A 12 year old male presents with a productive cough and fever that he has had for the past week. When percussing his lower lung fields you note dullness on the right side. If fluid from infection is accumulating in this area of dullness, what is happening to blood flow to that area?
Blood is being shunted away to areas with better ventilation due to arteriolar vasoconstriction in areas with low oxygen content.
What is an elastic structure?
A structure whose volume is directly proportional to pressure differences across a wall.
How do you determine the transmural pressure in a lung?
External surface pressure - internal surface pressure.
How does a positive pressure ventilator put a patient at risk for lung tissue rupture and pneumothorax?
The lung has an elastic limit it reaches with increasing volume (given by the ventilator) and increasing transmural pressure (a result of increasing volume). Beyond that it can no longer stretch and will rupture.
How do you calculate compliance in the pulmonary system? Where does the lung tend to be more and less compliant?
Change in volume/change in transmural pressure. This is the slope of the graph seen below. The lung tends to be more compliant at low volumes and less at higher volumes.
What is hysteresis?
Compliance differs in inflation and deflation
How do the lungs and chest wall interact during breathing as far as overall compliance goes?
The combination of compliance in both structures allows for an intermediate filling volume.
What % vital capacity is filling in the THORAX at rest? What bout in the LUNG? How do these two characteristics work with each other?
How do we get the same transmural pressure whether you are pumping air into a lung or breathing normally?
Transmural pressure = alveolar pressure - pleural pressure. When pumping air, alveolar pressure is greater than pleural and transmural pressure will be positive. When breathing normal, pleural pressure is negative and will still yield a positive transmural pressure.
What are the different pressure gradients indicated in the airway below?
What things are and are not determined by transpulmonary pressures?
Lung volume is, air flow is not. Pressure differences are what determine air flow.
How does lung surfactant increase compliance?
Surfactant coats the alveoli and decreases the surface tension you need overcome in order to expand the alveoli.
Where in the lung does the majority of ventilation take place when standing? When lying down?
At the base. At the apical portion the alveoli are fully expanded and at the top of the compliance curve. The alveoli at the base are still partially contracted, can expand and ventilate. When you lie down gravity has equal effects on the alveoli and the compliance in the lung will be equal in the other fields.
How do you calculate total lung capacity from a spirometry reading? Functional residual capacity (FRC)? Vital capacity (VC) & forced expiratory volume (FEV)?
Two patients present to the clinic with difficulty breathing. One was a smoker and the other has a family history of lung diseases. How do the structural characteristics of the lung in these two patient differ, but contribute to the same symptoms?
The smoker get emphysema which causes remodeling of the lung and increased total lung capacity with decreased ability to expel air. The person with the family history may have cystic fibrosis, which decreases total lung capacity and causes stiffening and decreased ability to expand the lung due to increased elastic recoil.
What opposing forces exist in TLC? FRC? RV?
TLC = balance between maximum inspiratory force from respiratory muscles and the expiratory force from the inward elastic recoil of the lung and chest wall. FRC = the volume where elastic recoil in the lung and in the chest wall are equal and opposite. RV = balance between the maximal expiratory force from the respiratory muscles/inward elastic recoil and the outward-directed elastic recoil of the lung
What is minute ventilation?
TV x breaths/min
What is alveolar ventilation? What is dead space?
(TV - Dead space) x breaths/min. Dead space is the portion of the respiratory system where there is no gas exchange occurring.
What are typical pressures seen in the trachea, pleural cavity and alveoli in the FRC? Inspiration? TLC?
During FRC, you have just expired your tidal volume and are not breathing in, thus there is no pressure difference between the outside and alveoli. During inspiration, you expand you chest, causing a negative pressure in the alveoli and air flows into the lung. During TLC, the lung has expanded to full capacity and consequently pleural pressure is maximized while alveolar and outside pressures are equal to zero.
When we talk about people having increased resistance in their lungs from fibrosis, what part of the lungs are we talking about?
The alveoli. The medium-sized bronchi already have a higher level of resistance. The cross-sectional area of the alveoli allows for low resistance, which is compromised with fibrosis.
At what point in the respiratory cycle is resistance the lowest?
Full inhalation causes an increase in volume and decreased resistance.
What is measured in the curve seen below?
This is a flow vs. volume curve. Flow being measured on the y-axis, volume on the x-axis and the rate of flow measured by the slope of the line.
What happens when you work harder at breathing?
The rate of flow and volume taken in during inspiration increases which causes an increase in the rate of flow and volume expelled during expiration. However, forced expiration reaches a point where the force of the outside pressure actually collapses the alveoli and is no longer efficient.
How does the transmural pressure change from end-inspiration to quiet expiration to forced expiration?
End-inspiration = all alveolar pressures are 0 and pleural pressures are negative. Quiet expiration = alveolar pressures are positive and pleural pressures are less negative. Forced expiration = alveolar and pressures are highly positive.