Importance Of Blood Flow In Wound Recovery

Introduction

Blood flow and wound recovery

A wound is a damage or disruption to the normal anatomical structure and function of a body part.¹ Wounds range in depth from a break in the epithelium of the skin to much deeper wounds, penetrating our subcutaneous tissues. Wounds that penetrate subcutaneous tissue also bare the risk of damaging the following:¹

• Veins
• Tendons
• Muscles
• Nerves
• Some organs
• Bone

The wound recovery process

Wound healing is sadly not a quick, regenerative process. This process involves many different cell populations within the body and the action of soluble mediators, such as growth factors and cytokines. ¹ Wound healing can be divided into four phases:¹

1. Coagulation and haemostasis: this protects the vascular system.¹
2. Inflammation: the immune system plays a role here, creating a protective barrier between the exposed tissue and harmful micro-organisms, which may cause infection.¹
3. Proliferation: this usually occurs at around day 3 of the recovery process, where there is a newly synthesised extracellular matrix that acts as a scaffold for the regeneration of new cells.¹
4. Wound remodelling with scar tissue.¹

What is the role of blood in supporting wound healing?

Blood contains many important substances for our cells, tissues and organs to survive. These substances include nutrients such as oxygen and glucose, which are needed for successful healing.24 Blood also contains white blood cells, which are part of our immune system, and ensure that any harmful micro-organisms that can cause infections in the open wound are destroyed. ²⁴ This is important as the wound’s first line of defence against micro-organisms, the skin, has been compromised.²⁴

The circulatory system and blood flow regulation

The circulatory system consists of the following:

• Heart: The heart is a vital muscular organ of the body, consisting of four chambers. The right atrium and right ventricle are the first two chambers, which receive deoxygenated blood from the body via a vein called the vena cava.²⁵ The right ventricle then pumps deoxygenated blood to the lungs to receive oxygen. The oxygenated blood then enters the pulmonary vein to the other two chambers of the heart: the left atrium and the left ventricle. The left ventricle then pumps blood all around the body, ensuring that all cells from the toes to the head receive the nutrients they need.²⁵
• Blood: Contains the nutrients that cells need to survive, including oxygen and glucose.²⁷ Blood also contains white blood cells, which are responsible for the immune response
• Arteries: Arteries almost always carry oxygenated blood away from the heart, The walls of arteries are thick and muscular, allowing blood to flow at high pressure, ensuring that the oxygenated blood reaches far distances, for example travelling down to the feet.²⁷ 
• Veins: Veins carry deoxygenated blood back to the heart. The veins have thinner walls and are less muscular, meaning that blood flows back to the heart at a lower pressure. The blood flowing in our veins lacks nutrients.²⁷
• Capillaries: Capillaries are the smallest blood vessels in the body and are responsible for nutrient exchange between the circulatory system and our body tissues, ensuring that oxygen and glucose enter our cells for their survival and that toxic waste products, such as urea, are removed.²⁷

Importance of blood vessels in delivering nutrients and oxygen to tissues

Oxygen is transported to tissues around the body via blood flow through blood vessels and is essential for cell metabolism. Blood also removes its waste products, such as carbon dioxide, away from tissues.²⁶ This is an essential function, as cells which do not metabolise will die, and if carbon dioxide is not removed, a wide range of conditions can result:²⁶

• Cushing’s disease
• Metabolic alkalosis
• Kidney failure

Mechanisms of blood flow regulation

Blood flow can be regulated to meet the metabolic needs of the body. Regulation of blood flow can be systemic, affecting the whole circulatory system, or it can target a specific tissue/organ that may require more or less perfusion depending on metabolic needs. This is achieved via contraction or relaxation of the smooth muscle fibres in the walls of arterioles and capillaries.

