Dynamic measurement of human capillary blood pressure

Nuclear rupture induced by capillary constriction forces promotes differential effects on metastatic and normal breast cells

During metastatic dissemination, circulating tumour cells (CTCs) enter capillary beds, where they experience mechanical constriction forces. The transient and persistent effects of these forces on CTCs behaviour remain poorly understood. Here, we developed a high-throughput microfluidic platform mimicking human capillaries to investigate the impact of mechanical constriction forces on malignant and normal breast cell lines. We observed that capillary constrictions induced nuclear envelope rupture in both cancer and normal cells, leading to transient changes in nuclear and cytoplasmic area. Constriction forces transiently activated cGAS/STING and pathways involved in inflammation (NF-κB, STAT and IRF3), especially in the non-malignant cell line. Furthermore, the non-malignant cell line experienced transcriptional changes, particularly downregulation of epithelial markers, while the metastatic cell lines showed minimal alterations. These findings suggest that mechanical constriction forces within capillaries may promote differential effects in malignant and normal cell lines.

Circulating tumor cells shed large extracellular vesicles in capillary-sized bifurcations

Circulating tumor cells (CTCs) and their clusters are the drivers of metastasis, but their interactions with capillary beds are poorly understood. Using microfluidic models mimicking human capillary bifurcations, we observed cell size- and bifurcation-dependent shedding of nuclei-free fragments by patient CTCs, CTC-derived explant cells and numerous cancer cell lines. Shedding reduced cell sizes up to 61%, facilitating their transit through bifurcations. We demonstrated that shed fragments were a novel class of large extracellular vesicles (LEVs), whose proteome was associated with immune-related and signaling pathways. LEVs were internalized by endothelial and immune cells, disrupted endothelial barrier integrity and polarized monocytes into M2 tumor-promoting macrophages. Cumulatively, these findings suggest that CTCs shed LEVs in capillary beds that drive key processes involved in the formation of pre-metastatic niches.

Mechanical study of blood flow through a permeable capillary with slippery wall

This research presents the mechanical behavior of blood flow through capillary having smooth inner surface. In this study modelling of blood flow via permeable and lubricated capillary caused by nutrients re-absorption has been done by the help of laws of momentum and mass. The nutrients re-absorption is assumed to be constant and inner walls of the capillary are smooth and slippery therefore slip condition on the velocity and constant rate in vertical direction at the wall has considered. The Kelvin Voigt model is employed to simulate blood flow via capillaries, and results for pressure, blood flow pattern, and shear force necessary for blood flow are discovered by recursive approach. Numerical results for nutrient re-absorption from the blood and impact of smooth and slippery surfaces on blood flow are shown through graphs. The novelty of the research invents that the smoothness and slickness of capillary wall is a crucial presumption to examine the blood as non-Newtonian fluid via capillary.

Capillary-Scale Hydrogel Microchannel Networks by Wire Templating

Microvascular networks are essential for the efficient transport of nutrients, waste products, and drugs throughout the body. Wire-templating is an accessible method for generating laboratory models of these blood vessel networks, but it has difficulty fabricating microchannels with diameters of ten microns and narrower, a requirement for modeling human capillaries. This study describes a suite of surface modification techniques to  selectively control the interactions amongst wires, hydrogels, and world-to-chip interfaces. This wire templating method enables the fabrication of perfusable hydrogel-based rounded cross-section capillary-scale networks whose diameters controllably narrow at bifurcations down to 6.1 ± 0.3 microns in diameter. Due to its low cost, accessibility, and compatibility with a wide range of common hydrogels of tunable stiffnesses such as collagen, this technique may increase the fidelity of experimental models of capillary networks for the study of human health and disease.

Biophysical studies of cancer cells' traverse-vessel behaviors under different pressures revealed cells' motion state transition

Circulating tumor cells (CTCs) survive in the bloodstream and then seed and invade to foster tumor metastasis. The arrest of cancer cells is favored by permissive flow forces and geometrical constraints. Through the use of high-throughput microfluidic devices designed to mimic capillary-sized vessels, we applied pressure differences to cancer cells (MCF-7 cell line) and recorded the cell traverse-vessel behaviors. Our results showed that cancer cells transform from a Newtonian droplet state to an adhesion/migration state when cancer cells traverse artificial vessels. To explain these phenomena, a modified Newtonian droplet model was also proposed. These phenomena and the modified model may reveal how CTCs in the blood seed and invade vessels under suitable conditions.

