Basal perfusion of the cutaneous microcirculation: measurements as a function of anatomic position

Benchmarking of Sensor Configurations and Measurement Sites for Out-of-the-Lab Photoplethysmography

Photoplethysmography (PPG) is used for heart-rate monitoring in a variety of contexts and applications due to its versatility and simplicity. These applications, namely studies involving PPG data acquisition during day-to-day activities, require reliable and continuous measurements, which are often performed at the index finger or wrist. However, some PPG sensors are susceptible to saturation, motion artifacts, and discomfort upon their use. In this paper, an off-the-shelf PPG sensor was benchmarked and modified to improve signal saturation. Moreover, this paper explores the feasibility of using an optimized sensor in the lower limb as an alternative measurement site. Data were collected from 28 subjects with ages ranging from 18 to 59 years. To validate the sensors' performance, signal saturation and quality, wave morphology, performance of automatic systolic peak detection, and heart-rate estimation, were compared. For the upper and lower limb locations, the index finger and the first toe were used as reference locations, respectively. Lowering the amplification stage of the PPG sensor resulted in a significant reduction in signal saturation, from 18% to 0.5%. Systolic peak detection at rest using an automatic algorithm showed a sensitivity and precision of 0.99 each. The posterior wrist and upper arm showed pulse wave morphology correlations of 0.93 and 0.92, respectively. For these locations, peak detection sensitivity and precision were 0.95, 0.94 and 0.89, 0.89, respectively. Overall, the adjusted PPG sensors are a good alternative for obtaining high-quality signals at the fingertips, and for new measurement sites, the posterior pulse and the upper arm allow for high-quality signal extraction.

Soft wireless sternal patch to detect systemic vasoconstriction using photoplethysmography

Vasoconstriction is a crucial physiological process that serves as the body's primary blood pressure regulation mechanism and a key marker of numerous harmful health conditions. The ability to detect vasoconstriction in real time would be crucial for detecting blood pressure, identifying sympathetic arousals, characterizing patient wellbeing, detecting sickle cell anemia attacks early, and identifying complications caused by hypertension medications. However, vasoconstriction manifests weakly in traditional photoplethysmogram (PPG) measurement locations, like the finger, toe, and ear. Here, we report a wireless, fully integrated, soft sternal patch to capture PPG signals from the sternum, an anatomical region that exhibits a robust vasoconstrictive response. With healthy controls, the device is highly capable of detecting vasoconstriction induced endogenously and exogenously. Furthermore, in overnight trials with patients with sleep apnea, the device shows a high agreement (r² = 0.74) in vasoconstriction detection with a commercial system, demonstrating its potential use in portable, continuous, long-term vasoconstriction monitoring.

Reallocation of cutaneous and global blood circulation during sauna bathing through a closed-loop model

OBJECTIVE

Sauna bathing (SB) is an important strategy in cardiovascular protection, but there is no mathematical explanation for the reallocation of blood circulation during heat-induced superficial vasodilation. We sought to reveal such reallocation via a simulated hemodynamic model.

METHODS

A closed-loop cardiovascular model with a series of electrical parameters was constructed. The body surface was divided into seven blocks and each block was modeled by a lumped resistance. These resistances were adjusted to increase skin blood flow (SBF), with the aim of reflecting heat-induced vasodilation during SB. Finally, the blood pressure was compared before and after SB, and the blood flow inside the aorta and visceral arteries were also analyzed.

RESULTS

With increasing SBF in this model, the systolic, diastolic, and mean blood pressure in the arterial trunk decreased by 13-29, 18-36, and 19-37 mmHg, respectively. Despite the increase in the peak and mean blood flow in the arterial trunk, the diastolic blood flow reversal in the thoracic and abdominal aortas increased significantly. Nevertheless, the blood supply to the heart, liver, stomach, spleen, kidney, and intestine decreased by at least 25%. Moreover, the pulmonary blood flow increased significantly.

CONCLUSION

Simulated heat-induced cutaneous vasodilation in this model lowers blood pressure, induces visceral ischemia, and promotes pulmonary circulation, suggesting that the present closed-loop model may be able to describe the effect of sauna bathing on blood circulation. However, the increase of retrograde flow in the aortas found in this model deserves further examination.

Imaging PPG for In Vivo Human Tissue Perfusion Assessment during Surgery

Surgical excision is the golden standard for treatment of intestinal tumors. In this surgical procedure, inadequate perfusion of the anastomosis can lead to postoperative complications, such as anastomotic leakages. Imaging photoplethysmography (iPPG) can potentially provide objective and real-time feedback of the perfusion status of tissues. This feasibility study aims to evaluate an iPPG acquisition system during intestinal surgeries to detect the perfusion levels of the microvasculature tissue bed in different perfusion conditions. This feasibility study assesses three patients that underwent resection of a portion of the small intestine. Data was acquired from fully perfused, non-perfused and anastomosis parts of the intestine during different phases of the surgical procedure. Strategies for limiting motion and noise during acquisition were implemented. iPPG perfusion maps were successfully extracted from the intestine microvasculature, demonstrating that iPPG can be successfully used for detecting perturbations and perfusion changes in intestinal tissues during surgery. This study provides proof of concept for iPPG to detect changes in organ perfusion levels.

Sources of Inaccuracy in Photoplethysmography for Continuous Cardiovascular Monitoring

Photoplethysmography (PPG) is a low-cost, noninvasive optical technique that uses change in light transmission with changes in blood volume within tissue to provide information for cardiovascular health and fitness. As remote health and wearable medical devices become more prevalent, PPG devices are being developed as part of wearable systems to monitor parameters such as heart rate (HR) that do not require complex analysis of the PPG waveform. However, complex analyses of the PPG waveform yield valuable clinical information, such as: blood pressure, respiratory information, sympathetic nervous system activity, and heart rate variability. Systems aiming to derive such complex parameters do not always account for realistic sources of noise, as testing is performed within controlled parameter spaces. A wearable monitoring tool to be used beyond fitness and heart rate must account for noise sources originating from individual patient variations (e.g., skin tone, obesity, age, and gender), physiology (e.g., respiration, venous pulsation, body site of measurement, and body temperature), and external perturbations of the device itself (e.g., motion artifact, ambient light, and applied pressure to the skin). Here, we present a comprehensive review of the literature that aims to summarize these noise sources for future PPG device development for use in health monitoring.

Myths and methodologies: Degrees of freedom - limitations of infrared thermographic screening for Covid-19 and other infections

Around the planet, in many different scenarios, skin temperature is being used as a surrogate measure of deep body (core) temperature in the assessment of whether an individual is infected with Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), which causes the coronavirus disease (Covid-19), as indicated by the presence of fever. The key question is whether this is a valid methodology. If it is not, we run the risk of falsely excluding individuals from places they may want, or need, to go. We also run the risk of falsely allowing people into places where they can spread the undetected infection they have. In this review, we explore these and associated questions. We establish the limited utility of the current methodology for the mass screening of individuals for Covid-19 related fever using infrared thermography. We propose the development of an alternative method that may prove to be more sensitive.

