Quantitation of skin vasomotor control in normal subjects and in diabetic patients with autonomic neuropathy

Thermoregulation in neuropathies

Peripheral neuropathy affecting autonomic and small sensory fibers can cause abnormalities of both autonomic and behavioral thermoregulation. Quantitative autonomic and sensory neurophysiologic tests and quantification of the linear density of intraepidermal nerve fibers potentially can stratify those at risk of impaired thermoregulation during cold and heat challenges. New data relating to thermoregulatory sweating impairment in neuropathy are presented in this chapter. Of 516 neuropathy patients analyzed, 345 were found to have thermoregulatory sweat test (TST) abnormalities with a mean percentage of anterior body surface anhidrosis (TST%) of 12% and a significant reduction in total body sweat rate, although the rate of core temperature rise with heating (slope) was not significantly different from that of patients with a normal TST. However a subset of abnormal TST patients having 25% or greater TST% showed a significantly more rapid rise in core temperature (lower slope) than age- and sex-matched neuropathy patients with a normal TST. Etiologies of neuropathy in this more severe group included diabetes, erythromelalgia, immune-mediated autonomic neuropathy, primary systemic amyloidosis, and neuropathy associated with postganglionic-autonomic degenerative disorders.

The relationship between pressure ulcers and skin blood flow response after a local cold provocation

OBJECTIVE

To study the relationship between an impaired blood flow response after a local cold stimulus, testing nerve regulation of the local blood flow response, and an increased risk of developing pressure ulcers.

DESIGN

An observational, longitudinal, prospective study.

SETTING

Dutch nursing home.

PATIENTS

Eighty-two newly admitted somatic nursing home patients, age 60 years and older.

INTERVENTION

A local cold stimulus (17 degrees C) applied to the trochanter major.

MAIN OUTCOME MEASURES

On admission, blood flow response to a local cold stimulus. As the stimulus was withdrawn, the temperature measured at the skin increased asymptotically toward the final temperature, T(f). The velocity of this rise was characterized by the time constant, tau, of the process. On admission, and weekly during a 4-week follow-up period, the presence or absence of pressure ulcers was verified.

RESULTS

The blood flow response time correlated significantly with the risk of developing pressure ulcers. The patients who developed pressure ulcers during the follow-up period had a significantly longer response time than the patients who did not.

CONCLUSIONS

Malfunction of the nervous regulatory mechanisms of the local blood flow is partially responsible for an increased susceptibility to pressure ulcer formation.

Influence of intense sound stimuli on skin microcirculation

Sound influences not only the organ of hearing but also other systems including the circulation. The purpose of the present study was to investigate the effect of strong sound on the skin microcirculation of the palmar area of the hand and of the plantar area of the foot, which are areas of dense microvasculature and rich sympathetic innervation. The laser Doppler technique was used for measuring cutaneous red cell flux (RCF). Eighteen normal subjects were studied. The results indicate that a pure tone sound of 1500 Hz, with an intensity of 100 dBA and duration 5 s, applied by earphones caused a significant decrease in RCF in 14 out of 18 subjects in the finger but not in the foot skin. A higher intensity (110 dBA) tone caused a stronger decrease of RCF in the finger. The latency and the duration of the reaction showed a dependence on the intensity of the sound, i.e. the reaction to the stronger stimulus was of shorter latency (p < 0.01) and longer duration (p < 0.05). The duration of the reaction did not show significant change when a longer stimulus of 30 s was applied. Repetitive stimuli evoked habituation (p < 0.05).

The validity and reproducibility of the skin vasomotor test--studies in normal subjects, after spinal anaesthesia, and in diabetes mellitus

Skin sympathetic vasomotor control can be examined in the extremities by the skin vasomotor test. In this test the change in skin blood flow and skin temperature in the hand and foot in response to a cold stimulus is utilized as an index of distal sympathetic nerve fibre integrity. This is of importance in conditions such as diabetes mellitus as peripheral autonomic neuropathy is associated with orthostatic hypotension and diabetic foot complications. The validity and reproducibility of the test as a marker of distal sympathetic nerve function has been studied. The test was performed in nine healthy control subjects and in nine subjects (undergoing minor surgery) after a sympathetic nerve conduction block (L2-L3) was achieved in the lower extremities by spinal analgesia. Changes in skin temperature (p < 0.001) and skin blood flow (p < 0.005) in responses to cooling were significantly larger in the control group than in the group with spinal analgesia. Repeated skin temperature measurements on 42 occasions (test-retest period of 4 weeks) in eight healthy and 34 diabetic subjects indicated a reliability coefficient of 80%. We conclude, therefore, that the skin vasomotor test provides a valid and reproducible quantitative assessment of skin sympathetic nerve function in upper and lower extremities.

Treatment of diabetic autonomic neuropathy with an aldose reductase inhibitor

To evaluate the effects of the aldose reductase inhibitor Ponalrestat (Statil) on diabetic autonomic neuropathy, a double-blind placebo controlled trial was carried out on a group of 34 diabetic patients with documented cardiac autonomic neuropathy. After a 4-week, placebo run-in period, patients were randomised for treatment with 600 mg Statil or placebo for another 24 weeks. Moreover, the reliability of the autonomic nerve function tests was investigated by comparing the results at onset and at week 4. Fifteen patients treated with Statil and 12 with placebo completed the study. Neither symptom scores nor cardiovascular reflexes, pupil reflexes and skin vasomotor reflexes improved after Statil therapy, which led us to conclude that Statil is not effective in the treatment of diabetic autonomic neuropathy. Reliability coefficients for cardiovascular reflexes and pupil reflex showed high values, ranging from 60% to 80%. Therefore these methods are recommended in future therapy trials.