Automated evaluation of typical patient-ventilator asynchronies based on lung hysteretic responses

BACKGROUND

Patient-ventilator asynchrony is common during mechanical ventilation (MV) in intensive care unit (ICU), leading to worse MV care outcome. Identification of asynchrony is critical for optimizing MV settings to reduce or eliminate asynchrony, whilst current clinical visual inspection of all typical types of asynchronous breaths is difficult and inefficient. Patient asynchronies create a unique pattern of distortions in hysteresis respiratory behaviours presented in pressure-volume (PV) loop.

METHODS

Identification method based on hysteretic lung mechanics and hysteresis loop analysis is proposed to delineate the resulted changes of lung mechanics in PV loop during asynchronous breathing, offering detection of both its incidence and 7 major types. Performance is tested against clinical patient data with comparison to visual inspection conducted by clinical doctors.

RESULTS

The identification sensitivity and specificity of 11 patients with 500 breaths for each patient are above 89.5% and 96.8% for all 7 types, respectively. The average sensitivity and specificity across all cases are 94.6% and 99.3%, indicating a very good accuracy. The comparison of statistical analysis between identification and human inspection yields the essential same clinical judgement on patient asynchrony status for each patient, potentially leading to the same clinical decision for setting adjustment.

CONCLUSIONS

The overall results validate the accuracy and robustness of the identification method for a bedside monitoring, as well as its ability to provide a quantified metric for clinical decision of ventilator setting. Hence, the method shows its potential to assist a more consistent and objective assessment of asynchrony without undermining the efficacy of the current clinical practice.

A Pacing-Controlled Protocol for Frequency-Diastolic Relations Distinguishes Diastolic Dysfunction Specific to A Mouse HFpEF Model

BACKGROUND

Heart failure with preserved ejection fraction (HFpEF) is characterized as an insufficient exercise capacity and is a growing health problem worldwide. One major difficulty with experimental research of HFpEF is the lack of methods to consistently detect diastolic dysfunction in mouse models. We focus on the exercise intolerance and developed a pacing-controlled PV loop protocol for the assessment of diastolic function at different heart rates in mouse cardiac disease models, including a HFpEF model and a pressure-overload hypertrophy model (PO).

METHODS

A HFpEF model was generated by high-fat diet (HFD)-feeding with concomitant L-NAME administration, and a PO model was produced by surgical constriction of transverse aorta (TAC). HR was slowed (lower than 400 bpm) by i.p. injection of ivabradine. PV loop data were acquired at HR incrementing by 100 bpm from 400 to 700 bpm via atrial pacing.

RESULTS

At baseline without pacing, no significant difference was detected between groups. Frequency-diastolic pacing, however, distinguished HFpEF from other two groups in diastolic parameters like tau or stiffness-coefficient of end-diastolic pressure volume relationship. No remarkable difference was observed with systolic parameters.

CONCLUSIONS

Frequency-dependent pressure-volume analysis could detect and characterize diastolic dysfunction specific to the HFpEF, though no significant difference between HFpEF and pressure overload models could be detected at baseline analysis. One of characteristic of HFpEF is exercise intolerance, but no physiological analysis or modality associated with exercise capacity was available in analyzing cardiac functions of murine models. This protocol would significantly contribute to the basic research for HFpEF.

The Underlying Cardiovascular Mechanisms of Resuscitation and Injury of REBOA and Partial REBOA

Introduction: Resuscitative Endovascular Balloon Occlusion of the Aorta (REBOA) is used for aortic control in hemorrhagic shock despite little quantification of its mechanism of resuscitation or cardiac injury. The goal of this study was to use pressure-volume (PV) loop analysis and direct coronary blood flow measurements to describe the physiologic changes associated with the clinical use of REBOA. Methods: Swine underwent surgical and vascular access to measure left ventricular PV loops and left coronary flow in hemorrhagic shock and subsequent placement of occlusive REBOA, partial REBOA, and no REBOA. PV loop characteristics and coronary flow are compared graphically with PV loops and coronary waveforms, and quantitatively with measures of the end systolic and end pressure volume relationship, and coronary flow parameters, with accounting for multiple comparisons. Results: Hemorrhagic shock was induced in five male swine (mean 53.6 ± 3.6 kg) as demonstrated by reduction of stroke work (baseline: 3.1 vs. shock: 1.2 L*mmHg, p < 0.01) and end systolic pressure (ESP; 109.8 vs. 59.6 mmHg, p < 0.01). ESP increased with full REBOA (178.4 mmHg; p < 0.01), but only moderately with partial REBOA (103.0 mmHg, p < 0.01 compared to shock). End systolic elastance was augmented from baseline to shock (1.01 vs. 0.39 ml/mmHg, p < 0.01) as well as shock compared to REBOA (4.50 ml/mmHg, p < 0.01) and partial REBOA (3.22 ml/mmHg, p = 0.01). Percent time in antegrade coronary flow decreased in shock (94%-71.8%, p < 0.01) but was rescued with REBOA. Peak flow increased with REBOA (271 vs. shock: 93 ml/min, p < 0.01) as did total flow (peak: 2136, baseline: 424 ml/min, p < 0.01). REBOA did not augment the end diastolic pressure volume relationship. Conclusion: REBOA increases afterload to facilitate resuscitation, but the penalty is supraphysiologic coronary flows and imposed increase in LV contractility to maintain cardiac output. Partial REBOA balances the increased afterload with improved aortic system compliance to prevent injury.