The Cutaneous Wound Innate Immunological Microenvironment

The skin represents the first line of defense and innate immune protection against pathogens. Skin normally provides a physical barrier to prevent infection by pathogens; however, wounds, microinjuries, and minor barrier impediments can present open avenues for invasion through the skin. Accordingly, wound repair and protection from invading pathogens are essential processes in successful skin barrier regeneration. To repair and protect wounds, skin promotes the development of a specific and complex immunological microenvironment within and surrounding the disrupted tissue. This immune microenvironment includes both innate and adaptive processes, including immune cell recruitment to the wound and secretion of extracellular factors that can act directly to promote wound closure and wound antimicrobial defense. Recent work has shown that this immune microenvironment also varies according to the specific context of the wound: the microbiome, neuroimmune signaling, environmental effects, and age play roles in altering the innate immune response to wounding. This review will focus on the role of these factors in shaping the cutaneous microenvironment and how this ultimately impacts the immune response to wounding.

Fundamental supply of skin blood flow in the Chinese Han population: Measurements by a full-field laser perfusion imager

BACKGROUND

Skin blood flow is believed to link with many diseases, and shows a significant heterogeneity. There are several papers on basal cutaneous microcirculation perfusion in different races, while the data in Chinese is vacant.

OBJECTIVE

The aim was to establish the database of absolute fundamental supply of skin blood flow in the Chinese Han population.

METHODS

With a full-field laser perfusion imager (FLPI), the skin blood flow can be quantified. Cutaneous perfusion values were determined in 17 selected skin areas in 406 healthy participants aged between 20 and 80 years (mean 35.05 ± 11.33). Essential parameters such as weight, height were also measured and values of BMI were calculated. The perfusion values were reported in Arbitrary Perfusion Units (APU).

RESULTS

The highest cutaneous perfusion value fell on eyelid (931.20 ± 242.59 in male and 967.83 ± 225.49 in female), and pretibial had the lowest value (89.09 ± 30.28 in male and 85.08 ± 33.59 in female). The values were higher in men than women on the bank of fingertips, nose, forehead, cheek, neck and earlobe (P < .05). Perfusion values on stretch and flexion side of forearm had negative correlation with age (P = .01 and P = 4.88 × 10^-3 , respectively) in male. Abdomen was negatively correlated with BMI in both gender (P = .02, respectively).

CONCLUSIONS

Skin blood flow values vary with skin regions. There is a tendency to measure higher perfusion values in men than in women. And the values are irrelevant with age or BMI.

Camera-based photoplethysmography in an intraoperative setting

Background

Camera-based photoplethysmography (cbPPG) is a measurement technique which enables remote vital sign monitoring by using cameras. To obtain valid plethysmograms, proper regions of interest (ROIs) have to be selected in the video data. Most automated selection methods rely on specific spatial or temporal features limiting a broader application. In this work, we present a new method which overcomes those drawbacks and, therefore, allows cbPPG to be applied in an intraoperative environment.

Methods

We recorded 41 patients during surgery using an RGB and a near-infrared (NIR) camera. A Bayesian skin classifier was employed to detect suitable regions, and a level set segmentation approach to define and track ROIs based on spatial homogeneity.

Results

The results show stable and homogeneously illuminated ROIs. We further evaluated their quality with regards to extracted cbPPG signals. The green channel provided the best results where heart rates could be correctly estimated in 95.6% of cases. The NIR channel yielded the highest contribution in compensating false estimations.

Conclusions

The proposed method proved that cbPPG is applicable in intraoperative environments. It can be easily transferred to other settings regardless of which body site is considered.

Electronic supplementary material

The online version of this article (10.1186/s12938-018-0467-7) contains supplementary material, which is available to authorized users.

Measuring niacin-associated skin toxicity (NASTy) stigmata along with symptoms to aid development of niacin mimetics

Though cardioprotective, niacin monotherapy is limited by unpleasant cutaneous symptoms mimicking dermatitis: niacin-associated skin toxicity (NASTy). Niacin is prototypical of several emerging drugs suffering off-target rubefacient properties whereby agonizing the GPR109A receptor on cutaneous immune cells provokes vasodilation, prompting skin plethora and rubor, as well as dolor, tumor, and calor, and systemically, heat loss, frigor, chills, and rigors. Typically, NASTy effects are described by subjective patient-reported perception, at best semi-quantitative and bias-prone. Conversely, objective, quantitative, and unbiased methods measuring NASTy stigmata would facilitate research to abolish them, motivating development of several objective methods. In early drug development, such methods might better predict clinical tolerability in larger clinical trials. Measuring cutaneous stigmata may also aid investigations of vasospastic, ischemic, and inflammatory skin conditions. We present methods to measure NASTy physical stigmata to facilitate research into novel niacin mimetics/analogs, detailing characteristics of each technique following niacin, and how NASTy stigmata relate to symptom perception. We gave niacin orally and measured rubor by colorimetry and white-light spectroscopy, plethora by laser Doppler flowmetry, and calor/frigor by thermometry. Surprisingly, each stigma's abruptness predicted symptom perception, whereas peak intensity did not. These methods are adaptable to study other rubefacient drugs or dermatologic and vascular disorders.

Robust respiration detection from remote photoplethysmography

Continuous monitoring of respiration is essential for early detection of critical illness. Current methods require sensors attached to the body and/or are not robust to subject motion. Alternative camera-based solutions have been presented using motion vectors and remote photoplethysmography. In this work, we present a non-contact camera-based method to detect respiration, which can operate in both visible and dark lighting conditions by detecting the respiratory-induced colour differences of the skin. We make use of the close similarity between skin colour variations caused by the beating of the heart and those caused by respiration, leading to a much improved signal quality compared to single-channel approaches. Essentially, we propose to find the linear combination of colour channels which suppresses the distortions best in a frequency band including pulse rate, and subsequently we use this same linear combination to extract the respiratory signal in a lower frequency band. Evaluation results obtained from recordings on healthy subjects which perform challenging scenarios, including motion, show that respiration can be accurately detected over the entire range of respiratory frequencies, with a correlation coefficient of 0.96 in visible light and 0.98 in infrared, compared to 0.86 with the best-performing non-contact benchmark algorithm. Furthermore, evaluation on a set of videos recorded in a Neonatal Intensive Care Unit (NICU) shows that this technique looks promising as a future alternative to current contact-sensors showing a correlation coefficient of 0.87.

Do plasma catecholamines influence microcirculatory blood flow in cardiac surgery patients?

To investigate whether plasma catecholamines influence blood flow on the microcirculatory level, forehead and forearm skin blood flow was measured by a two-channel laser Doppler blood flux monitor in 50 patients undergoing aortocoronary bypass grafting. Macrohaemodynamics, plasma viscosity, and skin temperatures were additionally monitored. Plasma catecholamines (adrenaline [AD] and noradrenaline [NOR] ) were determined using high-pressure liquid chromatography (HPLC) from arterial blood samples.

