Laser Speckle Contrast Imaging for Assessment of Cutaneous Perfusion and Treatment Response During Hyperbaric Oxygen Therapy in Chronic Wounds: A Case Series

ABSTRACT

Hyperbaric oxygen therapy (HBOT) is an adjunctive treatment for selected chronic wounds with microcirculatory impairment, but treatment response is typically assessed clinically after several weeks. This case series evaluated the feasibility and potential utility of laser speckle contrast imaging (LSCI) for monitoring cutaneous perfusion during HBOT. Six patients with chronic wounds refractory to conventional management underwent HBOT. Cutaneous perfusion was assessed using LSCI before and after HBOT sessions at three predefined regions of interest: referent healthy skin, wound margin and wound bed. Perfusion was quantified in laser speckle perfusion units (LSPUs). Baseline perfusion differed significantly among anatomical regions (Friedman test, p < 0.001). Median perfusion was highest at the wound margin (109 [70–172] LSPU), compared with the wound bed (58 [32–92] LSPU; p = 0.001) and referent healthy skin (45 [36–61] LSPU; p < 0.001). Across monitored HBOT sessions, perfusion increased significantly after treatment in referent skin (+11 [−2 to +18] LSPU; p = 0.022), at the wound margin (+30 [−2 to +64] LSPU; p = 0.005) and in the wound bed (+10 [+1 to +32] LSPU; p = 0.010). Pre‐HBOT wound‐bed perfusion tended to decrease over the treatment course in most patients, although substantial inter‐individual variability was observed. This case series demonstrates the feasibility of repeated, non‐invasive LSCI assessment to characterize spatial and acute changes in cutaneous microcirculatory perfusion during HBOT. LSCI appears feasible for monitoring cutaneous perfusion during HBOT. Prospective studies with standardized assessment time points are needed to determine whether LSCI‐derived perfusion trajectories or thresholds are associated with wound‐healing outcomes and can inform HBOT decision‐making.

Key Points

• Laser speckle contrast imaging (LSCI) appears feasible for repeated assessment of cutaneous microcirculatory perfusion during hyperbaric oxygen therapy (HBOT), detecting spatial differences and post‐session changes in six patients with chronic wounds.

• Pre‐session perfusion was higher at wound margins than in wound beds or referent healthy skin, highlighting spatial heterogeneity.

• HBOT sessions were associated with perfusion increases in all three regions, with substantial variability between patients.

1. Introduction

Chronic wounds remain a major therapeutic challenge, particularly, in patients with impaired microcirculation [1]. Conditions such as thromboangiitis obliterans, systemic sclerosis, diabetes and peripheral vascular disease can cause tissue hypoxia and impaired healing. Despite advances in local wound management, some patients fail to achieve adequate healing and remain at risk of infection, amputation and long‐term disability.

Hyperbaric oxygen therapy (HBOT) has emerged as a second‐line treatment for selected refractory chronic wounds. By increasing plasma‐dissolved oxygen and redistributing blood flow toward poorly perfused regions through the so‐called ‘Robin Hood’ effect, HBOT may improve tissue oxygenation, promote angiogenesis and stimulate growth factors including vascular endothelial growth factor [2, 3]. In patients with diabetic foot ulcers, previous studies have reported improved wound healing and tissue oxygenation during HBOT. Fahmy et al. observed reductions in wound surface area and ulcer volume during HBOT, whereas Wadee et al., in a randomized controlled trial, demonstrated progressive improvement in transcutaneous oxygen tension during treatment [4, 5]. However, the clinical benefit of HBOT is not uniform across patient populations. A systematic review by Lalieu et al. found no clear improvement in healing or amputation rates in patients with non‐ischemic diabetic foot ulcers, underscoring the importance of appropriate patient selection [6].