Left Ventricular Pressure Volume Assessment Using Carotid Artery Access in the Rat

Left ventricular (LV) catheterization with either a pressure catheter or pressure-volume catheter provides a means to measure cardiac function, an important endpoint in many studies including cardiac gene therapy. While the catheter can be inserted directly into the heart using a surgical approach, utilizing the carotid artery for access has the advantage of being a closed-chest procedure. This negates the need for intubation, prevents myocardial trauma, and preserves normal intrathoracic pressure, providing more accurate assessments of cardiac physiology parameters. We describe a protocol for obtaining carotid artery access and insertion of a pressure-volume catheter into the LV of rodents.

Early hemodynamic changes after transcatheter aortic valve implantation in patients with severe aortic stenosis measured by invasive pressure volume loop analysis

Replacement of a stenotic aortic valve reduces immediately the ventricular to aortic gradient and is expected to improve diastolic and systolic left ventricular function over the long term. However, the hemodynamic changes immediately after valve implantation are so far poorly understood. Within this pilot study, we performed an invasive pressure volume loop analysis to describe the early hemodynamic changes after transcatheter aortic valve implantation (TAVI) with self-expandable prostheses. Invasive left ventricular pressure volume loop analysis was performed in 8 patients with aortic stenosis (mean 81.3 years) prior and immediately after transfemoral TAVI with a self-expandable valve system (St. Jude Medical Portico Valve). Parameters for global hemodynamics, afterload, contractility and the interaction of the cardiovascular system were analyzed. Left ventricular ejection fraction, (53.9% vs. 44.8%, p = 0.018), preload recruitable stroke work (68.5 vs. 44.8 mmHg, p = 0.012) and end-systolic elastance (3.55 vs. 2.17, p = 0.036) both marker for myocardial contractility declined significantly compared to baseline. As sign of impaired diastolic function, TAU, a preload-independent measure of isovolumic relaxation (37.3 vs. 41.8 ms, p = 0.018) and end-diastolic pressure (13.1 vs. 16.4 mmHg, p = 0.015) raised after valve implantation. Contrarily, a smaller ratio of end-systolic to arterial elastance (ventricular-arterial coupling) indicates an improvement of global cardiovascular energy efficiency (1.40 vs. 0.97 p = 0.036). Arterial elastance had a strong correlation with the number of conducted rapid ventricular pacings (Pearson correlation coefficient, r = 0.772, p = 0.025). Invasive left ventricular pressure volume loop analysis revealed impaired systolic and diastolic function in the early phase after TAVI with self-expandable valve for the treatment of severe aortic stenosis. Contrarily, we found indications for early improvement of global cardiovascular energy efficiency.

Superior restoration of left ventricular performance after prolonged single-dose del Nido cardioplegia in conjunction with terminal warm blood cardioplegic reperfusion

OBJECTIVES

An incomplete restoration of left ventricular contractility after del Nido cardioplegia was noted in our recent study. This study tested the hypothesis that terminal warm blood cardioplegia promotes a prompt restoration of left ventricular performance after a prolonged single-dose del Nido cardioplegia.

METHODS

Fourteen piglets were subjected to 120 minutes of arrest by del Nido cardioplegia without terminal warm blood cardioplegia (del Nido cardioplegia group; n = 7) or with terminal warm blood cardioplegia before reperfusion (terminal warm blood cardioplegia group; n = 7). The other 7 piglets underwent total cardiopulmonary bypass without ischemia/reperfusion for 150 minutes (control group). Left ventricular function was assessed by percent recovery of end-systolic elastance as the contractility and percent end-diastolic pressure-volume relationship as the compliance using a conductance catheter. Troponin T and the mitochondrial score were also measured.