In the prebypass period, blood concentrations of both catecholamines increased slightly showing a wide range of values (AD ranging from 3 to 955 pg/ml; NOR ranging from 27 to 5326 pg/ml). In spite of the tremendous increase in plasma catecholamines before and after bypass, laser Doppler flow (LDF) remained almost stable in this period. Neither LDF nor macrocirculatory parameters were correlated to plasma catecholamines. Cardiopulmonary bypass (CPB) resulted in a significant increase in catecholamines (AD ranging from 80 to 2480 pg/ml; NOR ranging from 188 to 9898 pg/ml). Although haematocrit and plasma viscosity were significantly reduced during CPB, LDF decreased in comparison to baseline values (LDF forehead: -25%; LDF forearm: -35%) ( p<0.05).

It is concluded that plasma catecholamine levels were markedly changed during cardiac surgery showing a wide range of concentrations. Microcirculatory flow assessed by laser Doppler remained almost unaffected by these alterations and was not correlated to AD or NOR plasma concentrations. However, during CPB a significant increase in catecholamines can contribute to the risk of microperfusion abnormalities which can be assessed by laser Doppler technique.

Effects of body region and time on hair cortisol concentrations in chimpanzees (Pan troglodytes)

Hair cortisol concentrations (HCC) are increasingly recognized as an integrated measure of the systemic cortisol secretion. Yet, we still know very little about confounding effects on HCC in animals. The present study therefore used hair from semi-wild and zoo living chimpanzees to investigate (1) intra-individual variability of HCC (body-region effect), and (2) the stability of HCC along the hair shaft (traditionally called the washout effect). Our results indicate that absolute HCC varied substantially between certain body regions, but a factor analysis revealed that these HCC differences were mainly attributable to one common source of variance. Thus, hair from all body regions provides similar biological signals and can be mixed, albeit at the cost of a lower signal-to-noise ratio. With regard to potential underlying mechanisms, we studied skin blood flow, as observed through thermal images from one chimpanzee. We found the general HCC pattern was reflected in differences in surface body temperature observed in this individual in three out of four body regions. In a separate set of samples, we found first evidence to suggest that the systematic cortisol decrease along the hair shaft, as observed in humans, is also present in chimpanzee hair. The effect was more pronounced in semi-wild than in zoo chimpanzees presumably due to more exposure to ambient weather conditions.

Toward a Smartphone Application for Estimation of Pulse Transit Time

Pulse transit time (PTT) is an important physiological parameter that directly correlates with the elasticity and compliance of vascular walls and variations in blood pressure. This paper presents a PTT estimation method based on photoplethysmographic imaging (PPGi). The method utilizes two opposing cameras for simultaneous acquisition of PPGi waveform signals from the index fingertip and the forehead temple. An algorithm for the detection of maxima and minima in PPGi signals was developed, which includes technology for interpolation of the real positions of these points. We compared our PTT measurements with those obtained from the current methodological standards. Statistical results indicate that the PTT measured by our proposed method exhibits a good correlation with the established method. The proposed method is especially suitable for implementation in dual-camera-smartphones, which could facilitate PTT measurement among populations affected by cardiac complications.

Photoplethysmography Revisited: From Contact to Noncontact, From Point to Imaging

Photoplethysmography (PPG) is a noninvasive optical technique for detecting microvascular blood volume changes in tissues. Its ease of use, low cost and convenience make it an attractive area of research in the biomedical and clinical communities. Nevertheless, its single spot monitoring and the need to apply a PPG sensor directly to the skin limit its practicality in situations such as perfusion mapping and healing assessments or when free movement is required. The introduction of fast digital cameras into clinical imaging monitoring and diagnosis systems, the desire to reduce the physical restrictions, and the possible new insights that might come from perfusion imaging and mapping inspired the evolution of the conventional PPG technology to imaging PPG (IPPG). IPPG is a noncontact method that can detect heart-generated pulse waves by means of peripheral blood perfusion measurements. Since its inception, IPPG has attracted significant public interest and provided opportunities to improve personal healthcare. This study presents an overview of the wide range of IPPG systems currently being introduced along with examples of their application in various physiological assessments. We believe that the widespread acceptance of IPPG is happening, and it will dramatically accelerate the promotion of this healthcare model in the near future.

Toward Ubiquitous Blood Pressure Monitoring via Pulse Transit Time: Theory and Practice

Ubiquitous blood pressure (BP) monitoring is needed to improve hypertension detection and control and is becoming feasible due to recent technological advances such as in wearable sensing. Pulse transit time (PTT) represents a well-known potential approach for ubiquitous BP monitoring. The goal of this review is to facilitate the achievement of reliable ubiquitous BP monitoring via PTT. We explain the conventional BP measurement methods and their limitations; present models to summarize the theory of the PTT-BP relationship; outline the approach while pinpointing the key challenges; overview the previous work toward putting the theory to practice; make suggestions for best practice and future research; and discuss realistic expectations for the approach.

Thermoregulatory modeling for cold stress

Modeling for cold stress has generated a rich history of innovation, has exerted a catalytic influence on cold physiology research, and continues to impact human activity in cold environments. This overview begins with a brief summation of cold thermoregulatory model development followed by key principles that will continue to guide current and future model development. Different representations of the human body are discussed relative to the level of detail and prediction accuracy required. In addition to predictions of shivering and vasomotor responses to cold exposure, algorithms are presented for thermoregulatory mechanisms. Various avenues of heat exchange between the human body and a cold environment are reviewed. Applications of cold thermoregulatory modeling range from investigative interpretation of physiological observations to forecasting skin freezing times and hypothermia survival times. While these advances have been remarkable, the future of cold stress modeling is still faced with significant challenges that are summarized at the end of this overview.

Effectiveness of laser Doppler perfusion monitoring in the assessment of microvascular function in patients undergoing on-pump coronary artery bypass grafting

OBJECTIVES

To evaluate the effectiveness of single-point laser Doppler perfusion monitoring (LDPM) in the assessment of microvascular reactivity in the skin during cardiopulmonary bypass (CPB).

DESIGN

Cross-sectional observational study.

SETTING

Government-affiliated teaching hospital.

PARTICIPANTS

Twenty male patients aged 60 ± 2 years who underwent coronary artery bypass grafting under CPB.

INTERVENTIONS

The authors assessed the endothelium-dependent vasodilation of the skin microcirculation at the forehead and forearm using LDPM coupled with thermal hyperemia. This measurement was performed before and after the induction of anesthesia, during and after CPB, and 24 h after the end of the surgical procedure.

RESULTS

The basal values of microvascular flow before the induction of anesthesia were significantly higher in the skin of the forehead compared with that of the forearm. There were no significant alterations in microvascular reactivity throughout the recording periods for both recording sites, as assessed by the vasodilation range expressed as cutaneous vascular conductance (arbitrary perfusion units/mean arterial pressure).

