Aging is associated with a diminished axon reflex response to local heating on the gaiter skin area

Contactless photoplethysmography for assessment of small fiber neuropathy

Chronic pain is a prevalent condition affecting approximately one-fifth of the global population, with significant impacts on quality of life and work productivity. Small fiber neuropathies are a common cause of chronic pain, and current diagnostic methods rely on subjective self-assessment or invasive skin biopsies, highlighting the need for objective noninvasive assessment methods. The study aims to develop a modular prototype of a contactless photoplethysmography system with three spectral bands (420, 540, and 800 nm) and evaluate its potential for assessing peripheral neuropathy patients via a skin topical heating test and spectral analyses of cutaneous flowmotions. The foot topical skin heating test was conducted on thirty volunteers, including fifteen healthy subjects and fifteen neuropathic patients. Four cutaneous nerve fiber characterizing parameters were evaluated at different wavelengths, including vasomotor response trend, flare area, flare intensity index, and the spectral power of cutaneous flowmotions. The results show that neuropathic patients had significantly lower vasomotor response (50%), flare area (63%), flare intensity index (19%), and neurogenic component (54%) of cutaneous flowmotions compared to the control group, independent of photoplethysmography spectral band. An absolute value of perfusion was 20%-30% higher in the 420 nm band. Imaging photoplethysmography shows potential as a cost-effective alternative for objective and non-invasive assessment of neuropathic patients, but further research is needed to enhance photoplethysmography signal quality and establish diagnostic criteria.

Ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, with no effect on β-adrenergic sweating

NEW FINDINGS

What is the central question of this study? β-Adrenergic receptor activation modulates cutaneous vasodilatation and sweating in young adults. In this study, we assessed whether age-related differences in β-adrenergic regulation of these responses exist and whether they differ between men and women. What is the main finding and its importance? We showed that ageing augmented β-adrenergic cutaneous vasodilatation, although the pattern of response differed between men and women. Ageing had no effect on β-adrenergic sweating in men or women. Our findings advance our understanding of age-related changes in the regulation of cutaneous vasodilatation and sweating and provide new directions for research on the significance of enhanced β-adrenergic cutaneous vasodilatation in older adults.

ABSTRACT

β-Adrenergic receptor agonists, such as isoprenaline, can induce cutaneous vasodilatation and sweating in young adults. Given that cutaneous vasodilatation and sweating responses to whole-body heating and to pharmacological agonists, such as acetylcholine, ATP and nicotine, can differ in older adults, we assessed whether ageing also modulates β-adrenergic cutaneous vasodilatation and sweating and whether responses differ between men and women. In the context of the latter, prior reports showed that the effects of ageing on cutaneous vasodilatation (evoked with ATP and nicotine) and sweating (stimulated by acetylcholine) were sex dependent. Thus, in the present study, we assessed the role of β-adrenergic receptor activation on forearm cutaneous vasodilatation and sweating in 11 young men (24 ± 4 years of age), 11 young women (23 ± 5 years of age), 11 older men (61 ± 8 years of age) and 11 older women (60 ± 8 years of age). Initially, a high dose (100 µm) of isoprenaline was administered via intradermal microdialysis for 5 min to induce maximal β-adrenergic sweating. Approximately 60 min after the washout period, three incremental doses of isoprenaline were administered (1, 10 and 100 µm, each for 25 min) to assess dose-dependent cutaneous vasodilatation. Isoprenaline-mediated cutaneous vasodilatation was greater in both older men and older women relative to their young counterparts. Augmented cutaneous vasodilatory responses were observed at 1 and 10 µm in women and at 100 µm in men. Isoprenaline-mediated sweating was unaffected by ageing, regardless of sex. We show that ageing augments β-adrenergic cutaneous vasodilatation differently in men and women, without influencing β-adrenergic sweating.

The impact of age on vascular smooth muscle function in humans

AIM

Advanced age is associated with vascular endothelial dysfunction, characterized by reductions in the endothelium-dependent vasodilation of the conduit and resistance arteries, in part, from decreased nitric oxide bioavailability. Although vascular smooth muscle function (SMF), assessed by responsiveness to an exogenous nitric oxide donor, is typically reported to be intact, many of these studies are limited by a small sample size. Therefore, the purpose of this meta-analysis is to systematically review and determine whether vascular SMF is different between older versus young healthy individuals.

DESIGN

We conducted a systematic search of MEDLINE, Cochrane and Scopus, since their inceptions until January 2014, for articles evaluating SMF in the brachial artery and/or resistance arteries (BASMF and RASMF, respectively), as assessed by the endothelium-independent vasodilator response to exogenous nitric oxide donors in older (≥60 years) and young (<30 years) groups of healthy individuals. Meta-analyses were performed to compare the mean difference in BASMF and the standardized mean difference in RASMF between older and young groups. Subgroup analyses were performed to identify sources of heterogeneity.

