Estimated pulse-wave velocity predicts survival in patients requiring extracorporeal membrane oxygenation

INTRODUCTION

Arterial stiffness, measured by estimated pulse-wave velocity is a known predictor of major adverse cardiovascular events, however its predictive value in patients requiring extracorporeal membrane oxygenation (ECMO) is unknown.

METHODS

A retrospective cohort study was performed at the London Health Science Centre in London, Canada between 1996-2021, totaling 255 patients requiring ECMO. Estimated pulse-wave velocity (ePWV) was calculated using an algorithm from the Reference Values for Arterial Stiffness Collaboration. Recorded outcomes included in-hospital death, ischemic stroke, hemorrhagic stroke, renal failure and need for renal replacement therapy (RRT). For adjusted analysis, survival-to-discharge was used. Multivariate logistic regression and propensity-score matching were utilized to control for confounding.

RESULTS

On univariate analysis, higher ePWV was significantly predictive of ischemic stroke (OR 1.676, p = 0.0002) and in-hospital death (OR 1.20, p = 0.006), but insignificant for predicting hemorrhagic stroke (OR 1.07, p = 0.710), and appeared protective for renal failure (OR 0.88 [0.78-0.99], p = 0.034) and RRT (OR 0.87, p = 0.027). On multivariate analysis and propensity-score matching, five of six models demonstrated ePWV as an independent predictor of survival-to-discharge. (OR 0.70, p = 0.00,021; OR 0.72, p = 0.0002; OR 0.87, p = 0.045; OR 0.85, p = 0.013; OR 0.57, p = 0.012).

CONCLUSIONS

ePWV is a promising marker for risk-stratification in ECMO patients. Further investigation is required to better delineate the role of arterial health assessment in disease trajectory and strengthen the validity of AS as a marker of interest in medical and surgical management.

Postarrest Care Bundle Improves Quality of Care and Clinical Outcomes in the Normothermia Era

PURPOSE

Temperature targets in patients with cardiac arrest and return of spontaneous circulation (ROSC) have changed. Changes to higher temperature targets have been associated with higher breakthrough fevers and mortality. A post-ROSC normothermia bundle was developed to improve compliance with temperature targets.

METHODS

In August 2021, "ad hoc" normothermia at the discretion of the attending intensivist was initiated. In December 2021, a post-ROSC normothermia protocol was implemented, incorporating a rigorous, stepwise approach to fever prevention (temperature ≥ 37.8). We conducted a before-after cohort study of all adult patients post-ROSC who survived to intensive care unit admission between August 1, 2021, and April 1, 2022. They were divided into "ad hoc" and "protocol" groups. Clinical outcomes compared included fevers, active cooling, and paralytic use.

RESULTS

Fifty-eight post-ROSC patients were admitted; 24 in the "ad hoc" and 34 in the "protocol" groups. Patient demographics were similar between groups. The "ad hoc" group had more shockable rhythms (67% vs 24%, P = .001) and cardiac catheterizations (42% vs 15%, P = .03). The "protocol" group were significantly less likely to have a fever at 40 h (6% vs 40%, P < .001) and 72 h (14% vs 65%, P ≤ .001). Patients in the normothermia "protocol" used significantly less neuromuscular blocking agents (24% vs 50%, P = .05). The normothermia "protocol" resulted in similar mortality (56% vs 58%, P = 1.0).

CONCLUSION

Use of a normothermia "protocol" resulted in fewer fevers and less neuromuscular blocker administration compared to "ad hoc" management. A protocolized approach for improved quality of care should be considered in institutions adopting normothermia.

CEPP: Canadian Extracorporeal Life Support (ECLS) Protocol Project

Background

Extracorporeal life support (ECLS) is associated with high morbidity and mortality. Complications and mortality are higher at lower-volume centres. Most Canadian ECLS institutions are low-volume centres. Protocols offer one way to share best practices among institutions to improve outcomes. Whether Canadian centres have ECLS protocols, and whether these protocols are comprehensive and homogenous across centres, is unknown.

Methods

Purposeful sampling with mixed methods was used. A Delphi panel defined key elements relevant to the ECLS process. Documentation used in the delivery of ECLS services was requested from programs. Institutional protocols were assessed using deductive coding to determine the presence of key elements.

