How oximeters work:
First, the cardiovascular system (cardio-heart, vascular-blood vessel). The blood flows into the heart, out of the heart into the lungs (left and right simultaneously), out the lungs back into the heart, out of the heart and into the rest of the body (upper and lower simultaneously), out of the rest of the body into the heart again, out of the heart.... The circulatory system comprises, therefore, the pulmonary circuit and the systemic circuit. Blood flows into the lungs to be oxygenated and carbon dioxide to be removed. Oxygen is taken up by the hemoglobin in the red blood cells. The systemic circuit carries blood around the body to deliver the oxygen and returns de-oxygenated blood to the heart. Blood also carries nutrients and waste. The amount of blood pumped per minute (cardiac output) = heart rate times stroke volume. The heart has four chambers, two atria, two ventricles. the atria collect the blood and the ventricles pump it out of the heart. Valves prevent the blood from flowing backwards.The atrium on the right side of the heart collects deoxygenated blood from the body and the ventricle on the right side of the heart pumps it to the lungs to pick up oxygen. The atrium on the left side of the heart collects oxygenated blood from the lungs and the ventricle on the left side of the heart pumps it around the rest of the body.So the blood flows into the right atrium, then into the right ventricle, then into the lungs, then into the left atrium, then into the left ventricle, then into the body, then into then into the right atrium again. It flows into the right atrium from two pathways, from lower body and from upper body. And it flows into the left atrium from two pathways, from the left lung and from the right lung.
A person who is anemic due to reduced hemoglobin in their blood could get a normal reading (95% or higher) with a pulse oximeter because what hemoglobin they have is saturated with oxygen, but the bottom line is that their body tissues still would not be getting enough oxygen delivered to them.
The blood vessels are the pathways the blood takes. The arteries which flow away from the left ventricles of the heart carry oxygen to the capillaries (found in muscles). There gas exchange takes places (the gases are oxygen and carbon dioxide). Oxygen passes through the capillary walls into the tissue and carbon dioxide passes through the capillary walls into the blood. The capillaries are only one cell thick. Blood pressure is very low. Capillaries are also found in the lungs. Arteries have thick muscular walls, veins have thin walls. Arteries carry blood under high pressure, veins under low pressure. veins have valves to prevent blood flowing backwards.
Blood comprises: red blood cells (made in the bone marrow, contain haemoglobin which carries oxygen - the more exercise you do, the more red blood cells are made), white blood cells (make antibodies and destroy harmful micro-organisms - white blood cells are also made in the bone marrow), platelets (clump together to form clots, protects the body by stopping bleeding), plasma (fluid part of the blood, carries carbon dioxide, waste and hormones).
Pulse oximeters measure how much of the haemoglobin in blood is carrying oxygen (oxygen saturation). Oxygen is carried in our blood is by means of haemoglobin. Haemoglobin is a molecule, a protein, that is found inside a red blood cell. You can imagine haemoglobin molecules( Hb) as “cars” and the “roads” being our blood vessels e.g. veins, arteries (veins carry oxygen to heart, arteries away from heart). The haemoglobin without oxygen we will call de- oxygenated haemoglobin (deoxy Hb). The haemoglobin with oxygen, we will call oxygenated haemoglobin (oxy Hb). Oxygen saturation simply refers to the percentage of the available hemoglobin that carries oxygen. If there are 16 hemoglobin units and none of the 16 have oxygen, the oxygen saturation is 0 %. If 8 of the 16 Hb have oxygen, the oxygen saturation is 50 %. So oxygen saturation tells you the percentage of the total haemoglobin that is carrying oxygen.
Pulse oximetry uses light to work out oxygen saturation. If a finger is placed in between the light source and the light detector, the light will now have to pass through the finger to reach the detector. Part of the light will be absorbed by the finger and the part not absorbed reaches the light detector. The amount of light that is absorbed by the finger depends on many physical properties and these properties are used by the pulse oximeter to calculate the oxygen saturation. The amount of light absorbed depends on the following:
1. concentration of the light absorbing substance.
2. length of the light path in the absorbing substance
3. oxyhaemoglobin and deoxyhaemoglobin absorbs red and infrared light differently
Physical property one: Hemoglobin (Hb) absorbs light. The amount of light absorbed is proportional to the concentration of Hb in the blood vessel (the channel e.g. artery or vein). Each single Hb absorbs some of the light, so more the Hb per unit area, more is the light is absorbed. This property is described in a law in physics called “Beer’s Law”.
Physical property two. Amount of light absorbed is proportional to the length of the light path. So it depends on how wide the artery or vein is. The light travels in a shorter path in the narrow artery and travels through a longer path in the wider artery. Though the concentration of Hb is the same in both arteries, the light meets more Hb in the wider artery, since it travels in a longer path. Therefore, longer the path the light has to travel, more is the light absorbed. This property is described in a law in physics called “Lambert’s Law”.
Physical property No.3 : oxyhaemoglobin absorbs more infrared light than red light & deoxyhemoglobin absorbs more red light than infrared light.The pulse oximeter uses two lights to analyze hemoglobin. One is a red light, which has a wavelength of approximately 650 nm. The other is an infrared light, which has a wavelength of 950 nm.oxy Hb absorbs more infrared light than red light.
The pulse oximeter works out the oxygen saturation by comparing how much red light and infra red light is absorbed by the blood.
