lung – легкое
tidal – вдыхаемый и выдыхаемый
inspired – вдохновленный
breath – дыхание
human – человек
residual – oстаточный
helium – гелий
dilution – растворение
techniques – методы
the conducting – проведение
30. Ventilation
Total ventilation (VT, minute ventilation) is the total gas flow into the lungs per minute. It is equal to the tidal volume (VT) x the respiratory rate (n). Total ventilation is the sum of dead space ventilation and alveolar ventilation.
Anatomic dead space is equivalent to the volume of the conducting airways (150 mL in normal individuals), i. e., the trachea and bronchi up to and including the terminal bronchioles. Gas exchange does not occur here. Physiologic dead space is the volume of the respiratory tract that does not participate in gas exchange. It includes the anatomic dead space and partially functional or nonfunctional alveoli (e. g., because of a pulmonan embolus preventing blood supply to a region of alveoli). In normal individuals, anatomic and physiologic dead space are approximately equal. Physiologic dead space can greatly exceed anatomic dead space in individuals with lung disease.
Dead space ventilation is the gas flow into dead space per minute. Alveolar ventilation is the gas flow entering functional alveoli per minute.
Alveolar ventilation: It is the single most important parameter of lung function. It cannot be measured directly. It must be adequate for removal of the CO2 produced by tissue metabolism whereas the partial pressure of inspired O2 is 150 mmHg, the partial pressure of O2 in the alveoli is typically 100 mmHg because of the displacement of O2 with CO2. PAo2 cannot be measured directly.
total – общее количество
ventilation – вентиляция
flow – поток
per minute – в минуту
equal – равный
airways – воздушные пути
exchange – обмен
tract – трактат
to be measured – быть измеренным
directly – непосредственно
displacement – смещение
Air moves from areas of higher pressure to areas of lower pres sure just as fluids do. A pressure gradient needs to be established to move air.
Alveolar pressure becomes less than atmospheric pressure when the muscles of inspiration enlarge the chest cavity, thus lowering the intrathoracic pressure. Intrapleural pressure decreases, causing expansion of the alveoli and reduction of intra-alveolar pressure. The pressure gradient between the atmosphere and the alveoli drives air into the airways. The opposite occurs with expiration.
Air travels in the conducting airways via bulk flow (mL/min). Bulk flow may be turbulent or laminar, depending on its velocity. Velocity represents the speed of movement of a single particle in the bulk flow. At high velocities, the flow may be turbulent. At lower velocities transitional flow is likely to occur. At still lower velocities, flow may be laminar (streamlined). Reynold's number predicts the air flow. The higher the number, the more likely the air will be turbulent. The velocity of particle movement slows as air moves deeper into the lungs because of the enormous increase in cross-sectional area due to branching. Diffusion is the primary mechanism by which gas moves between terminal bronchioles and alveoli (the respiratory zone).
Airway resistance: The pressure difference necessary to produce gas flow is directly related to the resistance caused by friction at the airway walls. Medium-sized airways (› 2 mm diameter) are the major site of airway resistance. Small airways have a high individual resistance. However, their total resistance is much less because resistances in parallel add as reciprocals.
Factors affecting airway resistance: Bronchocon-striction (increased resistance) can be caused by parasympathetic stimulation, histamine (immediate hyper-sensitivity reaction), slow-reacting substance of anaphylaxis (SRS-A = leukotrienes C4, D4, E4; mediator of asthma), and irritants. Bronchodilation (decreased resistance) can be caused by sympathetic stimulation (via beta-2 receptors). Lung volume also affects airway resistance. High lung volumes lower airway resistance because the surrounding lung parenchyma pulls airways open by radial traction. Low lung volumes lead to increased airway resistance because there is less traction on the airways. At very low lung volumes, bronchioles may collapse. The viscosity or density of inspired gases can affect airway resistance. The density of gas increases with deep sea diving, leading to increased resistance and work of breathing. Low-density gases like helium can lower airway resistance During a forced expiration, the airways are compressed by increased intrathoracic pressure. Regardless of how forceful the expiratory effort is, the flow rate plateaus and cannot be exceeded. Therefore, the air flow is effort-independent; the collapse of the airways is called dynamic compression. Whereas this phenomenon is seen only upon forced expiration in normal subjects, this limited flow can be seen during normal expiration in patients with lung diseases where there is increased resistance (e. g., asthma) or increased compliance (e. g., emphysema).
