Heat-washout: a new method for measuring cutaneous blood flow rate in areas with and without arteriovenous anastomoses

Advanced thermal sensing techniques for characterizing the physical properties of skin

Measurements of the thermal properties of the skin can serve as the basis for a noninvasive, quantitative characterization of dermatological health and physiological status. Applications range from the detection of subtle spatiotemporal changes in skin temperature associated with thermoregulatory processes, to the evaluation of depth-dependent compositional properties and hydration levels, to the assessment of various features of microvascular/macrovascular blood flow. Examples of recent advances for performing such measurements include thin, skin-interfaced systems that enable continuous, real-time monitoring of the intrinsic thermal properties of the skin beyond its superficial layers, with a path to reliable, inexpensive instruments that offer potential for widespread use as diagnostic tools in clinical settings or in the home. This paper reviews the foundational aspects of the latest thermal sensing techniques with applicability to the skin, summarizes the various devices that exploit these concepts, and provides an overview of specific areas of application in the context of skin health. A concluding section presents an outlook on the challenges and prospects for research in this field.

Graphene-based ultrasensitive optical microfluidic sensor for the real-time and label-free monitoring of simulated arterial blood flow

Highly sensitive, real-time and label-free sensing of liquid flow in microfluidic environments remains challenging. Here, by growing high-quality graphene directly on a glass substrate, we designed a microfluidic-integrated graphene-based flow sensor (GFS) capable of detecting complex, weak, and transient flow velocity and pressure signals in a microfluidic environment. This device was used to study weak and transient liquid flows, especially blood flow, which is closely related to heart and artery functions. By simulating cardiac peristalsis and arterial flow using peristaltic pumps and microfluidic systems, we monitored simulated arterial blood flow. This ultrasensitive graphene-based flow sensor accurately detected a flow velocity limit as low as 0.7 mm/s, a pumping frequency range of 0.04 Hz to 2.5 Hz, and a pressure range from 0.6 kPa to 14 kPa. By measuring the blood flow velocities and pressures, pathological blood flow signals were distinguished and captured by the corresponding flow velocities or pressures, which can reflect vascular occlusion and heart functions. This sensor may be used for the real-time and label-free monitoring of patients' basic vital signs using their blood flow and provide a possible new method for the care of critically ill patients.

Heat-washout measurements compared to distal blood pressure and perfusion in orthopaedic patients with foot ulcers

Distal blood pressure and local skin perfusion pressure were compared to measurement of blood flow rate (BFR) measured by the heat-washout method in orthopaedic patients with and without diabetes, all with a foot ulcer in one foot, compared to healthy controls. The correlation was good between heat-washout and distal blood pressure in patients with diabetes with and without an ulcer (P = 0·024 and 0·059, respectively). The correlation was weak in patients without diabetes with and without an ulcer, most probably due to power problems (P = 0·118 and 0·116, respectively). The correlation in the healthy controls was poor (P = 0·333 and 0·685 for right and left 1. Toe, respectively) probably because not all measurements were performed under optimal conditions with maximally dilated arterioles and warm hands and feet. The patients already have maximally dilated arterioles to extract the maximal amount of oxygen from the surrounding tissue, and therefore, measurements are easier made in these subjects. BFR in the first toe increased significantly in all patients when the foot was moved from heart level to 50 cm below heart level (P = between 0·03 and 0·05) as previously seen in patients with claudication. There was no statistical difference in the healthy controls, consistent with previous findings. These results may indicate that the heat-washout method can be used as an alternative to strain gauge blood pressure in the evaluation of peripheral artery disease and wound healing potentials. Furthermore, the heat-washout measurements can be used bedside.

Heat-washout - an objective method for diagnosing neuropathy and atherosclerosis in diabetic patients

BACKGROUND

The heat-washout method is an objective method that measures cutaneous blood flow rate (BFR) in ml (100 g. min)(-1), previously found useful for measuring toe BFR in non-diabetic patients with claudication.

AIM

The method is used for evaluating the presence of a veno-arteriolar reflex (VAR) in the forefoot and signs of atherosclerosis in the first toe in type 2 diabetics.

