Mechanical effects of negative pressure wound therapy on abdominal wounds - effects of different pressures and wound fillers.

The mechanical deformation of the wound edge resulting from negative pressure wound therapy (NPWT) at the standard setting of around -120 mmHg has positive effects in promoting wound healing. However, it may cause pain to the patient during treatment. It is therefore important to study the mechanical effects of the wound edges using lower pressure and different wound fillers. Abdominal wounds were created on eight pigs. The wounds were sealed for NPWT using foam or gauze. Negative pressures between -20 and -160 mmHg were applied, and the decrease in wound diameter and the force with which the edges of the wound were drawn together (wound edge force) were measured. Increasing levels of negative pressure resulted in a gradual decrease in wound diameter and increase in wound edge force and reached a maximum at -120 mmHg, which is the pressure commonly used in clinical practice. Both the decrease in wound diameter and the increase in wound edge force was greater with foam than with gauze. A pressure of -80 mmHg has only 15% less effect than -120 mmHg, while a lower pressure (-40 mmHg) diminished the effects on diameter and force markedly. The NPWT-induced decrease in wound diameter and increase in wound edge force are greater at higher levels of negative pressure and when using foam than when using gauze as a wound filler. It may be possible to tailor the type of wound filler and level of negative pressure to obtain the best balance between wound healing and patient comfort.

Use of heated tobacco products (IQOS) causes an acute increase in arterial stiffness and platelet thrombus formation.

BACKGROUND AND AIMS: Heated tobacco products (HTPs) are novel alternative tobacco products being promoted as an alternative to cigarettes. To evaluate the impact of HTP use on vascular function, we investigated the effects of a brief HTP usage on arterial stiffness and platelet thrombus formation in healthy volunteers. METHODS: In a randomised crossover study, twenty-four healthy young adults with occasional tobacco use smoked the HTP IQOS 3 Multi (Phillip Morris Int.) and "no-exposure" was used as a control, with a wash-out period of at least one week in-between. Arterial stiffness was assessed through pulse wave velocity and pulse wave analysis. Blood samples, collected at baseline and 5 min following exposure, were analysed with the Total-Thrombus-formation analysis system evaluating platelet and fibrin-rich thrombus formation tendency. RESULTS: HTP exposure caused immediate heightened pulse wave velocity (+0.365 m/s, 95% CI: +0.188 to 0.543; p = 0.004) and enhanced augmentation index corrected to heart rate (+6.22%, 95% CI: +2.33 to 10.11; p = 0.003) compared to the no-exposure occasion. Similarly, blood pressure and heart rate transiently increased immediately following HTP inhalation. Platelet thrombus formation significantly increased following HTP exposure (area under the curve +59.5, 95% CI: +25.6 to 93.4; p < 0.001) compared to no-exposure. No effect was seen on fibrin-rich thrombus formation following HTP-exposure. CONCLUSIONS: Brief HTP use in healthy young adults had immediate adverse effects on vascular function resulting in increased arterial stiffness and platelet thrombus formation, known risk factors for the development of atherosclerosis. Further research is needed to address long term health impacts.

A rigid disc for protection of exposed blood vessels during negative pressure wound therapy.

BACKGROUND: There are increasing reports of serious complications and deaths associated with negative pressure wound therapy (NPWT). Bleeding may occur when NPWT is applied to a wound with exposed blood vessels. Inserting a rigid disc in the wound may protect these structures. The authors examined the effects of rigid discs on wound bed tissue pressure and blood flow through a large blood vessel in the wound bed during NPWT. METHODS: Wounds were created over the femoral artery in the groin of 8 pigs. Rigid discs were inserted. Wound bed pressures and arterial blood flow were measured during NPWT. RESULTS: Pressure transduction to the wound bed was similar for control wounds and wounds with discs. Blood flow through the femoral artery decreased in control wounds. When a disc was inserted, the blood flow was restored. CONCLUSIONS: NPWT causes hypoperfusion in the wound bed tissue, presumably as a result of mechanical deformation. The insertion of a rigid barrier alleviates this effect and restores blood flow.

Electronic Cigarette Vaping with Nicotine Causes Increased Thrombogenicity and Impaired Microvascular Function in Healthy Volunteers: A Randomised Clinical Trial.