First, the cardiovascular system (cardio-heart, vascular-blood vessel). The blood flows into the heart, out of the heart into the lungs (left and right simultaneously), out the lungs back into the heart, out of the heart and into the rest of the body (upper and lower simultaneously), out of the rest of the body into the heart again, out of the heart.... The circulatory system comprises, therefore, the pulmonary circuit and the systemic circuit. Blood flows into the lungs to be oxygenated and carbon dioxide to be removed. Oxygen is taken up by the hemoglobin in the red blood cells. The systemic circuit carries blood around the body to deliver the oxygen and returns de-oxygenated blood to the heart. Blood also carries nutrients and waste. The amount of blood pumped per minute (cardiac output) = heart rate times stroke volume. The heart has four chambers, two atria, two ventricles. the atria collect the blood and the ventricles pump it out of the heart. Valves prevent the blood from flowing backwards.The atrium on the right side of the heart collects deoxygenated blood from the body and the ventricle on the right side of the heart pumps it to the lungs to pick up oxygen. The atrium on the left side of the heart collects oxygenated blood from the lungs and the ventricle on the left side of the heart pumps it around the rest of the body.So the blood flows into the right atrium, then into the right ventricle, then into the lungs, then into the left atrium, then into the left ventricle, then into the body, then into then into the right atrium again. It flows into the right atrium from two pathways, from lower body and from upper body. And it flows into the left atrium from two pathways, from the left lung and from the right lung.
A person who is anemic due to reduced hemoglobin in their blood could get a normal reading (95% or higher) with a pulse oximeter because what hemoglobin they have is saturated with oxygen, but the bottom line is that their body tissues still would not be getting enough oxygen delivered to them.
The blood vessels are the pathways the blood takes. The arteries which flow away from the left ventricles of the heart carry oxygen to the capillaries (found in muscles). There gas exchange takes places (the gases are oxygen and carbon dioxide). Oxygen passes through the capillary walls into the tissue and carbon dioxide passes through the capillary walls into the blood. The capillaries are only one cell thick. Blood pressure is very low. Capillaries are also found in the lungs. Arteries have thick muscular walls, veins have thin walls. Arteries carry blood under high pressure, veins under low pressure. veins have valves to prevent blood flowing backwards.
Blood comprises: red blood cells (made in the bone marrow, contain haemoglobin which carries oxygen - the more exercise you do, the more red blood cells are made), white blood cells (make antibodies and destroy harmful micro-organisms - white blood cells are also made in the bone marrow), platelets (clump together to form clots, protects the body by stopping bleeding), plasma (fluid part of the blood, carries carbon dioxide, waste and hormones).
Pulse oximeters measure how much of the haemoglobin in blood is carrying oxygen (oxygen saturation). Oxygen is carried in our blood is by means of haemoglobin. Haemoglobin is a molecule, a protein, that is found inside a red blood cell. You can imagine haemoglobin molecules( Hb) as “cars” and the “roads” being our blood vessels e.g. veins, arteries (veins carry oxygen to heart, arteries away from heart). The haemoglobin without oxygen we will call de- oxygenated haemoglobin (deoxy Hb). The haemoglobin with oxygen, we will call oxygenated haemoglobin (oxy Hb). Oxygen saturation simply refers to the percentage of the available hemoglobin that carries oxygen. If there are 16 hemoglobin units and none of the 16 have oxygen, the oxygen saturation is 0 %. If 8 of the 16 Hb have oxygen, the oxygen saturation is 50 %. So oxygen saturation tells you the percentage of the total haemoglobin that is carrying oxygen.
Pulse oximetry uses light to work out oxygen saturation. If a finger is placed in between the light source and the light detector, the light will now have to pass through the finger to reach the detector. Part of the light will be absorbed by the finger and the part not absorbed reaches the light detector. The amount of light that is absorbed by the finger depends on many physical properties and these properties are used by the pulse oximeter to calculate the oxygen saturation. The amount of light absorbed depends on the following:
1. concentration of the light absorbing substance.
2. length of the light path in the absorbing substance
3. oxyhaemoglobin and deoxyhaemoglobin absorbs red and infrared light differently
Physical property one: Hemoglobin (Hb) absorbs light. The amount of light absorbed is proportional to the concentration of Hb in the blood vessel (the channel e.g. artery or vein). Each single Hb absorbs some of the light, so more the Hb per unit area, more is the light is absorbed. This property is described in a law in physics called “Beer’s Law”.
Physical property two. Amount of light absorbed is proportional to the length of the light path. So it depends on how wide the artery or vein is. The light travels in a shorter path in the narrow artery and travels through a longer path in the wider artery. Though the concentration of Hb is the same in both arteries, the light meets more Hb in the wider artery, since it travels in a longer path. Therefore, longer the path the light has to travel, more is the light absorbed. This property is described in a law in physics called “Lambert’s Law”.
Physical property No.3 : oxyhaemoglobin absorbs more infrared light than red light & deoxyhemoglobin absorbs more red light than infrared light.The pulse oximeter uses two lights to analyze hemoglobin. One is a red light, which has a wavelength of approximately 650 nm. The other is an infrared light, which has a wavelength of 950 nm.oxy Hb absorbs more infrared light than red light.
The pulse oximeter works out the oxygen saturation by comparing how much red light and infra red light is absorbed by the blood.