CONCLUSIONS

Using LDPM, the authors showed that the microcirculatory bed of the skin of the forehead, which is readily accessible during cardiac surgery, is a suitable model for the study of microvascular reactivity and tissue perfusion in cardiovascular surgical procedures using CPB. This technique could, thus, be suitable for evaluating the effects of drugs or technical procedures on tissue perfusion during cardiac surgery under cardiopulmonary bypass.

The Effects of Different Lying Positions on Interface Pressure, Skin Temperature, and Tissue Blood Flow in Nursing Home Residents

Background:

Although repositioning is considered an important intervention to prevent pressure ulcers, tissue response during loading in different lying positions has not been adequately explored.

Aim:

To compare the effects of different lying positions on interface pressure, skin temperature, and tissue blood flow in nursing home residents.

Method:

From May 2011 to August 2012, interface pressure, skin temperature, and blood flow at three tissue depths were measured for 1 hr over the sacrum in 30° supine tilt and 0° supine positions and over the trochanter major in 30° lateral and 90° lateral positions in 25 residents aged 65 years or older. Measurement of interface pressure was accomplished using a pneumatic pressure transmitter connected to a digital manometer, skin temperature using a temperature sensor, and blood flow using photoplethysmography and laser Doppler flowmetry.

Results:

Interface pressure was significantly higher in the 0° supine and 90° lateral positions than in 30° supine tilt and 30° lateral positions. The mean skin temperature increased from baseline in all positions. Blood flow was significantly higher in the 30° supine tilt position compared to the other positions. A hyperemic response in the post pressure period was seen at almost all tissue depths and positions.

Conclusion:

The 30° supine tilt position generated less interface pressure and allowed greater tissue perfusion, suggesting that this position is the most beneficial.

Forehead reflectance photoplethysmography to monitor heart rate: preliminary results from neonatal patients

Around 5%-10% of newborn babies require some form of resuscitation at birth and heart rate (HR) is the best guide of efficacy. We report the development and first trial of a device that continuously monitors neonatal HR, with a view to deployment in the delivery room to guide newborn resuscitation. The device uses forehead reflectance photoplethysmography (PPG) with modulated light and lock-in detection. Forehead fixation has numerous advantages including ease of sensor placement, whilst perfusion at the forehead is better maintained in comparison to the extremities. Green light (525 nm) was used, in preference to the more usual red or infrared wavelengths, to optimize the amplitude of the pulsatile signal. Experimental results are presented showing simultaneous PPG and electrocardiogram (ECG) HRs from babies (n = 77), gestational age 26-42 weeks, on a neonatal intensive care unit. In babies ⩾32 weeks gestation, the median reliability was 97.7% at ±10 bpm and the limits of agreement (LOA) between PPG and ECG were +8.39 bpm and -8.39 bpm. In babies <32 weeks gestation, the median reliability was 94.8% at ±10 bpm and the LOA were +11.53 bpm and -12.01 bpm. Clinical evaluation during newborn deliveries is now underway.

Laser Doppler imaging of skin microcirculation under fiber-reinforced composite framework of facial prosthesis

OBJECTIVE

Glass-fiber reinforced composite has been suggested to be used as framework material in silicone elastomer facial prostheses. The glass-fiber reinforced framework makes it possible to make the margin of the prosthesis very tight, so that it will lean tightly against the skin even during facial expressions and jaw movements. The purpose of this study was to study how the compression of the glass-fiber reinforced framework would affect the microcirculation of the facial skin.

MATERIALS AND METHODS

A face mask, with a compression pad corresponding to the outer margin of a glass fiber-reinforced composite framework beam of a facial prosthesis, was used to apply pressure on the facial skin of healthy volunteers. The skin blood flow during touch, light and moderate compression of the skin was measured by laser Doppler imaging technique.

RESULTS

None of the compressions had any marked effects on local skin blood flow. No significant differences between the blood flow of the compressed skin, compared to the baseline values, were found.

CONCLUSIONS

The pressure applied to the skin by the tight margins of a facial prosthesis, fabricated with a framework of glass-fiber reinforced composite, does not remarkably alter the skin blood flow.

Distinct locational differences observable in biophysical functions of the facial skin: with special emphasis on the poor functional properties of the stratum corneum of the perioral region

The face is composed of complicated anatomical components, presenting unique portions, such as the eyes, nose and mouth in a relatively narrow area. Moreover, the facial skin is densely populated by the pilosebaceous units and sweat glands, and its stratum corneum (SC) is much thinner than that of the trunk and limbs, although it is always exposed to the environment. Among various portions of the facial skin, some are more easily irritated than others by environmental stimuli, or are more often affected by certain dermatoses. However, the functional aspects of the different portions of the facial skin have not been studied in detail under a strictly controlled environment in sufficiently large numbers of subjects covering different age groups. Thus, we conducted studies in winter with various biophysical techniques, such as transepidermal water loss (TEWL), as a parameter for SC barrier function, high-frequency conductance as that for skin surface hydration state, skin surface lipids, pH, blood flow and skin surface temperature on the forehead, mid-portion of the cheek (cheek in short), nasal tip (nose in short), nasolabial fold and chin of 20 healthy Japanese females aged 22-37 years (average 25 years) in a climate chamber adjusted to 21 degrees C and 50% relative humidity. Thereafter, we studied the influence of ageing on these biophysical parameters by collecting data of TEWL, high-frequency conductance and size of superficial corneocytes on the cheek, nasolabial fold and chin of 303 healthy Japanese female volunteers of different ages. The obtained results showed that the barrier function of the SC was best on the cheek, presenting the lowest TEWL, which was significantly higher on the nasolabial fold and chin than on the cheek. TEWL showed a decrease with age. In contrast, skin hydration state was higher on the nose, but it tended to be lower on the nasolabial fold, showing a mild age-related increase. The corneocytes on the nasolabial fold and chin were smaller than those on the cheek. They revealed a clear increase in size with age. Skin surface lipids were richest on the nose, whereas the superficial pH on the nose was the lowest among the regions tested. The skin temperature was lowest on the cheek than on other areas of the face; although, together with the nose, its blood flow was higher than that of the others. These data indicate great regional differences observable in SC functions on the face. In general, the SC barrier function increases with age, probably because of a decreased epidermal turnover rate as recognized by the increase in corneocyte size. Among the various sites, the skin of the nasolabial fold and chin, whose SC consisted of the smallest corneocytes, showed poorest SC properties in barrier function, suggesting the presence of mild invisible inflammation. It is understandable that this area easily develops not only the complaint of sensitive skin to cosmetics but also dermatitis because of various external agents.

Relationship between measurement site and motion artifacts in wearable reflected photoplethysmography

Pulse rates obtained from wearable photoplethysmography (PPG) sensors are important for monitoring cardiovascular condition, especially during exercise. However, it is difficult to precisely count pulse rates during exercise because PPG is sensitive to body movement. The artifacts from body movement are caused by a change in the blood volume at the measurement site, in addition to pulsatile changes. Here, we investigated the influence of motion artifact with respect to light source and anatomical sites. In this study, we compared the signal from green-light PPG to that from infrared PPG at different anatomical sites. In these experiments, 11 subjects were asked to either assume a resting position or generate spontaneous motion artifact by jumping and swinging their arm. As a result, pulse rates obtained from green-light PPG showed a higher correlation with the ECG R-R interval as compared to those obtained with infrared. Additionally, the signal from the upper arm showed less artifact than did the peripheral one. Therefore, the green-light PPG may be useful for pulse rate monitoring.

