Heart Pump Design

Following Graver and Bechtel, mechanistic explanations are constituted by answers to certain how -questions (in a non-evaluative sense, as one should hasten to add (cf. Schnieder 2009)). Such questions take the form How does x cpT A corresponding explanation is, then, a by -explanation of the following form a -s by (ft s) r -ing . Reference to b is relevant insofar as we sometimes face explanations such as the heart pumps blood by the organized contraction of its constituent muscles . To connect this to the less precise talk above In the position of a or b we substitute an expression that designates the bearer of an event in... 

Moderate power batteries have been developed for total artificial hearts (TAHs). The TAH is a mechanical heart pump that essentially replaces the patient s natural heart. According to the TAH designer, the device contains two chambers, each of which is capable of pumping more than 7 L of blood per minute, which is equal to the heart s natural pumping rate. The TAH device uses an implantable Li-ion battery pack, which is recharged through the skin of the patient. 

This section provides specific details on the critical elements of the pump and the types of batteries most suitable for the artificial heart pump application. The design of this replacement heart pump consists of two chambers each capable of pumping more than 7 liters of blood per minute. The artificial pump deploys an implantable Li-ion battery pack that is recharged through the patient s skin, if and when necessary. All implantable Li-ion battery packs must meet the following stringent requirements ... 

As mentioned earlier, CEC couples the separating power of HPLC and the high efficiency of CE. The packed capillary can be considered the heart of the CEC system because it acts as a pump and provides chromatographic selectivity. The design of the stationary phase related parameters such as mobile phase and pH and instrumental parameters such as pressurization, injection modes, temperature, and voltage polarity play an important role in this technique. 

The simplest heart assist device is the intraaortic balloon pump (lABP) which consists of two small PEUU balloons mounted on a hollow catheter that is about 30 cm long. The distal occluding balloon is 18 mm in diameter, and the proximal pumping balloon is 14 mm in diameter. The device is inserted into the aorta via the femoral artery and connected to a pump that then expands and contracts the balloons in rhythm with the heart beat. This prosthesis is considered to be the best heart assist device because it is simple in design and easy to insert. Improved circulation does occur in about three-fourths of the patients, but the mortality rate still remains high (65-90%) in cases of refractory cardiogenic shock. The lABP is used over 15,000 times annually (51. 52). 

William Harvey [77] taught that the heart is the only pump that propels blood around the closed circulatory loop. Liebau [78], on the other hand, based on experiments with fluid mechanical models of his own design, concluded that blood could be propelled around the loop without the benefit of cardiac and venous valves. Liebau demonstrated with his simplest model, consisting of two tubes with different elastic properties, free of valves, making a closed water-filled loop, that periodic compression at an appropriate, fixed site caused steady net fluid flow around the loop, but could not explain the reason why this occurred. The explanation, developed in 1998 [57], was that Liebau worked with an asymmetric loop to which he provided energy by periodic compression at some site. This was termed impedance defined flow, in view of the nonuniform distribution of impedances around the loop. (Compression at a symmetric point, if any, generates no steady net flow, either experimentally or theoretically.)... 

FIGURE 44.8 Typical prototype designs of total artificial hearts (a) pneumatically powered TAH. The right and left ventricular chambers, inflow and outflow valves, as well as the connector for the pneumatic line are visible in the photograph (b) electrically powered TAH. Shown are the external battery pack, transcutaneous energy transmission system (TETS) primary and secondary coils, implanted electronics, energy converter and the blood pumps, compliance chamber and the subcutaneous access port. (Courtesy of G. Rosenberg, Pennsylvania State University.)... 

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