How Hyperbaric Oxygen Therapy Influences New Blood Vessel Formation, Cellular Signaling, and Tissue Repair

Angiogenesis is the formation of new capillary branches from existing blood vessels. It is a critical part of wound healing because newly repaired tissue requires a dependable microvascular network to deliver oxygen, nutrients, immune cells, and signaling molecules.

Hyperbaric oxygen therapy, commonly abbreviated as HBOT, may support this process by temporarily increasing tissue oxygen tension and influencing several pathways involved in vascular repair. These include vascular endothelial growth factor, nitric oxide signaling, endothelial cell activity, and the mobilization of circulating progenitor cells.

The relationship is more complex than the simple statement that oxygen grows blood vessels. Angiogenesis depends on coordinated cycles of signaling, vessel sprouting, extracellular matrix remodeling, blood flow, and vessel maturation. HBOT may influence several of these steps, but it cannot restore circulation through a completely obstructed artery or create viable tissue where irreversible necrosis has already occurred.

Angiogenesis and Vasculogenesis Are Related but Distinct

Angiogenesis describes the growth of new capillary branches from blood vessels already present within the tissue. Endothelial cells lining an existing vessel become activated, migrate into the surrounding matrix, proliferate, and organize into new vascular structures.

Vasculogenesis refers to the contribution of circulating progenitor cells to vascular development and repair. These cells may be mobilized from bone marrow, enter the bloodstream, and participate directly or indirectly in the response to ischemic tissue.

Both processes may be relevant during HBOT.

Laboratory and human studies have reported that hyperbaric oxygen can influence endothelial cells already present in tissue while also increasing circulating populations of CD34-positive progenitor cells. These effects are related, but an increase in circulating progenitor cells does not prove that the cells have reached the wound or formed functional blood vessels. (PubMed)

Why New Blood Vessels Matter in Wound Healing

Healthy tissue depends on a microvascular network capable of adjusting oxygen and nutrient delivery to local metabolic demand. When tissue is injured, that demand increases. Leukocytes require oxygen to support microbial killing, fibroblasts need an adequate metabolic environment to produce extracellular matrix, and epithelial cells must migrate and proliferate to restore the tissue surface.

Chronic wounds may have difficulty meeting these demands because of:

• Peripheral arterial disease
• Small-vessel dysfunction
• Edema
• Infection
• Radiation-related vascular damage
• Repetitive pressure or trauma
• Fibrosis
• Diabetes-associated impairment of cellular signaling

Hypoxia can initiate signals that encourage vascular growth. Persistent or severe hypoxia, however, may prevent cells from producing enough energy to complete the repair process. A wound can therefore be hypoxic enough to signal distress while also being too oxygen deprived to respond effectively.

HBOT is intended to create temporary periods of markedly increased oxygen availability. These exposures may support cellular activity and trigger signaling responses that continue after the patient returns to normal atmospheric pressure.

HBOT Creates a Strong Oxygen Diffusion Gradient

During HBOT, increased ambient pressure raises the partial pressure of inspired oxygen. This substantially increases the amount of oxygen dissolved directly in plasma.

The oxygen-rich plasma moves through functioning blood vessels and creates a stronger pressure gradient between capillary blood and surrounding tissue. Oxygen can therefore diffuse farther from the remaining microcirculation into hypoxic but viable areas.

This does not mean the tissue remains hyperoxygenated permanently. Tissue oxygen tension rises during treatment and then gradually returns toward baseline after the session. In an experimental wound model, hyperbaric exposure produced a substantial temporary rise in wound oxygen tension and was followed by increased wound concentrations of vascular endothelial growth factor, or VEGF. (PubMed)

The temporary nature of the oxygen exposure is clinically important. HBOT is usually delivered as a series of intermittent treatments rather than as continuous hyperoxia. The repeated transition between high oxygen tension and the patient’s baseline environment may influence redox-sensitive and oxygen-sensitive signaling pathways involved in repair.

VEGF Signaling and Capillary Sprouting

VEGF is one of the principal signaling proteins involved in angiogenesis. It promotes endothelial cell survival, migration, proliferation, and increased vascular permeability. These activities help initiate the development of new capillary structures in response to tissue injury or ischemia.

Preclinical studies have reported increased VEGF expression following hyperbaric oxygen exposure. Experimental research has also connected HBOT with pathways involving hypoxia-inducible factor 1-alpha, stromal cell-derived factor 1, VEGF receptors, and related signaling systems. In a diabetic wound model, HBOT was associated with activation of HIF-1α signaling and increased expression of VEGF and SDF-1 within fibroblasts. (PubMed)

These findings help explain a possible mechanism, but they should not be interpreted as proof that every HBOT session produces clinically significant angiogenesis in every patient. Much of the detailed molecular evidence comes from animal models or cultured cells, where conditions differ from a complex human wound.

Other angiogenic mediators may also be involved. One endothelial-cell study found that hyperbaric oxygen selectively increased angiopoietin-2 expression without increasing VEGF in that particular model. Angiopoietin-2 participates in vascular remodeling by altering the stability of existing vessels and helping prepare them to respond to other growth signals. (PubMed)

The vascular response to HBOT is therefore unlikely to depend on one growth factor alone.