Cutaneous blood perfusion as a perturbing factor for noninvasive glucose monitoring

It is widely accepted that noninvasive glucose monitoring (NIGM) has the potential to revolutionize diabetes therapy. However, current approaches to NIGM studied to date have not yet demonstrated a level of acceptable functionality to allow real-time use, beyond restricted fields of application. A number of reviews have been devoted to the subject of NIGM with different focuses related to challenges and a description of the respective underlying problems. This review is aimed at addressing a fundamental topic in the application of NIGM that seems to have received less attention, by describing the perturbations that result in a reduced functionality of NIGM in daily use. Here we provide a short general introduction to glucose monitoring and a basic illustration of the electromagnetic spectrum with a description of the respective physical mechanisms underlying the measurement techniques. This allows for a better understanding of how these perturbing factors affect the measured properties. Cutaneous blood perfusion is one of the major perturbing factors to NIGM, along with variations in temperature, migration of water, and the effect of attachment of the sensor to the skin. An understanding of the mechanisms underlying perfusion variation over time and within the measured human skin tissue matrix is required to enable a discrimination between glucose-induced effects within the tissue and various biophysical impacts to be made. It is suggested that a plurality of probing frequencies is required to discriminate glucose-related changes from the perturbations. A system designed to perform the measurements in different regions of the electromagnetic spectrum with dedicated sensors (multisensor approach) has the potential to more efficiently and reliably discriminate glucose-related information from perturbations. This can be achieved by combining signals related to measurements with different physical underlying mechanisms of the interaction between the probing field propagation and the tissue to help account for the different sources of perturbations.

Measurement of hemodynamics during postural changes using a new wearable cephalic laser blood flowmeter

BACKGROUND

Patients with orthostatic hypotension have pathologic hemodynamics related to changes in body posture. A new cephalic laser blood flowmeter that can be worn on the tragus to investigate the hemodynamics upon rising from a sitting or squatting posture was developed.

METHODS AND RESULTS

The relationship between cephalic hemodynamics and cerebral ischemic symptoms in 63 subjects in a sitting, squatting, and standing positions using the new device was evaluated. Transient decrease in blood pressure within 15 s after rising to an erect position possibly causes dizziness, syncope, and fall. Subjects exhibiting dizziness upon standing showed a significant decrease in the cephalic blood flow (CBF) and indirect beat-to-beat systolic blood pressure, as monitored by the Finometer, and a significant correlation was observed between the drop ratio (drop value on rising/mean value in the squatting position) of CBF and that of systolic blood pressure.

CONCLUSIONS

This new wearable CBF-meter is potentially useful for estimating cephalic hemodynamics and objectively diagnosing cerebral ischemic symptoms of subjects in a standing posture.

New finger-occlusion plethysmograph for estimating peripheral blood flow and vascular resistance

BACKGROUND

The aim of the present study was to measure peripheral blood flow (BF) with a new finger-occlusion plethysmograph (FOP) and to compare this to BF measured with a laser Doppler flowmeter (LDF). An additional objective was to investigate the relationship between hypertension-related clinical parameters and peripheral vascular resistance (PVR) estimated from BF and mean blood pressure (BP) (PVR=mean BP/BF) in young subjects.

METHODS AND RESULTS

The present study employed 101 young volunteers (61 males, 40 females, mean age 23.2+/-2.5 years). The FOP was attached to the third finger and an LDF to the fourth fingertip of each subject. BF was measured simultaneously by the 2 devices. A multi-biomedical recorder (TM2425) measured 24-h BP. A high correlation was observed between BF measured by the FOP and LDF (r=0.79, p<0.001). In multiple linear regression analysis, PVR was independently correlated with a family history of hypertension (p<0.01) and with base diastolic BP during sleep (p<0.01), which is a sensitive predictor of severity of hypertension.

CONCLUSIONS

Our newly developed FOP can estimate peripheral absolute BF easily. Furthermore, BF determined by the FOP can be used to calculate PVR, and an elevated PVR may be a useful predictor of hypertension.

Laser Doppler scanning study of axillary skin before and after liposuction curettage in patients with focal hyperhidrosis

BACKGROUND

Minimally invasive surgeries are frequently used in patients suffering from focal axillary hyperhidrosis (FAH). Sweat glands are removed surgically and the axillary skin is thinned out, with skin necrosis being a possible complication due to reduced microcirculation. Although of considerable interest, studies evaluating pre- and postoperative skin perfusion are unavailable.

OBJECTIVE

To evaluate the blood flow of axillary skin in patients with severe focal axillary hyperhidrosis before and after liposuction curettage (LC).

MATERIAL AND METHODS

The blood flow in the axillary skin of 11 patients was measured by laser Doppler perfusion imaging before surgery and on days 1, 7 and 28 after LC with a rasping cannula. Skin perfusion was measured in arbitrary units (AU) with measuring points in the axillary center (AC), the operated skin 2 cm from the center (2C) and the surrounding healthy skin (HS).

RESULTS

No significant differences of preoperative skin perfusion were found (AC: 0.39 +/- 0.08 AU/2C: 0.38 +/- 0.07 AU/HS: 0.39 +/- 0.07 AU; p > 0.05). On the first and seventh postoperative days, AC (0.2 +/- 0.04 AU/0.27 +/- 0.81 AU) and 2C (0.2 +/- 0.03 AU/0.28 +/- 0.06 AU) area were significantly less perfused, whereas the HS showed higher perfusion values (0.59 +/- 0.1 AU/0.53 +/- 0.09 AU). Twenty-eight days after LC the 2C (0.36 +/- 0.07 AU) and HS (0.4 +/- 0.06 AU) skin revealed no significant differences compared to preoperative skin perfusion (p > 0.05). The AC perfusion was still slightly reduced (0.37 +/- 0.09 AU) without significant difference compared to preoperative findings.

CONCLUSION

LC reduces the axillary skin blood flow with the axillary center being the least perfused area. However, in our collective, no correlation to possible side effects was observed.

Combined photoplethysmographic monitoring of respiration rate and pulse: a comparison between different measurement sites in spontaneously breathing subjects

BACKGROUND

The non-invasive photoplethysmographic (PPG) signal reflects blood flow and volume in a tissue. The PPG signal shows variation synchronous with heartbeat (PPGc), as used in pulse oximetry, and variations synchronous with breathing (PPGr). PPGr has been used for non-invasive monitoring of respiration with promising results. Our aim was to investigate PPG signals recorded from different skin sites in order to find suitable locations for parallel monitoring of variations synchronous with heartbeat and breathing.