Electronic cigarette (EC) vaping is increasingly popular, despite growing evidence of adverse health effects. To further evaluate the impact of EC use on vascular health, we investigated the effects of brief EC inhalation on flow-dependent thrombus formation and microcirculation in healthy volunteers. The study was performed with a randomised double-blind crossover design. Twenty-two healthy subjects aged between 18 and 45 years with occasional tobacco use were recruited. Subjects inhaled 30 puffs of EC aerosol with and without nicotine on two occasions separated by a wash-out period of at least 1 week. Blood samples were collected at baseline and at 15 and 60 min following exposure and analysed with the Total-Thrombus-formation analysis system evaluating fibrin-rich thrombus formation and platelet thrombus formation in whole blood under flow. Microvascular function was assessed at baseline and 30 min after exposure by laser speckle contrast imaging and iontophoresis of acetylcholine and sodium nitroprusside (SNP) to evaluate the endothelium-dependent and independent pathways of vasodilation. Compared with nicotine free EC aerosol, exposure to EC aerosol with nicotine significantly increased platelet thrombus formation and fibrin-rich thrombus formation at 15 min (p = 0.017 and p = 0.037, respectively) with normalisation after 60 min. Peak SNP-mediated microvascular perfusion, i.e. endothelium-independent vasodilation, was reduced following EC vaping with nicotine compared with baseline (p = 0.006). Thirty puffs of EC aerosol with nicotine increased platelet and fibrin-dependent thrombus formation and reduced microvascular dilatation capacity. No compelling effects of EC vaping without nicotine were observed, indicating nicotine as the main effector. Trial registration: ClinicalTrials.gov Identifier: NCT04175457 URL: https://clinicaltrials.gov/ct2/show/NCT04175457.

The use of a rigid disc to protect exposed structures in wounds treated with negative pressure wound therapy: effects on wound bed pressure and microvascular blood flow.

There are increasing reports of deaths and serious complications associated with the use of negative pressure wound therapy (NPWT). Bleeding may occur in patients when NPWT is applied to a wound with exposed blood vessels or vascular grafts, possibly due to mechanical deformation and hypoperfusion of the vessel walls. Recent evidence suggests that using a rigid barrier disc to protect underlying tissue can prevent this mechanical deformation. The aim of this study was to examine the effect of rigid discs on the tissue exposed to negative pressure with regard to tissue pressure and microvascular blood flow. Peripheral wounds were created on the backs of eight pigs. The pressure and microvascular blood flow in the wound bed were measured when NPWT was applied. The wound was filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. The discs were created with or without channels (to accommodate exposed sensitive structures such as blood vessels and nerves), perforations, or a porous dressing that covered the underside of the discs (to facilitate pressure transduction and fluid evacuation). When comparing the results for pressure transduction to the wound bed, no significant differences were found using different discs covered with dressing, whereas pressure transduction was lower with bare discs. Microvascular blood flow in the wound bed decreased by 49 ± 7% when NPWT was applied to control wounds. The reduction in blood flow was less in the presence of a protective disc (e.g., -6 ± 5% for a dressing-covered, perforated disc, p = 0.006). In conclusion, NPWT causes hypoperfusion of superficial tissue in the wound bed. The insertion of a rigid barrier counteracts this effect. The placement of a rigid disc over exposed blood vessels or nerves may protect these structures from rupture and damage.

Measurements of wound edge microvascular blood flow during negative pressure wound therapy using thermodiffusion and transcutaneous and invasive laser Doppler velocimetry.

The effects of negative pressure wound therapy (NPWT) on wound edge microvascular blood flow are not clear. The aim of the present study was therefore to further elucidate the effects of NPWT on periwound blood flow in a porcine peripheral wound model using different blood flow measurement techniques. NPWT at -20, -40, -80, and -125 mmHg was applied to a peripheral porcine wound (n = 8). Thermodiffusion, transcutaneous, and invasive laser Doppler velocimetry were used to measure the blood perfusion 0.5, 1.0, and 2.5 cm from the wound edge. Thermodiffusion (an invasive measurement technique) generally showed a decrease in perfusion close to the wound edge (0.5 cm), and an increase further from the edge (2.5 cm). Invasive laser Doppler velocimetry showed a similar response pattern, with a decrease in blood flow 0.5 cm from the wound edge and an increase further away. However, 1.0 cm from the wound edge blood flow decreased with high pressure levels and increased with low pressure levels. A different response pattern was seen with transcutaneous laser Doppler velocimetry, showing an increase in blood flow regardless of the distance from the wound edge (0.5, 1.0, and 2.5 cm). During NPWT, both increases and decreases in blood flow can be seen in the periwound tissue depending on the distance from the wound edge and the pressure level. The pattern of response depends partly on the measurement technique used. The combination of hypoperfusion and hyperperfusion caused by NPWT may accelerate wound healing.

