The effects of intermittent negative pressure on the lower extremities' peripheral circulation and wound healing in four patients with lower limb ischemia and hard-to-heal leg ulcers: a case report

Medicine's Glass Slipper: The PAVAEX Boot and 20th Century Negative Pressure Therapy

Before the 20th century, peripheral artery disease (PAD) manifested as extreme pain, chronic wounds, and, eventually, gangrene requiring amputation. Despite this, it was rarely diagnosed. However, at the turn of the century, Western medicine shifted focus from infectious to chronic illnesses, and with this change, physicians' engagement with PAD transformed. Aiming to mitigate long-term injury, physicians now worked to identify and treat vessel disease to restore meaningful blood circulation. This article explores the development and deployment of a new device resulting from this refocus, the PAssive VAscular EXerciser (PAVAEX) Boot, and its role as a creative response to a previously intractable clinical problem. The PAVAEX Boot, designed in 1933 by vascular surgeons Louis G. Herrmann and Mont R. Reid, was one of the few interventions for PAD at the time. Based on the observation that continuous negative pressure results in vasoconstriction, while short bursts transiently increase blood flow, the PAVAEX Boot utilized intermittent negative pressure to enhance peripheral vascular perfusion. Well-marketed and praised throughout the 1930s, it vanished from public writing and academic literature just 20 years later. However, negative pressure wound therapy resurged in the late 20th century, and though its inventors failed to recognize the precedent of the PAVAEX Boot, many of these devices and therapies are rooted in identical theories. We examine why the PAVAEX Boot faded from use and argue that the device remains a crucial advancement in negative pressure therapy.

The Utility of Prevena Negative Pressure Wound Therapy on Groin Incisions for Critical Limb-Threatening Ischemia: A Single Institution Experience

BACKGROUND

Incisional negative pressure wound therapy (iNPWT) is an adjunctive treatment that uses constant negative pressure suction to facilitate healing. The utility of this treatment modality on vascular operations for critical limb-threatening ischemia (CLTI) has yet to be elucidated. This study compares the incidence of postoperative wound complications between the Prevena Incision Management System, a type of iNPWT, and standard wound dressings for vascular patients who also underwent plastic surgery closure of groin incisions for CLTI.

METHOD

We performed a retrospective cohort study of 40 patients with CLTI who underwent 53 open vascular surgeries with subsequent sartorius muscle flap closure. Patient demographics, intraoperative details, and wound complications were measured from 2015 to 2018 at the University of California San Francisco. Two cohorts were generated based on the modality of postoperative wound management and compared on wound healing outcomes.

RESULTS

Of the 53 groin incisions, 29 were managed with standard dressings, and 24 received iNPWT. Patient demographics, comorbidities, and operative characteristics were similar between the 2 groups. Patients who received iNPWT had a significantly lower rate of infection (8.33% vs 31.0%, P = 0.04) and dehiscence (0% vs 41.3%, P < 0.01). Furthermore, the iNPWT group had a significantly lower rate of reoperation (0% vs 17.2%, P = 0.03) for wound complications within 30 days compared with the control group and a moderately reduced rate of readmission (4.17% vs 20.7%, P = 0.08).

CONCLUSIONS

Rates of infection, reoperation, and dehiscence were significantly reduced in patients whose groin incisions were managed with iNPWT compared with standard wound care. Readmission rates were also decreased, but this difference was not statistically significant. Our results suggest that implementing iNPWT for the management of groin incisions, particularly in patients undergoing vascular operations for CLTI, may significantly improve clinical outcomes.

The effect of 12-week treatment with intermittent negative pressure on blood flow velocity and flowmotion, measured with a novel Doppler device (earlybird). Secondary outcomes from a randomized sham-controlled trial in patients with peripheral arterial disease

OBJECTIVES

Treatment with intermittent negative pressure (INP) is proposed as an adjunct to standard care in patients with peripheral arterial disease (PAD). The aims of this study were to evaluate the applicability of a novel ultrasound Doppler device (earlybird) to assess blood flow characteristics in patients with PAD during a treatment session with INP, and whether certain flow-properties could determine whom could benefit INP treatment.

