Oxygen supply to the heart occurs through the coronary circulation. Coronary blood flow is determined by vascular resistance, and perfusion pressure, both hemodynamic factors. Vascular resistance on its own is dependent on the anatomy of the vascular tissues and the structure, as well as alterations in diameter of the blood vessels resulting from contraction and relaxation of the smooth muscles of the vascular tissues.
Oxygen delivery to the heart muscles is determined by two factors – coronary blood flow, and concentration of oxygen in the arterial blood.
The units of oxygen delivery are ml O2/min. normally, the concentration of oxygen in the arterial blood is about 20 ml O2/100ml blood, or 20 vol. percent. Coronary blood flow, expressed per 100 grams of tissue weight is about 80ml/min for every 100g of tissue weight at resting heart rates. Hence, oxygen delivery to the heart under resting conditions is about 16ml O2/min per 100 grams of heart tissue.
The concentration of oxygen in the arterial blood is mainly determined by the oxygen that is attached to the haemoglobin in erythrocytes. Just a minimal amount gets dissolved in the plasma. Hence, conditions that alter the red blood cell count, that is, the hematocrit, which is usually 40 percent of the entire blood volume, will equally alter the concentration of oxygen, and subsequently, oxygen supply to the blood tissues. Also, the concentration of haemoglobin within the red blood cells also determines what concentration of oxygen is supplied to the heart by the blood. In the case of anemia for instance, which may be due to a reduced hematocrit or reduced concentration of haemoglobin within the red blood cells, oxygen delivery to the tissues is decreased.
Ordinarily, not much changes takes place in the oxygen content of arterial blood. Therefore, coronary blood flow remains the primary determinant of oxygen delivery in the absence of hypoxemia.
In heart disease, specifically coronary artery disease, so many factors may cause reduction in blood flow, and by extension, oxygen delivery. Stenotic lesions for instance narrows the blood vessel, especially the large epicardial coronary. The stenosis may occur at a special site, or it may diffuse along the length of the vessel. In either case, there is a reduction in coronary flow. Flow is reduced because the fixed stenosis lies in series with the distal micro-circulation. Coronary vessels that are diseased are more susceptible to vasospasm, which may result in a temporary restriction of flow to the coronaries at rest. This may occur during periods of stress or during exercise in individuals that are susceptible. Also, thrombus formation, especially at the site of a ruptured atherosclerotic plaque, can completely or partially block a coronary vessel, resulting in an unstable angina or a myocardial infarction – heart diseases.
The study making waves is that of the relationship between heart disease and photosynthesis. It has been discovered that blue-green algae and light can be used to trigger photosynthesis within the cardiomyocytes to help in the treatment of heart disease.
The idea is that a bacteria is injected into the heart of a mammal with a cardiac disease. With light, photosynthesis is triggered, and oxygen flow to the heart is increases, resulting in an improvement in heart function. What makes this concept tick is that it is a recycling system. While you deliver the bacteria, it traps carbon-dioxide, and with light energy, it forms oxygen. The origin of this mind-boggling concept arises from the need to deliver oxygen to the heart when flow of blood is restricted. This is major feature of cardiac ischemia and is often attributed to coronary artery disease.
Naturally, humans exhale carbon-dioxide, while plants convert it to oxygen. In a heart attack for instance, the heart muscle attempts to pump the blood – there is a large concentration of carbon di-oxide but very little or no oxygen. So the idea is… is there a way that plant cells could be placed next to the cardiomyocytes (heart cells) to generate oxygen from the carbon-dioxide?
In an earlier research, the researchers attempted grinding up kale and spinach, and combining each with cardiac cells in a dish, but the chloroplasts of these plants were so unstable that they could not survive for long outside of the plant cell.
Thereafter, an attempt was made with photosynthetic bacteria, as it has a more rugged structure that can help it adapt to life under water.
Though advances in pharmacology and revascularization techniques have resulted in a decrease in mortality, a great percentage of the survivors are still at risk of and eventually succumb to heart failure. This is secondary to deficit of microvascular perfusion that remains after revascularization.
Our goal is to join other researchers to develop a novel system that delivers the myocardium from ischemia via photosynthesis through intramyocardial delivery of the cyanobacterium Synechococcus elongatus. By substituting blood flow with light as an energy source, photosynthetic therapy increases oxygenation of tissues, maintains metabolism in the myocardium, resulting in lasting improvements in heart function prior to and after ischemia. We believe that by circumventing blood flow to furnish the tissue with nutrients and oxygen, this system can create a paradigm shift in the treatment of ischemic heart disease.
Synechoccus elongatus is a unicellular cyanobacterium that occurs naturally, and enhances photosynthesis across a broad spectrum wavelength. This bacterium has been traditionally used as a research model for the study of circadian rhythms, and also, for the production of CO2-based bio-fuels.
This species can be engineered genetically, to boost its metabolic activity for improved production of glucose and CO2. Based on these astounding characteristics, it is hypothesized that S. elongatus can be used within the body to clear carbon di-oxide and supply essential oxygen to ischemic cardiomyocytes, and potentially, glucose, which is required for metabolic functions in the absence of blood flow.
It is important to note that S. elongatus can cause a balance in an unbalanced ischemic milieu involving glucose, water, and oxygen and carbon di-oxide. This enhances the use of light as a fuel source for the heart cells (cardiomyocytes) while negating the need for revascularization and restoration of perfusion.