RESULTS

Depressed percent recovery of end-systolic elastance was sustained in the del Nido cardioplegia group, and a prompt restoration of end-systolic elastance was achieved using terminal warm blood cardioplegia (57.9 ± 17.8 vs 94.7 ± 13.1, P < .028). Percent end-diastolic pressure-volume relationship at the early phase was better in the terminal warm blood cardioplegia compared with the del Nido group (88.5 ± 24.0 vs 101.4 ± 16.8, P = .050). Troponin T was higher in the terminal warm blood cardioplegia compared with the control group (0.80% ± 0.21% and 1.49% ± 0.31%, respectively, P = .002). The mitochondrial score was equivalent in all groups. Spontaneous restoration to sinus rhythm was more frequent in the terminal warm blood cardioplegia group than in the del Nido cardioplegia group (6/7 vs 1/7, P < .028).

CONCLUSIONS

The supplementary use of terminal warm blood cardioplegia achieved prolongation of the safe ischemic time up to 120 minutes for a single-dose application.

Modified Del Nido Cardioplegia and Its Evaluation in a Piglet Model

Del Nido cardioplegia (DN) is not available worldwide as the required solution is made from a commercial base (PlasmaLyte) that is not approved in all countries. We report our own modified DN solution and confirm its safety and effectiveness. Fourteen piglets were subjected to 90 minutes of global ischemia on cardiopulmonary bypass induced by original DN (n = 7) or NS (normal saline)-based DN (n = 7). Our DN solution begins with a base of NS (800 mL) and distilled water (200 mL), to which are added 15 mL KCl (2 mEq/mL), 17 mL NaHCO₃ (1 mEq/mL), 10 mL MgSO₄ (0.2 g/mL), 13 mL lidocaine 1%, and 13 mL mannitol 25%. LV function recovery was assessed in end-systolic elastance (EES) as systolic function and end-diastolic pressure-volume relationship (EDPVR) as diastolic function using a conductance catheter. Creatine kinase-MB (CK-MB) and mitochondrial score were also measured. Left ventricular (LV) contractility after ischemia (%EES ± SD) was not significantly different between the group induced by original DN (89.3 ± 20.6%) and the group induced by NS-based DN (99.3 ± 18.4%). LV compliance (%EDPVR ± SD) was likewise not significantly different between these groups (102.7 ± 28.2% vs 94.4 ± 22.8%, PL vs NS, respectively). CK-MB was equivalent between the groups. Mitochondrial scores were not significantly different between the groups, and this difference did not cause severe damage. NS-based DN preserves LV function recovery after prolonged global ischemia as effectively and as safely as original DN does. NS-based modified DN can be substituted for original DN.

Finite state machine implementation for left ventricle modeling and control

Background

Simulation of a left ventricle has become a critical facet of evaluating therapies and operations that interact with cardiac performance. The ability to simulate a wide range of possible conditions, changes in cardiac performance, and production of nuisances at transition points enables evaluation of precision medicine concepts that are designed to function through this spectrum. Ventricle models have historically been based on biomechanical analysis, with model architectures constituted of continuous states and not conducive to deterministic processing. Producing a finite-state machine governance of a left ventricle model would enable a broad range of applications: physiological controller development, experimental left ventricle control, and high throughput simulations of left ventricle function.

Methods

A method for simulating left ventricular pressure-volume control utilizing a preload, afterload, and contractility sensitive computational model is shown. This approach uses a logic-based conditional finite state machine based on the four pressure-volume phases that describe left ventricular function. This was executed with a physical system hydraulic model using MathWorks’ Simulink^® and Stateflow tools.

Results

The approach developed is capable of simulating changes in preload, afterload, and contractility in time based on a patient’s preload analysis. Six pressure–volume loop simulations are presented to include a base-line, preload change only, afterload change only, contractility change only, a clinical control, and heart failure with normal ejection fraction. All simulations produced an error of less than 1 mmHg and 1 mL of the absolute difference between the desired and simulated pressure and volume set points. The acceptable performance of the fixed-timestep architecture in the finite state machine allows for deployment to deterministic systems, such as experimental systems for validation.

Conclusions

The proposed approach allows for personalized data, revealed through an individualized clinical pressure–volume analysis, to be simulated in silico. The computational model architecture enables this control structure to be executed on deterministic systems that govern experimental left ventricles. This provides a mock circulatory system with the ability to investigate the pathophysiology for a specific individual by replicating the exact pressure–volume relationship defined by their left ventricular functionality; as well as perform predictive analysis regarding changes in preload, afterload, and contractility in time.