METHODS

Secondary outcomes of data from a randomized sham-controlled trial were explored. Patients were randomized to 12 weeks of treatment with 40 mmHg or 10 mmHg INP, for one hour twice daily. Earlybird blood flow velocity recordings were made before and after the 12-week treatment-period and consists of a 5-minute recording in rest, 3-minute during INP treatment and 5-minute recording after ended INP test-treatment. Mean blood flow velocity (v_mean), relative changes in flow and frequency spectrum by Fourier-transform of the respective bandwidths of endothelial, sympathetic, and myogenic functions, were analyzed for the different series of blood flow measurements.

RESULTS

In total, 62 patients were eligible for analysis, where 32 patients were treated with 40 mmHg INP. The acquired recordings were of good quality and was used for descriptive analyses of flow characteristics. An immediate increase in v_mean during the negative pressure periods of the INP test-treatment was observed in the 40 mmHg INP treatment group at both pre- and post-test. There was a significant difference between the treatment groups, with a difference between the medians of 13.7 (p < 0.001) at pretest and 10.7 (p < 0.001) at posttest. This finding was confirmed with spectrum analysis by Fourier-transform of the bandwidth corresponding to INP treatment. The change in amplitude corresponding to myogenic function after 12 weeks of treatment, was significantly different in favor of the 40 mmHg INP treatment group. We were not able to detect specific flow characteristics indicating whom would benefit INP-treatment.

CONCLUSIONS

Earlybird is an applicable tool for assessing blood flow velocity in patients with PAD. Analysis of the flow velocity recordings shows that INP induce an immediate increase in blood flow velocities during INP. The positive effects of INP may be attributed to recruitment of arterioles, and thereby increasing blood flow. In these analyses no flow characteristics was determined which could predict whom would benefit INP-treatment.

Vascular ageing and peripheral pulse: an improved model for assessing their relationship

Objective.Vascular ageing is associated with several alterations, including arterial stiffness and endothelial dysfunction. Such alterations represent an independent factor in the development of cardiovascular disease (CVD). In our previous works we demonstrated the alterations occurring in the vascular system are themselves reflected in the shape of the peripheral waveform; thus, a model that describes the waveform as a sum of Gaussian curves provides a set of parameters that successfully discriminate betweenunder(≤35 years old) andoversubjects (>35 years old). In the present work, we explored the feasibility of a new decomposition model, based on a sum of exponential pulses, applied to the same problem.Approach.The first processing step extracts each pulsation from the input signal and removes the long-term trend using a cubic spline with nodes between consecutive pulsations. After that, a Least Squares fitting algorithm determines the set of optimal model parameters that best approximates each single pulse. The vector of model parameters gives a compact representation of the pulse waveform that constitutes the basis for the classification step. Each subject is associated to his/her 'representative' pulse waveform, obtained by averaging the vector parameters corresponding to all pulses. Finally, a Bayesan classifier has been designed to discriminate the waveforms of under and over subjects, using the leave-one-subject-out validation method.Main results.Results indicate that the fitting procedure reaches a rate of 96% in under subjects and 95% in over subjects and that the Bayesan classifier is able to correctly classify 91% of the subjects with a specificity of 94% and a sensibility of 84%.Significance.This study shows a sensible vascular age estimation accuracy with a multi-exponential model, which may help to predict CVD.

Patient and clinician experiences and opinions of the use of a novel home use medical device in the treatment of peripheral vascular disease - a qualitative study

BACKGROUND

Peripheral vascular diseases have a significant impact on functional quality of life. Previous research has demonstrated the complex, limiting and costly economic implications of these conditions such as lower limb ulceration chronicity and ischaemic amputation. These complex, limb and life threatening conditions demand the development of novel interventions with objective research as part of that development. Hence, a novel intermittent negative pressure medical device in the form of a wearable boot (FlowOx™) was developed. As part of the development process, this study aimed to explore patient and clinician opinions of the boot.