intrapleural – внутриплевральный
intra-alveolar – внутриальвеолярный
collapse – коллапс
viscosity – вязкость
density – плотность
32. Mechanics of breathing
Muscles of respiration: inspiration is always an active process. The following muscles are involved: The diaphragm is the most important muscle of inspiration. It is convex at rest, and flattens during contraction, thus elongating the thoracic cavity. Contraction of the external intercostals lifts the rib cage upward and outward, expanding the thoracic cavity. These muscles are more important for deep inhalations. Accessory muscles of inspiration, including the scalene (elevate the first two ribs) and sternocleidomastoid (elevate the sternum) muscles, are not active during quiet breathing, but become more important in exercise. Expiration is normally a passive process. The lung and chest wall are elastic and naturally return to their resting positions after being actively expanded during inspiration. Expiratory muscles are used during exercise, forced expiration and certain disease states. Abdominal muscles (rectus abdominis, internal and external obliques, and transversus abdominis) increase intra-abdominal pressure, which pushes the diaphragm up, forcing air out of the lungs. The internal intercostal muscles pull the ribs downward and inward, decreasing the thoracic volume. Elastic properties of the lungs: the lungs collapse if force is not applied to expand them. Elastin in the alveolar walls aids the passive deflation of the lungs. Collagen within the pulmonary interstitium resists further expansion at high lung volumes. Compliance is defined as the change in volume per unit change in pressure (AV/AP). In vivo, compliance is measured by esophageal balloon pres sure vs. lung volume at many points during inspiration and expiration. Each measurement is made after the pressure and volume have equilibrated and so this is called static compliance. The compliance is the slope of the pressure-volume curve. Several observations can be made from the pressure-volumecurve.
Note that the pressure-volume relationship is different with deflation than with inflation of air (hysteresis). The compliance of the lungs is greater (the lungs are more distensible) in the middle volume and pressure ranges.
The equation for oxygen is:
QO2 = CO х 1,34 (ml/g) х [Hg] Ч SaO2 + 0,003 (ml/ml per mm Hg) х РаО2,
where QO2 is oxygen delivery (ml/min), CO is cardiac output (L/min). Hg is hemoglobin concentration (g/L), SaO2 is the fraction of hemoglobin saturated with oxygen, and PaO2 is the partial pressure of the oxygen dissolved in plasma and is trivial compare to the amount of oxygen carried by hemoglobin. Examination of this equation reveals that increasing hemoglobin concentration and increasing cardiac output can enhance oxygen delivery. Saturation is normally greater than 92 % and usually is easily maintained through supplemental oxygen and mechanical ventilation. Cardiac output is supported be insuring adequate fluid resuscitation (cardiac preload) and manipulating contractility and after load pharmacologically (usually cat-echolamines).
Equation – уравнение
Delivery – доставка
Cardiac output – сердечный выброс
Fraction – фракция
Contractility – сократимость
33. Surface tension forces
In a liquid, the proximity of adjacent molecules results large, intermolecular, attractive (Van der Waals) forces that serve to stabilize the liquid. The liquid-air surface produces inequality of forces that are strong on the liquid side and weak on the gas side because of the greater distance between molecules in the gas phase. Surface tension causes the surface to maintain as small an area as possible. In alveoli, the result a spherically-curved, liquid lining layer that tends to be pulled inward toward the center of curvature of the alveolus. The spherical surface of the alveolar liquid lining behaves in manner similar to a soap bubble. The inner and outer surface of a bubble exert an inward force that creates a greater pressure inside than outside the bubble. Interconnected alveoli of different sizes could lead to collapse of smaller alveoli (atelectasis) into larger alveoli, because of surface tension, the pressure inside the small alveolus (smaller radius of curvature) is greater than that of the larger alveolus. Without surfactant, gas would therefore move from smaller to larger alveoli, eventually producing or giant alveolus.