Nitric Oxide and Progenitor Cell Mobilization

Nitric oxide plays an important role in endothelial function, vascular signaling, and the mobilization of progenitor cells from bone marrow.

A human study found that a single exposure to oxygen at 2.0 atmospheres absolute increased circulating CD34-positive cells approximately twofold. After a course of 20 treatments, the circulating population was reported to have increased approximately eightfold. The investigators identified a nitric oxide-dependent mechanism as an important part of this response. (PubMed)

A later study found that progenitor-cell mobilization varied with the treatment pressure, with greater mobilization observed following exposures at 2.5 ATA than at 2.0 ATA. The newly mobilized cells also demonstrated changes in regulatory proteins associated with cell activity and vascular repair. (PubMed)

These results demonstrate a biologic response to a defined oxygen dose. They do not establish that a higher pressure is automatically better for wound healing. Treatment pressure must account for the indication, desired physiologic effect, oxygen exposure, patient risk, and clinical protocol.

Mobilization Does Not Guarantee Homing to the Wound

For a progenitor cell to contribute meaningfully to tissue repair, it must do more than enter the bloodstream. It must respond to signals from the injured tissue, adhere to the local endothelium, migrate into the wound, survive, and participate in vascular recovery.

This process may be impaired in diabetes.

In experimental diabetic wounds, HBOT increased circulating endothelial progenitor cells, but the cells did not consistently reach the wound because local production of SDF-1α was inadequate. SDF-1 is an important signal involved in directing progenitor cells toward ischemic or injured tissue. (PubMed)

This finding highlights why the presence of more circulating cells should not be confused with completed angiogenesis. The wound environment must still provide the biochemical and structural signals needed for recruitment.

Later preclinical work has suggested that HBOT may influence both sides of this relationship by increasing SDF-1 and VEGF signaling within wound-associated cells while supporting receptors such as CXCR4 and VEGFR on endothelial cells. (PubMed)

Human research in peripheral arterial occlusive disease has also reported increased circulating endothelial progenitor cells, angiogenesis-related factors, and improved blood flow measurements following HBOT. These findings are encouraging, although they do not prove that progenitor-cell mobilization alone caused the clinical changes. (PubMed)

Endothelial Cells Must Migrate, Organize, and Mature

The appearance of a vascular growth signal is only the beginning of angiogenesis.

Endothelial cells must loosen their connections with the existing vessel, break through the surrounding basement membrane, and migrate toward the source of the angiogenic signal. Selected cells form the leading tip of the new vascular sprout, while others proliferate behind them to lengthen the developing vessel.

The sprout must then:

• Form a functional lumen
• Connect with another vascular branch
• Establish blood flow
• Recruit stabilizing support cells
• Develop a new basement membrane
• Mature into a vessel capable of sustained perfusion

A fragile, poorly organized vessel network may not provide durable tissue oxygenation. Effective repair depends on vascular maturation and integration with the surrounding extracellular matrix.

HBOT may influence endothelial activity, inflammatory signaling, growth-factor expression, and the fibroblast response that helps form this structural environment. Cell research has shown changes in endothelial nitric oxide synthase, inflammatory adhesion molecules, and oxidative signaling after hyperbaric exposure, supporting a broader role in vascular recovery beyond increasing oxygen content alone. (PubMed)

Angiogenesis Requires an Extracellular Matrix

New capillaries do not develop in empty space. They grow through an extracellular matrix composed of collagen, fibronectin, proteoglycans, and other structural molecules.

Fibroblasts are central to the production and organization of this matrix. Their activity is influenced by oxygen availability, growth factors, inflammation, glucose control, and the mechanical condition of the wound.

HBOT may temporarily improve the oxygen environment needed for fibroblast metabolism and collagen production. At the same time, the controlled oxidative stimulus created by hyperbaric exposure may alter gene expression and growth-factor activity.

The result is not simply more blood vessels. Ideally, HBOT helps create a wound environment in which vascular development, matrix formation, immune function, and epithelial repair can progress together.

This is one reason angiogenesis should not be evaluated as an isolated laboratory endpoint. An increase in VEGF or capillary density has limited clinical value if the wound remains infected, repeatedly traumatized, inadequately perfused by larger vessels, or filled with nonviable tissue.

Why Intermittent Hyperoxia Matters

Continuous excessive oxygen exposure can produce cellular injury. Therapeutic HBOT instead uses a controlled dose defined by treatment pressure, oxygen-breathing time, treatment frequency, air breaks, and total number of sessions.

Short, repeated exposures may trigger adaptive responses while allowing tissue oxygen tension to return toward baseline between treatments.

Experimental work involving isolated tissue constructs found that short-term hyperbaric exposure increased angiogenic activity, while prolonged exposure could lead to vascular pruning. This reinforces the principle that oxygen behaves like a medication: dose and timing influence whether the response is therapeutic, ineffective, or harmful. (PubMed)

More pressure, longer sessions, or additional treatments should not be assumed to create more angiogenesis. The prescribed regimen should be selected for the clinical diagnosis and reassessed according to the patient’s response.