METHODS

A qualitative approach was used to collect patient and clinician experiences in Norway. An advisory group informed the semi-structured questions used in seven patient interviews and one clinician focus group (n = 5). The data were recorded digitally and transcribed verbatim. Patient and clinician data were analysed as distinct groups using a thematic process.

RESULTS

Data analysis resulted in five themes from the patients which gave insight into; the impact of the disease process; practicalities of using the boot, positive experiences of use; perceived outcomes; reflecting on use. Six themes were created from the clinicians. These gave insight into; ideal outcomes and how to measure them; ways to potentially use the boot; using research in healthcare; positives of the device; observed effects and next steps; potential improvements to the device.

CONCLUSION

This study provides insight into the experiences and opinions of FlowOx™. Patients and clinicians were positive about the device due to its ease of use. Those patients with peripheral arterial disease experienced significantly more benefit, especially for ischaemic ulceration than those with a chronic venous condition. Clinicians placed value on the patient reported outcomes in the treatment decision-making process. This preliminary study into experiences of FlowOx™ use provides valuable feedback that will inform design modification and ongoing research into implementation points and prospective user groups. FlowOx™ demonstrates potential as a conservative therapy offering users a convenient, home use, self-care management solution for improving symptomatic peripheral arterial disease and quality of life.

Economic model to examine the cost-effectiveness of FlowOx home therapy compared to standard care in patients with peripheral artery disease

BACKGROUND

Critical limb ischaemia is a severe stage of lower limb peripheral artery disease which can lead to tissue loss, gangrene, amputation and death. FlowOx™ therapy is a novel negative-pressure chamber system intended for home use to increase blood flow, reduce pain and improve wound healing for patients with peripheral artery disease and critical limb ischaemia.

METHODS

A Markov model was constructed to assess the relative cost-effectiveness of FlowOx™ therapy compared to standard care in lower limb peripheral artery disease patients with intermittent claudication or critical limb ischaemia. The model used data from two European trials of FlowOx™ therapy and published evidence on disease progression. From an NHS analysis perspective, various FlowOx™ therapy scenarios were modelled by adjusting the dose of FlowOx™ therapy and the amount of other care received alongside FlowOx™ therapy, in comparison to standard care.

RESULTS

In the base case analysis, consisting of FlowOx™ therapy plus nominal care, the cost estimates were £12,704 for a single dose of FlowOx™ therapy per annum as compared with £15,523 for standard care. FlowOx™ therapy patients gained 0.27 additional quality adjusted life years compared to standard care patients. This equated to a dominant incremental cost-effectiveness ratio per QALY gained. At the NICE threshold WTP of £20,000 and £30,000 per QALY gained, FlowOx™ therapy in addition to standard care had a 0.80 and 1.00 probability of being cost-effectiveness respectively.

CONCLUSIONS

FlowOx™ therapy delivered as a single annual dose may be a cost-effective treatment for peripheral artery disease. FlowOx™ therapy improved health outcomes and reduced treatment costs in this modelled cohort. The effectiveness and cost-effectiveness of FlowOx™ therapy is susceptible to disease severity, adherence, dose and treatment cost. Research assessing the impact of FlowOx™ therapy on NHS resource use is needed in order to provide a definitive economic evaluation.

Negative-Pressure Wound Therapy in Foot and Ankle Surgery

Negative Pressure Wound Therapy (NPWT) is frequently utilized to manage complex wounds, however its mechanisms of healing remain poorly understood. Changes in growth factor expression, micro- and macro-deformation, blood flow, exudate removal, and bacterial concentration within the wound bed are thought to play a role. NPWT is gaining widespread usage in foot and ankle surgery, including the management of traumatic wounds; diabetic and neuropathic ulcers; wounds left open after debridement for infection or dehiscence; high-risk, closed incisions; tissue grafts and free flaps. This article reviews the rationale for NPWT, its proposed mechanisms of action, and the evidence regarding its clinical applications within the field of foot and ankle surgery. Level of Evidence: Level V, expert opinion.

