Intrapleural pressure is more subatmospheric in the uppermost part of the thorax than in the lowermost parts in the standing horse (Figure 2-6).18 Consequently the lung is more distended and therefore less compliant dorsally than ventrally. C. O2 cost of eupneic breathing is normally less than 5% of total body O2 consumption. These small downward movements of the diaphragm are possible because the abdominal viscera can push out against the relatively compliant abdominal wall. III. g. Surfactant is not produced by the fetal lung until approximately the fourth month of gestation and may not be fully functional until the seventh month or later. c. The alveolar fluid lining has a lower surface tension than would be predicted by a plasma-air interface. For example, if the expiratory flow through a piece of apparatus with a high resistance is great enough to induce turbulence, while the inspiratory rate is low (as it often is in horses) so that during inspiration the flow is laminar, the mean intrathoracic pressure will be above atmospheric. The diaphragm is the primary muscle of inspiration. (Levitzky Fig.2-3). An opening in the thoracic cage, combined with the negative intrapleural pressure, allows air to enter the pleural space. Total compliance of the respiratory system (that is, of the lung and the chest wall, which   are in series) is normally about 0.1 L/cm H2O. . Forced breathing is facilitated by a variety of accessory muscles (Table 10-1). . In some cases small amount of air causing partial pneumothorax will reabsorb spontaneously without causing any serious damage. (Remember that linear velocity is inversely proportional to cross-sectional area for any given flow). . . The muscles of expiration are involved in active expiration: exercise, speech, cough, sneeze, forced expiration, etc. d. The alveolar liquid lining surface tension changes with the size of the alveoli: the smaller the area the lower the surface tension. Trapping of gas in the lungs occurs more readily at low lung volumes and gas trapping produces widespread airway obstruction with serious impairment of respiratory function. 11. Pulmonary ventilation is the process of breathing, which is driven by pressure differences between the lungs and the atmosphere. . A. . . Intrapleural pressure is always negative, which acts like a (This increases pulmonary compliance and lowers pulmonary work). Forced vital capacity (FVC); forced expiratory volume in first second (FEV1); forced expiratory flow rate between 25 and 75% of the vital capacity (FEF25 - 75%). Intrapulmonary pressure is the pressure within the lungs. 3. The internal intercostal muscles and the external intercostal muscles are arranged at right angles to each other. After this point contraction of the diaphragm against the fixed central tendon elevates the lower ribs. Relaxation of the inspiratory muscles allows the increased alveolar elastic recoil to decrease the volume of the alveoli, increasing alveolar pressure above atmospheric pressure. . During normal resting respiration, the flow was about 0.3 L s−1. 9. Dynamic compliance = compliance calculated during breath. Expiration during eupneic breathing is passive. We use ρ=1.13 g L−1 and η=19.1×10−6 Pa s=191×10−6 dyne cm−2 s. These conversions use the cgs system, which is often more convenient.First, we calculate ⟨V⟩=10 L s−1/π×(0.9 cm)2=3.93 L s−1 cm−2×1000 cm3 L−1=3.93×103 cm s−1.During peak expiration, the Reynolds number is1.8cm×3.93×103cms−1×1.13gL−1×10−3Lcm−3/191×10−6gcms−2cm−2s=41,851, Example 6.2.2 Calculate the Reynolds Number. . 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