Non-Invasive Capillary Blood Pressure Measurement Enabling Early Detection and Classification of Venous Congestion

Capillary blood pressure (CBP) is the primary driving force for fluid exchange across microvessels. Subclinical systemic venous congestion prior to overt peripheral edema can directly result in elevated peripheral CBP. Therefore, CBP measurements can enable timely edema control in a variety of clinical cases including venous insufficiency, heart failure and so on. However, currently CBP measurements can be only done invasively and with a complicated experimental setup. In this work, we proposed an opto-mechanical system to achieve non-invasive and automatic CBP measurements through modifying the widely implemented oscillometric technique in home-use arterial blood pressure monitors. The proposed CBP system is featured with a blue light photoplethysmography sensor embedded in finger/toe cuffs to probe skin capillary pulsations. The experimental results demonstrated the proposed CBP system can track local CBP changes induced by different levels of venous congestion. Leveraging the decision tree technique, we demonstrate the use of a multi-site CBP measurement at fingertips and toes to classify four categories of subjects (total N = 40) including patients with peripheral arterial disease, varicose veins and heart failure. Our work demonstrates the promising non-invasive CBP measurement as well as its great potential in realizing point-of-care systems for the management of cardiovascular diseases.

Role of mechanosignaling on pathology of varicose vein

Varicose veins are the most common vascular disease in humans. Veins have valves that help the blood return gradually to the heart without leaking blood. When these valves become weak, blood and fluid collect and pool by pressing against the walls of the veins, causing varicose veins. In the cardiovascular system, mechanical forces are important determinants of vascular homeostasis and pathological processes. Blood vessels are constantly exposed to a variety of hemodynamic forces, including shear stress and environmental strains caused by the blood flow. In varicose veins within the leg, venous blood pressure rises in the vein of the lower extremities due to prolonged standing, creating a peripheral tension in the vessel wall thereby causing mechanical stimulation of endothelial cells and vascular smooth muscle. Studies have shown that long-term increased exposure to vascular wall tension is associated with the overexpression of HIF-1α and HIF-2α and increased levels of MMP-2 and MMP-9, thereby reducing venous contraction and progressive venous dilatation, which is involved in the development of varicose veins. Following the expression of metalloproteinase, the expression of type 1 collagen increases, and the amount of type 3 collagen decreases. Therefore, collagen imbalance will cause the varicose veins to not stretch. Loss of structural proteins (type 3 collagen and elastin) in the vessel wall causes the loss of the biophysical properties of the varicose vein wall. This review article tries to elaborate on the effect of mechanical forces and sensors of these forces on the vascular wall in creating the mechanism of mechanosignaling, as well as the role of the onset of molecular signaling cascades in the pathology of varicose veins.

Association of remote imaging photoplethysmography and cutaneous perfusion in volunteers

Remote imaging photoplethysmography (iPPG) senses the cardiac pulse in outer skin layers and is responsive to mean arterial pressure and pulse pressure in critically ill patients. Whether iPPG is sufficiently sensitive to monitor cutaneous perfusion is not known. This study aimed at determining the response of iPPG to changes in cutaneous perfusion measured by  Laser speckle imaging (LSI). Thirty-seven volunteers were engaged in a cognitive test known to evoke autonomic nervous activity and a Heat test. Simultaneous measurements of iPPG and LSI were taken at baseline and during cutaneous perfusion challenges. A perfusion index (PI) was calculated to assess iPPG signal strength. The response of iPPG to the challenges and its relation to LSI were determined. PI of iPPG significantly increased in response to autonomic nervous stimuli and to the Heat test by 5.8% (p = 0.005) and 11.1% (p < 0.001), respectively. PI was associated with LSI measures of cutaneous perfusion throughout experiments (p < 0.001). iPPG responses to study task correlated with those of LSI (r = 0.62, p < 0.001) and were comparable among subjects. iPPG is sensitive to autonomic nervous activity in volunteers and is closely associated with cutaneous perfusion.

Pressure ulcer following circumferential head dressing

PURPOSE

To report four patients with forehead pressure ulcer (PU) following encircling head dressing and review the literature.

METHODS

Uneventful endoscopic forehead lift procedure was performed with moderate skin elevation in three patients. Left upper eyelid crease incision was made to remove the sub-brow dermoid cyst uneventfully in one patient. All procedures were performed under general anesthesia. Mixed topical antibiotic and steroid ointments were placed on the incision sites before putting the encircling forehead dressing (using gauze and elastic bandage). The dressing was then removed on the first postoperative examination.