Fluctuation in shear rate, with unaltered mean shear rate, improves brachial artery flow-mediated dilation in healthy, young men

Increase in mean shear stress represents an important and potent hemodynamic stimulus to improve conduit artery endothelial function in humans. No previous study has examined whether fluctuations in shear rate patterns, without altering mean shear stress, impacts conduit artery endothelial function. This study examined the hypothesis that 30-min exposure to fluctuations in shear rate patterns, in the presence of unaltered mean shear rate, improves brachial artery flow-mediated dilation. Fifteen healthy men (27.3 ± 5.0 yr) completed the study. Bilateral brachial artery flow-mediated dilation was assessed before and after unilateral exposure to 30 min of intermittent negative pressure (10 s, −40mmHg; 7 s, 0 mmHg) to induce fluctuation in shear rate, while the contralateral arm was exposed to a resting period. Negative pressure significantly increased shear rate, followed by a decrease in shear rate upon pressure release (both P < 0.001). Across the 30-min intervention, mean shear rate was not different compared with baseline ( P = 0.458). A linear mixed model revealed a significant effect of time observed for flow-mediated dilation ( P = 0.029), with exploratory post hoc analysis showing an increase in the intervention arm (∆FMD +2.0%, P = 0.008), but not in the contralateral control arm (∆FMD +0.5%, P = 0.664). However, there was no effect for arm ( P = 0.619) or interaction effect ( P = 0.096). In conclusion, we found that fluctuations in shear patterns, with unaltered mean shear, improves brachial artery flow-mediated dilation. These novel data suggest that fluctuations in shear pattern, even in the absence of altered mean shear, represent a stimulus to acute change in endothelial function in healthy individuals.

NEW & NOTEWORTHY Intermittent negative pressure applied to the forearm induced significant fluctuations in antegrade and retrograde shear rate, while mean shear was preserved relative to baseline. Our exploratory study revealed that brachial artery flow-mediated dilation was significantly improved following 30-min exposure to intermittent negative pressure. Fluctuations in blood flow or shear rate, with unaltered mean shear, may have important implications for vascular health; however, further research is required to identify the underlying mechanisms and potential long-term health benefits.

Peritoneal dialysis catheter leakage following intermittent vacuum therapy

Peripheral arterial disease and diabetic foot syndrome are common comorbidities in dialysis patients. These conditions are treated with intermittent vacuum therapy in order to increase angiogenesis and perfusion. Some devices encase the lower extremities up to the abdomen. Here we report the case of a patient who had performed peritoneal dialysis for 2 years without complications. Following postoperative intermittent vacuum therapy, he presented with extensive catheter leakage. Ultimately the patient had to be switched to haemodialysis and the catheter had to be removed. This case exemplifies that peritoneal dialysis patients have a substantial risk for noninfectious catheter-related complications using vacuum therapy.

Intermittent mild negative pressure applied to the lower limb in patients with spinal cord injury and chronic lower limb ulcers: a crossover pilot study

STUDY DESIGN

Randomized, assessor-blinded crossover pilot study.

OBJECTIVES

To explore the use of an intermittent negative pressure (INP) device for home use in addition to standard wound care (SWC) for patients with spinal cord injury (SCI) and chronic leg and foot ulcers before conducting a superiority trial.

SETTING

Patient homes and outpatient clinic.

METHODS

A 16-week crossover trial on 9 SCI patients (median age: 57 years, interquartile range [IQR] 52-66), with leg ulcers for 52 of weeks (IQR: 12-82) duration. At baseline, patients were allocated to treatment with INP + SWC or SWC alone. After 8 weeks, the ulcers were evaluated. To assess protocol adherence, the patients were then crossed over to the other group and were evaluated again after another 8 weeks. Lower limb INP treatment consisted of an airtight pressure chamber connected to an INP generator (alternating 10 s -40mmHg/7 s atmospheric pressure) used 2 h/day at home. Ulcer healing was assessed using a photographic wound assessment tool (PWAT) and by measuring changes in wound surface area (WSA).

