Pressure & flow relationship in the pulmonary circulation in man

Background: Current gold standard pulmonary artery pressure measurements (PAP) are not accurate using a fluid filled catheter. High fidelity micromanometer tipped catheters are more accurate both at rest and during exercise. They have been used to examine the pattern of pulmonary artery pressure waveforms under various physiological conditions. A new thoracic impedance device has been developed, the Physioflow 1 ((c)Manatee, France), which has been shown to measure cardiac output (CO) accurately in a variety of respiratory conditions. It is known that PAP varies with changes in posture, sleep and exercise, and may sometimes appear normal at rest in early disease. Resting pressures vary daily. However, pressure and flow is linearly related in physiological ranges and the relationship is relatively constant. Changes in pressure-flow relationships may be missed at rest. It has been shown that response to a given treatment may be missed if measurements are based solely on resting PAP. For this reason the slopes of pressure-flow plots, are more useful than spot measures of pressure and flow. This has not adequately been explored in humans

Strain threshold for ventilator-induced lung injury

Introduction Unphysiological lung strain (tidal volume/functional residual capacity, TV/FRC) may cause ventilator-induced lung injury (VILI) [1]. Whether VILI develops proportionally to the applied strain or only above a critical threshold remains unknown. Methods In 20 healthy, mechanically ventilated pigs, FRC and lung weight were measured by computed tomography. Animals were then ventilated for up to 54 hours with a TV set to produce a predetermined strain. At the end, lung weight was measured with a balance. VILI was defi ned as fi nal lung weight exceeding the initial one. Results Lung weight either did not increase at all (no-VILI group; lung weight change \u201373 \ub1 42 g, n = 9) or markedly augmented (VILI group; 264 \ub1 80 g, n = 11). In the two groups, strain was 1.38 \ub1 0.68 and 2.16 \ub1 0.50 (P <0.01), respectively. VILI occurred only when lung strain reached or exceeded a critical threshold, between 1.5 and 2.1 (Figure 1). Conclusions In animals with healthy lungs VILI only occurs when lung strain exceeds a critical threshold. Reference 1. Gattinoni L, Carlesso E, Cadringher P, et al.: Physical and biological triggers of ventilator-induced lung injury and its prevention [review]. Eur Respir J 2003, 22(Suppl 47):15s-25s

Cardiac cycle efficiency as prognostic index in ICUs

We implement a beam steering system based on a directly-modulated unseeded R-SOA, allowing the distribution of 2.4 GHz 64QAM OFDMA signals with 2048-subcarriers satisfying IEEE 802.16e specifications

Whole blood lactate kinetics in patients undergoing quantitative resuscitation for septic shock

Introduction We sought to compare the association of whole blood lactate kinetics with survival in patients with septic shock undergoing early quantitative resuscitation. Methods Preplanned analysis of a multicenter emergency department (ED)-based randomized control trial of early sepsis resuscitation targeting three physiological variables: central venous pressure, mean arterial pressure, and either central venous oxygen saturation or lactate clearance. Inclusion criteria: suspected infection, two or more systemic inflammatory response syndrome criteria, and either SBP 4 mmol/l. All patients had a lactate measured initially and subsequently at two hours. Normalization of lactate was defined as a lactate decline to 2.0 mmol/l was seen in 187/272 (69%), and 68/187 (36%) patients normalized their lactate. Overall mortality was 19.7%. AUCs for initial lactate, relative lactate clearance, and absolute lactate clearance were 0.70, 0.69, and 0.58, respectively. Lactate normalization best predicted survival (OR = 6.1, 95% CI = 2.2 to 21), followed by lactate clearance of 50% (OR = 4.3, 95% CI = 1.8 to 10.3), initial lactate of <2 mmol/l (OR = 3.4, 95% CI = 1.5 to 7.8), and initial lactate <4 mmol/l (OR = 2.3, 95% CI = 1.3 to 4.3), with lactate clearance of 10% not reaching significance (OR = 2.3, 95% CI = 0.96 to 5.6). Conclusions In ED sepsis patients undergoing early quantitative resuscitation, normalization of serum lactate during resuscitation was more strongly associated with survival than any absolute value or absolute/ relative change in lactate. Further studies should address whether strategies targeting lactate normalization leads to improved outcomes

Model-based cardiovascular monitoring of acute pulmonary embolism in porcine trials