Results

A total of 37 key elements spanning 5 domains (referral, initiation, maintenance, termination, and administration) were identified. Documentation from 13 institutions across 10 provinces was obtained. Institutions with heart or lung transplantation programs had more-complete documentation than did non-transplantation programs. Only 5 key elements were present in at least 50% of protocols (anticoagulation strategy, ventilation strategy, defined referral process, selection criteria, weaning process), and variation was seen in how institutions approached each of these elements.

Conclusions

The completeness of ECLS protocols varies across Canada. Programs describe variable approaches to key elements. This variability might represent a lack of evidence or consensus in these areas and creates the opportunity for collaboration among institutions to share protocols and best practice. The key-element framework provides a common language that programs can use to develop ECLS programs, initiate quality-improvement projects, and identify research agendas.

Effect of Probiotics on Incident Ventilator-Associated Pneumonia in Critically Ill Patients: A Randomized Clinical Trial

IMPORTANCE

Growing interest in microbial dysbiosis during critical illness has raised questions about the therapeutic potential of microbiome modification with probiotics. Prior randomized trials in this population suggest that probiotics reduce infection, particularly ventilator-associated pneumonia (VAP), although probiotic-associated infections have also been reported.

OBJECTIVE

To evaluate the effect of Lactobacillus rhamnosus GG on preventing VAP, additional infections, and other clinically important outcomes in the intensive care unit (ICU).

DESIGN, SETTING, AND PARTICIPANTS

Randomized placebo-controlled trial in 44 ICUs in Canada, the United States, and Saudi Arabia enrolling adults predicted to require mechanical ventilation for at least 72 hours. A total of 2653 patients were enrolled from October 2013 to March 2019 (final follow-up, October 2020).

INTERVENTIONS

Enteral L rhamnosus GG (1 × 1010 colony-forming units) (n = 1321) or placebo (n = 1332) twice daily in the ICU.

MAIN OUTCOMES AND MEASURES

The primary outcome was VAP determined by duplicate blinded central adjudication. Secondary outcomes were other ICU-acquired infections including Clostridioides difficile infection, diarrhea, antimicrobial use, ICU and hospital length of stay, and mortality.

RESULTS

Among 2653 randomized patients (mean age, 59.8 years [SD], 16.5 years), 2650 (99.9%) completed the trial (mean age, 59.8 years [SD], 16.5 years; 1063 women [40.1%.] with a mean Acute Physiology and Chronic Health Evaluation II score of 22.0 (SD, 7.8) and received the study product for a median of 9 days (IQR, 5-15 days). VAP developed among 289 of 1318 patients (21.9%) receiving probiotics vs 284 of 1332 controls (21.3%; hazard ratio [HR], 1.03 (95% CI, 0.87-1.22; P = .73, absolute difference, 0.6%, 95% CI, -2.5% to 3.7%). None of the 20 prespecified secondary outcomes, including other ICU-acquired infections, diarrhea, antimicrobial use, mortality, or length of stay showed a significant difference. Fifteen patients (1.1%) receiving probiotics vs 1 (0.1%) in the control group experienced the adverse event of L rhamnosus in a sterile site or the sole or predominant organism in a nonsterile site (odds ratio, 14.02; 95% CI, 1.79-109.58; P < .001).

CONCLUSIONS AND RELEVANCE

Among critically ill patients requiring mechanical ventilation, administration of the probiotic L rhamnosus GG compared with placebo, resulted in no significant difference in the development of ventilator-associated pneumonia. These findings do not support the use of L rhamnosus GG in critically ill patients.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT02462590.

Current Use, Capacity, and Perceived Barriers to the Use of Extracorporeal Cardiopulmonary Resuscitation for Out-of-Hospital Cardiac Arrest in Canada

BACKGROUND

Extracorporeal cardiopulmonary resuscitation (ECPR) is a therapeutic option for refractory cardiac arrest. We sought to perform an environmental scan to describe ECPR utilization in Canada and perceived barriers for application to out-of-hospital cardiac arrest (OHCA).

METHODS

This was a national cross-sectional study. We identified all cardiovascular surgery- and extracorporeal membrane oxygenation (ECMO)-capable hospitals in Canada and emergency medical services (EMS) agencies delivering patients to those centres. We requested the medical lead from each hospital's ECMO service and each EMS agency to submit data regarding ECMO and ECPR utilization, as well as perceived barriers to ECPR provision for OHCA.