RESULTS

Forehead and eyebrow PUs were observed on the first follow-up visit (16-72 h) after removing the dressing. Patients were otherwise healthy. They did not have significant pain or burning postoperatively. Management included pressure release, wound debridement, daily dressing, topical antibiotic and steroid, and silicone-based anti-scar cream. None had infected ulcer and all except one ended up with atrophic scar in the last follow-up (2-14 months). External pressure and shearing forces were assumed to be the main causative factors, even though reperfusion injury could contribute in the development of PU.

CONCLUSION

Encircling head dressing can cause PU and result in scar formation in healthy immunocompetent patients. If there is a low risk of postoperative hematoma, encircling dressing should be avoided. Early loosening of the dressing and frequent examination of the skin are the best preventive and diagnostic measures. Treatment includes pressure removal, daily debridement, and topical medications.

Nucleus of Circulating Tumor Cell Determines Its Translocation Through Biomimetic Microconstrictions and Its Physical Enrichment by Microfiltration

The mechanism of cells passing through microconstrictions, such as capillaries and endothelial junctions, influences metastasis of circulating tumor cells (CTCs) in vivo, as well as size-based enrichment of CTCs in vitro. However, very few studies observe such translocation of microconstrictions in real time, and thus the inherent biophysical mechanism is poorly understood. In this study, a multiplexed microfluidic device is fabricated for real-time tracking of cell translocation under physiological pressure and recording deformation of the whole cell and nucleus, respectively. It is found that the deformability and size of the nucleus instead of the whole cell dominate cellular translocation through microconstrictions under a normal physiological pressure range. More specifically, cells with a large and stiff nucleus are prone to be blocked by relatively small constrictions. The same phenomenon is also observed in the size-based enrichment of CTCs from peripheral blood of metastatic cancer patients. These findings are different from a popular viewpoint that the size and deformability of a whole cell mainly determine cell translation through microconstrictions, and thus may elucidate interactions between CTCs and capillaries from a new perspective and guide the rational design of size-based microfilters for rare cell enrichment.

Burst mode pumping: A new mechanism of drinking in mosquitoes

Mosquitoes transport liquid foods into the body using two muscular pumps in the head. In normal drinking, these pumps reciprocate in a stereotyped pattern of oscillation, with a high frequency but small stroke volume. Do mosquitoes modulate their neuromotor programs for pumping to produce different drinking modes? More broadly, what are the mechanical consequences of a two-pump system in insects? To address these questions, we used synchrotron x-ray imaging and fluid mechanical modeling to investigate drinking performance in mosquitoes. X-ray imaging of the pumps during drinking revealed two modes of pumping: continuous reciprocation with multiple small strokes, and a newly discovered ‘burst mode’ involving a single, large-volume stroke. Results from modeling demonstrate that burst mode pumping creates a very large pressure drop and high volume flow rate, but requires a massive increase in power, suggesting that continuous pumping is more economical for drinking. Modeling also demonstrates that, from one mode of pumping to the other, the mechanical role of the individual pumps changes. These results suggest that the advantage of a two-pump system in insects lies in its flexibility, enabling the animal to pump efficiently or powerfully as demanded by environmental considerations.

Flow-Induced Transport of Tumor Cells in a Microfluidic Capillary Network: Role of Friction and Repeated Deformation

INTRODUCTION

Circulating tumor cells (CTCs) in microcirculation undergo significant deformation and frictional interactions within microcapillaries. To understand the physical parameters governing their flow-induced transport, we studied the pressure-driven flow of cancer cells in a microfluidic model of a capillary network.

METHODS

Our microfluidic device contains an array of parallel constrictions separated by regions where cells can repetitively deform and relax. To characterize the transport behavior, we measured the entry time, transit time, and shape deformation of tumor cells as they squeeze through the network.

RESULTS

We found that entry and transit times of cells are much lower after repetitive deformation as their elongated shape enables easy transport in subsequent constrictions. Furthermore, upon repetitive deformation, the cells were able to relieve only 25% of their 40% imposed compressional strain, suggesting that tumor cells might have undergone plastic deformation or fatigue. To investigate the influence of surface friction, we characterized the transport behavior in the absence and presence of bovine serum albumin (BSA) coating on the constriction walls. We observed that BSA coating reduces the entry and transit time significantly. Finally, using two breast tumor cell lines, we investigated the effect of metastatic potential on transport properties. We found that the cell lines could be distinguished only upon surface treatment with BSA, thus surface-induced friction is an indicator of metastatic potential.

CONCLUSIONS

Our results suggest that pre-deformation can enhance the transport of CTCs in microcirculation and that frictional interactions with capillary walls can play an important role in influencing the transport of metastatic CTCs.

