January 19, 2016 - SG4 - Dyspnea I

Question 1

Pneumothoraces and Water Seals

Answer 1

This works by running a tube from the patient’s chest into water. When the patient exhales, the pressure in the lungs rises and air is pushed through the tube into the water, creating bubbles. When the patient inhales, the pressure in the lungs drops and water is sucked into the tube, but it weighs more so it doesn’t reach the chest.

This can effectively return a lung to its normal size once the air is removed.

Question 2

Asthma and Inspiratory/Expiratory Flow

Answer 2

During inspiration, the more negative pressure in the lungs will help keep the airways open and allow air to flow in. This inspiratory flow will be slightly reduced (but not as much as expiratory) because of increased mucous, inflammation, and remodelling of the airways, decreasing the radius.

During expiration, the lungs become more positive in terms of pressure, and some of the tubes in the airway will collapse. This increases resistance further, and makes it very difficult to breath out. Expiratory flow will be greatly reduced.

Question 3

Formula for Flow

Answer 3

Flow = (P_mouth - P_pleural) / Resistance

Question 4

Lung Volume with Pulmonary Fibrosis

Answer 4

Lung volume would be smaller because of reduced compliance

Question 5

AA Gradient

Answer 5

AA Gradient = P_AO₂ - P_aO₂

AA Gradient = [FiO₂ (P_atm - P_H2O) - (P_CO2 / 0.8)] - P_aO₂

Question 6

Hypoxemia Scheme

Answer 6

Under High AA Gradient, there should also be a category for diffusion limitation. This would occur when the membrane itself is damaged and gas cannot diffuse across it. This would be seen if carbon monoxide would not diffuse.

Question 7

Loss of Surfactant

Answer 7

Can occur with infection.

Loss of surfactant increases the surface tension in the alveoli and they tend to collapse. Wide-scale collapse of the alveoli is known as atalectasis.

Question 8

Atalectasis

Answer 8

Is the collapse or closure of a lung resulting in reduced or absent gas exchange. This may affect all, or part of a lung and is usually not bilaterial. It is a condition where the alveoli are deflated down to little or no volume.

Question 9

Why O₂ Can Make CO₂ Rise

Answer 9

1. In some patients with severe lung disease, their body has become accustomed to high levels of CO₂. Normally CO₂ creates the drive to breath, but in these patients who chronically have high levels of carbon dioxide, they rely on their hypoxic drive to breath. When you put the patient on supplemental oxygen, their brain does not want to breath anymore, causing CO₂ levels to rise even further and can create dangerous acidemic conditions.
2. Hypoxic vasoconstriction. This is the tendency for pulmonary vessels to constrict in areas of low PaO₂ in an attempt to match ventilation and perfusion. The use of supplemental oxygen may increase bloodflow to diseased areas of the lung, and subsequently drop the pulmonary pressure in good areas of the lung.
3. Deoxygenated blood (reduced hemoglobin) has a greater ability to carry carbon dioxide. Increasing the amount of oxygen in the blood reduces the amount of hemoglobin available for CO₂ binding, thus increasing the dissolved CO₂. This is known as the Haldane Effect.

Question 10

Haldane Effect

Answer 10

Deoxygenated blood (reduced hemoglobin) has a greater ability to carry carbon dioxide. Increasing the amount of oxygen in the blood reduces the amount of hemoglobin available for CO2 binding, thus increasing the dissolved CO2.