RESULTS

We identified and received survey data from 39 of 39 Canadian hospital institutions and 21 of 22 EMS agencies. Of hospitals, 38 (97%) perform ECMO and 27 (69%) perform ECPR (74% of which perform ≤5 cases per year). Of the 18 (46%) sites offering ECPR for OHCA, 8 apply a formal protocol for eligibility and initiation procedures. EMS agencies demonstrate heterogeneity with intra-arrest transport practices. The primary rationale for nontransport of refractory OHCA is that hospital-based care offers no additional therapies. Perceived barriers to the use of ECPR for OHCA were primarily related to limited evidence supporting its use, rather than resources required.

CONCLUSION

Many Canadian cardiovascular surgery- or ECMO-equipped hospitals use ECPR; roughly half employ ECPR for OHCAs. Low case volumes and few formal protocols indicate that this is not a standardized therapy option in most centres. Increased application may be dependent on a stronger evidence base including data from randomized clinical trials currently underway.

Transfusion Thresholds for Adult Respiratory Extracorporeal Life Support: An Expert Consensus Document

Severe acute respiratory distress syndrome (ARDS) can complicate novel pandemic coronavirus disease (COVID-19). Extracorporeal life support (ECLS) represents the final possible rescue strategy. Variations in practice, combined with a paucity of rigourous guidelines, may complicate blood-product resource availability and allocation during a pandemic. We conducted a literature review around venovenous extracorporeal membrane oxygenation (VV-ECMO) transfusion practices for platelets, packed red blood cells, fresh frozen plasma, prothrombin complex concentrate, and antithrombin. Pertinent society guidelines were examined, and the practice of Canadian ECLS experts was sampled through an environmental scan. This paper represents a synthesis of these explorations, combined with input from the Canadian Cardiovascular Critical Care (CANCARE) Society, Canadian Society of Cardiac Surgeons, and the Canadian Critical Care Society. We offer a pragmatic guidance document for restrictive transfusion thresholds in nonbleeding patients on VV-ECMO, which may attenuate transfusion-related complications and simultaneously shield national blood product inventory from strain during pandemic-induced activation of the National Plan for the Management of Shortages of Labile Blood Components.

The hematopoietic transcription factor GATA2 is a novel regulator of apoptotic cell clearance by macrophages in atherosclerosis

Atherosclerosis is an inflammatory disease involving formation of lipid-rich lesions within the arteries. Macrophages clear apoptotic cells that accumulate within these lesions. Defective apoptotic cell clearance is a hallmark of advanced atherosclerotic disease, yet mechanisms that drive this defect are poorly understood. In this study, we identify the hematopoietic transcription factor GATA2 as a novel regulator of macrophage-mediated apoptotic cell clearance.

Macrophages were isolated by laser capture microdissection from atherosclerotic lesions in aortic tissue obtained from patients undergoing open heart surgery. Gene expression profiling was performed on these macrophages by microarray, with macrophages derived from peripheral blood monocytes used as a control.

We found approximately 3,000 genes to be differentially expressed in aortic punch macrophages, with enrichment in pathways involved in apoptotic cell clearance. In particular, we identified upregulation of GATA2. Mutations in GATA2 have previously been associated with increased risk of coronary artery disease and we found that overexpression of GATA2 in vitro resulted in decreased ability of macrophages to both internalize and degrade apoptotic cells. Conversely, GATA2 downregulation is sufficient to abrogate oxLDL-induced defective apoptotic cell clearance.

Atherosclerotic macrophages exhibit dysregulated expression of genes involved in apoptotic cell clearance and upregulation of GATA2. Recapitulation of GATA2 overexpression is sufficient to impair apoptotic cell clearance in vitro. To our knowledge, we are the first to identify a potential role for GATA2 in driving defective apoptotic cell clearance in atherosclerosis.

Acceptability of cardiac donation after circulatory determination of death: a survey of the Canadian public

PURPOSE

Cardiac transplantation is a definitive therapy for end-stage heart failure, but demand exceeds supply. Cardiac donation after circulatory determination of death (cardiac DCDD) can be performed using direct procurement and perfusion (DPP), where cardiac activity is restored after heart recovery, or (NRP), where brain blood supply is surgically interrupted, circulation to the thoraco-abdominal organs is restored within the donor's body, followed by heart recovery. While cardiac DCDD would increase the number of heart donors, uptake of programs has been slowed in part because of ethical concerns within the medical community. These debates have been largely devoid of discussion regarding public perceptions. We conducted a national survey of public perceptions regarding cardiac DCDD.