The influence of different sizes and types of wound fillers on wound contraction and tissue pressure during negative pressure wound therapy.

Negative pressure wound therapy (NPWT) contracts the wound and alters the pressure in the tissue of the wound edge, which accelerates wound healing. The aim of this study was to examine the effect of the type (foam or gauze) and size (small or large) of wound filler for NPWT on wound contraction and tissue pressure. Negative pressures between --20 and --160 mmHg were applied to a peripheral porcine wound (n = 8). The pressure in the wound edge tissue was measured at distances of 0·1, 0·5, 1·0 and 2·0 cm from the wound edge and the wound diameter was determined. At 0·1 cm from the wound edge, the tissue pressure decreased when NPWT was applied, whereas at 0·5 cm it increased. Tissue pressure was not affected at 1·0 or 2·0 cm from the wound edge. The tissue pressure, at 0·5 cm from the wound edge, was greater when using a small foam than when using than a large foam. Wound contraction was greater when using a small foam than when using a large foam during NPWT. Gauze resulted in an intermediate wound contraction that was not affected by the size of the gauze filler. The use of a small foam to fill the wound causes considerable wound contraction and may thus be used when maximal mechanical stress and granulation tissue formation are desirable. Gauze or large amounts of foam result in less wound contraction which may be beneficial, for example when NPWT causes pain to the patient.

The influence on wound contraction and fluid evacuation of a rigid disc inserted to protect exposed organs during negative pressure wound therapy.

The use of a rigid disc as a barrier between the wound bed and the wound filler during negative pressure wound therapy (NPWT) has been suggested to prevent damage to exposed organs. However, it is important to determine that the effects of NPWT, such as wound contraction and fluid removal, are maintained during treatment despite the use of a barrier. This study was performed to examine the effect of NPWT on wound contraction and fluid evacuation in the presence of a rigid disc. Peripheral wounds were created on the backs of eight pigs. The wounds were filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. Wound contraction and fluid evacuation were measured after application of continuous NPWT at -80 mmHg. Wound contraction was similar in the presence and the absence of a rigid disc (84 ± 4% and 83 ± 3%, respectively, compared with baseline). Furthermore, the rigid disc did not affect wound fluid removal compared with ordinary NPWT (e.g. after 120 seconds, 71 ± 4 ml was removed in the presence and 73 ± 3 ml was removed in the absence of a disc). This study shows that a rigid barrier may be placed under the wound filler to protect exposed structures during NPWT without affecting wound contraction and fluid removal, which are two crucial features of NPWT.

Intracoronary near-infrared spectroscopy and the risk of future cardiovascular events.

Objectives: The objectives of this study were to investigate if findings by intracoronary near-infrared spectroscopy (NIRS) and intravascular ultrasound (IVUS) are associated with future cardiovascular events and if NIRS can differentiate culprit from non-culprit segments in patients with coronary artery disease. Methods: The study included 144 patients with coronary artery disease undergoing percutaneous coronary intervention and combined NIRS-IVUS imaging at two Swedish hospitals. The NIRS-derived lipid core burden index (LCBI), the 4 mm segment with maximum LCBI (MaxLCBI4mm) and the IVUS-derived maximum plaque burden (MaxPB) were analysed within the culprit segment and continuous 10 mm non-culprit segments of the index culprit vessels. The association with future major adverse cardiovascular and cerebrovascular events (MACCE), defined as all-cause mortality, acute coronary syndrome requiring revascularisation and cerebrovascular events during follow-up was evaluated using multivariable Cox regressions. A receiver operating characteristic (ROC) analysis was performed to test the ability of NIRS to discriminate culprit against non-culprit segments. Results: A non-culprit maxLCBI4mm ≥400 (HR: 3.67, 95% CI 1.46 to 9.23, p=0.006) and a non-culprit LCBI ≥ median (HR: 3.08, 95% CI 1.11 to 8.56, p=0.031) were both significantly associated with MACCE, whereas a non-culprit MaxPB ≥70% (HR: 0.61, 95% CI 0.08 to 4.59, p=0.63) was not. The culprit segments had larger lipid cores compared with non-culprit segments (MaxLCBI4mm 425 vs 74, p<0.001), and the ROC analysis showed that NIRS can differentiate culprit against non-culprit segments (c-statistics: 0.85, 95% CI 0.81 to 0.89). Conclusion: A maxLCBI4mm ≥400 and LCBI ≥ median, assessed by NIRS in non-culprit segments of a culprit artery, were significantly associated with patient-level MACCE. NIRS furthermore adequately discriminated culprit against non-culprit segments in patients with coronary disease.