Assessment of HBOT efficacy remains largely dependent on serial clinical and visual wound evaluation, with treatment response often becoming apparent only after several weeks and multiple HBOT sessions. The lack of an objective early response marker may lead to prolonged ineffective treatment or delayed alternative interventions. This limitation is particularly relevant in hyperbaric medicine centrs with limited treatment capacity, where earlier identification of patients likely or unlikely to benefit from HBOT could improve clinical decision‐making and resource allocation.

Laser speckle contrast imaging (LSCI) is a non‐invasive, contact‐free optical imaging technique that provides real‐time, two‐dimensional assessment of cutaneous microcirculatory perfusion [7]. With the near‐infrared wavelength used by the PeriCam system, measurements predominantly reflect superficial skin perfusion, with an estimated sampling depth of approximately 300 μm corresponding mainly to the superficial dermal microvascular plexus, without contamination from larger or deeper vessels. Image acquisition requires only a few seconds, although complete assessment, including device positioning and ROI definition, requires approximately 3 min under the present protocol. Unlike transcutaneous oxygen measurements, LSCI assesses blood‐flow perfusion expressed as laser speckle perfusion units (LSPU), while unlike laser Doppler techniques, it provides rapid wide‐field imaging. Its main limitations are the use of relative rather than absolute perfusion units and sensitivity to motion, tissue curvature and camera angulation. LSCI has been used to assess cutaneous perfusion in vascular disorders and wound healing and perfusion patterns have been shown to differ between wounds with favourable and unfavourable healing potential [8]. However, its ability to monitor microcirculatory changes during HBOT has not been characterized. This case series, therefore, evaluated the feasibility of repeated LSCI measurements during HBOT and explored whether longitudinal changes in cutaneous perfusion could provide clinically relevant information on treatment response in patients with chronic wounds.

2. Materials and Methods

2.1. Study Setting and Patients

This observational case series was conducted at the hyperbaric medicine centre of a tertiary university hospital in Lyon, France, which serves as a regional HBOT referral centre.

Six consecutive patients (median age, 54 years; range, 33–80 years) with chronic wounds refractory to conventional management were included (Table 1). Written informed consent was obtained from all patients. This case series was reported in accordance with the CARE recommendations.

TABLE 1.

Patient characteristics and clinical outcomes.

Patient number	Age (years)	Chronic wounds	No. HBOT session monitored	LSCI perfusion analysis	Clinical outcome
1	33	Toe tip, Buerger's disease	30‐31‐33	Repeated post‐HBOT perfusion increases. Suggesting HBOT continuation.	Favourable healing trajectory after 60 HBOT sessions
2	80	Great toe, systemic sclerosis and chronic arterial disease	15‐16‐17‐18‐20	Variable post‐HBOT perfusion changes across monitored sessions. Suggesting HBOT continuation.	Favourable healing trajectory after 32 HBOT sessions
3	64	Necrosis of thumb amputation flap, sickle cell disease	25‐26‐27	Low pre‐session perfusion with repeated post‐HBOT increases. Suggesting HBOT continuation.	Favourable healing trajectory after 53 HBOT sessions
4	61	Digital necrosis, necrotizing microangiopathy	37‐38‐39‐40	Heterogeneous changes across monitored sessions. Suggesting limited reserve with partial response.	Favourable healing trajectory after 68 HBOT sessions
5	47	Toe tip, Buerger's disease and chronic arterial disease	58‐59‐60	Pre‐session perfusion approaching referent‐skin values, with limited post‐HBOT changes. Suggesting HBOT discontinuation.	Unfavourable healing trajectory after 65 HBOT sessions. HBOT discontinuation.
6	40	Toe tip, Buerger's disease	24	Post‐HBOT perfusion increase during the monitored session Suggesting HBOT continuation.	Favourable healing trajectory after 25 HBOT sessions

2.2. Therapeutic Intervention

HBOT was delivered in a multiplace hyperbaric chamber at 2.5 atm absolute with 100% oxygen. Patients received HBOT sessions every 2 days, based on clinician assessment and availability on working days. An initial course of 30–40 sessions was prescribed, with additional sessions considered according to clinical response and the treating physician's assessment.

