Assessing Absent Functionality

A curious dilemma occasionally emerges when one is required to assess functionality which is not present. At a most basic level one might conclude that it is simply impossible to assess functionahty which is not there - after all without any designs, architecture or user interface what is there to evaluate But the situation is worthy of closer examination. 

Firstly one must differentiate between functionality which has never been available and that which becomes unavailable in the live environment. Should a clinician rely upon a particular system, module or function to deliver safe care and that entity become unexpectedly unavailable that is clearly a hazard and is discussed in Chapter 7. 

One argument which is occasionally developed by healthcare organisations goes as follows  

We have a directive to effectively manage chnical risk and patient safety 

The shortcomings of the system do not allow us to realise the benefits we were hoping to realise 

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Some patients with reduced or absent parathyroid function, e.g., primary hypoparathyroidism, harbor anti-CaR antibodies (Fig. 2) [4]. In two patients, the antibodies were shown to activate the CaR as assessed by stimulation of MAPK and PLC. Tims, analogous to activating mutations of the CaR, anti-CaR antibodies can increase the sensitivity of the receptor to CaQ+, thereby resetting parathyroid and kidney to maintain hypocalcemia. 

The longitudinal effects of experimental vitamin E deficiency on visual function in the rat have been studied by Goss-Sampson et al. (1992). After 12 months of deficiency, visual function as assessed by electroretinography was absent or grossly abnormal. This was associated with... 

The National Research Council (NRC) published a report, Science and Judgment in Risk Assessment, that critiqued the current approaches to characterizing human cancer risks from exposure to chemicals. One issue raised in the report relates to the use of default options for assessing of cancer risks. These general guidelines can be used for risk assessment when specific information about a chemical is absent. Research on 1,3-butadiene indicates that two default options may no longer be tenable Humans are as sensitive as the most sensitive animal species and the rate of metabolism is a function of body surface area rather than inherent species differences in metabolic capacity. 

MRT (atypical teratoid/rhabdoid tumor) frequently demonstrates deletion and mutation of the hSNF5/INIl gene, with decreased or absent INIl protein expression. An antibody to INIl can be used to assess INIl loss, characterized by absence of immunoreactivity in contrast to functional INIl with positive immunoreactivity in normal tissues and other neoplasms." Like MRT of the kidney and extrarenal soft tissues, atypical teratoid/rhabdoid tumors of the central nervous system showed absence of nuclear staining for INIl in a recent study." 3i... 

Cyclophosphamide can also cause tubular necrosis in experimental animals [82]. No clinical counterpart has been described, despite careful assessment in patients receiving high doses of cyclophosphamide [83, 84]. Although detectable alterations of renal function tests are absent, subtle changes in renal tubular physiology have been noted. Bode et al. [85] studied the mechanism of water retention that occurs following cyclophosphamide. They concluded that cyclophosphamide directly affected the tubules, causing increased water reabsorption and sodium loss. This water retention is self-hmited to a day or two and does not present a major dinical problem. 

It is therefore important to have a system of in-house characterization of raw materials alongside the stability and functional tests for the finished product. Whenever possible, tests carried out should yield quantitative results rather than a pass/ fail or present/absent assessment. Retrospective studies of the finished product test... 

Rigorous assessments of sensory and motor function ai also absent. Conventional clinical techniques are unlikely to detect the subtle deficits said to arise fhjm moderately elevated lead exposures. Visual science, for example, now provides assessment tools, based on engineering models of the visual system, capable of probing the boundaries of visual function. Motor function also demands more refined procedures than the industrial screening tests or measures of motor conduction velocity used by some investigators. Evaluation of fine motor control and perceptu ll-motor performance requires an engineering cinalysis similar to those applied to studies of Parkinsonism. ... 

Fault tolerant architectures are amenable to the same treatment. Different configurations can be modelled in terms of their dependability properties when fully functional and under various stages of degradation. Assessment of complex systems will have degrees of tolerance. Formality as an assessment criterion can only be applied to elements of the system which are accessible and accurately documented. Hence a two layered approach may be taken to specify intra-module reliability criteria which are either present or absent (e.g. degrees of formal specification of the module internals and interface) and inter-module dependability in terms of formal assessment of interprocess communication. 

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