Cardiac electrodes

The Caldwell-Reswick electrode is a helix of nichrome resistance wire filled internally with a silicone rubber core. A retaining hook is located on the distal end The electrode is placed by means of a 23-gauge hypodermic needle in the same manner as the cardiac electrode shown in Figure 8.1. This electrode can be placed directly into a muscle. The silastic core and the helical assembly minimize electrode breakage. Placement and removal of the electrode is quick and easy. 

Myocardial tissue pH measurement has been used in the studies of different approaches to myocardial protection in various cardiac operations. A needle type glass membrane miniature electrode has been used in studies for pH-guided myocardial management [127], As described in the previous section, this electrode was also adapted to measure brain pH [132], The electrode has a right-angled glass electrode... 

Electrical Stimulation Devices. Bioelectrodes that transmit electrical signals into the body are generally known as electrical stimulation devices, examples of which include cardiac pacemakers, transcutaneous electronic nerve stimulators (TENs) for pain suppression, and neural prostheses such as auditory stimulation systems for the deaf and phrenic nerve stimulators for artificial respiratory control. In these, and other similar devices, electrodes transmit current to appropriate areas of the body for direct control of, or indirect influence over, target cells. 

At the end of this chapter, some readers may wonder why we did not present one of the three most famous and beneficial neural prostheses that are in clinical use since several years the cardiac pacemaker, the cochlea implant and the urinary bladder stimulator of Brindley. In our view, the devices may not be considered microsystems. Only the electronic parts are built of monolithic integrated circuitry in silicon technology. The electrodes are still manufactured in a conventional way not reaching miniaturization levels that were presented here. 

Experiments showed that coagulation increases for applied potential differences greater than +0.2 V vs. NHE below this value, clot formation is very small. The rest potential of various materials used for vascular prostheses and cardiac valves was determined. In Table 17.2 some of the materials tested are mentioned. It was concluded that metallic electrodes with a negative potential vs. NHE in the blood are anticoagulant while those with positive potential are coagulant. Unfortunately, the metals most useful for prostheses are the most easily corroded those of platinum and gold, not corroded, are unsuitable because of their positive rest potentials. Attempts to resolve the problem have utilized prostheses of plastic materials compatible in terms of their qualities of physical resistance, durability, etc. with their end use. 

Q5 When there is a cardiac problem a 12-lead ECG is usually taken. Where are the electrodes placed and what do these leads measure ... 

The calcium ion liquid-membrane electrode is a valuable tool for physiological investigations because this ion plays important roles in such processes as nerve conduction, bone formation, muscle contraction, cardiac expansion and contraction, renal tubular function, and perhaps hypertension. Most of these processes are influenced more by the activity than the concentration of the calcium ion activity, of course, is the parameter measured by the membrane electrode. Thus, the calcium ion electrode (and the potassium ion electrode and others) is an important tool in studying physiological processes. 

FIGURE 11-4. A. Electrode positions of the precordial leads (Vi = fourth intercostal space at the rightsternal border V2 = fourth intercostal space at the left sternal border V3 = halfway between V2 and V4 V4 = fifth intercostal space at the midclavicular line V5 = anterior axillary line directly lateral to V4 Ve = anterior axillary space directly lateral V5. B. The precordial reference figure. Leads Vi and V2 are called right-sided precordial leads leads V3 and V4, midprecordial leads and leads V5 and Ve, left-sided precordial leads. (Redrawn from Kinney MR, Packa DR (eds). Andreoli s Comprehensive Cardiac Care, 8th ed. St. Louis, Mosby, 7 996, with permission.)... 

In-Vivo Percutaneous Implant Experiment. The principle of percutaneous attachment has extensive application in many biomedical areas, including the attachment of dental and orthopedic prostheses directly to skeletal structures, external attachment for cardiac pacer leads, neuromuscular electrodes, energy transmission to artificial heart and for hemodialysis. Several attempts to solve the problem of fixation and stabilization of percutaneous implants(19) have been made. Failures were also attributed to the inability of the soft tissue interface to form an anatomic seal and a barrier to bacteria. In the current studies, the effect of pore size on soft tissue ingrowth and attachment to porous polyurethane (PU) surface and the effect of the flange to stem ratio and biomechanical compliance on the fixation and stabilization of the percutaneous devices have been investigated.(20)... 

---