Hemodynamic team decision making in the cardiac surgical intensive care context

Purpose
The purpose of this study was to explore the extent and sources of variability of critical care nurses’ hemodynamic decision making as a function of contextual factors in the immediate 2-hour period after cardiac surgery.

Methods
A qualitative exploratory design with observation and interview was used. Eight critical care nurses were observed on different occasions in clinical practice for a 2-hour period. A brief interview immediately followed each observation to clarify observation data.

Findings
Analysis of the data revealed that patient management decisions were made both by individual nurses and by a team of nurses and health professionals. Team decision making (TDM) is described in this study as integrated or non-integrated and refers to an intra-professional nursing team. During displays of integrated TDM, the primary nurse, who was assigned to care for the patient, made most hemodynamic decisions and nurses who assisted the primary nurse deferred decisions. During displays of non-integrated TDM, nurses assisting the primary nurse assumed responsibilities for most patient-related decisions. Non-integrated TDM occurred more frequently when inexperienced cardiac surgical intensive care nurses were in the role of primary nurse, whereas integrated TDM was more common among experienced cardiac surgical intensive care nurses.

Conclusions
This observed variability can occur in multiple ways and in hemodynamic decision making has implications for patient outcomes as behaviors of non-integrated TDM led to nurses sensing a loss of control of patient management.

Naturalistic decision making: a model to overcome methodological challenges in the study of critical care nurses` decision making about patients` hemodynamic status

The quality of critical care nurses' decision making about patients' hemodynamic status in the immediate period after cardiac surgery is important for the patients' well-being and, at times, survival. The way nurses respond to hemodynamic cues varies according to the nurses' skills, experiences, and knowledge. Variability in decisions is also associated with the inherent complexity of hemodynamic monitoring. Previous methodological approaches to the study of hemodynamic assessment and treatment decisions have ignored the important interplay between nurses, the task, and the environment in which these decisions are made. The advantages of naturalistic decision making as a framework for studying the manner in which nurses make decisions are presented.

A state space based approach in non-linear hemodynamic response modeling with fMRI data

In this paper we use the modified and integrated version of the balloon model in the analysis of fMRI data. We propose a new state space model realization for this balloon model and represent it with the standard A,B,C and D matrices widely used in system theory. A second order Padé approximation with equal numerator and denominator degree is used for the time delay approximation in the modeling of the cerebral blood flow. The results obtained through numerical solutions showed that the new state space model realization is in close agreement to the actual modified and integrated version of the balloon model. This new system theoretic formulation is likely to open doors to a novel way of analyzing fMRI data with real time robust estimators. With further development and validation, the new model has the potential to devise a generalized measure to make a significant contribution to improve the diagnosis and treatment of clinical scenarios where the brain functioning get altered. Concepts from system theory can readily be used in the analysis of fMRI data and the subsequent synthesis of filters and estimators.

Development of a novel pulsatile bioreactor for tissue culture

The construction of tissue-engineered parts such as heart valves and arteries requires more than just the seeding of cells onto a biocompatible/biodegradable polymeric scaffold. It is essential that the functionality and mechanical integrity of the cell-seeded scaffold be investigated in vitro prior to in vivo implantation. The correct hemodynamic conditioning would lead to the development of tissues with enhanced mechanical strength and cell viability. Therefore, a bioreactor that can simulate physiological conditions would play an important role in the preparation of tissue-engineered constructs. In this article, we present and discuss the design concepts and criteria, as well as the development, of a multifunctional bioreactor for tissue culture in vitro. The system developed is compact and easily housed in an incubator to maintain sterility of the construct. Moreover, the proposed bioreactor, in addition to mimicking in vivo conditions, is highly flexible, allowing different types of constructs to be exposed to various physiological flow conditions. Initial verification of the hemodynamic parameters using Laser doppler anemometry indicated that the bioreactor performed well and produced the correct physiological conditions.