METHODS

Nine type 2 diabetics for +10 years, peripheral neuropathy, median age 62, and 9 healthy subjects without diabetes, median age 52 were examined for the presence of a VAR in the forefoot. A VAR was present when BFR decreased 25% or more with the foot 50 cm below heart level. Examinations for atherosclerosis were made in the pulp of the first toe. An increase in BFR of 50% or more with the foot 50 cm below heart level indicated the presence of atherosclerosis.

RESULTS

The VAR was significantly attenuated in type 2 diabetics with neuropathy compared to controls, (P<0·01). Only one patient with known neuropathy and diabetes showed a reflex compared to eight out of nine controls (P<0·01). The VAR was correlated to the vibration perception threshold measured with biothesiometry (r = -0·661, P = 0·0003). Two patients with type 2 diabetes and neuropathy without clinical sign of peripheral artery disease (PAD) had an abnormal response similar to that seen in subjects with intermittent claudication.

CONCLUSION

The heat-washout method seems useful as and objective method for evaluating as well the presence of a VAR as atherosclerosis in type 2 diabetics.

Does comprilan bandage have any influence on peripheral perfusion in patients with oedema?

AIM

Comprilan bandage may be an attractive treatment of leg oedema, but theoretically bandage could compromise peripheral circulation. The present study was undertaken to investigate circulation in the first toe before, during, and after treatment with comprilan bandage.

METHODS AND STUDY POPULATION

Blood flow rate was measured by the heat-washout method in the pulp of the first toe of 10 patients (eight women, two men, aged 75-94) with leg oedemas, and systolic toe blood pressure was determined by the strain gauge method. Oedema was scored according to a visual scale, and the patients were treated with comprilan (short stretch) bandage for 1 week. Toe blood flow rate was measured before, during and after the use of the bandages, and toe blood pressure was measured before and after the use of bandages.

RESULTS

According to the visual scale, all subject benefited from the treatment by reduction of oedema, and they reported increased well-being after. Blood flow rate was not significantly altered during and after the treatment. Systolic toe pressure was normal in all patients (R/L = 94/83 mmHg), and no significant change took place during and after the use of the bandages (92/90 mmHg).

CONCLUSION

Comprilan bandage has a positive effect on legs oedemas, visually as well as according to the patients well-being. The treatment does not have any significant influence on toe blood pressure. It cannot, however, be excluded that the use of comprilan bandage may compromise toe blood flow rate slightly (<5%). A larger study with more subjects has to be made to come this closer, and additional capillary blood flow rate should be measured in an area without arteriovenous anastomoses.

Physiologic measures of sexual function in women: a review

OBJECTIVE

To review and describe physiologic measures of assessing sexual function in women.

DESIGN

Literature review.

SETTING

Studies that use instruments designed to measure female sexual function.

PATIENT(S)

Women participating in studies of female sexual function.

INTERVENTION(S)

Various instruments that measure physiologic features of female sexual function.

MAIN OUTCOME MEASURE(S)

Appraisal of the various instruments, including their advantages and disadvantages.

RESULT(S)

Many unique physiologic methods of evaluating female sexual function have been developed during the past four decades. Each method has its benefits and limitations.

CONCLUSION(S)

Many physiologic methods exist, but most are not well-validated. In addition there has been an inability to correlate most physiologic measures with subjective measures of sexual arousal. Furthermore, given the complex nature of the sexual response in women, physiologic measures should be considered in context of other data, including the history, physical examination, and validated questionnaires. Nonetheless, the existence of appropriate physiologic measures is vital to our understanding of female sexual function and dysfunction.

Supraorbital cutaneous blood flow rate during carotid endarterectomy

BACKGROUND

The supraorbital skin region is supplied by the supraorbital artery, which is a branch of the internal carotid artery. The supraorbital cutaneous blood flow rate may therefore be influenced by changes in the internal carotid artery flow during carotid endarterectomy.

METHODS

The supraorbital cutaneous blood flow rate was measured by the application of heat to the skin and following the subsequent dissipation of the heat in seven patients undergoing carotid endarterectomy. At the same time, the oxygenation in the right and left frontal region was monitored by near-infrared spectroscopy (NIRS).