METHODS

PPG sensors were applied to the forearm, finger, forehead, wrist and shoulder on 48 awake healthy volunteers. From these sites, seven PPG signals were simultaneously recorded during normal spontaneous breathing over 10 min. Capnometry served as respiration and electrocardiogram (ECG) as pulse reference signals. PPG signals were compared with respect to power spectral content and squared coherence.

RESULTS

Forearm PPG measurement showed significantly higher power within the respiratory region of the power spectrum [median (quartile range) 42 (26)%], but significantly lower power within the cardiac region [9 (10)%] compared with the other skin sites. PPG finger measurement showed the opposite; in transmission mode, the power within the respiratory region was significantly lower [4 (10)%] and within the cardiac region significantly higher [45 (25)%] than the other sites. PPGc coherence values were generally high [>0.96 (0.08)], and PPGr coherence values lower [0.83 (0.35)-0.94 (0.17)].

CONCLUSION

Combined PPG respiration and pulse monitoring is possible, but there are significant differences between the respiratory and cardiac components of the PPG signal at different sites.

Photoplethysmography and its application in clinical physiological measurement

Photoplethysmography (PPG) is a simple and low-cost optical technique that can be used to detect blood volume changes in the microvascular bed of tissue. It is often used non-invasively to make measurements at the skin surface. The PPG waveform comprises a pulsatile ('AC') physiological waveform attributed to cardiac synchronous changes in the blood volume with each heart beat, and is superimposed on a slowly varying ('DC') baseline with various lower frequency components attributed to respiration, sympathetic nervous system activity and thermoregulation. Although the origins of the components of the PPG signal are not fully understood, it is generally accepted that they can provide valuable information about the cardiovascular system. There has been a resurgence of interest in the technique in recent years, driven by the demand for low cost, simple and portable technology for the primary care and community based clinical settings, the wide availability of low cost and small semiconductor components, and the advancement of computer-based pulse wave analysis techniques. The PPG technology has been used in a wide range of commercially available medical devices for measuring oxygen saturation, blood pressure and cardiac output, assessing autonomic function and also detecting peripheral vascular disease. The introductory sections of the topical review describe the basic principle of operation and interaction of light with tissue, early and recent history of PPG, instrumentation, measurement protocol, and pulse wave analysis. The review then focuses on the applications of PPG in clinical physiological measurements, including clinical physiological monitoring, vascular assessment and autonomic function.

Kinetics of blood flow after topical application of benzyl nicotinate on different anatomic sites

Cutaneous characteristics, e.g., thickness of the SC and density of follicles, affect the penetration of topically applied substances. In the present study, the penetration of benzyl nicotinate, causing a vasodilation, was studied on three anatomic sites (forearm, forehead and calf) differing in their skin characteristics. Therefore, the blood flow of the superficial dermal plexus and that of the larger capillaries in the deeper skin layers was simultaneously measured using a laser Doppler flowmeter. In addition, the cutaneous temperature and redness were determined as a function of time. These four biological reactions were measured in turn on a skin area treated with a gel containing benzyl nicotinate and on an untreated control area. The highest basal levels were observed on the forehead. Topical application of benzyl nicotinate resulted in an increase in each biological response. Compared to the other sites, the maximal values were reached earliest on the forehead, which also showed the fastest decrease. No significant differences were obtained comparing the kinetic data of the calf with that of the forearm. The results indicate an additional contribution by the numerous vellus hair follicles of the forehead to the penetration and exposure of the drug.

Persistent erythema and edema of the midthird and upper aspect of the face (morbus morbihan): evidence of hidden immunologic contact urticaria and impaired lymphatic drainage

BACKGROUND

A persistent erythema and edema of the midthird and upper aspect of the face, which bears some resemblance to Melkersson-Rosenthal syndrome and rosaceous lymphedema, has been characterized as morbus morbihan (MM) by French dermatologists. The disease of yet unknown cause starts with recurrent facial edema of short duration, which ultimately leads to persistent swelling after a period of weeks or months.

METHODS

We recruited 6 patients with MM and acquired their history, routine blood tests, and individual UV light tolerability. To check for contact allergies the allergen patch test and the open epicutaneous patch test were performed. To objectify the skin conditions laser Doppler flowmetry and 20-MHz ultrasound were used. Five patients with similar symptoms, but with definitely transient facial erythema and edema caused by proven contact urticaria on cosmetics served as a comparison group.

RESULTS

In all patients, routine blood tests and UVA/UVB light tests showed no pathologic results. Observations of 6 patients with MM revealed the common feature of a clinically relevant immunologic contact urticaria caused by various cosmetic ingredients, which could be diagnosed in all of them. Delayed resorption of the acute edema and prolonged inflammation were shown by laser Doppler flowmetry and 20-MHz ultrasound in the affected skin areas in patients with MM after induction of immunologic contact urticaria by a cosmetic ingredient. Strict avoidance of cosmetics yielded a remarkable clinical benefit in the follow-up examinations.

CONCLUSIONS

We conclude that recurrent and possibly subclinical inflammation caused by immunologic contact urticaria in conjunction with a locally pre-existing lowered lymphatic drainage plays a crucial role in the evolution of MM.

Pulse transit time changes observed with different limb positions

Pulse transit time (PTT) is a non-invasive measure of arterial compliance. It can be used to assess instantaneous blood pressure (BP) changes in continual cardiovascular measurement such as during overnight respiratory sleep studies. In these studies, periodic changes in limb position can occur randomly. However, little is known about their possible effects on PTT monitored on the various limbs. The objective of this study was to evaluate PTT differences on all four limbs during two positional changes (lowering and raising of a limb). Ten healthy adults (seven male) with a mean age of 27.0 years were recruited in this study. The results showed that the limb that underwent a positional change had significant (p < 0.05) local PTT differences when compared to its nominal baseline value, whereas PTT changes in the other remaining limbs were insignificant (p > 0.05). The mean PTT value measured from a vertically-raised limb increased by 42.7 ms, while it decreased by 28.1 ms with a half-lowered limb. The PTT differences observed during positional change can be contributed to by the complex interactions between hydrostatic pressure changes, autonomic and local autoregulation experienced in these limbs. Hence the findings herein suggest that PTT is able to reflect local circulatory responses despite changes in the position of other limbs. This can be useful in prolonged clinical observations where limb movements are expected.

Estimation of breathing interval from the photoplethysmographic signals in children

Two important parameters that are generally under continual observation during clinical monitoring are heart rate (HR) variability and breathing interval (BI) of patients. Current HR monitoring during night-long childhood respiratory sleep studies is well tolerated but BI monitoring requires instrumentation, like nasal cannula, that can be less accommodating for children. In this study, BI was extracted from the photoplethysmographic (PPG) signals using a two-stage signal processing technique termed zero-phase digital filtering. Eight children (7 male) aged 8.6 +/- 2.6 years were recruited to perform two breathing activities: during tidal and with customized externally applied inspiratory resistive loading (IRL). The accuracy of BI derived from the PPG signals was compared with that estimated by a calibrated air pressure transducer in children. Statistical analysis revealed that mean BI attained from the PPG signals were significantly related during tidal breathing (r(2) = 0.76; range 0.61-0.83; p < 0.05) and with the IRL (r(2) = 0.79; range 0.68-0.85; p < 0.05) in the absence of motion artefacts. Preliminary findings herein suggest that besides having the capability to monitor HR and arterial blood oxygen saturation measurements, the PPG signals can be used to derive BI for children. This can be an attractive alternative for children who are more disturbed by intrusive techniques in prolonged clinical monitoring.