2.3. Standard Wound Care

HBOT was used as an adjunct to ongoing standard wound care rather than as a stand‐alone treatment. Local wound management was individualized according to wound characteristics and clinical evidence of infection. Dressings were selected by the treating care team according to wound characteristics; no uniform dressing type or predefined dressing‐change schedule was mandated by the protocol. Other vascular, medical or surgical treatments were continued or modified according to the underlying disease and clinical course.

2.4. LSCI Assessment

The primary objective was to assess the feasibility of integrating repeated LSCI measurements into routine clinical practice. Feasibility was defined by the ability to obtain repeated, interpretable perfusion maps before and after HBOT sessions without technical difficulties or adverse events.

Following training by an experienced LSCI user (S.A.), the clinical team measured cutaneous perfusion in LSPU according to a previously published protocol by Van Vuuren et al. [8]. Measurements were obtained immediately before and after HBOT sessions to assess baseline perfusion and the acute microcirculatory response. HBOT LSCI was not performed at every session but during selected sessions according to investigator and device availability.

All measurements were performed with participants at rest in a temperature‐controlled room (22°C ± 1°C). The laser head of the PeriCamC LSCI device (Perimed, Järfälla, Sweden) was positioned as perpendicular as possible to the wound surface at a distance of 10–30 cm. Spatial resolution ranged from 0.12 to 0.18 mm/pixel. Participants were instructed not to move or speak during image acquisition.

Three predefined regions of interest (ROIs) were analysed: (1) visually unaffected referent skin distant from the wound, (2) the wound margin at the best‐defined wound edge and (3) the centre of the wound bed (Figure 1). To standardize ROI dimensions while excluding the wound margin from the wound‐bed ROI, Patient 1, who had the smallest wound, was used to define the ROI size for the study. ROIs of approximately 4 ± 1 mm² were used for the wound bed and wound margin. A larger ROI of approximately 7 ± 2 mm² was used for referent healthy skin to reduce the influence of local perfusion heterogeneity. ROI placement and perfusion measurements were performed using PIMSoft software (Perimed, Järfälla, Sweden).

FIGURE 1.

Photograph of the initial lesion and LSCI images before/after an HBOT session. Regions of interest (ROIs): (1) (Blue) distant referent skin, (2) (red) edge of the wound, (3) (green) centre of the wound. HBOT: hyperbaric oxygen therapy.

Secondary outcomes included differences in baseline perfusion among the three anatomical regions, acute perfusion changes following HBOT sessions, longitudinal changes in perfusion within each ROI and the clinical course of wound healing. Healing outcome was assessed clinically by the treating physician at the end of the HBOT course.

2.5. Statistical Methods

Continuous variables are presented as median (interquartile range). Perfusion across the three anatomically matched ROIs was compared using the related‐samples Friedman two‐way analysis of variance by ranks. When the overall test was significant, pairwise comparisons were performed using Wilcoxon signed‐rank tests with Bonferroni correction for multiple comparisons. Acute changes in perfusion before and after HBOT within each ROI were assessed using the Wilcoxon signed‐rank test. A p value < 0.05 was considered statistically significant.

Given the case‐series design, small sample size and unequal number and timing of repeated LSCI assessments between participants, statistical analyses were considered exploratory. No longitudinal modelling or between‐patient regression analysis was performed because measurements were not collected at standardized treatment time points and were therefore unsuitable for estimating a common temporal perfusion trajectory. Individual measurements over the HBOT course were presented descriptively.

3. Results

3.1. Feasibility

LSCI measurements were successfully obtained in all six patients without technical difficulties or adverse events and all perfusion maps were interpretable.

Baseline perfusion differed significantly among anatomical regions (Friedman test, p < 0.001). Median perfusion was highest at the wound margin (109 [70–172] LSPU), compared with the wound bed (58 [32–92] LSPU; p = 0.001) and referent healthy skin (45 [36–61] LSPU; p < 0.001) (Figure 1). Pairwise analyses confirmed higher perfusion at the wound margin than at the wound bed (p = 0.001) and referent healthy skin (p < 0.001). No significant difference was observed between the wound bed and referent healthy skin.

