Left ventricular model parameters and cardiac rate variability.

A recent functional model of the left ventricle characterizes the ventricle's contractile state with parameters, rather than variables. The ventricle is treated as a pressure generator that is time and volume dependent. The heart's complex dynamics develop from a single equation based on the formation and relaxation of crossbridge bonds within underlying heart muscle.

The influence of nonlinear intra-thoracic vascular behaviour and compression characteristics on cardiac output during CPR.

Clinical observations suggest that the assumption of a linear relationship between chest compression pressure and cardiac output may be oversimplified. More complex behaviour may occur when the transmural pressure is large, changing the compliances and resistances in the intra-thoracic vasculature. A fundamental understanding of these compression induced phenomena is required for improving CPR.

Functional requirements of a mathematical model of the heart.

Functional descriptions of the heart, especially the left ventricle, are often based on the measured variables pressure and ventricular outflow, embodied as a time-varying elastance. The fundamental difficulty of describing the mechanical properties of the heart with a time-varying elastance function that is set a priori is described. As an alternative, a new functional model of the heart is presented, which characterizes the ventricle's contractile state with parameters, rather than variables.

Comparative analysis of seismocardiogram waves with the ultra-low frequency ballistocardiogram.

Simultaneous seismocardiogram (SCG) and ultra-low frequency ballistocardiogram (BCG) signals are recorded. Preliminary results from the BCG helped tag which waves on the SCG are related to the rapid systolic ejection and aortic valve closure events. These results agreed with and further confirmed previous findings using the echocardiogram.

Video assisted thoracoscopic surgery (VATS) for pneumothorax: a reason for unscheduled surgery?

Timing of urgent surgery, with full schedules and the businesslike attitude of operating room management, can lead to animated discussions, affecting quality of care and job satisfaction. No publication appears to address the timing of definitive care for a stable, spontaneous, pneumothorax (SP) by unscheduled, or urgent, video assisted thoracoscopic surgery (VATS). We reviewed the literature and describe our series of 38 patients with SP and VATS.

The impact of compliant surfaces on in-hospital chest compressions: effects of common mattresses and a backboard.

Purpose: To evaluate, in a hospital setting, the influence of different, common mattresses, with and without a backboard, on chest movement during CPR.

Design And Setting: Sixty CPR sessions (140s each, 30:2, C:R ratio 1:1) were performed using a manikin on standard hospital mattresses, with or without a backboard in combination with variable weights. Sternum-to-spine compression distance was controlled (range 30-60mm) allowing evaluation of the underlying compliant surface on total hand travel.

Systemic arterial response to exercise in patients with aortic valve stenosis.

Background: Systemic arterial hemodynamics play an important role in the assessment of the severity and hemodynamic consequences of aortic valve stenosis (AVS).

Methods And Results: Systemic vascular resistance, total arterial compliance, effective arterial elastance, and aortic characteristic impedance were derived from high-fidelity catheter recordings of ascending aortic pressure and blood flow velocity at rest and with supine bicycle exercise in 18 patients with AVS and 11 control subjects. Mean aortic pressure was similar between groups.

Does use of the CPREzy involve more work than CPR without feedback?

Aim: Feedback during CPR may facilitate quality in chest compressions, but has also been associated with caregiver complaints such as stiff wrists, the need for more force and increased fatigue. This concern about extra work is, when using the CPREzy with its own spring-loaded surface, particularly relevant in the face of an increased number of successive compressions. This manuscript evaluates the objective workloads for caregivers with and without the CPREzy.

Defining muscle elastance as a parameter.

Functional descriptions of striated muscle are often based on the measured variables force and initial velocity of shortening, embodied as Hill's contractile element. The fundamental difficulty of describing the mechanical properties of muscle with a force-velocity relation that is set a priori, and the practical problem of the act of measurement changing muscle's force-velocity relation or elastance curve, are described. As an alternative, a new model of muscle contraction is presented, which characterizes muscle's contractile state with parameters, rather than variables.

The Donders model of the circulation in normo- and pathophysiology.

The solution of some recent as well as of long standing problems, unanswerable due to experimental inaccessibility or moral objections are addressed. In this report, a model of the closed human cardiovascular loop is developed. This model, using one set of 88 equations, allows variations from normal resting conditions to exercise, as well as to the ultimate condition of a circulation following cardiac arrest.

Resolving the hemodynamic inverse problem.

The "hemodynamic inverse problem" is the determination of arterial system properties from pressures and flows measured at the entrance of an arterial system. Conventionally, investigators fit reduced arterial system models to data, and the resulting model parameters represent putative arterial properties. However, no unique solution to the inverse problem exists-an infinite number of arterial system topologies result in the same input impedance (Zin) and, therefore, the same pressure and flow.

The quality of chest compressions by trained personnel: the effect of feedback, via the CPREzy, in a randomized controlled trial using a manikin model.