Sonoreperfusion Therapy Kinetics in Whole Blood Using Ultrasound, Microbubbles and Tissue Plasminogen Activator

Coronary intervention for myocardial infarction often results in microvascular embolization of thrombus. Sonoreperfusion therapy (SRP) using ultrasound and microbubbles restored perfusion in our in vitro flow model of microvascular obstruction. In this study, we assessed SRP efficacy using whole blood as the perfusate with and without tissue plasminogen activator (tPA). In a phantom vessel bearing a 40-μm-pore mesh to simulate the microvasculature, microthrombi were injected to cause microvascular obstruction and were treated using SRP. Without tPA, the lytic rate increased from 2.6 ± 1.5 mmHg/min with 1000-cycle pulses to 7.3 ± 3.2 mmHg/min with 5000-cycle ultrasound pulses (p < 0.01). The lytic index was similar for tPA-only ([2.0 ± 0.5] × 10^-3 mmHg^-1 min^-1) and 5000 cycles without tPA ([2.3 ± 0.5] × 10^-3 mmHg^-1 min^-1) (p = 0.5) but increased ([3.6 ± 0.8] × 10^-3 mmHg^-1 min^-1) with tPA in conjunction with 5000-cycles ultrasound (p < 0.01). In conclusion, SRP restored microvascular perfusion in whole blood, SRP lytic rate in experiments without tPA increased with ultrasound pulse length and efficacy increased with the addition of tPA.

The Effect of Hosiery on Interstitial Fluid Pressure and Arm Volume Fluctuations in Breast Cancer Related Arm Oedema

Objectives:

(1) To measure interstitial fluid pressure under one brand of hosiery in arm lymphoedema. (2) To assess the stability of the swelling over various time scales.

Setting:

Human microvascular studies laboratory of a teaching hospital.

Subjects:

Patients with arm oedema following successful breast cancer treatment.

Main outcome measures:

(1) Arm volume calculations using multiple circumferential measurements by tape measure. (2) Interstitial fluid pressure measurements by wick-in-needle technique in subcutis.

Results:

The mean swollen arm was 33% greater in volume than the contralateral arm ( n = 50). There was no significant correlation between the size of the arm and the duration of the swelling. There was no significant change in arm volume over 2 weeks ( n = 8) but there was a small (50 ml), significant increase overnight ( p < 0.05). The mean (SD) interstitial fluid pressure while wearing one brand of hosiery (Sigvaris) was 18.7 (5.8) cmH2O compared with 1.2 (2.8) cmH2O after its removal. There was a significant correlation between the pressure under the sleeve and the pressure without the sleeve ( r = 0.68, p < 0.05).

Conclusions:

The Sigvaris sleeve exerts sufficient compression to underlying tissue to raise interstitial fluid pressure. This may control arm swelling by reducing fluid filtration rate and/or raising fluid drainage rate from the arm.

Clusters of circulating tumor cells traverse capillary-sized vessels

Multicellular aggregates of circulating tumor cells (CTC clusters) are potent initiators of distant organ metastasis. However, it is currently assumed that CTC clusters are too large to pass through narrow vessels to reach these organs. Here, we present evidence that challenges this assumption through the use of microfluidic devices designed to mimic human capillary constrictions and CTC clusters obtained from patient and cancer cell origins. Over 90% of clusters containing up to 20 cells successfully traversed 5- to 10-μm constrictions even in whole blood. Clusters rapidly and reversibly reorganized into single-file chain-like geometries that substantially reduced their hydrodynamic resistances. Xenotransplantation of human CTC clusters into zebrafish showed similar reorganization and transit through capillary-sized vessels in vivo. Preliminary experiments demonstrated that clusters could be disrupted during transit using drugs that affected cellular interaction energies. These findings suggest that CTC clusters may contribute a greater role to tumor dissemination than previously believed and may point to strategies for combating CTC cluster-initiated metastasis.

An artificial blood vessel implanted three-dimensional microsystem for modeling transvascular migration of tumor cells

Reproducing a tumor microenvironment consisting of blood vessels and tumor cells for modeling tumor invasion in vitro is particularly challenging. Here, we report an artificial blood vessel implanted 3D microfluidic system for reproducing transvascular migration of tumor cells. The transparent, porous and elastic artificial blood vessels are obtained by constructing polysaccharide cellulose-based microtubes using a chitosan sacrificial template, and possess excellent cytocompatibility, permeability, and mechanical characteristics. The artificial blood vessels are then fully implanted into the collagen matrix to reconstruct the 3D microsystem for modeling transvascular migration of tumor cells. Well-defined simulated vascular lumens were obtained by proliferation of the human umbilical vein endothelial cells (HUVECs) lining the artificial blood vessels, which enables us to reproduce structures and functions of blood vessels and replicate various hemodynamic parameters. Based on this model, the adhesion and transvascular migration of tumor cells across the artificial blood vessel have been well reproduced.

