Our heart provides blood supply in our organism via two simultaneous mechanisms. Systemic circuit brings oxygenated blood to all organs and tissues, removing carbon dioxide from them at the same time. Pulmonary circuit is responsible for delivering blood from heart to lungs – this mechanism enriches blood with oxygen and “cleans” it of carbon dioxide. A great mystery of our life is how enormous volumes of blood tend to get oxygen-enriched in lungs within very short periods of time. Little is known about blood microcirculation in lungs.

Russian biologists introduced photo camera inside a living rat’s chest and made panoramic images of lungs in operation. Blood microcirculation in lungs is a very hard thing to study. Vascular network of brain, liver, muscles and other organs can be examined by a microscope in the form of cross sections. There’s no way of doing this to lungs – when removed from a chest, vascular network of lungs immediately deteriorates due to extreme dependence of lung tissue on pressure. Only one solution to this problem exists – observing lungs in their natural state: inside a chest.

Researchers inserted a microscope’s tube through a tiny hole (in order not to disturb natural pressure in lungs) inside rat’s chest. The animal was sleeping under anesthesia and didn’t feel any discomfort. The tube was inserted in such a way it touched lung’s surface. The experiment resulted in panoramic images of 10-15 alveoli with 3-4 hundred magnification, as well as a close-up with 6-8 hundred magnification.

What researchers wanted to understand is how blood gets inside alveoli, how relatively small lungs “pump” 5-6 liters of blood per minute, and how such a large volume of blood gets rich in oxygen in only 1 minute.

 

 

Alveoli, looking like bubbles, are smallest structural “units” of lungs. They accumulate oxygen, when we inhale. After that, during lung ventilation process blood takes oxygen from alveoli and gives them carbon dioxide in return.

Physiology textbooks say that alveoli are surrounded by a dense network of capillaries, however, Russian researchers didn’t find any signs of capillary circulation inside them. Images they got demonstrate that alveoli were arranged in parallel rows. Quite large compared to capillaries micro-vessels (20-30 nanometers in diameter) start in a pulmonary artery and run between alveoli. Peculiar feature of pulmonary circulation is that a pulmonary artery is the only artery of any mammalian organism, which is full of depleted in oxygen venous blood. In other arteries blood is rich in this essential gas. Blood from micro-vessels enters alveoli, washes them and gets saturated with oxygen, and after that returns to micro-vessels. Blood moves so fast, that researchers fail to distinguish individual cells. Total volume of micro-vessels is about one third of a lung’s volume, which explains extremely high “discharge capacity” of this organ.

Since alveoli have extremely thin walls – about 0.2 micron – oxygen easily spreads from these “bubbles” to blood and has enough time to enrich all blood volume, passing through lungs. Researchers expect more interesting information to be obtained from image processing.