Lung Mechanics

Surfactant is a substance that is produced in the lungs and helps to reduce surface tension in the alveoli. In infants with IRDS, the production of surfactant is insufficient, leading to high surface tension in the lungs. This high surface tension causes the alveoli to collapse and makes it difficult for the infant to breathe, resulting in breathlessness and cyanosis. By providing artificial surfactant, the surface tension in the lung is decreased, allowing the alveoli to remain open and improving the infant's ability to breathe.

Alveolar surfactant acts to increase pulmonary compliance. Compliance refers to the ability of the lungs to stretch and expand during inhalation. By reducing surface tension within the alveoli, surfactant decreases the forces that work against lung expansion, allowing for easier and more efficient breathing. Therefore, an increase in pulmonary compliance means that the lungs are more flexible and have a higher capacity for expansion.

During forced (maximum) expiration, the contraction of the abdominal muscles plays a crucial role. This contraction increases the intra-abdominal pressure, which helps to push the diaphragm upward and compress the thoracic cavity. As a result, more air is forcefully expelled from the lungs, allowing for a deeper and more complete expiration. In contrast, during normal (quiet) expiration, the diaphragm relaxes and the abdominal muscles are not actively involved in the breathing process. Therefore, the correct answer is forced (maximum) expiration.

To determine the compliance of the patient's chest wall, you need to measure changes in intra pleural pressure (D,Ppl). Compliance is a measure of how easily the chest wall expands and contracts, and it is influenced by changes in intra pleural pressure. By measuring the changes in intra pleural pressure, you can assess the elasticity and flexibility of the chest wall, which will help determine its compliance. Changes in alveolar pressure, airway pressure, alveolar O2-partial pressure, and inspired O2-partial pressure are not directly related to measuring the compliance of the chest wall.

The respiratory system's compliance refers to its ability to stretch or expand. Compliance is highest at the functional residual capacity (FRC), which is the volume of air remaining in the lungs after a normal exhalation. At this point, the lungs are neither fully expanded nor fully deflated, allowing for optimal flexibility and ease of breathing. Therefore, FRC is the lung volume at which the respiratory system has its greatest compliance.

The lung compliance can be calculated by dividing the change in lung volume by the change in lung transmural pressure. In this case, the change in lung volume is 2 L (since the patient inhales 2 L of air) and the change in lung transmural pressure is 5 cm H20 (from +5 cm H20 to +10 cm H20). Therefore, the lung compliance is 2 L / 5 cm H20, which simplifies to 0.4 L / cm H20.

During forced expiration of a large volume (3 L), the pressure in the intra pleural space can become positive (greater than atmospheric pressure). This is because during forced expiration, the diaphragm and other respiratory muscles contract forcefully, causing a rapid decrease in lung volume. This increase in pressure within the lungs can lead to a positive intra pleural pressure, which helps to push air out of the lungs.

1/Crs = 1/Cl + 1/Ccw therefore 1/Crs - 1/Ccw = 1/Cl
1/100 - 1/200 = 1/Cl = 1/200 thererore Cl = 200

A premature baby with difficulty breathing is likely to have a decreased RV (residual volume). This is because the RV is the volume of air remaining in the lungs after a maximum exhalation, and a decreased RV indicates that the baby is not able to fully exhale and clear the lungs properly. This can be a result of underdeveloped lung function in premature babies, leading to difficulty in breathing and inadequate lung ventilation.