Week 1 Flashcards
Using Henry’s Law, explain why a solution stored under 1 atm of Nitrogen, with a concentration of Oxygen identical to that in air, might continue to increase in O2 concentration when suddenly exposed to air?
According to Henry’s Law: Cg = K * Pg The concentration of a gas (Cg) dissolved in a liquid is dependent on its solubility coefficient (K—ie a proportionality constant representing the solubility of the gas in the solvent) and the partial pressure (Pg) of the gas above it. If the solubility coefficient is high enough, the solvent may continue to dissolve O2, even when the concentration in the solvent is equal to, or above the concentration in air. It will continue to do so until the partial pressure in the solvent is equal to the partial pressure of O2 in air. Put another way, a higher K requires a higher concentration of dissolved gas to match a particular partial pressure (Cg/K = Pg). Lecture: 150 Gas Laws (Mechanics 1) Objective: 6. Explain why gases diffuse down a partial pressure gradient, NOT necessarily down a concentration gradient.
A new respiratory virus is discovered that enters type II pneumocytes and prevents them from forming lamellar bodies. What symptoms might one expect as a result of infection by this virus?
Type II pneumocytes, via their lamellar bodies, excrete surfactant that coats the inner surface of the alveolae and reduce the surface tension. Without surfactant alveolae would collapse more easily leading symptoms similar to neonatal respiratory distress syndrome, including coughing, shortness of breath, pursing of the lips to increase upstream pressure and decrease the tendency for alveolar collapse. Surfactant also aids the immune system in capturing and recognizing pathogens, so secondary infections might also be likely. Lecture: 151 Lung Anatomy and Histology Objective: 3. Describe the histological components of lung stroma and pulmonary lobules and how they relate to lung function.
What effect does decreased chest wall compliance have on functional residual capacity and intrapleural pressure?
Decreased chest wall compliance means that the chest wall resists the inward pull of the lungs resulting in an increased FRC and a more negative intrapleural pressure. Lecture: 152, Mechanics II Objective: 2. How do changes in lung and chest wall compliances affect FRC and intrapleural pressure?
Pulmonary embolism increases what type of dead space?
A pulmonary embolism does not increase the size of airway where gas exchange doesn’t occur so it doesn’t increase anatomical dead space. However it can decrease or completely stop perfusion of the alveolae thus increasing alveolar dead space. As physiologic dead space = anatomical + alveolar dead space, pulmonary embolism can also increase physiologic dead space. Lecture: 155 Ventilation Objective: 2. What are the differences between alveolar and physiologic dead space?
In order to study gas exchange in mice with fibrotic pulmonary disease you measure oxygen levels in pulmonary capillary blood. You find that the PcO2 = 0.8*PAO2. Is gas exchange in these mice, diffusion or perfusion limited?
A PcX that is less than the PAX of a gas indicates a diffusion limited process. Gas exchange is perfusion limited if the PAX = PcX.
In other words because the gas diffuses rapidly, thereby equilibrating the partial pressure between an alveolus and the associated capillary, gas exchange is not limited by the rate of diffusion.
Lecture: 156 Diffusion and Gas Transport Objective: 3. Explain the factors determining whether alveolar-capillary gas exchange is “perfusion” or “diffusion” limited and the implications of each for gas transport.
Neurons responsible for generating inspiratory rhythm are found in what region of the central nervous system?
Neurons in the preBotzinger complex (preBotc) are responsible for generating the inspiratory rhythm. The preBotc can be found in the ventral respiratory column (VRC) of the ventrolateral medulla.
Lecture: 157 Control of Breathing Objective: 1. Be able to recite the names and anatomical locations of the major groups of neurons within the medulla and pons regulating breathing.
A patient visits your clinic complaining of shortness of breath. They have an increased rate of breathing and upon performing an arterial blood gas, you learn that they are normocapnic but markedly hypoxemic. Upon placing them on 90% O2 you see little improvement to their PaO2, they remain hypoxemic. What is the most likely cause of their hypoxia?
A. Diffusion Impairment
B. Shunt
C. Hypoventilation
D. V/Q Inequality
E. Ambient Hypoxia
B. Shunt
Normocapnia (normal PaCO2 levels) with hypoxemia that is refractory to increased FIO2 is likely sdue to a capillary shunt. The increased breathing rate is sufficient to increase alveolar ventilation to non-collapsed lung regions thereby lowering Pc’CO2 (end-capillary PCO2) in these regions. When blood from these regions mixes with the shunted blood (with a PcCO2 that is the same as in mixed venous blood) the resulting PaCO2 is normal. However, the associated increase in Pc’O2 in ventilated portions of the lung does not significantly increase the end-capillary O2 content (remember the oxygen-Hb dissociation curve is fairly flat at PO2 > 60 mmHg). Hence, when this blood mixes with the shunted blood with low O2 content in the pulmonary veins the O2 content and associated PO2 are low.
Lecture: 158 Causes of Hypoxemia Objective: 2. Explain why some causes of hypoxemia are refractory and others are responsive to oxygen therapy.
How do metabolic and respiratory acidosis differ in terms of PCO2, pH and [HCO3-]?
Metabolic acidosis is caused by increase in a fixed acid (eg lactic acid) or decrease in base. Thus in metabolic acidosis there is a sharp decrease in [HCO3-] as the primary cause of acidosis. This is the result of either an increase in fixed acid (which results in H+ + HCO3- –> CO2 + H2O shifting to the right), or a decrease in HCO3- which shifts the same reaction to the left with an increase in [H+].
In respiratory acidosis, hypoventilation leads to an increase in PCO2 resulting in increases in both [HCO3-] and [H+] and a decrease in the pH. In short low pH but high bicarb is usually respiratory. Low pH with low bicarb is usually metabolic.
Lecture: 159 Acid-Base Balance Objective: 5. Given values for arterial PCO2, pH and [HCO3-], be able to distinguish primary respiratory and metabolic acid base disorders.
What four causes of hypoxemia result in an increased A – a O2 difference?
- Shunt (VA/Q = 0)
- Decreased VA/Q
- Diffusion limitation
- Decreased MvO2 / SvO2 (if present with #s 1-3)
Lecture: 160 Hypoxemia Objective: List common causes of hypoxemia and separate those that elevate A – a and those that do not
A patient in your service who began recovering from sepsis approximately 5 days ago develops progressive hypoxemia. Her chest x-ray is shown below. She has no clinical evidence of elevated lef-sided filling pressures. What is the most likely diagnosis?
The chest x-ray shows bilateral alveolar opacities, which together with sepsis in the previous week, likely indicates acute respiratory distress syndrome (ARDS)
Lecture: 160 Hypoxemia
Objective: 4. Describe the subset of patients with acute hypoxemic respiratory failure
What effect does increasing VA have on PaCO2?
VA and PaCO2 are inversely related so an increase in alveolar ventilation at a constant VCO2 results in a decrease in PaCO2.
Remember: PaCO2=(V ̇CO2×863 mmHg)/(VA)
Lecture: 162 Ventilation Disorders
Objective: 1. Derive the PaCO2 equation
