Ventilation Flashcards
(34 cards)
True or False: Ultimately, what is important is the amount of air-flow, which is affected by compliance and resistance.
True
What is ventilation?
Airflow in the lung
What is minute ventilation (VE)?
Volume of air-flow through the lung in one minute Minute ventilation = Tidal Volume (TV) x Breathing Rate
What is average minute ventilation in an adult?
6 L 0.5 L/breath x 12 breaths/min = 6 L
What is alveolar ventilation (VA)?
Volume of air-flow in alveolar space in one minute
What is average alveolar ventilation in an adult?
~4.2 L
True or False: Alveolar ventilation is the most important parameter when considering gas exchange.
True
What are factors that affect alveolar ventilation (VA)?
- Obstructive disease (e.g. COPD) 2. Compliance problems 3. Exercise (ventilation can increase up to 10x) 4. High altitude 5. Gravity (introduces regional variations in ventilation) Note: Generally, total alveolar ventilation (VA) is affected only by severe disease conditions.
How does gravity cause regional variations in ventilation?
Alveoli near the top of the lung are weighted down by the remainder of the lung below it. So, if you have three alveoli, the top one has the greatest volume while the bottom has the smallest volume. The top alveoli is being pulled open by the weight. Vol-top-alveolus is greater than Vol-bottom-alveolus However, counterintuitively, the alveoli closer to the bottom of the lung have more ventilation than the alveoli that are near the top. This is because ventilation depends on the change in volume during breathing. Even though the alveoli near the top have a greater volume, the alveoli near the bottom have a greater change in volume during breathing. Vent-top-alveolus is less than Vent-bottom-alveolus
About how many times more ventilation is there at the bottom of the lung than at the top?
2.5 times. Ventbottom / Venttop = 2.5
How can you use the compliance curve to analyze the difference in ventilation between bottom and top alveoli?
In the diagram, you can see that the bottom alveolus has greater compliance than the top alveolus. The top alveolus is already at a greater volume and is less compliant because there is only so much that you can inflate an alveolus. The bottom alveoli has greater compliance and has a greater change in volume when breathing resulting in greater ventilation.
What are the axis on the compliance curve and what does the slope stand for?
X axis - Transpulmonary pressure
Y axis - Alveolar/Lung volume
Slope - Compliance ( = delta V/ delta P)
True or False: Compliance and resistance problems can also affect HOW we breathe.
True
A 6 L minute ventilation can be achieved by:
Taking 5 breaths/minute with a tidal volume of 1.2 L each.
Taking 30 breaths/minute with a tidal volume of 0.2 L each
Which one of these scenarios would spend more joules of work going against resistance?
Taking 30 breaths/minute with a tidal volume of 0.2 L each would spend more joules of work going against resistance. At lower tidal volumes, the airways are smaller. The smaller radius of the airways results in higher resistances to overcome.
A 6 L minute ventilation can be achieved by:
Taking 5 breaths/minute with a tidal volume of 1.2 L each.
Taking 30 breaths/minute with a tidal volume of 0.2 L each
Which one of these scenarios would spend more joules of work going against elastance?
Taking 5 breaths/minute with a tidal volume of 1.2 L each would spend more joules of work going against elastance. As you reach higher lung volumes, you are getting further and further away from the lung’s resting state and it takes increasingly more work to cause a change (compliance decreases at higher volumes).
Explain this diagram
On the left, you have the work vs. freq-TV curves of a healthy person. You can see that the least total work can be found at about 12 breaths/min at 0.5 L tidal volume per breath. People naturally breathe at a rate that uses least work.
In an obstructive disease, the resistances in the airways are higher across the board. This makes the freq-TV of least total work around 6 breaths/min at 1 L tidal volume per breath. This means that compared to a healthy individual, an individual with bronchitis will be breathing at a slower rate with higher lung volumes. This is to compensate for the obstruction because increasing lung volume will decrease the resistance in the airways. While 6 breaths/min at 1 L tidal volume per breath is the most energy efficient point for a patient with obstructive disease to breathe at, it is still more total work than if the patient was healthy.
True or False: Not all of the ventilated air contributes to gas exchange
True
What is dead-space?
Volume of lung that does not engage in gas exchange
What is anatomical dead-space? How much (%) of total lung volume is anatomical dead-space?
Anatomical dead-space is the airways. This makes up about 30% of the total lung volume and does not engage in gas exchange.
What is alveolar dead-space? Give one example that could cause this
Alveolar dead-space is when an alveolus that normally engages in gas exchange isn’t able to. This can happen if there is an occlusion in pulmonary capillary that’s next to the alveolus (e.g. pulmonary embolism). The alveolus is still ventilated but that ventilation doesn’t participate in useful gas exchange.
What is physiologic dead-space? Why is this important?
Physiological dead-space = Anatomical dead-space + alveolar dead-space
Physiological dead-space is measurable with pulmonary function tests while the individual parameters (anatomical and alveolar dead-space) are not. In real situations, you measure the physiological dead-space, make an assumption about how mcuh anatomical dead-space is present, and then you can make a decent assumption about how much alveolar dead-space is present.
What does deadspace do to efficiency of breathing?
Deadspace reduces the efficiency of breathing since there is more wasted ventilation. This increases the work required to breathe.
The example used in class was that when snorkling, more deliberate breathing is necessary because the snorkel is essentially increasing the airway/anatomical dead-space. You have to breathe in more deliberately to get the ventilation down to the alveoli.
What is total lung capacity?
Total lung capacity: the volume in the lungs at maximal inflation, the sum of VC (vital capacity) and RV (residual volume).
What is vital capacity?
Vital capacity: the volume of air breathed out after the deepest inhalation.