RESULTS

During cross-clamping of the carotid artery, the ipsilateral NIRS-determined frontal oxygenation tended to decrease [67 +/- 13% to 61 +/- 11% (P = 0.06); contralateral 68 +/- 11% to 66 +/- 8%] as did the supraorbital cutaneous blood flow rate from 56 +/- 23 to 44 +/- 7 ml 100 g(-1) min(-1). With the opening of the external carotid artery, the NIRS-determined frontal oxygenation reversed to 66 +/- 8% (P<0.05) on the ipsilateral side, with no significant change on the contralateral side and the supraorbital cutaneous blood flow rate increased to 53 +/- 11 (P<0.05). Opening of the internal carotid artery did not significantly affect the NIRS (67 +/- 8% and 69 +/- 9%; ipsilateral, contralateral), but the supraorbital cutaneous blood flow rate increased to 88 +/- 10 ml 100 g(-1) min(-1) (P<0.001).

CONCLUSION

Cross-clamping of the internal carotid artery affects the supraorbital cutaneous blood flow rate as well as the frontal lobe oxygenation.

Non-invasive methods and stimuli for evaluating the skin's microcirculation

Vessels in the skin are arranged into superficial and deep horizontal plexuses and they are involved in thermoregulation, oxygen and nutritional support. The skin has a large number of functions and broad appeal spanning basic mechanistic and clinical research. Indeed, the skin can be used as a marker of normal and impaired vascular control and, owing to its accessibility and frequent involvement, is easy to investigate non-invasively. A large number of non-invasive methods are available for investigating the skin, ranging from those that permit the visualisation of microvessels, to those that monitor blood flow or one of its derivatives (e.g., skin temperature and transcutaneous oxygen). Such methods can be combined with non-invasive, dynamic stimuli (e.g., the use of cold or warm stimuli, activation of the peripheral nervous system or local neuronal systems, and the topical application of vasoactive drugs) and this potentially enables the differentiation of underlying disorders (e.g., primary from secondary Raynaud's phenomenon) and also to quantify changes over time or following intervention. The present article outlines the non-invasive methods and dynamic tests that can be used to investigate the microcirculation of the skin.

Sleep Exacerbation of Persistent Sexual Arousal Syndrome in a Postmenopausal Woman

AIM

To investigate possible causes and treatment of persistent sexual arousal syndrome, which was exacerbated by sleep onset, in a postmenopausal subject.

METHODS

A clinical examination and interviews with the patient to obtain her case history and follow-up of the effects of drug treatments. Pretreatment laboratory investigations monitored vaginal blood flow by photoplethysmography and heated electrode. Routine blood chemistry and endocrine assessments were undertaken. Magnetic resonance imaging (MRI) scans of brain, pelvis, and spinal cord and genito-sensory neural analysis of clitoral and vaginal areas were performed. A selective internal iliac artery arteriogram was utilized to check the normality of the pelvic blood supply.

RESULTS

Genitalia appeared normal and uncongested. No structural abnormalities were observed in the MRI scans. Hormonal levels and blood chemistry were commensurate with the subject's postmenopausal status. Basal vaginal blood flow (heat electrode) was within the range of normal premenopausal women and showed (photoplethysmography) normal vasomotion. On becoming drowsy and falling lightly asleep in the laboratory the vaginal pulse amplitude (VPA) increased by 95% of the basal value and the low-amplitude VPAs were replaced by high-amplitude VPAs--all evidence of increased vaginal blood flow and congestion and confirming the subject's complaint of persistent sexual arousal during sleep. A simple cognitive task of repeatedly subtracting 7 from 500 out aloud did not hasten the reversion to the basal level. There was no evidence of malfunction of the brain, spinal cord, or pelvic area by MRI but genito-sensory analysis of the clitoral and vaginal area showed evidence of reduced sensory function.

CONCLUSIONS

Of the treatments tried only risperidone has been effective allowing the subject to sleep throughout the night without disturbance and according to the subject has significantly reduced the aggravation of the arousal during the day.

Physiologically based pharmacokinetic modeling of arterial - antecubital vein concentration difference

BACKGROUND

Modeling of pharmacokinetic parameters and pharmacodynamic actions requires knowledge of the arterial blood concentration. In most cases, experimental measurements are only available for a peripheral vein (usually antecubital) whose concentration may differ significantly from both arterial and central vein concentration.

