J. Swanson Beck

Spectrophotometric measurements of haemoglobin saturation and concentration in skin during the tuberculin reaction in normal human subjects

A non-invasive technique employing light-guide spectrophotometry is described for the measurement of haemoglobin concentration and oxygenation in human skin. Measurements were carried out in the visible wavelength range (500-620 nm) and a series of experiments were carried out in vitro and in vivo in order to calibrate the system. Indices were derived for the measurement of relative haemoglobin concentration and absolute oxygen saturation. The technique was applied to measure the changes in these parameters occurring during the course of the tuberculin reaction in human skin. The results are compared with those from laser Doppler flowmetry and transcutaneous oxygen measurements which were carried out concurrently. Divergence between the intracapillary and tissue oxygenation during the course of the reaction provides evidence for the existence of increased diffusion resistance for oxygen; a model is proposed. The study demonstrates the potential clinical usefulness of light-guide spectrophotometry for the non-invasive investigation of tissue oxygen supply.

Total and anti-mycobacterial ige levels in serum from patients with tuberculosis and leprosy

A radioallergosorbent assay (RAST) was developed and used to determine the levels of IgE antibodies to soluble antigens of Mycobacterium tuberculosis (BCG vaccine strain) in sera from patients with tuberculosis and leprosy and in healthy control subjects. Total IgE levels in the same sera were quantitated with a commercial radioimmunoassay kit. Patients with tuberculosis and leprosy had higher total and specific IgE levels than the control groups but the overlap of levels in patients and controls was too great to render the difference diagnostically useful. Specific IgE levels were elevated in both tuberculosis and leprosy patients, suggesting that this antibody response is towards the shared mycobacterial antigens. No differences in total or specific IgE levels were found between healthy hospital workers occupationally exposed to patients with tuberculosis and factory workers who are not exposed.

Skin changes in the tuberculin test

This review describes the recent advances in knowledge of the nature and range of physiological changes that occur in the skin at the site of a positive tuberculin reaction. The infiltration of T-cells and monocyte/macrophages shows a marked compartmentalisation suggesting that the functions of particular cell types depend on their localisation. The extent of cutaneous oedema (detectable as induration) is not closely related to other features of the reaction or to systemic indicators of cell mediated immunity. The intensity of hyperaemia is maximal at the centre of the reaction and is correlated in most cases with the density of cellular infiltration in the dermis suggesting a functional coordination. Despite this correlation between cell numbers and velocity of blood flow, the reaction normally shows hypoxia, hypercapnia and local acidosis, but this metabolic modification may not be a wholly disadvantageous effect since these conditions appear to facilitate the growth and metabolism of activated lymphocytes and macrophages. In very strong reactions, there is central relative slowing of the circulation and this may lead to necrosis in extreme cases. There are however a minority of cases where cell infiltration occurs but induration is not palpable: this situation has been named pseudoanergy, and its pathogenesis has not yet been established. The occurrence of pseudoanergy must throw some doubt on the conventional criteria for positivity in the reading of tuberculin skin tests (induration greater than 5 mm) and this may have relevance to future strategies for assessment of new vaccines.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of macro- and micro-lightguide spectrophotometric measurements of microvascular haemoglobin oxygenation in the tuberculin reaction in normal human skin

The changes in haemoglobin oxygenation (SO2) occurring in the tuberculin reaction in human skin were measured using macro- and micro-lightguide spectrophotometry and the results compared. A significant difference was found between the measurements from the respective instruments, demonstrating that the micro-lightguide technique measures only in the most superficial capillaries. Laser Doppler flux (LDF) and transcutaneous oxygen (tcpO2) measurements were also obtained concurrently. At the height of the reaction, heating did not significantly change SO2 or LDF, showing that the vessels in the skin were maximally vasodilated. Although SO2 was increased in the reaction, tcpO2 decreased. This suggests that the infiltrating cells may present a diffusion barrier to oxygen between the capillaries and the tissue cells. This study has shown that micro-lightguide spectrophotometry gives a local picture of intracapillary oxygen supply, which is useful in elucidating the pathophysiological changes occurring during chronic inflammation.

A PASSIVE HAEMAGGLUTINATION (TRC) INHIBITOR IN THYROTOXIC SERUM

The tanned red cell haemagglutination test system is widely used in the screening of thyroid and other auto‐immune diseases. We report a phenomenon which casts some doubt on the reliability of the technique.