Pulmonary surfactant: Pulmonary surfactant is a phospholipid (comprised primarily of dipalmitoyl phosphatidylcholine) synthesized by type II alveolar epithelial cells. Surfactant reduces surface tension, thereby preventing the collapse of small alveoli. Surfactant increases the compliance of the lung and reduces the work of breathing.
Surfactant keeps the alveoli dry because alveolar collapse tends to draw fluid into the alveolar space. Surfactant can be produced in the fetus as early as gestational week 24, but is synthesized most abundantly by the 35 th week of gestation. Neonatal respiratory distress syndrome can occur with premature infants, and results in areas of atelectasis, filling of alveoli with transudate, reduced lung compliance, and V/Q mismatch leading to hypoxia and CO2 retention.
surface tension forces – поверхностные силы напряжения
liquid – жидкость
proximity – близость
adjacent – смежный
intermolecular – межмолекулярный
to stabilize – стабилизироваться
surface – поверхность
distance – расстояние
phase – фаза
tension – напряжение
spherically-curved – сферически-кривой
lining – выравнивание
inward – внутрь
toward – к
curvature – искривление
spherical – сферическийsoap bubble – мыльный пузырь
inner – внутренний
to exert – проявить
interconnected – связанный
34. The nose
The respiratory system permits the exchange of oxygen and carbon dioxide between air and blood by providing a thin cellular membrane deep in the lung that separates capillary blood from alveolar air. The system is divided into a conduct ing portion (nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles) that carries the gases during inspiration and expiration, and a respiratory portion (alveoli) that provides for gas exchange between air and blood.
The nose contains the paired nasal cavities separated by the nasal septum. Anteriorly, each cavity opens to the outside at a nostril (naris), and posteriorly, each cavity opens into the nasopharynx. Each cavity contains a vestibule, a respiratory area, and an olfactory area, and each cavity communicates with the paranasal sinuses.
Vestibule is located behind the nares and is continuous with the skin.
Epithelium is composed of stratified squamous cells that are similar to the contiguous skin.
Hairs and glands that extend into the underlying connective tissue constitute the first barrier to foreign particles entering the respiratory tract.
Posteriorly, the vestibular epithelium becomes pseudo-stratified, ciliated, and columnar with goblet cells (respiratory epithelium).
Respiratory area is the major portion of the nasal cavity.
Mucosa is composed of a pseudostratified, ciliated, columnar epithelium with numerous goblet cells and a subjacent fibrous lamina propria that contains mixed mucous and serous glands.
Mucus produced by the goblet cells and the glands is carried toward the pharynx by ciliary motion.
The lateral wall of each nasal cavity contains three bony pro jections, the conchae, which increase the surface area and pro mote warming of the inspired air. This region is richly vascularized and innervated.
Olfactory area is located superiorly and posteriorly in each of the nasal cavities.
The pseudostratified epithelium is composed of bipolar neurons (olfactory cells), supporting cells, brush cells, and basalcells. The receptor portions of the bipolar neurons are modified dendrites with long, nonmotile cilia.
Under the epithelium, Bowman's glands produce serous fluid, which dissolves odorous substances.
Paranasal sinuses are cavities in the frontal, maxillary, ethmoid and sphenoid bones' that communicate with the nasal cavities.
The respiratory epithelium is similar to that of the nasal cavi ties except that it is thinner.
Numerous goblet cells produce mucus, which drains to the nasal passages. Few glands are found in the thin lamina propria.
respiratory system – дыхательный аппарат
oxygen – кислород
carbon – углерод
dioxide – диоксид
nasal cavity – носовая впадина
pharynx – зев
larynx – гортань
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