METHODS

A physiologically based pharmacokinetic (PBPK) model for the tissues drained by the antecubital vein (referred to as "arm") is developed. It is assumed that the "arm" is composed of tissues with identical properties (partition coefficient, blood flow/gm) as the whole body tissues plus a new "tissue" representing skin arteriovenous shunts. The antecubital vein concentration depends on the following parameters: the fraction of "arm" blood flow contributed by muscle, skin, adipose, connective tissue and arteriovenous shunts, and the flow per gram of the arteriovenous shunt. The value of these parameters was investigated using simultaneous experimental measurements of arterial and antecubital concentrations for eight solutes: ethanol, thiopental, 99Tcm-diethylene triamine pentaacetate (DTPA), ketamine, D2O, acetone, methylene chloride and toluene. A new procedure is described that can be used to determine the arterial concentration for an arbitrary solute by deconvolution of the antecubital concentration. These procedures are implemented in PKQuest, a general PBPK program that is freely distributed http://www.pkquest.com.

RESULTS

One set of "standard arm" parameters provides an adequate description of the arterial/antecubital vein concentration for ethanol, DTPA, thiopental and ketamine. A significantly different set of "arm" parameters was required to describe the data for D2O, acetone, methylene chloride and toluene - probably because the "arm" is in a different physiological state.

CONCLUSIONS

Using the set of "standard arm" parameters, the antecubital vein concentration can be used to determine the whole body PBPK model parameters for an arbitrary solute without any additional adjustable parameters. Also, the antecubital vein concentration can be used to estimate the arterial concentration for an arbitrary input for solutes for which no arterial concentration data is available.

Thoracic sympatholysis with epidural blockade assessed by quantitative measurement of cutaneous blood flow

BACKGROUND

Quantifying sympathetic activity is difficult. Direct measurement is possible and superior to indirect techniques, but nerves to internal organs are not accessible in humans. Recently, we validated a quantitative technique for measurement of cutaneous blood flow using heat as an indicator. The aim of the study was to investigate whether sympatholysis during thoracic epidural blockade (TEA) may be documented by changes in regional cutaneous blood flow. A secondary aim was to assess whether, during TEA, local heating itself enhances regional blood flow.

METHODS

Six patients scheduled for elective coronary artery bypass grafting (CABG) were studied. An epidural catheter was inserted at the T2-3 interspace. Measurements were performed with an electrode, which can measure the local temperature of the skin. The probe is covered with a thermostatically controlled cap to avoid a thermic gradient to air. As a result of the cap, a change in temperature of the central disc depends almost solely on the blood flow in the underlying tissue. Regional cutaneous blood flow rates were measured before and after epidural anesthesia with and without local heating.

RESULTS AND COMMENTS

All patients had a sensory blockade covering at least T1-5. Cutaneous blood flow increased in all six patients after blockade (13.6 ml/min/100 g, range 10.6-14.6 vs. 18.4 ml/min/100 g, range 13.9-24.5; P<0.05). Local heating did not further enhance blood flow.

CONCLUSION

High TEA is associated with a uniform increase in thoracic cutaneous blood flow, and is suggestive of regional sympatholysis. Quantitative measurements of skin blood flow appear promising for documenting regional sympatholysis during TEA.

Blood flow rate in arteriovenous anastomoses: from the cradle to the grave

Blood flow rate was measured in the arteriovenous anastomoses (AVAs) in the cutaneous tissue of the pulp of the first toe in 15 children between 3 and 15 years old, and in the pulp of the thumb and the first toe in 16 adults between 27 and 93 years old (two subjects from each decade) by the heat-washout method. The examinations showed that AVA-blood flow rate decreased with increasing age, and the difference between children and adults was highly significant (P=0.001). Blood flow rate in the finger pulp was higher than in the toe pulp (P=0.025). No significant difference in blood flow rate was found in either thumb pulp or toe pulp between men and women.

Is non-specific aneurysmal disease of the infrarenal aorta also a peripheral microvascular disease?

OBJECTIVES

to examine whether aneurysmal disease of the aorta has a functional component in the peripheral microIvasculature.

MATERIALS

ten normal persons; and 15 patients who had been operated on for ruptured non-specific infrarenal aortic aneurysm months to years previously were studied.

METHODS

blood flow rates were measured: (a) in the subcutaneous adipose tissue of the forefoot by the(133)xenon local washout method (perfusion through nutritive capillaries supplied by arterioles with elastin in the tunica media); and (b) in the arteriovenous anastomoses of the pulp of the first toe as measured by the heat washout method (perfusion predominantly through thick-walled tubes without elastin). Perfusion rates were measured in supine subjects at heart level, at 30 cm above and at 30 cm below heart level.

