Ventilation Flashcards
What is pulmonary ventilation?
The cyclic process of inspiration and expiration.
What happens when the sternocleodomastoid contracts?
They elevate the sternum and clavicle (front)
What happens when the trapezius contracts?
They stabilize and move the scapula (back)
What happens when the scalenes (anterior, middle, posterior) contract?
They elevate the upper ribs
How many time do the airways branch?
23 generations
How many branching points are included in the conducting zone
16 generations
What is an acinus?
Smallest functional unit of the lungs.
It consists of a cluster of alveolar ducts, alveolar sacs and alveoli supplied b a bronchiole.
Typically, tidal volume is about … at rest, but can increase up to … with exercise.
Typically, tidal volume is about 500mL at rest, but can increase up to 3 L or more with exercise.
What is minute ventilation? What is the formula for minute ventilation?
Total amount of air inhaled or exhaled from the lungs in one minute.
VE = f x Vt
What is alveolar ventilation? What is the formula?
The volume of fresh air reaching the respiratory zone (alveoli) per minute.
VA = f x (Vt-Vds)
What is dead space ventilation? What is the formula?
Volume of fresh gas reaching the anatomic dead space per minute (i.e. that does not participate in gas exchange because it occupies areas of the respiratory system where no alveoli are present or where alveoli are not functioning properly).
What is the anatomic dead space?
Volume of inspired gas (~150 mL) that never makes it past the conducting zone and never participates in gas exchange.
What must be the relationship of tidal volume (Vt) relative anatomic dead space volume (Vd) for gas exchange to occur?
Tidal volume must be greater than the volume of the anatomic dead space.
Under what circumstances can the anatomic dead space appear increased?
When increases in minute ventilation are not matched by increases in alveolar ventilation (i.e. minute ventilation increases but alveolar ventilation stays the same).
Under what circumstances can someone have a relatively high minute ventilation, yet a normal or even increased PaCO2?
In certain diseases that dissociate minute ventilation from alveolar ventilation.
In other words, it is possible to hypoventilate DESPITE having a high minute ventilation!
What is physiological dead space?
Total dead space, i.e. volume of inspired gas that does not exchange CO2. It is the sum of anatomic dead space and alveolar dead space
What is alveolar dead space?
When air reaches the alveoli but does not participate in gas exchange (when alveoli become dysfunctional and no longer participate in gas exchange, they contribute to alveolar dead space).
Minute ventilation is the sum of …
dead space ventilation and alveolar ventilation (all expressed in L/minute)
What is a partial pressure?
The pressure that a specific gas in a mixture would exert if that gas alone would occupy the entire volume of the mixture.
The relative amounts of each gas in a mixture are reflected by their…
partial pressures
Partial pressures are exerted in proportion to…
the number of molecules present in the mixture.
What is the sea level atmospheric pressure?
760 mmHg
At body temperature (37°C), what is the water vapour pressure?
47 torr (47 mmHg)
In a humidified gas mixture that is fully saturated with water, what does the partial pressure of water vapour depend on?
Temperature
What are the typical partial pressures of the following gases in alveolar gas?
a) N2
b) O2
c) CO2
d) H2O
a) N2: 573 mmHg
b) O2: 100 mmHg
c) CO2: 40 mmHg
d) H2O: 47 mmHg (water vapour)
What is the purpose of ventilation?
To ensure O2 delivery to the tissues and to remove waste products (CO2) produced by cells.
Minute CO2 ventilation (definition and formula)
Volume of CO2 eliminated from the lungs per minute.
Review the formula!
What is the difference between PA and Pa (convention)?
PA - alveolar pressure
Pa - arterial pressure
What is the alveolar air equation for CO2? How can it be interpreted?
PACO2 ∝ VdotCO2/VdotA
The alveolar partial pressure of CO2 is determined by the rate of CO2 production and alveolar ventilation.
What is hypoventilation? Describe its features
- Alveolar ventilation is lower than normal.
- CO2 accumulates in the alveoli (PACO2 increases)
- Respiratory acidosis (physiological process leading to an excess of acids within the body) - can lead to acidemia (lowered blood pH)
What is hyperventilation? Describe its features
- Alveolar ventilation is higher than normal.
- Excessive loss of CO2 from the alveoli (PACO2 decreases)
- Respiratory alkalosis (physiological process leading to a decrease in acidity on the body) - can lead to alkalemia (elevated blood pH)
Define “eupnea”
Normal, unlabored breathing (ventilation that maintains a normal PaCO2)
Define “hypercapnia”
High arterial PCO2 (usually due to alveolar hypoventilation)
Define “hypocapnia”
Low arterial PCO2 (usually due to hyperventilation)
Why is the PACO2 so similar to PaCO2?
Because CO2 is very soluble
What is the major metabolic buffering system in the blood?
Bicarbonate (HCO3-)
Processes that alter [H+] that don’t involve the lungs are termed…
metabolic (rather than respiratory)
What regulates the level of blood HCO3-?
Kidneys - however, kidneys are slow so changes in HCO3- occur relatively slowly compared to CO2.
What is metabolic alkalosis? How does it differ from respiratory akalosis?
Metabolic alkalosis: increased [HCO3-]
Respiratory alkalosis: decreased [H+]
Metabolic alkalosis is due to issues with kidney function!
What is metabolic acidosis? How does it differ from respiratory acidosis?
Metabolic acidosis: decreased [HCO3-]
Respiratory acidosis: increased [H+]
Metabolic acidosis is due to issues with kidney function!
Understand the difference between:
“-osis”
“-emia”
“-osis” is a physiological process
“-emia” is a blood value
What is the formula for acid-base balance?
[H+][HCO3-] = 24 x PaCO2
What are the 4 types of acid-base disturbances?
- respiratory acidosis
- metabolic acidosis
- respiratory alkalosis
- metabolic alkalosis
What compensates for respiratory acidosis?
Metabolic compensation
*review
If the compensatory mechanisms stop working, what happens?
respiratory acidemia, metabolic acidemia, respiratory alkalemia, metabolic alkalemia
How does the intrapleural pressure differ at the top compared to the bottom of the top of the lungs?
?
When you are standing up, most of the air goes…
What influences the distribution of inhaled gas?
What types of diseases increase respiratory workload, forcing the respiratory muscles to work harder?
- asthma, COPD (increased resistance)
- lung fibrosis (decreased compliance)
- kyphoscoliosis (deformed chest wall)
What is respiratory failure?
When the respiratory system is unable to keep up and cannot accomplish its function of of gas exchange.
What are the two types of respiratory failure?