A microfluidics device to monitor platelet aggregation dynamics in response to strain rate micro-gradients in flowing blood

This paper reports the development of a platform technology for measuring platelet function and aggregation based on localized strain rate micro-gradients. Recent experimental findings within our laboratories have identified a key role for strain rate micro-gradients in focally triggering initial recruitment and subsequent aggregation of discoid platelets at sites of blood vessel injury. We present the design justification, hydrodynamic characterization and experimental validation of a microfluidic device incorporating contraction–expansion geometries that generate strain rate conditions mimicking the effects of pathological changes in blood vessel geometry. Blood perfusion through this device supports our published findings of both in vivo and in vitro platelet aggregation and confirms a critical requirement for the coupling of blood flow acceleration to downstream deceleration for the initiation and stabilization of platelet aggregation, in the absence of soluble platelet agonists. The microfluidics platform presented will facilitate the detailed analysis of the effects of hemodynamic parameters on the rate and extent of platelet aggregation and will be a useful tool to elucidate the hemodynamic and platelet mechano-transduction mechanisms, underlying this shear-dependent process.

Implementation of a management guideline aimed at minimizing the severity of primary graft dysfunction after lung transplant

Objective
Primary graft dysfunction, a severe form of lung injury that occurs in the first 72 hours after lung transplant, is associated with morbidity and mortality. We sought to assess the impact of an evidence-based guideline as a protocol for respiratory and hemodynamic management.

Methods
Preoperative and postoperative data for patients treated per the guideline (n = 56) were compared with those of a historical control group (n = 53). Patient data such as ratio of arterial Po2 to inspired oxygen fraction, central venous pressure, cumulative fluid balance, vasopressor dose, and serum urea and creatinine were measured and documented at specific times. Primary outcome was severity of primary graft dysfunction within the first 72 hours.

Results
Primary graft dysfunction grade was progressively lower in patients treated after introduction of the guideline (P = .01). Lower postoperative fluid balances (P = .01) and vasopressor doses (P = .007) were seen, with no associated renal dysfunction. There were no differences in duration of mechanical ventilation or mortality. Nonadherence to the guideline occurred in 10 cases (18%).

Conclusions
Implementation of an evidence-based guideline for managing respiratory and hemodynamic status is feasible and safe and was associated with reduction in severity of primary graft dysfunction. Further studies are required to determine whether such a guideline would lead to a consistent reduction in severity of primary graft dysfunction at other institutions. Creation of a protocol for postoperative care provides a template for further studies of novel therapies or management strategies for primary graft dysfunction.

Home hemodialysis : a successful option for obese and bariatric people with end-stage kidney disease

The increasing prevalence of obesity in developed countries is reflected in the chronic kidney disease, dialysis, and transplant populations. The added risk factor of obesity increases the risk of vascular events, inflammation, insulin resistance, blood pressure, dyslipidemia, and mortality risk. Nephrology center policies may exclude obese people from transplantation programs resulting in many years of dialysis. The case of a 215-kg Australian male who has successfully dialyzed at home for more than 8 years will be used to illustrate the important considerations and clinical support that these people require for successful home dialysis treatment. The aim of this paper is to report on a program that has successfully trained 23 obese (body mass index >30) people who commenced on home hemodialysis between 2001 and 2009. Body weight ranged between 94.0 and 215 kg (mean 126, SD 26.19) and body mass index ranged between 34.9 and 71 (mean 43.38, SD 9.99) at the start of home training. During the 8.5 years of follow-up, average time on home dialysis was 43.7 months. Home hemodialysis is a feasible treatment for obese people to facilitate longer and more frequent dialysis, resulting in improved hemodynamic stability and improved quality of life. For obese people with end-stage kidney disease, home hemodialysis has shown to be cost-effective and can result in greater treatment efficacy than in-center hospital dialysis.

Identification of nonlinear fMRI models using Auxiliary Particle Filter and kernel smoothing method

Hemodynamic models have a high potential in application to understanding the functional differences of the brain. However, full system identification with respect to model fitting to actual functional magnetic resonance imaging (fMRI) data is practically difficult and is still an active area of research. We present a simulation based Bayesian approach for nonlinear model based analysis of the fMRI data. The idea is to do a joint state and parameter estimation within a general filtering framework. One advantage of using Bayesian methods is that they provide a complete description of the posterior distribution, not just a single point estimate. We use an Auxiliary Particle Filter adjoined with a kernel smoothing approach to address this joint estimation problem.