How blood flow affects wound healing

Oxygen and nutrient delivery to the wound site

Wounds result in damage to the blood vessels and a reduction in the amount of blood, and therefore oxygen and nutrients, that reach a wound.² This can result in hypoxia (reduced oxygen delivery to the wound site) or anoxia (lack of oxygen delivery to the wound site).² The oxygen and nutrients carried to the wound are essential to the healing process, and reduced delivery to the wound site can prolong the healing process, resulting in chronic wound formation.⁵

Removal of waste products and toxins

Blood plays a key role in removing metabolic waste products, such as carbon dioxide, and toxins, such as urea, from body tissues.²⁸ These are then filtered out of the blood by the kidneys.²⁸

Role of white blood cells in infection prevention

Specialized white blood cells known as macrophages play a key role in preventing infection at the wound site. Macrophages are attracted to the wound site approximately 24 hours after the wound is sustained, and once localised, they patrol and destroy any bacteria present in the wound, preventing infection.³ Neutrophils are another type of specialized white blood cell which play a role in infection prevention. Bacteria ingested by macrophages are destroyed by oxygen free radicals that neutrophils generate, thus preventing infection by bacteria.³

Stimulation of cell proliferation and tissue regeneration

Stage three of wound healing is proliferation. Blood plays a key role here as macrophages, specialised white blood cells within the blood, produce a variety of substances that result in tissue regeneration and angiogenesis, which is the formation of new blood vessels.⁴

Impacts of poor blood flow on wound healing

Delayed healing process

Poor blood flow can set back the healing process of wounds. This is due to a lack of oxygen reaching the wound, resulting in a hypoxic wound.⁵ Hypoxic wounds take longer to heal due to oxygen being an important nutrient for metabolism.⁵

Increased risk of infections

Oxygen levels in the blood influence superoxide production.⁵ Superoxide is needed to kill pathogens, which cause infection, via the mechanism of oxidative killing.⁵ Therefore, poor blood flow to the wound results in less oxygen flow, and less superoxide is available to aid in killing harmful micro-organisms.

Formation of chronic wounds

Chronic wounds are defined as wounds which have failed to heal after 12 weeks and form due to the following:⁶

• Diabetes: High levels of blood sugar can increase blood pressure and damage blood vessels, resulting in less blood flow to a wound and a reduction in nutrient availability at the site.⁷
• Poor circulation: Less nutrients reach the wound, required for wound healing.⁷
• Weakened immune system: Higher susceptibility to infection, which can prolong wound healing.⁷
• Mechanical pressure: Those who spend prolonged time lying down or in a wheelchair put pressure on parts of their body, preventing healing.⁷

Potential complications for individuals with circulatory issues

Those with circulatory issues are at risk of developing chronic wounds, which can result in the development of tissue necrosis and gangrene³¹

Enhancing blood flow for improved wound recovery

Physical activity and exercise

There has been reported evidence that exercise induces vasodilation and thus increases blood flow to wounds and damaged tissues.⁸ However, there are conflicting results when it comes to exercise aiding in wound recovery, which makes this a topic for future research.⁸

Importance of a balanced diet

The following nutrients are required for a healthy diet and to promote wound healing:

Protein: protein has a role in repairing body tissues and can be found in meat, fish and poultry, to name a few.⁹

Iron: Iron is required for the production of haemoglobin, which facilitates the transport of oxygen via red blood cells, meaning that iron has a key role in blood oxygenation. Iron can be found in green beans and pulses, as well as vegetables such as broccoli.⁹

Zinc: Zinc is needed for regenerating skin tissue after a wound has been sustained; zinc can be found in foods such as bread, lentils and shellfish.⁹

Vitamin C: Helps with iron absorption, which is needed for blood oxygenation; vitamin C is found in many fruits and vegetables but is broken down during cooking. This can be overcome by steaming the vegetables.⁹ Techniques to improve circulation

Massages cause mechanical pressure on the part of the body being massaged, increasing blood flow to the damaged tissue by increasing blood pressure.¹⁰

Elevating your legs above heart level can increase blood flow to the heart, allowing gravity to assist in blood flow.²⁹

Medical interventions to promote blood flow

Vasodilation increases blood flow; therefore, medications known as vasodilators can be used to promote blood flow.¹¹ Some examples of vasodilating medication are as follows:

• Calcium channel blockers¹²
• Angiotensin-Converting Enzyme (ACE) inhibitors¹¹

Chronic conditions and blood flow's role in healing

Diabetes and its impact on blood circulation and wound healing

As aforementioned,  diabetes can affect blood circulation due to high blood sugar damaging the arteries, resulting in less blood flow to the wound and prolonging healing.⁷ Diabetes can lead to the formation of chronic wounds.

