Artificial heart values

Current introduced to the body is often held to low values by the electrical resistance of dry skin, between 5,000 and 10,000 ohms (Kantrowitz, 1972). Wet skin will have electrical resistance levels as low as one-tenth of this. Where electrical leads are introduced subcutaneously, resistance falls to 10-50 ohms, and this situation is potentially dangerous. Subcutaneous leads are used for heart pacemakers, artificial hearts, transcutaneous electrical neural stimulation (TENS) to block pain, and subdural leads for the control of Parkinson s disease. 

The clear detection of both reversible active-site and biocatalytic waves represents a completeness that establishes the feasibility of applying direct elec-tochemistry to probe the mechanism of action of complex redox enzymes. To take this further, I shall take up the author s prerogative for mentioning studies currently underway in the laboratory and mention, briefly, another membrane-bound enzyme, fumarate reductase (FR), isolated from Escherichia coll Structurally, this is closely related to the more familiar succinate dehydrogenase (SDH) which constitutes the major part of Complex II of the mitochondrial respiratory chain. Of the four subunits which make up the membrane-bound system, two may be freed to give a soluble enzyme that is active in fumarate reduction by artificial electron donors [230]. The larger of these, MW approx. 70000, contains, like SDH, a covalently bound FAD. The smaller, MW approx. 30000, appears to contain three Fe-S clusters. These are termed centre 1 ([2Fe-2S]), centre 2 ([4Fe-4S]) and centre 3 ([3Fe-4S]). Their respective reduction potentials as determined by potentiometry are — 20 mV, — 320 mV, and — 70 mV [231], (Although the potential of the FAD has not been determined for FR, the two-electron value for beef heart SDH is — 79 mV at pH 7.0. The radical form is unstable since the two one-electron reductions occur at potentials of — 127 and — 31 mV respectively [232].)... 

Thrombo-embolism is a well known complication in patients with prosthetic heart valves. The pathogenesis of thrombo-embolic incidents is unclear but it seems that platelets play a significant role, due to the interaction between these cells and the artificial surfaces of the prosthetic valve. In an attempt to detect possible metabolic abnormalities, heat production rate was measured in platelets from patients with prosthetic cardiac valves [84]. Significantly decreased calorimetric values were observed, indicating that the metabolic activity of platelets in these patients is abnormally low (see Table 16). 

---