METHODS

We surveyed 1,001 Canadians about their attitudes towards cardiac DCDD using a rigorously designed and pre-tested survey.

RESULTS

We found that 843 of 1,001 respondents (84.2%; 95% confidence interval [CI], 81.8 to 86.3) accepted the DPP approach, 642 (64.1%; 95% CI, 61.1 to 67.0) would agree to donate their heart using DPP, and 696 (69.5%; 95% CI, 66.6 to 72.3) would consent to the same for a family member. We found that 779 respondents of 1,001 respondents (77.8%; 95% CI, 75.1 to 80.3) accepted the NRP approach, 587 (58.6%; 95% CI, 55.5 to 61.6) would agree to donate their heart using NRP, and 636 (63.5%; 95% CI, 60.5 to 66.4) would consent to the same for a family member. Most respondents supported the implementation of DPP (738 respondents or 73.7%; 95% CI, 70.9 to 76.3) and NRP (655 respondents or 65.4%; 95% CI, 62.4 to 68.3) in Canada.

CONCLUSION

The results of this national survey of public attitudes towards cardiac DCDD will inform the implementation of cardiac DCDD programs in a manner that is consistent with public values.

Attitudes of healthcare providers towards cardiac donation after circulatory determination of death: a Canadian nation-wide survey

PURPOSE

The number of patients on cardiac transplant waitlists exceeds the number of available donor organs. Cardiac donation is currently limited to those declared dead by neurologic criteria in all but three countries. Cardiac donation after circulatory determination of death (cardiac DCDD) can be conducted using direct procurement and perfusion (DPP) or normothermic regional perfusion (NRP). Implementation of cardiac DCDD in many countries has been slowed by ethical debates within the donation and transplantation community. We conducted a national survey to determine the perceptions of healthcare providers regarding cardiac DCDD.

METHODS

We conducted an electronic survey of 398 healthcare providers who are involved in the management of heart donors and/or heart transplant recipients in Canada (226 nurses, 82 critical care physicians, 31 donation specialists, and 59 transplant specialists). Our primary outcomes were their attitudes towards and concerns regarding cardiac DCDD protocols and their implementation in Canada. We distributed the survey electronically through several Canadian donation and transplantation organizations.

RESULTS

We identified that 361 of 391 respondents (92.3%; 95% confidence interval [CI], 89.6 to 95.1) believed that DPP is acceptable, and 329 of 377 respondents (87.3%; 95% CI, 83.9 to 90.7) supported its implementation in Canada. We found that 301 of 384 respondents (78.4%; 95% CI, 74.2 to 82.6) believed that NRP is acceptable and 266 of 377 respondents (70.6%; 95% CI, 66.0 to 75.2) supported its implementation in Canada.

CONCLUSION

This is the first survey describing the attitudes of healthcare providers towards cardiac DCDD. We identified widespread support for cardiac DCDD and its implementation in Canada among Canadian healthcare providers within the organ donation and transplantation community in Canada.

Supplementing preservation solution with mitochondria-targeted H2 S donor AP39 protects cardiac grafts from prolonged cold ischemia-reperfusion injury in heart transplantation

Heart transplant has been accepted as the standard treatment for end-stage heart failure. Because of its susceptibility to ischemia-reperfusion injury, the heart can be preserved for only 4 to 6 hours in cold static preservation solutions. Prolonged ischemia time is adversely associated with primary graft function and long-term survival. New strategies to preserve donor hearts are urgently needed. We demonstrate that AP39, a mitochondria-targeting hydrogen sulfide donor, significantly increases cardiomyocyte viability and reduces cell apoptosis/death after cold hypoxia/reoxygenation in vitro. It also decreases gene expression of proinflammatory cytokines and preserves mitochondria function. Using an in vivo murine heart transplant model, we show that preserving donor hearts with AP39-supplemented University of Wisconsin solution (n = 7) significantly protects heart graft function, measured by quantitative ultrasound scan, against prolonged cold ischemia-reperfusion injury (24 hours at 4°C), along with reducing tissue injury and fibrosis. Our study demonstrates that supplementing preservation solution with AP39 protects cardiac grafts from prolonged ischemia, highlighting its therapeutic potential in preventing ischemia-reperfusion injury in heart transplant.

