Complete diagrams as instructed in the tasks.

Question

 Include proper values on the x & y-axis as well as labeling those. Make sure to label ESV, EDV, aortic and mitral valve opening and closing, and Isovolumetric relaxation and contraction where possible on the diagrams regarding blood volumes and pressure. You also need to make sure to list or provide explanation where necessary or where it is asked in the tasks.

Case Studies Tasks:

1. Sarah was recently diagnosed with an obstructive lung disorder. In their diagnostic process the doctors completed a Forced Vital Capacity test on Sarah to determine her lung function. Based on this, (A) diagram a Vital Capacity test with lung volumes for a healthy individual and on the same graph include the VC test with lung volumes for Sarah's diagnosis. The doctors also found that Sarah's oxygen saturation was at 87%. Therefore, (B) diagram an oxygen saturation curve graph that shows a normal oxygen saturation curve vs. a curve representing Sarah's condition.

Answer 1

For this question, we first have to think about the parameters that are changing with an obstructive lung disorder. When we think of obstructive lung disorders, what is the pathology that is occurring? Often times, there is a loss of elasticity within the lungs that causes air to be unable to escape ("air trapping"). This results in a decreased FEV₁ or FEV (forced expiratory volume) and an increased TLC (total lung capacity) due to air remaining in the lungs after expiration due to the inability to expel the full amount.

Part A

When we look at an air-volume flow loop, this typically results in a left shift of the diagram with a "scooped" appearance upon expiration. This is because there is more air residing in the lungs, causing a left-shift since the X-axis is typically inverted with higher volumes listed on the the left side. The blunting or scooped appearance is seen on expiration as less air is able to escape the lungs.

In the case of lung volumes, this is typically presented as a bar with a higher total volume (higher TLC) with a larger residual volume (increased air remaining due to decreased volume of expiration).

Part B

When we now think about O₂ saturation, we have to think about what's occurring at the level of the alveoli. In an obstructive lung disease, air is remaining trapped within the alveoli. That means there is a higher air pressure within the alveoli. This can result in decreased blood flow through alveolar vessels (think about a large alveoli stretching the capillaries to be thin with higher resistance), leading to a ventilation/perfusion mismatch. Additionally, since the pressure of CO₂ may be higher in the alveoli, there is less of a pressure gradient to drive O₂ diffusion across the alveolar surface area. Other considerations can include the thickness of the alveolar membrane or possible damage, as some obstructive diseases can damage or thicken the diffusion barrier, leading to a poor exchange of gas. Those are the factors that are contributing to the low oxygen saturation in this patient.

So when we think about how the saturation graph may change, the only parameter we're changing is the total amount of oxygen that can bind rather than a property of the hemoglobin itself. The affinity that hemoglobin has for oxygen with be the same, resulting in the same curve shape as a healthy patient, but the total amount will be lower since less oxygen is diffusing into the bloodstream.

Overall Tips and Tricks to Pulmonary Physiology Questions

1. Is the case asking about an obstructive or restrictive process?
2. Which parameters are actually changing?
3. What portion of the graph does each parameter change?