RESULTS

in subcutaneous adipose tissue, the capillary blood flow rate was four times higher in patients with aneurysmal disease than in normal subjects. Both groups exhibited autoregulation of blood flow and a normal veno-arteriolar sympathetic axon reflex. Blood flow rates in the arteriovenous anastomoses of the pulp did not differ between aneurysm patients and normal subjects. Autoregulation and the axon reflex were absent in the arteriovenous anastomoses of normal subjects as well as in aneurysm patients.

CONCLUSIONS

non-specific aneurysmal disease of the infrarenal aorta has a peripheral functional component affecting arterioles but not arteriovenous anastomoses.

Peripheral blood flow rates and microvascular responses to orthostatic pressure changes in claudicants before and after revascularisation

OBJECTIVES

To study the effect of arterial reconstruction for occlusive atherosclerotic disease with intermittent claudication on blood flow rate during rest and on microvascular responses to orthostatic pressure changes in the pulp skin of the first toe where arteriovenous anastomoses are numerous.

MATERIAL

Eleven patients with Fontaine IIa claudication (ankle blood pressure index > 0.30) before and 7 (range: 2-11) months after intervention.

METHODS

Blood flow rate was measured by the heat washout method with the toe at heart level and after passive lowering to 50 cm below this level using a Clark type electrode with thermostatically controlled cap that was fixed to the pulp of the first toe by adhesive tape.

RESULTS

At heart level, blood flow rate was lower in claudicants before reconstruction as compared to a group of previously published control subjects (p = 0.0076, Wilcoxon), blood flow rate increased in claudicants from before to after intervention (p = 0.0128), and postoperative blood flow rate was like that of normals (N.S.). Before surgery, blood flow rate in claudicants increased in median with a factor of 1.79 during lowering (p < 0.0051).

CONCLUSIONS

The disturbance of the microcirculatory responses to orthostatically induced pressure changes in claudicants reverted towards normal after arterial reconstruction.

Cutaneous blood flow rate in areas with and without arteriovenous anastomoses during exercise

In 10 healthy subjects, skin blood flow rate was measured in the thumb pulp by the heat-washout method, and in the skin fold between the thumb and the forefinger by the 133Xe-washout method. The former but not the latter skin area contains arteriovenous anastomoses (AVAs). In response to 10 min moderate bicycle exercise, an instantaneous decrease in flow was seen in the thumb pulp followed after about 4.6 min by an increase to resting levels. Blood flow in the skin fold remained constant. The results indicate that the initial reduction in blood flow rate and later increase observed in the finger at the onset of moderate exercise take place in the AVAs and not in the capillaries.

Blood flow rate during orthostatic pressure changes in the pulp skin of the first toe

OBJECTIVES

Determination of the local regulation of cutaneous blood flow through nutritive capillaries and through arteriovenous anastomoses of the pulp of the first toe in response to passively induced orthostatic blood pressure changes in normal subjects and in patients with occlusive atherosclerotic disease.

MATERIAL

Six normal subjects, seven patients with unilateral, crural intermittent claudication and six patients with unilateral, chronic critical ischaemia.

METHODS

Blood flow rates were measured in supine subjects by the heat washout method (the sum of blood flow rate in arteriovenous anastomoses and blood flow rate in nutritive capillaries) and by the 133Xenon washout method (blood flow rate in nutritive capillaries) after local, atraumatic labelling. Measurements were made with (a) the toe passively elevated to 50 cm above heart level, (b) at heart level and (c) passively lowered to 50 cm below heart level.

RESULTS

Autoregulation of nutritive blood flow was present in normal subjects and in claudicants, but the local sympathetic veno-arteriolar axon reflex was absent in both groups. In patients with critical ischaemia blood flow rate was the same in the supine position and during lowering in arteriovenous anastomoses and in nutritive capillaries. The arteriovenous anastomoses had distinct and characteristic reaction patterns in response to lowering in each of the three examined groups and to elevation in normal subjects and in patients with intermittent claudication (not measured in patients with critical ischaemia).

CONCLUSIONS

The microvascular responses to changes of orthostatic blood pressure differed among the three groups (normal subjects, patients with intermittent claudication, patients with critical chronic leg ischaemia). The heat washout method may be used to detect the functional significance of occlusive atherosclerotic disease.