Clinical Conditions Where Angiogenesis May Be Relevant

Angiogenesis is not the primary mechanism in every hyperbaric indication. Bubble compression is central to arterial gas embolism and decompression sickness, for example. Vascular repair becomes more relevant in chronic hypoxic and ischemic tissue conditions.

Clinical settings in which angiogenic effects may contribute include:

• Delayed radiation injury: Radiation may reduce capillary density and leave tissue chronically hypoxic and fibrotic. Repeated HBOT exposures are intended in part to support vascular remodeling in viable irradiated tissue. UHMS notes that angiogenesis may contribute to the response, while also cautioning that it should not be treated as the only mechanism involved in delayed radiation injury. (UHMS)
• Selected diabetic foot ulcers: HBOT may support angiogenic signaling in hypoxic wounds, particularly when standard wound care has been optimized. Preclinical evidence is stronger than direct human molecular evidence, and clinical benefit remains dependent on wound selection, perfusion, offloading, infection control, and vascular care. (PubMed)
• Compromised grafts and flaps: Increased oxygen diffusion may support threatened tissue while vascular connections develop or recover. Correctable causes such as pedicle thrombosis, venous congestion, hematoma, or excessive tension still require immediate surgical management.
• Refractory osteomyelitis and complex bone repair: Vascular growth can support oxygen delivery, immune function, bone remodeling, and antibiotic access. HBOT does not remove necrotic bone or replace antimicrobial and surgical source control.
• Chronic wounds in ischemic tissue: HBOT may augment the microvascular response when sufficient arterial inflow remains. A major arterial obstruction still requires vascular assessment and revascularization when feasible.

Angiogenesis is most likely to matter when the tissue is viable, inadequately oxygenated, and capable of responding to repeated treatment. Completely necrotic tissue cannot be restored by stimulating vascular signals.

Measuring Angiogenesis During HBOT

Directly measuring new vessel formation in a patient is difficult. Tissue biopsy can assess microvessel density or endothelial markers, but repeated biopsy may be impractical and can create additional injury.

A 2025 clinical study involving diabetic foot ulcers reported an apparent increase in CD31-positive microvessel density in tissue from HBOT-treated patients after one month. The tissue sample was limited, so the finding should be considered supportive rather than definitive proof of the mechanism in all diabetic wounds. (PubMed)

Clinicians more commonly evaluate indirect evidence of improved tissue function, including:

• Progressive granulation tissue
• Reduction in wound depth or surface area
• Improved tissue quality
• Greater durability of previously irradiated tissue
• Improved perfusion or oxygen measurements
• Successful graft or flap preservation
• Progress toward definitive closure

Transcutaneous oxygen measurement can provide information about tissue oxygen availability and response to supplemental oxygen. It does not directly count new blood vessels. A higher oxygen measurement may reflect improved delivery through existing vessels, reduced edema, increased blood flow, or vascular remodeling.

The most meaningful assessment remains clinical. Angiogenesis is valuable because it contributes to healing, tissue preservation, and functional recovery, not because a growth factor or cell marker increased in isolation.

Angiogenesis Is Not a Substitute for Blood Flow

HBOT acts primarily at the level of oxygen content, diffusion, signaling, and microvascular repair. It cannot replace adequate macroscopic circulation.

A patient with significant arterial disease may require:

• Vascular imaging
• Endovascular intervention
• Surgical bypass
• Thrombectomy
• Correction of external compression
• Management of venous congestion

Similarly, a wound requires debridement when nonviable tissue is present, antimicrobial treatment when clinically infected, and pressure relief when repetitive loading continues.

New capillaries also need a source of inflowing blood. Angiogenesis cannot compensate fully for an untreated proximal arterial obstruction.

This distinction helps prevent HBOT from being used as a delay or alternative to definitive vascular and surgical care.

Setting Realistic Clinical Expectations

Angiogenesis develops over time. HBOT can raise tissue oxygen tension during an individual treatment, but a durable vascular network does not appear after one chamber session.

Repeated treatments may create conditions that support endothelial activation, progenitor-cell mobilization, capillary sprouting, and vascular maturation. The pace and extent of that response depend on:

• Baseline perfusion
• Severity and duration of hypoxia
• Diabetes and metabolic control
• Infection
• Radiation injury
• Tobacco or nicotine exposure
• Nutrition
• Medication effects
• Local mechanical stress
• The viability of the tissue

HBOT should therefore be presented as an adjunct that may improve the environment for vascular repair, not as a direct or guaranteed method of growing new blood vessels.

The strongest clinical use of this mechanism occurs when angiogenesis supports a defined treatment goal, such as healing a selected hypoxic wound, improving the health of irradiated tissue, or preserving a compromised reconstruction.

Hyperbaric oxygen may influence angiogenesis through increased tissue oxygenation, VEGF-related signaling, nitric oxide activity, endothelial responses, and progenitor-cell mobilization. These mechanisms are biologically credible and supported by laboratory, animal, and selected human studies. Their clinical value still depends on the diagnosis, oxygen dose, tissue viability, standard treatment, and careful measurement of patient outcomes.