RESULTS

Fifteen studies assessing BASMF and 20 studies assessing RASMF were included, comprising 550 older and 516 young healthy individuals. After data pooling, BASMF and RASMF were lower in older compared with the young groups (mean difference = -1.89%, P = 0.04; standardized mean difference = -0.46, P = 0.0008, respectively). Significant heterogeneity was observed in the BASMF (I2 = 74%, P < 0.00001) and the RASMF (I2 = 57%, P = 0.0008) meta-analyses. Subgroup analyses revealed that studies with (predominantly) men showed similar SMF responses between the older and the young groups.

CONCLUSION

On the basis of the current published studies, vascular SMF is reduced in conduit and resistance arteries of otherwise healthy older individuals, particularly in women.

Relationship of age and body mass index to skin temperature and skin perfusion in primary Raynaud's phenomenon

OBJECTIVE

To assess the relationship of age and body mass index (BMI) to skin temperature and perfusion in patients with primary Raynaud's phenomenon (RP) compared with controls.

METHODS

Patients with RP as well as age- and sex-matched controls underwent external cold provocation by exposure to 20 °C water for 1 minute. Before and after cold provocation, skin temperature and skin perfusion were measured.

RESULTS

Twenty-six patients with RP (20 women and 6 men; median age 41.9 years) and 22 controls (17 women and 5 men; median age 42.9 years) were studied. In RP patients, cold exposure led to a median change in skin temperature of -7% (interquartile range [IQR] -13.1, -4.1) and to a median change in skin perfusion of -26.4% (IQR -36.2, 2.9). In controls, skin temperature changed by -15.7% (IQR -18.3, -11.6) and skin perfusion by -33% (IQR -53.3, -1.1) upon cold exposure. In patients with RP, age and BMI were related to skin temperature (for age, r = 0.683, P < 0.0001; for BMI r = 0.657, P < 0.0001) and skin perfusion (for age, r = 0.595, P = 0.002; for BMI, r = 0.653, P < 0.0001), while no association was found in controls. The cold-induced decrease in skin temperature was inversely related to age (r = -0.518, P = 0.003) and BMI (r = -0.662, P < 0.0001) in patients with RP; correlations were not observed in controls. The cold-induced change in skin perfusion was not related to age or BMI in either group.

CONCLUSION

The cold-induced decrease in skin temperature is related to age and BMI in patients with RP but not in controls. Further studies are needed to clarify the pathophysiology of digital ischemia in primary RP.

Intensified insulin treatment is associated with improvement in skin microcirculation and ischaemic foot ulcer in patients with type 1 diabetes mellitus: a long-term follow-up study

AIMS/HYPOTHESIS

We investigated skin microcirculation and its association with HbA1c and the incidence of ischaemic foot ulcer in patients with type 1 diabetes formerly randomised (1982-1984) to intensified conventional treatment (ICT) or standard treatment (ST) with insulin for a mean of 7.5 years.

METHODS

We re-determined the skin microcirculation of 72 patients (ICT 35 vs ST 37) from the original Stockholm Diabetes Intervention Study with iontophoresis topically applied with the following vasoactive stimuli: acetylcholine (ACh) (endothelial-dependent vasodilatation), sodium nitroprusside (SNP) (endothelial-independent vasodilatation), and capsaicin (C-nociceptive-dependent vasodilatation). HbA1c levels (mean of 14 values/patient) were prospectively collected between 1990 and 1995 and tested for association with skin microcirculation. The patients were followed until first hospitalisation for an ischaemic foot ulcer or until 2011.

RESULTS

During the median 28 years of follow-up, three patients developed ischaemic foot ulcers in the ICT group compared with ten in the ST group (logrank, p = 0.035). At the time of iontophoresis, HbA1c was lower in the ICT group (median 57 mmol/mol [minimum-maximum 40-79 mmol/mol]) compared with the ST group (68 mmol/mol [41-96 mmol/mol], p < 0.01) (DCCT: ICT 7.4% [5.8-9.4%] vs ST 8.4% [5.9-10.9%]). Stimulated blood flow was higher in the ICT vs ST group with significantly increased perfusion units (PU) for: ACh (8.1 PU [4.6-24.7 PU] vs 5.3 PU [1.7-21.4 PU], p < 0.01); SNP (8.1 PU [2.2-20.1 PU] vs 5.6 PU [2.3-19.2 PU], p = 0.03); and capsaicin (5.0 PU [1.7-22.9 PU] vs 3.4 PU [1.5-8.4 PU], p < 0.01). HbA1c was associated with vasodilatation induced by ACh (b = -0.02, p < 0.01) and capsaicin (b = -0.02, p = 0.03). HbA1c was independently associated with ACh (b = -1.48, p < 0.01) and capsaicin-induced vasodilatation (b = -1.45, p < 0.01).

CONCLUSIONS/INTERPRETATION

Improved glycaemic control in patients with type 1 diabetes is associated with an improvement in skin microcirculation and with a lower incidence of ischaemic foot ulcers.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01957930.