A 24-hour perioperative case study on argatroban use for left ventricle assist device insertion during cardiopulmonary bypass and veno-arterial extracorporeal membrane oxygenation

A 44-year-old male with ongoing chest pain and left ventricular ejection fraction <20% was transferred from a peripheral hospital with intra-aortic balloon pump placement following a non-ST-elevation myocardial infarction (STEMI). The patient underwent emergent multi-vessel coronary artery bypass grafting requiring veno-arterial (VA) extracorporeal membrane oxygenation (ECMO) on post-operative day (POD)#9 secondary to cardiogenic shock with biventricular failure. Due to clot formation, an oxygenator change-out was necessary shortly after initiation. Following a positive heparin-induced thrombocytopenia (HIT) assay, a total circuit exchange was required to eliminate all heparin coating and argatroban was deemed the anticoagulant of choice due to acute kidney injury. On POD#24, the decision was made to implant a left ventricle assist device (LVAD) as a bridge to heart transplantation. There was difficulty achieving an activated clotting time (ACT) >400 s: multiple argatroban bolus doses were required, along with accelerated up-titration of infusion dosing. Despite maintaining an ACT >484 s, clot formation was observed in the cardiotomy reservoir prior to separation. Subsequently, the patient developed severe disseminated intravascular coagulopathy, with both intra-cardiac and intravascular thrombi, requiring massive transfusion and continuous cell saving due to severe hemorrhage post cardiopulmonary bypass (CPB). The patient received a total of 105 units of plasma, 74 units of packed red cells, 19 units of platelets, 13 bottles of 5% albumin, 6 units of cryoprecipitate and 2 doses of factor VIIa intraoperatively over the course of 24 hours. A total of 19.7 L of washed red blood cells were returned to the patient from the cell saver. With the LVAD in place, the patient developed transfusion-related acute lung injury and acute respiratory distress syndrome with right ventricular dysfunction requiring VA ECMO once again. On POD#30, ECMO was discontinued and the patient was discharged from the intensive care unit (ICU) on POD 66. After a very complex post-operative stay with numerous surgeries and extensive rehabilitation, the patient was discharged home with the LVAD on POD#112.

Extracorporeal Cardiopulmonary Resuscitation for Refractory Out-of-Hospital Cardiac Arrest: The State of the Evidence and Framework for Application

Out-of-hospital cardiac arrest (OHCA) affects 134 per 100,000 citizens annually. Extracorporeal cardiopulmonary resuscitation (ECPR), providing mechanical circulatory support, may improve the likelihood of survival among those with refractory OHCA. Compared with in-hospital ECPR candidates, those in the out-of-hospital setting tend to be sudden unexpected arrests in younger and healthier patients. The aims of this review were to summarize, and identify the limitations of, the evidence evaluating ECPR for OHCA, and to provide an approach for ECPR program application. Although there are many descriptions of ECPR-treated cohorts, we identified a paucity of robust data showing ECPR effectiveness compared with conventional resuscitation. However, it is highly likely that ECPR, provided after a prolonged attempt with conventional resuscitation, does benefit select patient populations compared with conventional resuscitation alone. Although reliable data showing the optimal patient selection criteria for ECPR are lacking, most implementations sought young previously healthy patients with rapid high-quality cardiopulmonary resuscitation. Carefully planned development of ECPR programs, in high-performing emergency medical systems at experienced extracorporeal membrane oxygenation centres, may be reasonable as part of systematic efforts to determine ECPR effectiveness and globally improve care. Protocol evaluation requires regional-level assessment, examining the incremental benefit of survival compared with standard care, while accounting for resource utilization.

Levosimendan in Patients with Left Ventricular Dysfunction Undergoing Cardiac Surgery

BACKGROUND

Levosimendan is an inotropic agent that has been shown in small studies to prevent or treat the low cardiac output syndrome after cardiac surgery.

METHODS

In a multicenter, randomized, placebo-controlled, phase 3 trial, we evaluated the efficacy and safety of levosimendan in patients with a left ventricular ejection fraction of 35% or less who were undergoing cardiac surgery with the use of cardiopulmonary bypass. Patients were randomly assigned to receive either intravenous levosimendan (at a dose of 0.2 μg per kilogram of body weight per minute for 1 hour, followed by a dose of 0.1 μg per kilogram per minute for 23 hours) or placebo, with the infusion started before surgery. The two primary end points were a four-component composite of death through day 30, renal-replacement therapy through day 30, perioperative myocardial infarction through day 5, or use of a mechanical cardiac assist device through day 5; and a two-component composite of death through day 30 or use of a mechanical cardiac assist device through day 5.

