Deflation Time Research Articles

Control of intraaortic balloon pumping: theory and guidelines for clinical applications.

The effectiveness of intraaortic balloon pumping was investigated by using a lumped parameter model of the cardiovascular/assist device system. The model consists of a time-varying elastance left ventricular simulation, a 2-element windkessel arterial simulation, and an RC venous return and pulmonary simulation. The four major hemodynamic variables, stroke volume (SV), aortic mean diastolic pressure (MDP), tension time index (TTI), and aortic end diastolic pressure (EDP), were divided into two categories related to system energy supply and demand: "external" and "internal" variables. The effects of balloon pumping on these variables can be described by closed-form equations that yield an optimal solution. The model prediction suggests that, in the ideal case, optimization of balloon pumping calls for instantaneous inflation of the balloon to maximum volume at end systole and instantaneous complete deflation at end diastole. For finite inflation/deflation rates, the optimal time for the start of inflation is end systole. Deflation timing, however, involves a tradeoff between maximizing the external variables and minimizing the internal variables. These predictions were tested using a nonlinear digital computer model. The results also suggest that when SV is not being monitored, optimal inflation timing can be controlled from the measurements of TTI or pulmonary venous pressure; optimal deflation timing can be controlled by a weighted combination of MDP and EDP.

The Tourniquet in Surgery A Review

The tourniquet can be a valuable tool during surgery on extremities. However, its use is not without clanger. Tourniquet ischemia causes profound changes in tissue and venous pH, PO2, and PCO2 concentrations. An increased bleeding tendency has been noted in dogs after 4 hours of tourniquet ischemia. Muscular damage and nerve palsies are also important complicating factors. The inflation pressure should be the minimum that provides a bloodless field, and pressures greater than 300 mm Hg should be avoided. Duration of use should be minimized, and probably should not exceed 3 hours. A pneumatic tourniquet should be used. An Esmarch bandage should be used only to expel venous blood from the limb and not as a tourniquet device. The inflation and deflation time should be recorded. Previous planning of the operation will allow the surgeon to maximize usefulness of the ischemic period. The surgeon must ensure that the tourniquet has been removed after an operation.

Theoretical considerations regarding the optimization of cardiac assistance by intraaortic balloon pumping.

A lumped parameter model representing the effects of cardiac assistance by intraaortic balloon pumping was developed. The model permits closed-form calculations of important hemodynamic events in the system. The equations derived from the model were used to determine pumping parameters for optimum assistance. The model indicates that, in the ideal case, optimization of assistance requires instantaneous inflation of the balloon to maximum volume at end systole and instantaneous complete deflation at end diastole. Since an impulse flow rate is not realizable in practice, the model was used to investigate the effects of finite inflation/deflation periods. In general, it was found that fast inflation/deflation rates give higher benefits than slow rates. The optimal time to begin inflation is end systole. Timing of deflation was shown to involve a tradeoff between lower end diastolic pressure (achieved with early deflation) and increase of mean diastolic pressure and cardiac output (achieved with late deflation). The model's predictions were validated using a nonlinear distributed parameter digital computer model previously described. The lumped model results should make possible a quantitative as well as a simple approach to automatic control of in-series cardiac assistance.

Microprocessor control of intra-aortic balloon pumping.

An automatic control scheme for the control of intra-aortic balloon pumping has been implemented on a Digital Equipment Corporation LSI-11 micro-processor system and tested in experiments conducted on a mock circulatory loop as well as in a series of acute animal experiments. The control algorithm employed by the digital controller (LSI-11) is identical in form to that employed by Clark et al. (3), and consists of [1] the beat-by-beat evaluation of a performance index that reflects the objectives of balloon pumping, and [2] the adjustment of balloon inflation and deflation times within the diastolic period so as to maximize this performance index according to a steepest ascent algorithm. In order to reduce convergence time and minimize disturbances around the optimum operating point, a scheme that reduces search step size as the search proceeds from initial values is also incorporated in the algorithm. Importantly, this system obeys a bedside measurement constraint in that it requires only readily available physiologic signals for its operation; the ECG for timing purposes, and the central aortic pressure for evaluation of the system performance index. A number of conventional safety features are also implemented in the controller to, for example, guard against untimely balloon inflation in the occurrence of aberrant heart beats.

The Study of determination for optimal deflation timing on Sapporo IABP system

The Study of determination for optimal deflation timing on Sapporo IABP system

Left ventricular afterload and systemic hydraulic power during in-series cardiac assistance: studies using intraaortic balloon pumping in dogs.

The effects of in-series mechanical assistance on left ventricular (LV) afterload and aortic power dissipation were studied in four groups of open chest mongrel dogs: control, acute myocardial ischemia, cholinergic and beta-adrenergic blockade, and combined ischemia and blockade. Aortic root pressure, flow, power, and impedance and LV pressure and power were obtained. Assistance was provided by intraaortic balloon pumping. Times of inflation and deflation of the balloon were controlled to maintain a phase difference of 180° between the fundamental components of aortic root pressure and flow. Differences in hemodynamic parameters before and after 2–5 min of cardiac assistance were calculated. The results confirm other observations regarding effects of in-series assistance on LV and aortic pressure, cardiac output, and peripheral resistance. No consistent changes were obtained in the pulsatile components of aortic input impedance. A significant decrease (14–20%) was observed in the dc component of the impedance in all animals. The results reported here contradict previous reports regarding decreased LV power generation. It was found that LV power generation and aortic power dissipation increased significantly during assistance (LV, 3–17%; aortic, 4–19%). The results of this investigation also appear to conflict with previous reports regarding the role of cardiovascular control in “counteracting” the effects of assistance in the normal experimental preparation. They suggest that the short term effects are attributable directly to the device and are not mediated by the autonomic nervous system.

PULMONARY VENTILATION DURING OPEN THORACOTOMY: Inflation and Deflation Time Ratios and Pressures

PULMONARY VENTILATION DURING OPEN THORACOTOMY: Inflation and Deflation Time Ratios and Pressures