Rosacea: I. Etiology, pathogenesis, and subtype classification

Rosacea is one of the most common conditions dermatologists treat. Rosacea is most often characterized by transient or persistent central facial erythema, visible blood vessels, and often papules and pustules. Based on patterns of physical findings, rosacea can be classified into 4 broad subtypes: erythematotelangiectatic, papulopustular, phymatous, and ocular. The cause of rosacea remains somewhat of a mystery. Several hypotheses have been documented in the literature and include potential roles for vascular abnormalities, dermal matrix degeneration, environmental factors, and microorganisms such as Demodex folliculorum and Helicobacter pylori. This article reviews the current literature on rosacea with emphasis placed on the new classification system and the main pathogenic theories. Learning objective At the conclusion of this learning activity, participants should be acquainted with rosacea's defining characteristics, the new subtype classification system, and the main theories on pathogenesis.

Objective assessment of burn scar vascularity, erythema, pliability, thickness, and planimetry

BACKGROUND

There is currently a lack of objective methods to assess scars.

OBJECTIVES

The objectives of this study were to (1) determine the pattern of scar formation up to 24 months after a burn, compare clinical and photographic scar assessment, and determine what percentage of scars became hypertrophic after a major trauma and (2) replace each clinical parameter of a clinical scar scale by objective measurements.

METHODS

Scars from 62 patients were evaluated from the acute phase up to 24 months after the burn, using photographs and clinical assessment during visits. Photographic planimetry helped estimate the percentage of scars that became hypertrophic. Thereafter, 69 patients had scars evaluated using clinical assessment and several instruments to evaluate pigmentation, erythema, pliability, thickness, and perfusion. The sensitivity and specificity of each instrument were determined regarding their ability to correlate with the parameters of hypertrophic and nonhypertrophic scars. Analysis of variance and Tukey's test were used in statistical analysis, with p<.05 indicating significance.

RESULTS

Increased scar hypertrophy occurred between 6 and 12 months after the burn, and less than 30% of scars were hypertrophic at 18 to 24 months. Objective assessment of pliability and erythema, but not pigmentation, correlated significantly with clinical evaluation of hypertrophy. Hypertrophic scars had significantly higher perfusion than nonhypertrophic scars. A new scar rating system is proposed, based on the sensitivity and specificity of each instrument, to correlate with hypertrophic and nonhypertrophic scars.

CONCLUSIONS

Objective rating systems using reliable instruments can be used to replace subjective scar assessment. Larger multicenter prospective studies should test this new scale in scars due to other mechanisms of injury.

Dependence of human forearm skin postocclusive reactive hyperemia on occlusion time

INTRODUCTION

Human postocclusive forearm skin reactive hyperemia is not only a potential means of identifying early signs of cardiovascular diseases, it can also be used in the assessment of local microvascular response to topically applied compounds on skin. The method is not fully characterized. In this study, we investigated the influence of occlusion time on postocclusive forearm skin reactive hyperemia using laser Doppler fluximetry (LDF).

METHODS

Twenty healthy male volunteers were studied on three separate days (at least 24 h apart) via a randomized design. Volunteers were studied in a supine position while fasted. Laser Doppler probes were placed on the volar surface of the antebrachium. In preliminary studies, 3 min of upper arm blood flow occlusion at suprasystolic pressure was found to be the upper limit of tolerability. Subsequently, volunteers were randomized to receive 1, 2, or 3 min occlusion on 3 different days. Skin blood flux was measured before, during, and after occlusion using LDF. The primary outcome calculated was maximal change in skin blood flux before and after occlusion, expressed in arbitrary units (AU).

RESULTS

Skin blood flux changes (mean+/-S.E.M.) after 1, 2, and 3 min occlusion period were 15.39+/-1.27 AU, 24.84+/-1.62 AU, and 32.14+/-1.73 AU, respectively. Using repeated-measures analysis of variance (ANOVA), significant difference (P<.05) in skin blood flux changes were revealed between these three occlusion durations, where 3 min occlusion produced significantly greater in skin blood flux occlusion change compared to 1 and 2 min occlusion.

DISCUSSION

Three minutes of occlusion produces the greater postocclusive reactive hyperemia. It is recommended that studies using postocclusive forearm skin reactive hyperemia should occlude the forearm for at least 3 min.

Transcutaneous flow related variables measured in vivo: the effects of gender

BACKGROUND

The identification of potential sources of error is a crucial step for any new assessment technique. This is the case for transcutaneous variables, such as flow and arterial gases, which have been applied as functional indicators of various aspects of human health. Regarding gender, a particular subject-related determinant, it is often claimed that women present higher transcutaneous oxygen pressure (tcpO2) values than men. However, the statistical significance of this finding is still uncertain.

METHODS

The haemodynamical-vascular response to a local reactive hyperaemia procedure (the tourniquet cuff manoeuvre) was studied in two previously selected group of volunteers (n = 16; 8 women and 8 men). The effect of gender was assessed under standardised experimental conditions, using the transcutaneous flow-related variables tcpO2-tcpCO2 and Laser-doppler Flowmetry (LDF).

RESULTS

Regarding tcpO2, statistically significant differences between genders were not found, although higher values were consistently found for the gases in the female group. Regarding LDF, high statistically significant differences (p < 0.005) were found, with the men's group presenting the highest values and variability. Other derived parameters used to characterise the vascular response following the cuff-deflation (t-peak) were similar in both groups.

CONCLUSIONS

The relative influence of gender was not clearly demonstrated using these experimental conditions. However the gender-related LDF differences suggest that further investigation should be done on this issue. Perhaps in the presence of certain pathological disparities involving peripheral vascular regulation, other relationships may be found between these variables.

Neural network for photoplethysmographic respiratory rate monitoring

The reflection mode photoplethysmographic (PPG) signal was studied with the aim of determining respiratory rate. The PPG signal includes respiratory synchronous components, seen as frequency modulation of the heart rate (respiratory sinus arrhythmia), amplitude modulation of the cardiac pulse and respiratory-induced intensity variations (RIIVs) in the PPG baseline. PPG signals were recorded from the foreheads of 15 healthy subjects. From these signals, the systolic wave-form, diastolic waveform, respiratory sinus arrhythmia, pulse amplitude and RIIVs were extracted. Using basic algorithms, the rates of false positive and false negative detection of breaths were calculated separately for each of the five components. Furthermore, a neural network was assessed in a combined pattern recognition approach. The error rates (sum of false positive and false negative breath detections) for the basic algorithms ranged from 9.7% (pulse amplitude) to 14.5% (systolic waveform). The corresponding values for the neural network analysis were 9.5-9.6%. These results suggest the use of a combined PPG system for simultaneous monitoring of respiratory rate and arterial oxygen saturation (pulse oximetry).