3.2. Perfusion Changes Following HBOT

Across monitored HBOT sessions, perfusion increased significantly after treatment in all three regions. Median changes were + 11 [−2 to +18] LSPU in referent healthy skin (p = 0.022), +30 [−2 to +64] LSPU at the wound margin (p = 0.005) and + 10 [+1 to +32] LSPU in the wound bed (p = 0.010).

3.3. Longitudinal Perfusion Changes

Figures 2, 3, 4 provide complementary descriptive representations of LSCI measurements obtained during monitored HBOT sessions. Figure 2 shows absolute pre‐HBOT wound‐bed perfusion, illustrating changes in baseline wound perfusion across successive assessments. Figure 3 shows wound perfusion relative to referent healthy skin, illustrating changes in relative wound perfusion over time. Figure 4 shows the acute change in wound‐bed perfusion after each monitored HBOT session, illustrating variation in the immediate perfusion response over the treatment course.

FIGURE 2.

Individual pre‐HBOT wound perfusion measurements according to HBOT session number. Each point represents an HBOT session (measured immediately before the session). Numbers adjacent to the points indicate the HBOT session number in the study. Colours identify individual patients. HBOT: hyperbaric oxygen therapy.

FIGURE 3.

Individual pre‐HBOT wound‐to‐referent skin perfusion difference according to HBOT session number. The wound‐to‐referent skin perfusion difference (LSPU) was calculated as wound‐bed perfusion minus referent skin perfusion. Each point represents an HBOT session (measured immediately before the session). Numbers adjacent to the points indicate the HBOT session number in the study. Colours identify individual patients.

FIGURE 4.

Individual acute change in wound‐bed perfusion following HBOT session according to session number. The acute change in wound‐bed perfusion (delta wound‐bed perfusion, LSPU) was calculated as post‐HBOT wound‐bed perfusion minus pre‐HBOT wound‐bed perfusion. Each point represents an HBOT session. Numbers adjacent to the points indicate the HBOT session number in the study. Colours identify individual patients.

Across repeated assessments, pre‐HBOT wound‐bed perfusion tended to decrease over the treatment course in most patients, although substantial inter‐individual variability was observed. Patients 3 and 6 had lower pre‐session wound perfusion values during the monitored treatment period than several other patients (Figure 2). In Patient 3, baseline wound perfusion was relatively low at the 25th session and post‐HBOT increases in wound perfusion were observed during the monitored sessions (Figure 4). In contrast, Patient 5, who was monitored from the 58th HBOT session, showed pre‐session wound perfusion values approaching those measured in referent skin, with limited additional changes after HBOT. These LSCI findings were considered alongside clinical assessment and HBOT was subsequently discontinued after 65 sessions. Individual LSCI findings and clinical outcomes are summarized in Table 1.

4. Discussion

This case series demonstrated that LSCI could be integrated into routine HBOT monitoring and provide interpretable cutaneous perfusion measurements before and after treatment in six patients with chronic wounds. No adverse events were reported. Wound margins had higher pre‐session perfusion than wound beds and referent healthy skin, while HBOT was associated with acute perfusion increases across all three regions. These findings support the feasibility of LSCI for characterizing spatial and temporal changes in cutaneous microcirculatory perfusion during HBOT and are consistent with the physiological effect of HBOT on tissue perfusion [2].