RESULTS

A total of 882 patients underwent randomization, 849 of whom received levosimendan or placebo and were included in the modified intention-to-treat population. The four-component primary end point occurred in 105 of 428 patients (24.5%) assigned to receive levosimendan and in 103 of 421 (24.5%) assigned to receive placebo (adjusted odds ratio, 1.00; 99% confidence interval [CI], 0.66 to 1.54; P=0.98). The two-component primary end point occurred in 56 patients (13.1%) assigned to receive levosimendan and in 48 (11.4%) assigned to receive placebo (adjusted odds ratio, 1.18; 96% CI, 0.76 to 1.82; P=0.45). The rate of adverse events did not differ significantly between the two groups.

CONCLUSIONS

Prophylactic levosimendan did not result in a rate of the short-term composite end point of death, renal-replacement therapy, perioperative myocardial infarction, or use of a mechanical cardiac assist device that was lower than the rate with placebo among patients with a reduced left ventricular ejection fraction who were undergoing cardiac surgery with the use of cardiopulmonary bypass. (Funded by Tenax Therapeutics; LEVO-CTS ClinicalTrials.gov number, NCT02025621 .).

Cardiac Surgeons after Vacation: Refreshed or Rusty?

Introduction

Many surgeons describe feeling a bit out of practice when they return from a vacation. There have been no studies assessing the impact of surgeon vacation on patient outcomes.

Methods

We used administrative data from the province of Ontario to identify patients who underwent a coronary artery bypass grafting. Using a propensity score, we matched patients who underwent their procedure immediately after their surgeon returned from vacation of at least 7 days (n = 1,161) to patients who were not operated immediately before or after a vacation period (n = 2,138).

Results

There was no significant difference in patient mortality (odds ratio: 1.23, p = 0.52), length of operation (relative risk [RR]: 1.00 p = 0.58), or intensive care unit/ hospital stay (RR: 0.97 p = 0.66/RR: 0.98 p = 0.54, respectively).

Conclusion

There was not a significant change in risk of death, operative length, or hospital stay after a surgeon vacation.

Aging effects on contractility of longitudinal and circular detrusor and trigone of rat bladder

PURPOSE

Aging is associated with bladder dysfunction, including difficult voiding and urinary leakage. Voiding involves reduction in the bladder lumen in all dimensions brought about by contraction of the meshwork of longitudinal, circular and oblique layers of detrusor smooth muscles. Most in vitro physiological studies of the effects of aging on bladder function used the longitudinal detrusor. To understand the region specific effects of aging on bladder function the contractile responses of longitudinal and circular detrusor, and trigone segments of the bladder from young and old rats were monitored.

MATERIALS AND METHODS

These studies were performed using male Fisher 344 rats 6 months (young) and 27 months (old) old obtained through the National Institute on Aging. Each rat was anesthetized and the bladder was isolated. From each bladder a strip of longitudinal detrusor, circular detrusor and trigone was isolated and mounted in an in vitro multi-muscle chamber containing normal physiological solution at 37C. Isometric contractions of the 3 bladder strips were monitored after electrical field stimulation, 120 mM. potassium and 1 to 1,000 microM. bethanechol using a digital oscilloscope.

RESULTS

In longitudinal detrusor from old rats there was no significant difference in the contractions evoked by electrical stimulation or high potassium but there was a significant reduction in contractions evoked by bethanechol compared with the responses of longitudinal detrusor from young rats. In circular detrusor from old rats there was a significant increase in contractions evoked by electrical stimulation and a slight increase in contractions produced by high potassium but no significant change in contractions evoked by bethanechol compared with the responses of circular detrusor from young rats. In trigone from old rats there was a significant decrease in contractions evoked by electrical stimulation, high potassium and bethanechol compared with young trigone.

CONCLUSIONS

The reduction in contractions evoked by bethanechol suggests an age related reduction in muscarinic receptors in the longitudinal detrusor of aged rats. An increase in contractions evoked by electrical stimulation without a change in contractions evoked by bethanechol suggests a decrease in compliance caused by an increase in collagen in the circular detrusor of aged rats. A general decline in all contractile responses, including those evoked by high potassium, suggests reduced membrane depolarization in the trigone of aged rats. The effect of aging is specific to different regions and functional components of the bladder, probably due to changes in muscarinic receptors, collagen and depolarization.