Lecture 4 (Test 2) Flashcards
What happens to outside gas when it enters the body?
The body heats and humidifies the gas, displacing some incoming gases.
Humidification introduces a vapor pressure of about 47 mmHg.
What is the PO2 of inspired air after humidification?
150 mmHg for O2 and 0 mmHg for CO2.
These values reflect the gas composition after humidity is added.
What are the typical gas pressures in pulmonary arterial blood?
O2 = 40 mmHg, CO2 = 45 mmHg.
These values are the same as those in deoxygenated systemic venous blood.
What occurs during gas exchange in the lungs?
CO2 levels drop by about 5 mmHg, and O2 levels increase to about 100 mmHg.
The PO2 can be as high as 104 mmHg in healthy individuals.
What does PaO2 of 100 mmHg signify?
It represents systemic arterial blood.
Normal CO2 levels in systemic arterial blood should be about 40 mmHg.
How does aging affect arterial PO2?
Arterial PO2 decreases with age, dropping from about 100 mmHg at age 20 to closer to 80 mmHg by age 90.
Lung function begins to decline around age 20.
What is dead space ventilation?
It refers to the portion of each breath that is not used for gas exchange.
In a 500cc breath, typically 150cc is dead space.
What is anatomical dead space?
The conducting zones of the upper respiratory system.
This includes areas where no gas exchange occurs.
What is alveolar dead space?
Dead space that occurs when ventilated alveoli are not perfused.
An example is ventilation of a lung area affected by a pulmonary embolism.
What does physiologic dead space encompass?
It includes both anatomical and alveolar dead space.
Increased dead space may necessitate higher ventilation rates.
What is the tidal volume (VT) equation?
VT = VD + VA.
VD is dead space ventilation, and VA is alveolar ventilation.
What is minute ventilation?
The total amount of ventilation occurring over a minute.
Calculated as the product of tidal volume and respiratory rate.
What is the calculation for minute alveolar ventilation?
Minute alveolar ventilation = alveolar ventilation per breath x breaths per minute.
For example, 350cc x 12 breaths/min = 4.2 liters/min.
How is total ventilation per minute (VE) calculated?
VE = minute alveolar ventilation + minute dead space ventilation.
Example: 4.2 liters + 1.8 liters = 6 liters/min.
What does VE stand for?
Total minute ventilation, representing expired air.
It includes both dead space and alveolar air.
What is the significance of the first 150cc of an expired breath?
It consists of dead space gas.
The remaining 350cc is a mixture of lung air.
What is the expected alveolar PO2 with normal ventilation and blood flow?
About 104 mmHg.
This reflects the gas exchange efficiency in healthy lungs.
What is the normal minute alveolar ventilation?
4.2 liters per minute
If alveolar ventilation increases, what happens to alveolar PO2?
It should rise
True or False: You can have an alveolar PO2 of 150 mmHg breathing room air.
False
What happens to alveolar PO2 if alveolar ventilation decreases?
It probably goes down
What is the normal alveolar PCO2 with normal ventilation?
40 mmHg
What occurs to alveolar PCO2 with higher-than-normal alveolar ventilation?
It is expected to be lower
What happens to alveolar PCO2 with lower-than-normal alveolar ventilation?
It is expected to be higher
What is the pulmonary capillary pressure (hydrostatic)?
7 mmHg
What is the blood oncotic pressure in the pulmonary circulation?
28 mmHg
What is the interstitial hydrostatic pressure in the lungs?
-8 mmHg
What is the pleural pressure surrounding the lungs?
-5 mmHg
What is the total of all outward forces favoring filtration in the pulmonary capillaries?
29 mmHg
What is the net filtration pressure in the pulmonary capillaries?
1 mmHg
What role do lymphatics play in the lungs?
They suck up excess water
What can compress lymphatics and disrupt their normal function?
High pressure ventilation/positive pressure ventilation
What is a major obstacle to gas exchange in the lungs?
Fluid
What is the normal left atrial pressure?
2 mmHg
What can cause pulmonary edema due to increased left atrial pressure?
Left heart failure
What can decrease colloid osmotic pressure, leading to pulmonary edema?
Too much intravenous fluids or protein starvation
What happens to colloid osmotic pressure in conditions of proteinuria?
It decreases
What is a potential cause of flash pulmonary edema related to airway closure?
Strong inspiratory efforts against a closed airway
What happens to perfusion in the lungs due to gravity?
More blood flow at the lower regions
What is the perfusion pattern in an upright lung?
Continuous at the bottom, pulsatile at the top
Where does the body typically direct ventilation in relation to blood flow?
More ventilation to the base of the lung
What does V/Q stand for?
V stands for Ventilation, Q stands for Perfusion
Ventilation refers to the fresh air coming into the lungs, while perfusion refers to blood flow through the tissue.
What is the average pleural pressure in between breaths?
-5 cmH2O
Pleural pressure varies at different levels of the lung, being more negative at the apex and less negative at the base.
What happens to pleural pressure as you move from the apex to the base of the lung?
Pleural pressure becomes less negative or more positive
This gradient is influenced by gravity and the lung’s position.
At FRC, what is the pleural pressure at the top of the lung?
-8.5 cmH2O
This pressure helps keep alveoli at the top of the lung relatively full.
At FRC, what is the pleural pressure at the base of the lung?
-1.5 cmH2O
This pressure allows for less distension of the alveoli compared to the apex.
What does alveolar compliance refer to?
The ease with which alveoli can fill with air
Compliance is influenced by the volume of air already present in the alveoli.
At FRC, how full are the alveoli at the apex of the lung?
60% full
Compared to only 25% full at the base of the lung.
At FRC, where does most of the fresh air go?
To the base of the lung
This is due to the lower fullness of alveoli at the base compared to the apex.