Even after training, the ability to perform effective cardiac compressions has been found to be poor and to decrease rapidly. We assessed this ability with and without a non-invasive feedback device, the CPREzy, during a 270s CPR session in an unannounced, single-blinded manikin study using 224 hospital employees and staff chosen at random and using a non-cross over design. The two groups self-assessed their knowledge and skills as adequate.

The arterial system pressure-volume loop.

Although the ventricular P-V loop has become a popular tool to characterize aspects of the performance of the heart, an arterial system P-V loop has not yet been described. In principle, the volume stored in the arterial system (V) could be calculated by integrating the difference between inflow and outflow. In practice, however, flow out of the innumerable arterioles cannot be measured directly.

Efficacy and safety in patients on a resuscitator, Oxylator EM-100, in comparison with a bag-valve device.

The purpose of this study was to compare the Oxylator EM-100, a ventilator with a fixed flow and working pressure of 25 to 50 cm H(2)O, with a bag-valve device with respect to safety, efficiency, and efficacy when used by professionals. We conducted a prospective, controlled, caregiver-blind single center study. Induction was followed by ventilation with a bag-valve device oxylator in manual and automatic modes.

Can first responders achieve and maintain normocapnia when sequentially ventilating with a bag-valve device and two oxygen-driven resuscitators? A controlled clinical trial in 104 patients.

Background And Objective: To evaluate the capability of first responders to achieve and maintain normal ventilation of the lungs of victims employing a bag-valve device and two oxygen-driven resuscitators.

Methods: Prospective, controlled, blinded, single-centre clinical trial using a bag-valve device and one of two FR-300 devices, with 20 cmH2O working pressure, and flows of either 24 or 30 L min(-1). One hundred and four patients were analysed.

Airway management by first responders when using a bag-valve device and two oxygen-driven resuscitators in 104 patients.

Background And Objective: To evaluate the capability of first responders to ensure an airway and ventilate the lungs of a patient employing a bag-valve device and two oxygen-driven resuscitators.

Methods: Prospective, controlled, blinded, single-centre clinical trial using a bag-valve device and one of two FR-300 devices, with 20 cmH2O working pressure, flows of 24 and 30 L min(-1). One-hundred-and-four patients were analysed.

Shape of the left ventricle and its computer modelling.

A simple computer program was made to draw different left ventricle shapes in order to support the theory of elongation and to get a visual presentation of the shape of the left ventricle. Experimental data, obtained from echocardiography and Simpson's rule, were used for this program. The results yielded different shapes under different physiological circumstances, indicating the sensitivity of the method.

Elongation as a new shape index for the left ventricle.

Objectives: This study was done to quantify the shape of the left ventricle (LV). It was proposed that the shape of the LV is intimately related to its performance and that its elongation (ELO) is a sensitive measure of this performance. The performance was tested against classical cardiovascular parameters.

A paradigm for quantifying ventricular contraction.

The left ventricle may be described as a time, volume and flow dependent pressure generator. First, isovolumic pressure is measured at various end-diastolic volumes. Next, pressure is adjusted to account for small changes accompanying ejection, denoted the ejection effect.

Arterial pulse wave reflection as feedback.

Traditionally, input impedance (Z(in)) has been used to characterize the global dynamic properties of an arterial system independent of properties of the heart. Defined as the relationship of pressure and flow at the entrance of an arterial system, it describes the ability of an arterial system to dynamically impede blood flow. Recently, a new description has been developed that also characterizes the arterial system independent of properties of the heart.

Constructive and destructive addition of forward and reflected arterial pulse waves.

Although the physics of arterial pulse wave propagation and reflection is well understood, there is considerable debate as to the effect of reflection on vascular input impedance (Z(in)), pulsatile pressure, and stroke work (SW). This may be related to how reflection is studied. Conventionally, reflection is experimentally abolished (thus radically changing unrelated parameters), or a specific model is assumed from which reflection can be removed (yielding model-dependent results).

Infinite number of solutions to the hemodynamic inverse problem.

Investigators have had much success solving the "hemodynamic forward problem," i.e., predicting pressure and flow at the entrance of an arterial system given knowledge of specific arterial properties and arterial system topology.

The changing view of the heart through the centuries.

In human perception, the heart was not always part of the blood circulating system. It was later included as a suction pump until Harvey argued that the heart is actually a compression pump, the central organ of the circulation, and the only organ responsible for the motion of blood. Considered initially as an autonomous pump, the heart gradually became viewed as subservient to the needs of the peripheral organs it perfuses.

Human circulatory system model based on Frank's mechanism.

A new analytical model of the left ventricle as a pump, developed from isolated canine experiments, was adapted to describe each of the four heart chambers in a complete human circulatory system model. Each chamber is embodied as a volume and time dependent isovolumic pressure source, after Otto Frank's classic experiments. Analytical results show that a small set of equations is sufficient to describe the main features of the heart as a pump, including isovolumic and ejecting beats for a wide range of ventricular and circulation conditions.