary to chronic left ventricular myocardial interstitial edema provides direct evidence for structural remodeling. The resulting functional adaptation allows the chronically edematous heart to maintain left ventricular chamber compliance when challenged with acute edema, thus preserving cardiac function over a wide range of interstitial fluid pressures.

Induction of cardioplegic arrest immediately activates the myocardial apoptosis signal pathway.

Myocardial ischemia-reperfusion, including cardioplegic arrest (CA), has been associated with cardiac apoptosis induction. However, the time course of apoptosis activation and the trigger mechanisms are still unclear. Because apoptosis inhibition may represent a novel therapeutic strategy for long-term myocardial preservation, we sought to investigate the time course of apoptosis signal-pathway induction during CA. As to method, Sprague-Dawley rats (300-350 g) were anesthetized, intubated, and mechanically ventilated. CA was initiated by infusion of ice-cold crystalloid solution (Custodiol, 10 ml/kg) into the aortic root, and hearts were rapidly excised and stored for 0, 30, 60, and 120 min in 0.9% sodium chloride solution (28 degrees C). In controls, no CA was initiated before removal and storage at 28 degrees C. In another group, calcium-rich cardioplegia was used, and an additional group received a caspase-8 inhibitor before CA induction. Left ventricular cytosolic extracts were isolated and investigated for the activity of caspase-3 and -6 (effector caspases) and caspase-8 and -9 (involved in extrinsic and intrinsic pathways of apoptosis induction). Fluorometric activity assays were performed by using specific substrates. As a result, activities of all tested caspases were significantly increased immediately after CA induction compared with controls. Administration of the caspase-8 inhibitor significantly reduced activities of all caspases. With calcium-rich cardioplegia, caspase activities were significantly lower compared with low-calcium CA. Control hearts also showed an increase of caspase activities during cold-storage ischemia without CA but had significantly different time courses compared with hearts with CA. In conclusion, our data show rapid apoptosis signal-pathway induction immediately following CA exposure. Thus apoptosis signal-pathway inhibition as a potential strategy for improved myocardial preservation would have the greatest effect when applied before CA exposure.

Hypertonic saline reverses stiffness in a Sprague-Dawley rat model of acute intestinal edema, leading to improved intestinal function.

INTRODUCTION: Acute edema induced by resuscitation and mesenteric venous hypertension impairs intestinal transit and contractility and reduces intestinal stiffness. Pretreatment with hypertonic saline (HS) can prevent these changes. Changes in tissue stiffness have been shown to trigger signaling cascades via stress fiber formation. We proposed that acute intestinal edema leads to a decrease in intestinal transit that may be mediated by changes in stiffness, leading to stress fiber formation and decreased intestinal transit. Furthermore, HS administration will abolish these detrimental effects of edema. RESULTS: Intestinal edema causes a significant increase in tissue water and a significant decrease in intestinal transit and stiffness compared with sham. HS reversed these changes to sham levels. In addition, tissue edema led to significant stress fiber formation and decreased numbers of focal contacts. HS preserved tissue stiffness, prevented stress fiber formation, and was associated with improved intestinal function. CONCLUSION: HS eliminates intestinal tissue edema formation and improves intestinal transit. In addition, the action of HS may be mediated through its preservation of tissue stiffness, which leads to prevention of signaling via stress fiber formation, leading to preserved intestinal function. Finally, intestinal edema may provide a novel physiologic model for examining stiffness and stress fiber signaling.

Measurement of intestinal edema using an impedance analyzer circuit.

BACKGROUND: Acute intestinal edema adversely affects intestinal transit, permeability, and contractility. Current resuscitation modalities, while effective, are associated with development of acute intestinal edema. Knowledge of levels of tissue edema would allow clinicians to monitor intestinal tissue water and may help prevent the detrimental effects of edema. However, there is no simple method to measure intestinal tissue water without biopsy. We sought to develop a tissue impedance analyzer to measure tissue edema, without the need for invasive biopsy. METHODS: Oscillating voltage input was applied to the analyzer circuit and an oscilloscope measured the voltage output across any load. Rats were randomized to three groups: sham, mild edema (80 mL/kg of NS resuscitation), and severe edema (80 mL/kg of NS resuscitation with intestinal venous hypertension). Intestinal edema was measured by wet-to-dry tissue weight ratio. Bowel impedance was measured and converted to capacitance using a standard curve. RESULTS: Acute intestinal edema causes a significant increase in bowel capacitance. This capacitance can be used to predict tissue water concentration. CONCLUSION: Using an impedance analyzer circuit, it is possible to measure intestinal edema reliably and quickly. This may prove to be a useful tool in the resuscitation of critically ill patients.

Intestinal edema decreases intestinal contractile activity via decreased myosin light chain phosphorylation.

OBJECTIVE: The purpose of this study was to investigate the effects of interstitial edema on intestinal contractile activity. DESIGN: Randomized animal study. SETTING: University laboratory. SUBJECTS: Male Sprague-Dawley rats. INTERVENTION: Intestinal edema was induced in rats by a combination of fluid infusion and mesenteric venous hypertension. Rats were divided into four groups: CONTROL, sham; RESUS, saline infusion only; RESUS+VH, saline infusion and venous hypertension; and VH, venous hypertension only. Edema development, basal contractile activity, maximum agonist-induced contractile response (measured as total force generation during the first 2 mins after carbachol treatment), and myosin light chain phosphorylation were measured in the distal small intestine. MEASUREMENTS AND MAIN RESULTS: The amount of interstitial fluid, indicated by the wet-to-dry ratio, increased significantly in both the RESUS and RESUS+VH groups as early as 30 mins after surgery compared with the CONTROL group. Whereas the tissue fluid remained significantly elevated in the RESUS+VH group up to 6 hrs after surgery, the RESUS group wet-to-dry ratios returned to CONTROL group levels by 2 hrs after surgery. Basal contractile activity was significantly less in the RESUS+VH group compared with either the RESUS group or the CONTROL group 6 hrs after surgery. Maximum contractile response decreased significantly in the RESUS+VH group compared with the RESUS group. Basal contractile activity and maximum contractile response did not change significantly in the VH group compared with the CONTROL group. The phosphorylated fraction of myosin light chain was significantly lower in the RESUS+VH group compared with the CONTROL group at 0.5, 2, and 6 hrs after surgery. CONCLUSION: We conclude that edema decreases myosin light chain phosphorylation, leading to decreased intestinal contractile activity.