Effect of histamine and prostaglandin E2 on the microcirculation in the skin

The response of the, cutaneous microvasculature to two vasoactive mediators, histamine and prostaglandin E2, was measured by laser Doppler velocimetry. Four concentrations of histamine (1.01 to 65.1×10−5M, in fourfold dilutions) were injected intradermally into the forearms of six healthy subjects: Prostaglandin E2 (1.77 to 114.0×10−8M, also in fourfold dilutions) was injected several weeks later. The blood flow at the injection site was measured by laser Doppler velocimetry at five minute intervals until the response resolved. Both mediators produced hyperaemia with markedly accelerated cutaneous blood flow. Analysis of the dose response data showed that, for a given mediator, the differences in responses between subjects were not substantial and, in particular, that the kinetics of the decay of hyperaemia did not vary significantly between subjects. The response to histamine differed from that to Prostaglandin E2 in terms of time to maximum response, duration of maximum response and coefficient of decay.

Autoantibodies in thyrotoxicosis: a quantitative study of their behavior in relation to the course and outcome of treatment

Many previous investigations have looked into the association between thyroid autoantibodies and the course of thyrotoxicosis. However, the interpretation of these studies is often difficult, owing to their largely retrospective nature, and comparability is limited because of differences in criteria and sampling schedules. The purpose of this study was to investigate prospectively the serial changes in autoantibodies under carefully controlled conditions during treatment of thyrotoxicosis, and to relate these changes to clinical outcome and surgical histology. Sixty-seven patients with Graves’ disease were studied for 24 months; 34 were treated medically and 33 surgically. Anti-thyroglobulin (anti-Tg) and anti-microsomal (anti-M) antibodies were measured on 16 occasions. The frequency of patients showing anti-Tg fell progressively irrespective of the type of treatment, while that showing anti-M fell initially but rose again. Weak associations were found between anti-Tg and suppressibility after 5 months of drug treatment, between the cumulative amount of anti-M and the final TSH levels in those who remained euthyroid after drugs, and between the circulating levels of anti-M just before surgery and the frequency of clinical hypothyroidism 18 months later. However, no significant correlation emerged between the cumulative amount of antibody during the two-year period and the final TSH level or clinical result after surgery, nor between the prevailing antibody level and surgical histology. Wide, rapid and apparently random fluctuations of antibody levels in individuals cast considerable doubt upon the value of single estimations in the distinction of antibody-positive from antibody-negative members of a thyrotoxic population. We conclude that the measurement of thyroid autoantibodies in Graves’ disease has little practical value for the clinician.

Laser Doppler Perfusion Imaging Compared with Lightguide Laser Doppler Flowmetry, Dynamic Thermographic Imaging and Tissue Spectrophotometry for Investigating Blood Flow in Human Skin

Lightguide laser Doppler flowmetry (LDFc) is widely used both in micro-circulatory research and in clinical blood flow studies (for a review, see Shepherd and Oberg, 1990). Despite the inability to measure blood flow in absolute terms with the method (flux values are quoted in volts), physiological challenges can be used in order to test local and sympathetic control of the microvascular flow (Khan et al., 1991).

Effect of topically applied local anaesthesia on histamine flare in man measured by laser Doppler velocimetry

The direct and indirect effects of histamine on the cutaneous microvasculature were measured by laser Doppler velocimetry. Histamine (6.51×10−4M) was injected intradermally into the forearms of eight healthy subjects following treatment with a topically applied local anaesthetic cream (EMLA) or equivalent placebo. The blood flow at the injection site (0 cm) and at 1 and 2 cm proximally was measured by laser Doppler velocimetry over 80 minutes. Analysis of the changes in magnitude of the hyperaemic responses with time showed no difference at the 0 and 1 cm sites, but a marked reduction was found at the 2 cm site following EMLA treatment (p<0.05). At all three sites the decay of the histamine-induced hyperaemia was faster following EMLA treatment than with placebo (p<0.04). The experiments showed that the indirect effect of histamine on the cutaneous microvasculature in the peripheral flare around the injection site was greatly diminished by prior application of EMLA cream and this supports the neurogenic hypothesis: pre-treatment with EMLA cream did not affect the development of hyperaemia and oedema at the site of histamine injection where the mediator acts directly on the cutaneous microvasculature.

Protective Regulation of Oxygen Uptake as a Result of Reduced Oxygen Extraction During Chronic Inflammation

Previous studies of chronic inflammation using the tuberculin reaction in human skin as a model have demonstrated large increases in blood flow within the lesion (Beck and Spence, 1986). This occurs in response to the increase in oxygen consumption presented by the infiltration of cells, mainly T-lymphocytes and macrophages (Gibbs et al., 1984). Despite this increase in flow, transcutaneous pO2 (tcpO2) values remain low at the centre of the reaction (Abbot et al., 1990a). Extracellular pH falls (Harrison et al., 1986), but transcutaneous pCO2 measurements rise during the course of the tuberculin reaction (Abbot et al., 1990a), indicated that the tissue acidosis was purely respiratory in origin. Thus, despite a large observed increase in O2 uptake rate (Abbot et al., 1990b) and low tissue pO2, demand does not appear to exceed the rate of oxygen delivery to the cells.