What is transpulmonary pressure?
The pressure available to distend the alveoli
It is calculated as the difference between alveolar pressure and pleural pressure.
What is the transpulmonary pressure at the base of the lung at FRC?
+1.5 mmHg
This pressure allows alveoli at the base to fill to about 25% of their capacity.
What is the transpulmonary pressure at the top of the lung at FRC?
+8.5 mmHg
This pressure can fill the alveoli at the top of the lung to about 60% of their capacity.
What happens to compliance at the top of the lung as it approaches capacity?
Compliance decreases, resulting in a flattened curve
This indicates that it becomes harder to put more air into the lungs.
What is hysteresis in lung function?
The difference in lung behavior during inspiration and expiration
The lung typically shows more compliance during expiration than inspiration.
What is the pleural pressure at the apex of the lung at residual volume (RV)?
-2.2 cmH2O
This pleural pressure allows for a transpulmonary pressure of +2.2 mmHg at the apex.
What is the pleural pressure at the base of the lung at RV?
+4.8 cmH2O
This results in a negative transpulmonary pressure, indicating the alveoli are nearly empty.
What is the typical fullness of alveoli at the base of the lung at RV?
About 20% of their capacity
Alveoli cannot be completely emptied due to airway collapse.
During an inspired breath at RV, where does the air primarily go?
To the top of the lung
The top of the lung is relatively empty and has open airways, making it easier for air to enter.
What happens to air distribution at RV in the lungs?
Initially, air goes to the top of the lung first because it is relatively empty and the airways are open.
This allows for easier fresh air intake to the top of the lung.
Why is the top of the lung more compliant than the bottom at RV?
The top part of the lung is about 30% full and sits at the bottom of the compliance curve, indicating high compliance.
This means that the tissue at the top can easily expand.
What occurs when transpulmonary pressure increases?
At first, air is directed towards the top of the lung, and as the top fills, it helps open the lower regions.
The connection between alveoli allows for pressure change to affect airflow.
What is a characteristic of the base of the lung regarding compliance (at RV)?
The base of the lung has low compliance and does not accept volume until the top opens up.
At RV, the alveoli at the base may be collapsed.
What is the consequence of being in an upright position regarding blood flow and ventilation?
In an upright position, fresh air is directed to the base of the lung where blood flow is, enhancing gas exchange.
This alignment is crucial for effective ventilation-perfusion matching.
How does general anesthesia affect lung volumes?
General anesthesia can reduce lung volumes due to body position and muscle relaxation.
This can hinder effective ventilation and gas exchange.
What is hypoxic pulmonary vasoconstriction (HPV)?
HPV is the constriction of blood vessels upstream of poorly ventilated alveoli to redirect blood flow to better-ventilated areas.
This mechanism helps optimize gas exchange in the lungs.
What happens to blood vessels in poorly ventilated areas of the lung?
Blood vessels constrict to prevent blood flow to areas where gas exchange is inefficient.
This is in contrast to other vascular beds where low oxygen leads to relaxation.
What is the role of smooth muscle in the lungs?
Smooth muscle in the pulmonary blood vessels and airways helps direct ventilation and perfusion based on oxygen levels.
This allows for adaptive responses to varying conditions in the lungs.
What effect does elevated CO2 have on pulmonary blood flow?
Increased CO2 can also trigger upstream vasoconstriction in poorly ventilated regions.
While hypoxia is the primary trigger, CO2 levels also play a role.
What is the impact of volatile anesthetics on HPV?
Volatile anesthetics can interfere with hypoxic pulmonary vasoconstriction, reducing the body’s ability to manage blood flow.
This can lead to mismatches in ventilation and perfusion during anesthesia.
What happens to airway smooth muscle in response to hyperoxia?
Airway smooth muscle may tighten in response to high PO2, redirecting airflow to better perfused areas.
This is a protective mechanism against dead space ventilation.
What is the consequence of ventilating with 100% O2 for extended periods?
Ventilating with 100% O2 can lead to airway reactivity and difficulty in ventilation due to high PAO2 levels.
This can cause small airways to become overly active.
What is the most important smooth muscle compensation in the lungs?
The most important is hypoxic pulmonary vasoconstriction, which helps maintain effective gas exchange.
Other compensatory mechanisms are secondary to this primary response.
What is the primary mechanism of hypoxic pulmonary vasoconstriction?
Blood vessels constrict upstream to hypoxia in the alveoli.
What happens to CO2 levels when there is a blocked airway?
CO2 levels increase in the alveolar air.
Fill in the blank: The upright Functional Residual Capacity (FRC) is _______.
3L
Fill in the blank: The supine Functional Residual Capacity (FRC) is _______.
2L
What effect does the supine position have on Expiratory Reserve Volume (ERV)?
ERV is reduced.
True or False: Vital Capacity changes when moving from upright to supine position.
False
What happens to Inspiratory Reserve Volume (IRV) when in a supine position?
IRV expands.
What does tidal volume represent during normal breathing?
The volume of air breathed in and out normally.
What is measured during the effort to push out all the air from the lungs?
Expiratory Reserve Volume (ERV).
What is measured when a patient inspires as much air as possible?
Inspiratory Reserve Volume (IRV) or Total Lung Capacity.
What anatomical change occurs when moving from an upright to a supine position?
Abdominal contents push up against the diaphragm.
What can exacerbate the reduction of lung volume in the supine position?
Being top-heavy or obese.
Fill in the blank: The change in lung volumes when moving to supine is primarily due to _______.
Abdominal pressure on the diaphragm.
What happens to the depth of maximal breath effort when changing positions?
It remains the same.
What is the pleural pressure in mmHg? cmH20?
-4 mmHg; -5 cmH20