Peripheral artery disease (PAD) and compromised blood flow

PAD can result in a reduction of blood flow due to the narrowing of the arteries in the legs.¹³ Common causes of PAD are atherosclerosis, where a plaque in the arteries causes the arteries to become narrow.¹³

Strategies for managing chronic conditions to support wound recovery

Strategies for diabetic wound recovery include the following:

• Managing blood glucose levels
• Avoiding foods with added sugars and processed carbohydrates
• Increasing fibre intake

Strategies for managing PAD to support wound recovery include the following:

• Regularly exercising
• Quitting smoking
• Taking medication to lower blood pressure
• Having surgery to restore blood flow in severe circumstances

Surgical interventions and blood flow considerations

Importance of blood flow assessment before surgery

Blood flow assessments allow your general health to be assessed before surgery, and they help to assess the risk of complications arising, too. Blood flow in the arteries is assessed using a Doppler probe.

Surgical techniques to minimise blood flow disruption

Surgical techniques to minimise blood flow disruption include the following:

• Medications: coagulation (blood clotting) enhancers and antifibrinolytics ¹⁴
• Permissive hypotension: this lowers blood pressure and blood flow to a certain area of the body¹⁵

Post-operative care to promote optimal blood circulation

The following can be conducted to promote optimal blood circulation after surgery:

• Special support stockings can be worn to help blood circulation and prevent the risk of blood clots developing.³⁰
• Conducting gentle exercise, including leg exercises, to prevent blood clots.³⁰
• Injections to thin the blood and reduce the risk of blood clots.³⁰

Advanced approaches to enhance blood flow in wound healing

Hyperbaric oxygen therapy (HBOT)

HBOT is a therapy where patients breathe in 100% oxygen via a face mask, endotracheal tube or a hood, an increase opposed to the 21% that exists naturally in our atmosphere.¹⁶ Patients enter a  hyperbaric chamber that is pressurized to greater than sea level. HBOT improves the healing in wounds, including chronic wounds.¹⁶

Negative pressure wound therapy (NPWT)

NPWT is a system that aids wound healing by applying sub-atmospheric pressure to a wound to reduce inflammatory exudate, a fluid that has escaped from the blood vessels and has been deposited in bodily tissues. It also promotes the growth of granulation tissue (new connective tissue and blood vessels forming under a scab).¹⁷ NPWT has been used to treat both acute and chronic wounds.¹⁷

Angiogenesis-promoting treatments

Angiogenesis-promoting treatments include the following:

• Insulin increases wound healing time by increasing angiogenesis.¹⁸
• Growth factors: PDGF-BB and VEGF-A^.18
• Epidermal growth factor increases angiogenesis.¹⁸

Future directions and innovations

Emerging technologies for monitoring and improving blood flow in wound care

Monitoring blood flow and oxygen levels in the wound:

One of the crucial purposes of blood flow to a wound is to provide the healing tissue with oxygen.²² New methods to detect oxygen are useful in evaluating the healing wound.²² A 3D smart wound dressing, which can detect oxygen concentrations in the healing wound, has been developed. The bandage, combined with an oxygen sensor, microcontroller and wireless radio, gives direct information on the oxygen concentration during the wound healing process. Oxygen-sensing nanoparticles are also in development, which could be combined with current dressings to detect oxygen levels in the wound.²²

Improving blood flow to the wound:

New electrical stimulation technologies, including electroconductive materials, have been developed and have been shown to improve blood flow to a wound site by promoting angiogenesis.²³

Potential areas for further research and development

Whilst electrostimulation has been utilised and proven to improve blood flow to wound sites, it is not widely distributed in wound care and recovery.²³ Therefore, further research should investigate electrical stimulation as a possible mainstream treatment for wounds that lack blood flow and in wounds where angiogenesis is not stimulated.

Summary

• Blood has a vital role in blood recovery, with nutrients in the blood, such as oxygen, being crucial for cell metabolism
• Angiogenesis, the formation of new blood vessels, is a reported event in wound recovery, highlighting the importance of blood travelling to the wound site
• There are many different current wound treatments that target increasing blood flow, such as negative pressure therapy, angiogenesis-promoting treatments, and hyperbaric oxygen therapy
• Conditions such as diabetes and peripheral artery disease can prolong wound recovery
• When approaching wound care, whilst standard dressings are used, these are being looked at being combined with oxygen-detecting technology to monitor wound recovery
• Electrical stimulation is also being investigated as an angiogenesis-promoting treatment, which can treat wounds that have impaired blood flow, resulting in delayed healing