Microvascular fluid exchange and the revised Starling principle

Microvascular fluid exchange (flow J(v)) underlies plasma/interstitial fluid (ISF) balance and oedematous swelling. The traditional form of Starling's principle has to be modified in light of insights into the role of ISF pressures and the recognition of the glycocalyx as the semipermeable layer of endothelium. Sum-of-forces evidence and direct observations show that microvascular absorption is transient in most tissues; slight filtration prevails in the steady state, even in venules. This is due in part to the inverse relation between filtration rate and ISF plasma protein concentration; ISF colloid osmotic pressure (COP) rises as J(v) falls. In some specialized regions (e.g. kidney, intestinal mucosa), fluid absorption is sustained by local epithelial secretions, which flush interstitial plasma proteins into the lymphatic system. The low rate of filtration and lymph formation in most tissues can be explained by standing plasma protein gradients within the intercellular cleft of continuous capillaries (glycocalyx model) and around fenestrations. Narrow breaks in the junctional strands of the cleft create high local outward fluid velocities, which cause a disequilibrium between the subglycocalyx space COP and ISF COP. Recent experiments confirm that the effect of ISF COP on J(v) is much less than predicted by the conventional Starling principle, in agreement with modern models. Using a two-pore system model, we also explore how relatively small increases in large pore numbers dramatically increase J(v) during acute inflammation.

Silk fibroin microtubes for blood vessel engineering

Currently available synthetic grafts demonstrate moderate success at the macrovascular level, but fail at the microvascular scale (<6mm inner diameter). We report on the development of silk fibroin microtubes for blood vessel repair with several advantages over existing scaffold materials/designs. These microtubes were prepared by dipping straight lengths of stainless steel wire into aqueous silk fibroin, where the addition of poly(ethylene oxide) (PEO) enabled control of microtube porosity. The microtube properties were characterized in terms of pore size, burst strength, protein permeability, enzymatic degradation, and cell migration. Low porosity microtubes demonstrated superior mechanical properties in terms of higher burst pressures, but displayed poor protein permeability; whereas higher porosity tubes had lower burst strengths but increased permeability and enhanced protein transport. The microtubes also exhibited cellular barrier functions as low porosity tubes prevented outward migration of GFP-transduced HUVECs, while the high porosity microtubes allowed a few cells per tube to migrate outward during perfusion. When combined with the biocompatible and suturability features of silk fibroin, these results suggest that silk microtubes, either implanted directly or preseeded with cells, are an attractive biomaterial for microvascular grafts.

Direct coextensive plethysmography for non-invasive measurement of systemic pressures and volumes

A method for noninvasive measurement of pressures and fluid volumes of the complete systemic vascular circuit, called direct coextensive plethysmography, is proposed. This includes the pressures of the large veins, small veins, venules, capillaries, arterioles, small arteries, large arteries and nonvascular fluid compartments. It uses a conventional pressure cuff on the outside of the arm, combined with a tetrapolar bioimpedance electrode band to derive a fluid volume indication (impedance) versus pressure profile for the entire system. Determination of state changes in the residual fluid volume versus pressure profile yields physiologic information about the pressures and fluid volumes in the various segments of the vascular circuit and nonvascular fluid compartments. Advanced signal processing techniques have been applied to improve upon early slope change analysis. Initial confirmation of the correlation between the measured large vein pressure and the central venous pressure were made in a small clinical trial with intensive care unit subjects.

Interface pressure measurement during surgery: a comparison of four operating table surfaces

OBJECTIVE

To compare the pressure-reducing and pressure-redistributing characteristics of four operating room (OR) table mattresses using interface pressure measurements, in two positions adopted for surgical procedures.

METHOD

Support surfaces were randomly assigned to 80 patients. These were: an overlay pad filled with fibres (the standard OR mattress), a custom-made viscoelastic polyurethane foam mattress, an inflatable mattress with air-filled cells and a fluid mattress. An XSENSOR full-body pressure-mapping pad was used to record interface pressures of 40 patients in the supine position and 40 patients in the lithotomy position. Measurements were analysed for peak pressure, peak pressure index, total contact surface area and the occurrence of a significant increase in interface pressure during the surgical procedure.