Parameter estimation of the BOLD fMRI model within a general particle filter framework

This work demonstrates a novel Bayesian learning approach for model based analysis of Functional Magnetic Resonance (fMRI) data. We use a physiologically inspired hemodynamic model and investigate a method to simultaneously infer the neural activity together with hidden state and the physiological parameter of the model. This joint estimation problem is still an open topic. In our work we use a Particle Filter accompanied with a kernel smoothing approach to address this problem within a general filtering framework. Simulation results show that the proposed method is a consistent approach and has a good potential to be enhanced for further fMRI data analysis.

Optimization of bypass graft using FSI numerical method

It is well documented in literature that the coronary artery bypass graft is normally fail after a short period of time, due to the development of plaque known as intimal hyperplasia within the graft. Various in vivo and in vitro studies have linked the development of intimal hyperplasia to the abnormal hemodynamics and compliance mismatch. Therefore, it is essential to fully understand the relationship between the hemodynamics inside the coronary artery bypass and its mechanical and geometrical characteristics under the correct physiological conditions. In this work, hemodynamic of the bypass graft is studied numerically. The effect of the host and graft diameters ratio, the angle of anastomosis and the graft configuration on the local flow patterns and the distribution of wall shear stress are examined. The pulsatile waveforms boundary conditions are adopted from in vivo measurement data to study the hemodynamics of composite grafts namely Consequence and Y grafting in terms temporal and spatial distributions of the blood flows. Moreover, various non-Newtonian and Newtonian models of blood have been carried out to examine the numerical simulation of blood flow in stenosis artery. The results are presented and discussed for various operating conditions.

Unilateral bicep curl hemodynamics: low-pressure continuous vs high-pressure intermittent blood flow restriction

 Light-load exercise training with blood flow restriction (BFR) increases muscle strength and size. However, the hemodynamics of BFR exercise appear elevated compared with non-BFR exercise. This questions the suitability of BFR in special/clinical populations. Nevertheless, hemodynamics of standard prescription protocols for BFR and traditional heavy-load exercise have not been compared. We investigated the hemodynamics of two common BFR exercise methods and two traditional resistance exercises. Twelve young males completed four unilateral elbow flexion exercise trials in a balanced, randomized crossover design: (a) heavy load [HL; 80% one-repetition maximum (1-RM)]; (b) light load (LL; 20% 1-RM); and two other light-load trials with BFR applied (c) continuously at 80% resting systolic blood pressure (BFR-C) or (d) intermittently at 130% resting systolic blood pressure (BFR-I). Hemodynamics were measured at baseline, during exercise, and for 60-min post-exercise. Exercising heart rate, blood pressure, cardiac output, and rate–pressure product were significantly greater for HL and BFR-I compared with LL. The magnitude of hemodynamic stress for BFR-C was between that of HL and LL. These data show reduced hemodynamics for continuous low-pressure BFR exercise compared with intermittent high-pressure BFR in young healthy populations. BFR remains a potentially viable method to improve muscle mass and strength in special/clinical populations.

Medical textiles as vascular implants and their success to mimic natural arteries

Vascular implants belong to a specialised class of medical textiles. The basic purpose of a vascular implant (graft and stent) is to act as an artificial conduit or substitute for a diseased artery. However, the long-term healing function depends on its ability to mimic the mechanical and biological behaviour of the artery. This requires a thorough understanding of the structure and function of an artery, which can then be translated into a synthetic structure based on the capabilities of the manufacturing method utilised. Common textile manufacturing techniques, such as weaving, knitting, braiding, and electrospinning, are frequently used to design vascular implants for research and commercial purposes for the past decades. However, the ability to match attributes of a vascular substitute to those of a native artery still remains a challenge. The synthetic implants have been found to cause disturbance in biological, biomechanical, and hemodynamic parameters at the implant site, which has been widely attributed to their structural design. In this work, we reviewed the design aspect of textile vascular implants and compared them to the structure of a natural artery as a basis for assessing the level of success as an implant. The outcome of this work is expected to encourage future design strategies for developing improved long lasting vascular implants.