Pre‐session wound‐bed perfusion tended to decrease over treatment in most patients, although substantial inter‐individual variability was observed. This decrease may reflect resolution of inflammatory hyperemia and normalization of microvascular flow during wound healing [9]. However, without concurrent inflammatory or tissue‐oxygenation measurements, this interpretation remains hypothetical. Higher perfusion at the wound margin than at the wound centre and referent skin is consistent with the spatial heterogeneity expected during wound healing [6]. Repeated LSCI measurements also provided physiological information that could complement clinical wound assessment during HBOT. For example, some patients showed persistent post‐session perfusion increases despite low pre‐session values, whereas Patient 5 had perfusion values approaching those of referent skin with limited further changes after HBOT. These observations remain exploratory and do not establish LSCI criteria for continuing or discontinuing treatment. Nevertheless, LSCI may eventually help optimize patient selection and resource allocation in hyperbaric centres with limited treatment capacity.

LSCI has been investigated for assessing burn depth and healing potential in venous and diabetic wounds, as well as for evaluating and monitoring digital microvascular involvement in systemic sclerosis [8, 10, 11, 12, 13]. More broadly, several non‐invasive optical approaches have been developed to characterize superficial tissue perfusion and oxygenation. El‐Sharkawy et al. used diffuse reflectance combined with hyperspectral imaging to obtain noncontact maps of tissue oxygen saturation, whereas Fouad et al. demonstrated that hyperspectral imaging could distinguish cutaneous vascular structures based on differences in tissue oxygenation [14, 15]. These techniques highlight the potential of optical imaging for real‐time, non‐invasive assessment of tissue physiology. However, their information is complementary rather than equivalent to that provided by LSCI: hyperspectral approaches primarily characterize spectral and oxygenation‐related properties, whereas LSCI provides a spatial index of microvascular blood‐flow perfusion. Future studies should determine whether perfusion changes during HBOT reflect altered blood flow, oxygen delivery, oxygen extraction or a combination of these mechanisms.

The main strength of this study was the prospective implementation of repeated LSCI measurements in a real‐world hyperbaric setting. The inclusion of patients with Buerger's disease, systemic sclerosis, sickle cell disease, chronic arterial disease and necrotizing microangiopathy demonstrated the technical feasibility of LSCI across diverse clinical conditions. However, these diseases involve distinct mechanisms of microvascular dysfunction and wound healing and may therefore produce different responses to HBOT. This heterogeneity, together with the very small sample size, precludes disease‐specific interpretation and limits generalizability. Another important limitation was the sparse and non‐standardized timing of LSCI measurements throughout the HBOT course. The number of assessments varied substantially between patients and measurements were obtained at different treatment stages, ranging from early or middle treatment to sessions beyond 50. These data therefore cannot define the longitudinal evolution of wound perfusion over a complete HBOT course. Accordingly, additional longitudinal modelling was not performed. Additional limitations included the absence of a control group, limited LSCI measurements per patient and lack of standardized clinical endpoints, such as limb salvage or long‐term functional outcomes. Larger prospective studies are needed to determine whether LSCI‐derived trajectories or thresholds predict wound healing and whether incorporating LSCI into HBOT decision‐making algorithms improves patient selection, treatment duration or resource utilization.

5. Conclusion

LSCI appears feasible for repeated assessment of cutaneous microcirculatory perfusion during HBOT and detected both spatial differences in wound perfusion and acute changes after monitored treatment sessions. However, in this small and heterogeneous case series of patients with chronic wounds, LSCI should be considered an exploratory physiological monitoring tool rather than a validated method for identifying treatment responders or guiding HBOT discontinuation. Prospective studies should standardize acquisition conditions and determine whether baseline wound‐to‐reference perfusion, acute pre‐/post‐HBOT changes and longitudinal perfusion trajectories are associated with predefined wound‐healing outcomes and can establish clinically relevant thresholds for HBOT decision‐making.

Funding

The authors have nothing to report.

Ethics Statement

Due to the nature of the study (observational case series), the French Law waived the requirement for IRB.

Consent

Written informed consent was obtained from all the patients.

Conflicts of Interest

Stanislas Abrard has received honoraria for consulting from Viatris Inc. (France) and from Public Health Expertise (France). The other authors declare no conflicts of interest.

Data Availability Statement

The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.