RESULTS

The highest interface pressures were measured on the standard mattress, in both the supine and lithotomy position. Overall, the fluid mattress showed the best pressure-reducing and pressure-redistributing capacities.

CONCLUSION

As long as no reference values are available for interface pressures under which no pressure-related damage will occur, clinical testing of OR table surfaces is still necessary.

Capillary pressure in subjects with type 2 diabetes and hypertension and the effect of antihypertensive therapy

Raised capillary pressure has been implicated in the formation of diabetic microangiopathy in type I diabetes, in which it is elevated in those with the earliest signs of diabetic kidney disease but remains normal in those without complications. In subjects with type 2 diabetes without complications, capillary pressure is normal, although alterations in the pressure waveforms suggested enhanced wave reflections. The nature of skin capillary pressure in subjects with type 2 diabetes and hypertension remains to be elucidated, as does the effect of blood pressure-lowering therapy on capillary pressure in these subjects. Three studies were performed in well-matched groups. First, capillary pressure was elevated in hypertensive subjects with type 2 diabetes compared with normotensive subjects with type 2 diabetes (20.2 [17.4 to 22.7] mm Hg versus 17.7 [16.1 to 18.9] mm Hg, respectively, P<0.03, Mann-Whitney U test). Second, no significant difference was detected between hypertensive subjects with type 2 diabetes and hypertensive subjects without type 2 diabetes (19.4 [15.8 to 21.3] mm Hg versus 17.2 [15.1 to 19.8] mm Hg, respectively, P=0.5, Mann-Whitney U test). Finally, patients with type 2 diabetes were recruited to a case-control study. Seven subjects received blood pressure-lowering therapy and 8 did not. Therapy reduced capillary pressure from 18.2 [15.8 to 20.1] mm Hg to 15.9 [15.4 to 17.0] mm Hg (P=0.024 ANOVA), in contrast to the lack of effect of time alone. Mean arterial pressure was reduced from 110 [102 to 115] mm Hg to 105 [101 to 111] mm Hg (P=0.006, ANOVA). These findings provide a plausible mechanism by which reducing arterial hypertension may reduce the risk of microangiopathy in type 2 diabetes.

The feasibility and reliability of capillary blood pressure measurements in the fingernail fold

Capillary blood pressure is an essential parameter in the study of the (patho-)physiology of microvascular perfusion. Currently, capillary pressure measurements in humans are performed using a servo-nulling micropressure system containing an oil-water interface, which suffers some drawbacks. In addition, the effect of the preparation of the skin and the presence of the tip of the pipette in the capillary during the measurement on microcirculatory perfusion has never been described. Therefore, we assessed the feasibility of capillary pressure measurements using an alternative micropressure system using an air-water interface (900 A, WPI) and examined the effect of the measurement on local microcirculation. In 19 healthy male volunteers the apex of capillaries in the eponychium of the fourth finger was punctured, after skin peeling, by a micropipette connected to a servo-nulling micropressure system. Red blood cell velocity (RBCV) was assessed after peeling during the measurement and at an adjacent area. Mean capillary pressure (in 16/19 volunteers) was 20.5 +/- 3.7 mm Hg (systolic 26.2 +/- 5.6 mm Hg, diastolic 17.6 +/- 3.9 mm Hg). RBCV was not significantly different before (0.52 mm/s) and during the measurement (0.51 mm/s) and at an adjacent area (0.51 mm/s). Capillary pressure can be measured well with the alternative setup used without hampering capillary flow, while the pressures obtained are in agreement with the results reported previously by other investigators.

Hyperaemia

Hyperaemia is the process by which the body adjusts blood flow to meet the metabolic needs of its different tissues in health and disease. Meticulous control of the microcirculation--the arterioles, capillaries and venules--is essential to life. Reactive hyperaemia, the local vasodilatation which occurs in response to oxygen debt and accumulation of metabolic waste products due to interruption of blood flow; active hyperaemia, the increased blood flow in an organ during a period of activity; and the hyperaemic response to infection and trauma are vitally important. The microcirculation is controlled partly by sympathetic vasoconstrictor impulses from the brain and partly by vasoactive substances secreted locally by the endothelial cells. The most important of the latter is nitric oxide which facilitates flow by causing relaxation of vascular smooth muscle. Neural and endothelial control of blood flow are impaired by illness. Neurological disease and vascular disease which affect the microcirculation, predispose patients to develop ischaemic organ damage, including pressure sores, during periods of intercurrent illness. Severe sepsis or trauma may cause irreversible microcirculatory dysfunction resulting in multi-organ failure and death.