RESULTS

Seven of nine recruited patients adhered to a median of 90% (IQR: 80-96) of the prescribed 8-week INP-protocol, and completed the study without side effects. PWAT improvement was observed in 4/4 patients for INP + SWC vs. 2/5 patients for SWC alone (P = 0.13). WSA improved in 3/4 patients allocated to INP + SWC vs. 3/5 patients in SWC alone (P = 0.72).

CONCLUSIONS

INP can be used as a home-based treatment for patients with SCI, and its efficacy should be tested in an adequately sized, preferably multicenter randomized trial.

The effects of intermittent negative pressure on the lower extremities' peripheral circulation and wound healing in four patients with lower limb ischemia and hard-to-heal leg ulcers: a case report

Peripheral circulation is severely compromised in the advanced stages of peripheral arterial disease. Recently, it was shown that the application of -40 mmHg intermittent negative pressure (INP) to the lower leg and foot enhances macro- and microcirculation in healthy volunteers. In this case report, we describe the effects of INP treatment on four patients with lower limb ischemia and hard-to-heal leg and foot ulcers. We hypothesized that INP therapy may have beneficial hemodynamic and clinical effects in the patients. Four patients (age range: 61-79 years) with hard-to-heal leg and foot ulcers (6-24 months) and ankle-brachial pressure indices of ≤0.60 on the affected side were included. They were treated with an 8-week intervention period of -40 mmHg INP (10 sec negative pressure and 7 sec atmospheric pressure) on the lower limbs. A custom-made vacuum chamber was used to apply INP to the affected lower leg and foot for 2 h per day. After 8 weeks of INP therapy, one ulcer healed completely, while the other three ulcers were almost completely healed. These cases suggest that INP may facilitate wound healing. The theoretical foundation is that INP assists wound healing by improving blood flow to the small blood vessels in the affected limb, increasing the flow of oxygen and nutrients to the cells.

The acute effects of lower limb intermittent negative pressure on foot macro- and microcirculation in patients with peripheral arterial disease

Background

Intermittent negative pressure (INP) applied to the lower leg and foot increases foot perfusion in healthy volunteers. The aim of the present study was to describe the effects of INP to the lower leg and foot on foot macro- and microcirculation in patients with lower extremity peripheral arterial disease (PAD).

Methods

In this experimental study, we analyzed foot circulation during INP in 20 patients [median (range): 75 (63-84yrs)] with PAD. One leg was placed inside an air-tight vacuum chamber connected to an INP-generator. During application of INP (alternating 10s of -40mmHg/7s of atmospheric pressure), we continuously recorded blood flow velocity in a distal foot artery (ultrasound Doppler), skin blood flow on the pulp of the first toes (laser Doppler), heart rate (ECG), and systemic blood pressure (Finometer). After a 5-min baseline sequence (no pressure), a 10-min INP sequence was applied, followed by 5-min post-INP (no pressure). To compare and quantify blood flow fluctuations between sequences, we calculated cumulative up-and-down fluctuations in arterial blood flow velocity per minute.

Results

Onset of INP induced an increase in arterial flow velocity and skin blood flow. Peak blood flow velocity was reached 3s after the onset of negative pressure, and increased 46% [(95% CI 36–57), P<0.001] above baseline. Peak skin blood flow was reached 2s after the onset of negative pressure, and increased 89% (95% CI 48–130), P<0.001) above baseline. Cumulative fluctuations per minute were significantly higher during INP-sequences compared to baseline [21 (95% CI 12–30)cm/s/min to 41 (95% CI 32–51)cm/s/min, P<0.001]. Mean INP blood flow velocity increased significantly ~12% above mean baseline blood flow velocity [(6.7 (95% CI 5.2–8.3)cm/s to 7.5 (95% CI 5.9–9.1)cm/s, P = 0.03)].

Conclusion

INP increases foot macro- and microcirculatory flow pulsatility in patients with PAD. Additionally, application of INP resulted in increased mean arterial blood flow velocity.