Introduction: Diagnosis and treatment of cardiac and circulatory dysfunction can be error-prone and relies heavily on clinical intuition and experience. Model-based approaches utilising measurements available in the Intensive care unit (ICU) can provide a clearer physiological picture of a patient’s cardiovascular status to assist medical staff with diagnosis and therapy decisions. This research tests a subject-specific cardiovascular system (CVS) modelling technique on measurements from a porcine model of acute pulmonary embolism (APE). Methods: Measurements were recorded in 5 pig trials, where autologous blood clots were inserted every two hours into the jugular vein to simulate pulmonary emboli. Of these measurements only a minimal set of clinically available or inferable data were used in the identification process (aortic and pulmonary artery pressure, stroke volume, heart rate, global end diastolic volume, and mitral and tricuspid valve closure times). The CVS model was fitted to 46 sets of data taken at 30 minute intervals (t=0, 30, 60, …, 270) during the induction of APE to identify physiological model parameters and their change over time in APE. Model parameters and outputs were compared to experimentally derived metrics and measurements not used in the identification method to validate the accuracy of the model and assess its diagnostic capability. Results: Modelled mean ventricular volumes and maximum ventricular pressures matched measured values with median absolute errors of 4.3% and 4.4%, which are less than experimental measurement noise (~10%). An increase in pulmonary vascular resistance, the main hemodynamic consequence of APE, was identified in all the pigs and related well to experimental values (R=0.68). Detrimental changes in reflex responses, such as decreased right ventricular contractility, were noticed in two pigs that died during the trial, diagnosing the loss of autonomous control. Increases in the ratio of the modelled right to left ventricular end diastolic volumes, signifying the leftward shift of the intra-ventricular septum seen in APE, compared well to the clinically measured index (R=0.88). Conclusions: Subject-specific CVS models can accurately and continuously diagnose and track acute disease dependent cardiovascular changes resulting from APE using readily available measurements. Human trials are underway to clinically validate these animal trial results

Comparative evaluation of therapeutic interventions during hemorrhagic shock

Trabalho apresentado ao 31º International Symposium on Intensive Care and Emergency Medicine, 2011, Bruxelas

A radiological visual scale to predict the potentially recruitable lung in ALI/ARDS patients

Introduction In ALI/ARDS patients the amount of potentially recruitable lung is extremely variable and it is poorly predictable by the changes of oxygenation, carbon dioxide or compliance during a PEEP trial [1]. At the present time the gold standard to compute the lung recruitability is the quantitative lung CT scan, in which each lung image, after being manually drawn, is analyzed by dedicated software. However, this is both a laborious and time-consuming technique. The aim of this study was to evaluate the ability of a visual radiological scale compared with lung CT scan analysis to predict the lung recruitability in ALI/ARDS patients. Methods A whole lung CT scan was performed at 5 and 45 cmH2O airway pressure. For CT scan analysis each lung image was manually outlined and analyzed by a dedicated software. The potentially recruitable lung was defi ned as the proportion of the nonaerated lung tissue in which aeration was restored [1]. For radiological visual scale analysis, two radiologists performed a blinded evaluation of the consolidation/collapsed areas in each lobe by visual inspection [2]. The overall lung change in consolidation/collapsed was obtained by the sum of each lobe and computed as the diff erence between the two conditions. Results Twenty-four ALI/ARDS patients (age 59 \ub1 15 years, BMI 26 \ub1 4 kg/m2, PaO2/FiO2 170 \ub1 60, PEEP 10 \ub1 2 cmH2O) were enrolled. The percentage of potentially recruitable lung was 16.2 \ub1 7.1% and 14.7 \ub1 7.0%, computed by CT scan and by the visual radiological scale, respectively. The mean diff erence between CT scan analysis and visual radiological analysis was 3.3 \ub1 4.6% (median: 2.91, interquartile range: 0.38 to 6.56). The error of the visual method was lower than 5% in 14 patients (58.3%), between 5% and 10% in eight patients (33.3%) and between 10% and 15% in two patients (8.3%). Conclusions The application of a radiological visual scale is able to predict the amount of potentially recruitable lung similarly to those obtained by a dedicated software avoiding the need of manually drawing each lung image. References 1. Gattinoni L, et al.: N Engl J Med 2006, 354:1775-1786. 2. Pierce RJ, et al.: Thorax 1980, 35:773-780