Oxidative stress and lipids in diabetes: a role in endothelium vasodilator dysfunction?

Endothelial dysfunction is a key feature of diabetes mellitus and is thought to be the major cause of vascular complications associated with the disease. The vascular endothelium demonstrates impaired synthesis of vasodilators and increased release of procoagulants and vasoconstrictors, defects which theoretically could explain the increased incidence of atherosclerosis and hypertension found within this patient group. The pathways mediating endothelial cell layer dysfunction are unknown, although many candidates have been proposed. This review concentrates on the hypothesis that increased oxidative stress combined with abnormal plasma lipid composition leads to reduced synthesis of endothelial vasodilators and hence endothelial dysfunction. Free radical generation is undoubtedly raised in diabetes but the evidence for decreased antioxidant status is debatable. The role of antioxidant and lipid-lowering therapy is considered, but few studies have directly investigated the effect of treatment on vascular function. Concern arises from individual studies of vitamin E in diabetic animals which have proved deleterious. Current literature implies that a combination therapy of vitamin E and vitamin C may be beneficial, but this needs to be investigated further in both animal and human diabetes.

Peripheral microvascular disease in diabetes

In recent years a variety of techniques have been developed for studying peripheral microvascular function in man, which have provided important information regarding the functional breakdown of the microcirculation in diabetes mellitus. In insulin dependent diabetes a sequence of physiological changes have been described which support the so-called haemodynamic hypothesis: control-dependent increases in capillary pressure result in microvascular sclerosis leading to limitation of hyperaemia and loss of autoregulation. Furthermore, capillary pressure appears to be especially raised in patients with incipient nephropathy who are at particular risk of microangiopathy. The limitation of maximum hyperaemia is duration related, may be observed in early childhood, and is correlated with the degree of basement membrane thickening. In contrast in normotensive non-insulin dependent patients a different array of functional disturbances are described: Capillary pressure and capillary filtration coefficient are normal whereas maximum hyperaemia is profoundly depressed even at diagnosis. This differential pattern of abnormalities arguably reflects the impact of a prediabetic insulin resistant phase on the subsequent expression of microangiopathy. An understanding of the physiological breakdown of the microcirculation in diabetes permits the generation of plausible candidate cellular and molecular mechanisms, knowledge of which will accelerate the development of protective therapy.

The influence of hypertension on microvascular blood flow and resistance to flow in the skin of patients with type 2 (non-insulin-dependent) diabetes

Maximum microvascular blood flow and resistance to flow were determined in the skin of nine hypertensive and nine normotensive Type 2 (non-insulin-dependent) diabetic patients and nine control subjects to determine the influence of hypertension on these variables. Maximum blood flow was reduced in both the hypertensive (1.05 (0.70-1.42) V) and normotensive (1.04 (0.79-1.63) V) Type 2 diabetic patients when compared with control subjects (1.40 (1.26-2.13) V, p < 0.01 for hypertensive and p < 0.05 for normotensive patients, respectively); however, maximum blood flow was similar in both groups of diabetic patients (p = 0.82). In contrast, resistance to flow was significantly greater in the diabetic patients with hypertension (127.2 (87.5-181.3) mmHg V-1 vs 84.7 (61.9-123.0) mmHg V-1 normotensive diabetic patients, p < 0.02). In addition, R was greater in the normotensive Type 2 diabetic patients than in control subjects (70.7 (44.7-79.9) mmHg V-1, p < 0.05). These results suggest that hypertension is associated with an additional rise in pre-capillary vascular resistance in Type 2 diabetes which, while protecting the microcirculation from the effects of increased arterial pressure, may further diminish protective hyperaemic responses.

Starling pressures in the human arm and their alteration in postmastectomy oedema

