Введение
Принцип, применяемый к измерению кровотока в органе – закон диффузии. Принцип Фика утверждает, что кровоток в органе можно рассчитать, используя маркерное вещество, если известна следующая информация: количество маркерного вещества, потребляемое органом за единицу времени; концентрация маркерного вещества в артериальной крови, поступающей к органу; концентрация маркерного вещества в венозной крови, оттекающей от органа. Разработанный Адольфом Эугеном Фиком (1829–1901), принцип Фика применяется для измерения сердечного выброса. Его основополагающие принципы также могут применяться в различных клинических ситуациях. В оригинальном методе Фика «органом» являлся весь человеческий организм, а маркерным веществом – кислород. Первое опубликованное упоминание содержится в материалах конференции от 9 июля 1870 года, представляющих собой доклад, который он представил на этой конференции; именно эта публикация чаще всего цитируется в научных статьях при упоминании вклада Фика. Принцип может быть применен различными способами. Например, если известен кровоток к органу, а также артериальная и венозная концентрации маркерного вещества, то можно рассчитать потребление маркерного вещества органом.
the diffusion law
The Fick principle states that blood flow to an organ can be calculated using a marker substance if the following information is known:
Amount of marker substance taken up by the organ per unit time
Concentration of marker substance in arterial blood supplying the organ
Concentration of marker substance in venous blood leaving the organ
Developed by Adolf Eugen Fick (1829–1901), the Fick principle has been applied to the measurement of cardiac output. Its underlying principles may also be applied in a variety of clinical situations. In Fick's original method, the "organ" was the entire human body and the marker substance was oxygen. The first published mention was in conference proceedings from July 9, 1870 from a lecture he gave at that conference; it is this publishing that is most often used by articles to cite Fick's contribution. The principle may be applied in different ways. For example, if the blood flow to an organ is known, together with the arterial and venous concentrations of the marker substance, the uptake of marker substance by the organ may then be calculated.
Предполагаемое определение Fick
В действительности, этот метод используется редко из-за сложности сбора и анализа концентраций газа. Однако, используя предполагаемое значение потребления кислорода, можно достаточно точно оценить сердечный выброс без сложного и длительного измерения потребления кислорода. Это иногда называют расчетом Фика на основе предполагаемых данных. Обычно используемое значение потребления кислорода в состоянии покоя составляет 125 мл O2 в минуту на квадратный метр площади поверхности тела.
Основные принципы
Принцип Фика основан на наблюдении, что общее потребление (или выделение) вещества периферическими тканями равно произведению кровотока к периферическим тканям и разнице артериально-венозной концентрации (градиенту) этого вещества. При определении сердечного выброса веществом, которое чаще всего измеряют, является содержание кислорода в крови, что позволяет определить артериовенозную разницу в содержании кислорода, а рассчитываемый кровоток – кровоток через легочную систему. Это дает простой способ расчета сердечного выброса: при условии отсутствия внутрисердечного шунта, легочный кровоток равен системному кровотоку. Измерение содержания кислорода в артериальной и венозной крови включает взятие образцов крови из легочной артерии (с низким содержанием кислорода) и из легочной вены (с высоким содержанием кислорода). На практике, взятие образца периферической артериальной крови используется в качестве суррогата для легочной венозной крови. Определение потребления кислорода периферическими тканями является более сложной задачей. Расчет артериальной и венозной концентрации кислорода в крови – это простой процесс. Почти весь кислород в крови связан с молекулами гемоглобина в эритроцитах. Измерение содержания гемоглобина в крови и процента его насыщения (насыщенность крови кислородом) – простой и легкодоступный для врачей процесс. Используя тот факт, что каждый грамм гемоглобина может переносить 1,34 О2, содержание кислорода в крови (артериальной или венозной) можно оценить по следующей формуле:
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
При концентрации гемоглобина 15 и насыщении кислородом 99%, концентрация кислорода в артериальной крови составляет приблизительно 200 О2 на литр.
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
Насыщение смешанной венозной крови в норме составляет около 75%. Используя это значение в вышеуказанном уравнении, концентрация кислорода в смешанной венозной крови составляет приблизительно 150 О2 на литр.
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
Следовательно, при предполагаемом определении по Фику, приблизительный сердечный выброс для среднего мужчины (1,9 м3) равен:
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
Сердечный выброс = (125 О2/минуту × 1,9) / (200 О2/л − 150 О2/л) = 4,75
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
Сердечный выброс также можно оценить с помощью принципа Фика, используя продукцию углекислого газа в качестве маркерного вещества.
Assuming there is no intracardiac shunt, the pulmonary blood flow equals the systemic blood flow. Measurement of the arterial and venous oxygen content of blood involves the sampling of blood from the pulmonary artery (low oxygen content) and from the pulmonary vein (high oxygen content). In practice, sampling of peripheral arterial blood is a surrogate for pulmonary venous blood. Determination of the oxygen consumption of the peripheral tissues is more complex. The calculation of the arterial and venous oxygen concentration of the blood is a straightforward process. Almost all oxygen in the blood is bound to hemoglobin molecules in the red blood cells. Measuring the content of hemoglobin in the blood and the percentage of saturation of hemoglobin (the oxygen saturation of the blood) is a simple process and is readily available to physicians. Using the fact that each gram of hemoglobin can carry 1.34 of O2, the oxygen content of the blood (either arterial or venous) can be estimated by the following formula:
Assuming a hemoglobin concentration of 15 and an oxygen saturation of 99%, the oxygen concentration of arterial blood is approximately 200 of O2 per L.
The saturation of mixed venous blood is approximately 75% in health. Using this value in the above equation, the oxygen concentration of mixed venous blood is approximately 150 of O2 per L.
Therefore, using the assumed Fick determination, the approximated cardiac output for an average man (1.9 m3) is:
Cardiac Output = (125 O2/minute × 1.9) / (200 O2/L − 150 O2/L) = 4.75
Cardiac output may also be estimated with the Fick principle using production of carbon dioxide as a marker substance.
Применение в физиологии почек
Принцип также может быть использован в физиологии почек для расчета почечного кровотока. В этом случае измеряется не кислород, а маркер, например, пара-аминогиппурат. Однако принципы остаются в сущности теми же.