Basic Pulmonary Physiology Flashcards
What are the muscles of inspiration?
Normal inspiration: Diaphragm, all scalenes, external intercostals
Deep inspiration: Sternocleidomastoid
Maximal effort: large back muscles, paravertebral muscles, shoulder girdle muscles, and pectoralis muscles
Muscles of expiration?
Normal expiration:
Passive
Abdominal muscles and internal intercostals
(Think that the internal intercostals are lowering your ribs and collapsing your rib cage to force air out)
Lung volumes
Inspiratory capacity: TV + inspiratory reserve volume
Vital capacity: Expiratory reserve volume + TV + inspiratory reserve volume
Total lung capacity: Residual volume + Expiratory reserve volume + TV + inspiratory reserve volume
Functional residual capacity: Expiratory reserve volume + residual volume
REMEMBER: capacities are just multiple volumes added onto another
4 volumes and 4 capacities
What is the functional residual capacity? What is happening in your body at that point?
FRC is the expiratory residual volume + Residual volume
At this point the natural tendency for your lungs to collapse and your chest to outwardly expand are matched and airflow is at a stand still.
Airway resistance is primarily due to …
Conducting airways (90%)
What is the reynold’s number?
Large conducting airways: flow tends to be turbulent
-Turbulance is greatest near branching points in the airway and any deformities
The balance between laminar and turbulent flow is described by the reynold’s number.
-What you need to know is higher the density of the gas and faster the flow the more likely flow will be turbulant (usually reynold’s number >2000)
What does Poiseuille’s law explain?
Helps describe resistance or change of pressure within airways or blood vessels of certain radi.
Pressure drops by the fourth power as the radius drops, increases with increased length, viscosity and with flow rate
During which types of breaths would you get the most positive and negative pressures generated within the lungs?
Positive: to reach residual volume, you would use abdominal muscles and inspiratory intercostals to generate positive pressure and expel air
Negative: to reach total lung capacity you need to use interscalenes, external intercostals, back muscles to open the chest cavity and generate negative pressure to cause air to move in.
What is the effect of volatiles at MAC of 1, opioids at sedating doses and barbs at anesthesic doses on CO2 responsiveness? Meaning your ventilatory response?
Opioids and barbs: same responsiveness per unit change in CO2 but requires a higher CO2 level for the same ventilation.
Volatiles: Less response to a given rise in CO2 and is severely blunted.
What happens to dead space in a healthy individual when you put them on mechanical ventilation?
Normal circumstances: 1/3 of of TV is dead space.
PPV: increases to 50% of TV to dead space. Alveolar pressure is now positive and areas whre alveolar pressure is greater than perfusion pressure has increased.
Which venous systems contribute to anatomic shunts? What are the pathologic causes?
Anatomic meaning they are not pathologic - empty directly into the Left atrium bypassing the lungs
-Thebsian, bronchiolar and pleural veins
Pathologic:
- Intracardic lesions
- Pulmonary edema
- Pneumonia
- Atelectasis
How do you calculate the shunt fraction?
You use the VQI:
= (1-SaO2)/(1-SmvO2)
SaO2 is the saturation of arterial blood with oxygen (obtained with ABG)
AmvO2 is the mixed venous O2 saturation as it returns to the right side of the heart
At which shunt percentage would supplemental oxygen not expect to increase the PaO2 by 10 mmHg?
At 30% you get very little increase but at 40% shunt raising the FiO2 from 21% to 100% will have almost no effect on PaO2
What is venous admixture?
Venous admixture is the result of shunted blood mixing with oxygenated blood.
If someone has a forced vital capacity of 90% predicted, what does that tell us about restrictive vs obstructive lung disease?
They do not have restrictive lung disease. Even in mild restrictive lung disease, you have <80% predicted.
They could still have obstructive lung disease, likely not severe though.