1. Surgery and radiotherapy to axillary lymph nodes during breast cancer treatment is often followed, commonly years later, by chronic postmastectomy oedema (PMO). PMO is considered a 'high protein' oedema due to reduced axillary lymph drainage. Since oedema formation also depends on fluid input (capillary filtration), we studied the Starling pressures in the affected and contralateral arm. Colloid osmotic pressure was measured in patient serum (pi p) and interstitial fluid (pi i). Subcutis fluid was collected from PMO arms by both wick and aspiration methods, and from the control arm by the wick method only. Interstitial hydraulic pressure (P(i)) was measured by the wick-in-needle method. 2. Oedema pi i was 19.2 +/- 4.1 cmH2O (n = 13, wick) to 16.3 +/- 4.4 cmH2O (n = 41, aspirate; difference not significant; mean +/- S.D. throughout). This was significantly lower than pi i in the control arm (21.4 +/- 3.8 cmH2O, n = 14, P < 0.01, analysis of variance). Also, there was a negative correlation between oedema pi i and the percentage increase in arm volume (correlation coefficient r = -0.35, P < 0.05) in contrast to conventional expectation. 3. Oedema P(i) (1.9 +/- 2.0 cmH2O, n = 28) exceeded the subatmospheric control P(i) (-2.8 +/- 3.0 cmH2O; P < 0.01). Venous and arterial pressures were normal but pi p was subnormal (31.1 +/- 2.7 cmH2O, n = 47). 4. Net pressure opposing capillary blood pressure, P(o), was calculated as P(i) + sigma (pi p-pi i) for a reflection coefficient, sigma, of 0.90-0.99.(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the spinal board and the vacuum stretcher, spinal stability and interface pressure

The interface pressures were measured between the sacrum, mid-lumbar spine and various support surfaces. Thirty healthy male volunteers were recruited. The spinal board, padded spinal board and vacuum stretcher were the support surfaces evaluated. We found high and potentially ischaemic pressures between the sacrum and the spinal board interface (mean 147.3 mmHg). This was reduced in the padded board (115.5 mmHg) but dramatically reduced with the vacuum stretcher (36.7 mmHg). It was also noted that no support was given to the normal lumbar lordosis by the spinal board (padded and unpadded), but support was given by the vacuum stretcher. This raises the question of how stable is an unstable spinal injury on a flat supporting surface.

Microvascular investigations in diabetes mellitus

This paper reviews the current literature concerning the different investigative modalities available to assess the microcirculation in diabetic microangiopathy. The advantages and disadvantages of the different invasive and noninvasive methods available are presented objectively. We have concentrated on the tests that provide a quantitative assessment of the microcirculation, including laser Doppler fluxmetry, capillary microscopy, plethysmography, transcutaneous oximetry and radioactive isotope clearance. Some of the invasive methods described are now being replaced by noninvasive equivalents, providing similar information with less discomfort and risk to the patient.

Relation of skin capillary pressure in patients with insulin-dependent diabetes mellitus to complications and metabolic control

BACKGROUND

Microvascular disease is a major problem in patients with diabetes mellitus. It has been suggested that diabetic microangiopathy may result from an increase in capillary blood flow and capillary hypertension, but direct evidence of capillary hypertension in such patients is lacking.

METHODS

We measured capillary pressure at the summit of the capillary loop by direct microcannulation of skin nail-fold capillaries and a dynamic method of pressure measurement in 29 patients with insulin-dependent (Type I) diabetes and 29 normal subjects matched for age and sex. Among the diabetic patients, 7 had had diabetes for less than one year, 12 had incipient nephropathy (albumin excretion, 20 to 200 micrograms per minute), and 10 had overt nephropathy (albumin excretion, greater than 200 micrograms per minute). In addition, seven patients with no evidence of nephropathy were studied before and after three months of improved glycemic control.

RESULTS

The median capillary pressure in the diabetic patients was 20.4 mm Hg (range, 13.6 to 25.3), as compared with 16.7 mm Hg (range, 12.8 to 22.8; P less than 0.001) in the normal subjects. The values were higher in each subgroup of diabetic patients than in the corresponding group of normal subjects, but the values did not differ among the three subgroups of diabetic patients. In the seven patients who were studied before and after three months of improved glycemic control, the median capillary pressure fell from 20.0 mm Hg (range, 18.5 to 21.7) to 17.8 mm Hg (range, 14.1 to 20.3; P = 0.02).

CONCLUSIONS

Nail-fold capillary hypertension may develop early in the course of diabetes, before the emergence of microvascular disease, and may be influenced by changes in metabolic control.

Autonomic nervous system and microcirculation in diabetes

In order to evaluate the occurrence of sympathetic impairment of skin microvascular control in diabetes, we evaluated the spectral analysis of forearm skin laser-Doppler fluctuations in nine insulin-dependent diabetic subjects and in 21 controls of similar age. Low-frequency oscillations (around 0.1 Hz) were significantly lower in diabetics than in controls (2.333 +/- 0.340 (mean +/- SEM) units vs. 3.486 +/- 0.093 units, P less than 0.001), whereas no significant differences were found between the two groups regarding high-frequency respiration-related oscillations. These results suggest that the loss of rhythmicity in diabetic subjects is selectively related to low-frequency oscillations, mostly under sympathetic control, and is likely to be dependent on autonomic abnormality.