Hardware and software needs for the eventually ambulatory clinical chronobiologic laboratory

Abstract

A collection of urine or blood for a span of a day is still practical (1). Prominent circadian rhythms can thus be assessed in a number of variables, as illustrated in Figure 1 (2). There are rhythms with lower frequencies, however, as shown for the urinary excretions of calcium (3,4), illustrated in Figure 2, and of 17-ketosteroids (5), shown in Figure 3. Actually, about-yearly rhythms are not only ubiquitous (6), but they have already been documented for many variables, longitudinally (4). What is particularly noteworthy, circannual rhythms are of very great epidemiologic interest and serve for the prediction of the risk of developing major diseases of our civilization (7). Thus, the need arises for long-term in vivo monitoring- of variables that are of biomedical interest. It seems reasonable to anticipate that most of the variables determined in the clinical laboratory exhibit a spectrum of rhythms with different frequencies. Their monitoring by in vivo probes, placed, e.g., into the circulation or the tissue, can greatly help in continuously or intermittently monitoring biochemical processes, notably when the collection of biological material is not possible (as is the case on too many occasions) for practical or ethical reasons. Thus, there is a need for the following types of devices:

• 1. Biochemical sensors: specific ion electrodes and sensors coupling the specific action of immobilized enzymes, or receptors, or functional proteins or cells with an electrochemical detection system, implanted in tissues or veins (8–13).

• 2. Non-invasive methods: already-existing for p0₂, pC0₂, bilirubin and chloride, based on spectrophotometry or conductivity (14,15).

• 3. Nuclear magnetic resonance: non-invasive, can monitor some biochemical processes in a given region of the body. The specificity is to be increased (16-18).

• 4. Monitoring of¹⁴C0₂ or ³H i n expired air after administration of tracer substances along with biochemical loads.