Vasoconstrictive effect of topical applied corticosteroids measured by laser doppler imaging and reflectance spectroscopy

Topical application of corticosteroids induces blanching of the skin, based on changes of the underlying microcirculation of the skin. Usually the intensity of blanching after topical application of corticosteroids is measured subjectively by a trained observer using a visual score. In order to obtain an objective determination of the blanching effect and to assess the underlying effect of the skin perfusion, it is necessary to use noninvasive bioengineering techniques. The aim of this study was to compare changes in the vascular plexus during 72 h after topical application of corticosteroids of different potencies with control sites by two noninvasive techniques: laser Doppler imaging (LDI) and diffuse reflectance spectroscopy (DRS). We used the most potent vasoconstrictor, Clobetasol-di-propionate. After 8 h (1.49 Rm (mean reflectance) +/- 0.6 SEM) and after 30 h (0.52 Rm +/- 0.36) DRS showed significant changes in blood flow (during blanching and reactive hyperemia). LDI showed a slight change after 8 h (-0.04 aU (arbitrary units) +/- 0.02 blanching) and a second, significant reaction after 30 h (LDI: 0.18 aU +/- 0.04 reactive hyperemia). In LDI after 30 h higher values were found in men than in women (clobetasol-17-propionate under occlusion Deltat(30)-t(0) men: 0.47 aU +/- 0.18; n = 7; Deltat(30)-t(0) women: 0.14 aU +/- 0.02; n = 10; P = 0.025). This leads to the conclusion that DRS is of more value for the detection of blanching than LDI, which has its sensitivity in the hyperperfused skin. Measurement with both devices showed clear differences in men and women, which means that sex differences should be taken into account.

Monitoring of respiratory rate in postoperative care using a new photoplethysmographic technique

OBJECTIVE

Photoplethysmography (PPG) is a non-invasive optical technique that measures variations in skin blood volume and perfusion. The PPG signal contains components that are synchronous with respiratory and cardiac rhythms. We undertook this study to evaluate PPG for monitoring patients' respiratory rate in the postoperative care unit, using a new prototype device. We compared it with the established technique, transthoracic impedance (TTI).

METHODS

PPG signals from 16 patients (ASA classes 1-2, mean age 43 years) who were recovering from general anaesthesia after routine operations were recorded continuously for 60 minutes/patient. The respiratory synchronous part of the PPG signal was extracted by using a bandpass filter. Detection of breaths in the filtered PPG signals was done both visually and by using an automated algorithm. In both procedures, the detected breaths were compared with the breaths detected in the TTI reference.

RESULTS

A total of 10,661 breaths were recorded, and the mean +/- SD respiratory rate was 12.3 +/- 3.5 breaths/minute. When compared with TTI, the rates of false positive and false negative breaths detected by PPG (visual procedure) were 4.6 +/- 4.5% and 5.8 +/- 6.5%, respectively. When using the algorithm for breath detection from PPG, the rates of false positive and false negative breaths were 11.1 +/- 9.7% and 3.7 +/- 3.8%, respectively, when compared to TTI. Lower respiratory rates increased the occurrence of false-positive breaths that were detected by the PPG using visual identification (p < 0.05). The same tendency was seen with the automated PPG procedure (p < 0.10).

CONCLUSIONS

Our results indicate that PPG has the potential to be useful for monitoring respiratory rate in the postoperative period.

Evaluation of a combined laser Doppler flowmetry and iontophoresis technique for the assessment of equine cutaneous microvascular function

A combined laser Doppler flowmetry and iontophoresis (LDFI) technique, used routinely to assess human microvascular function, was evaluated as a noninvasive technique for assessment of equine microvascular function, to facilitate the study of diseases such as laminitis. Baseline and vasoactive agonist-induced (acetylcholine and nitroprusside) microvascular flux was quantified at 2 sites (on the dorsal pastern adjacent to the coronary band and over the gluteals) in 6 clinically normal horses on 5 or 6 separate occasions under standardised conditions. Both agonists significantly increased microvascular flux. Skin pigmentation significantly attenuated the baseline flux, but not the magnitude of the agonist-mediated vasodilatory response. While LDFI was simple to perform, its value as a clinical and research tool for assessing the equine cutaneous microcirculation is limited by its poor reliability, as indicated by the marked intra- and intersubject variability in baseline and agonist-mediated microvascular flux.

Blood extraction from lancet wounds using vacuum combined with skin stretching

Key factors and practical limits of blood extraction from lancet wounds on body sites other than the finger were determined by testing a large number of conditions. During these tests, the pain associated with lancing alternate body sites was rated as less painful than a fingerstick 98% of the time. Vacuum combined with skin stretching was effective in extracting an adequate volume of blood from the forearm for glucose testing, up to an average of 16 microl in 30 s. The amount of blood extracted increases with the application of heat or vacuum before lancing, the level of vacuum, the depth of lancing, the time of collection, and the amount of skin stretching. Vacuum and skin stretching led to significant increases, up to fivefold in the perfusion of blood in the skin as measured by laser Doppler. Our observations suggest that vacuum combined with skin stretching increases blood extraction at alternate sites by increasing the lancet wound opening, increasing the blood available for extraction by vasodilatation, and reducing the venous return of blood through capillaries.

[Evaluation of late radiation-induced changes in superficial microcirculation. I. Clinical benefit of the cutaneous Doppler laser]

OBJECTIVE

The changes that occur in the tissular microcirculation after therapeutic irradiation (RT) account for some of the late effects of irradiation, especially on the cutaneous level. As a rule, the methods of exploring the superficial microcirculation only measure blood flow indirectly. Only the Doppler laser can provide direct measurements of blood parameters in vivo in man.

METHODS

Thirty women who had been irradiated with 45 + 20 Gy of locoregional fractionated adjuvant RT for breast cancer developed local radiation-induced fibrosis six years later (+/- 5). The local microcirculation was measured in the resting state and during thermal stimulation at 42 degrees C, using a Periflux cutaneous Doppler laser with p413 probes. Three periods of six minutes each were continuously recorded: period 1 (P1) represented basal resting cutaneous perfusion, with the slope p corresponding to the increase in perfusion when two minutes of thermal stimulation at 42 degrees C began; P2 to plateau perfusion during this stimulation; and P3 to perfusion on the return to equilibrium. Each individual was its own control.

RESULTS

In the women treated by RT, the resting microcirculation in the skin underlying an area of late fibrosis rose by a factor of 2 during P1 (p < 0.001), and the P2/P1 ratio decreased by a factor of 2 (p < 0.001), compared to the control area. After thermal stimulation, there was no change in p, P2 or P3.

CONCLUSION

Although a hypovascularization is frequently found in late sequelae of RT, we observed an increase of the cutaneous microcirculation associated with a maladjustment of the endothelial response to a thermal stimulation. These observations seem to reflect the presence of dilated new capillaries of the telangiectatic type, which are macroscopically undetectable.