Exam 2: 27 Feb Humidity, Gas Exchange, and Lung Function Flashcards
What impact does humidity have on gas mixtures?
Humidity affects the water vapor pressure, which displaces some oxygen and other inspired gases in the total gas mixture.
The vapor pressure in humidified air is about 47 mmHg.
What are the normal pulmonary arterial blood gas levels for PO2 and PCO2?
Normal arterial blood gas levels are PO2 of 40 mmHg and PCO2 of 45 mmHg.
How does age affect arterial PO2 levels?
Older individuals typically have lower arterial PO2 levels compared to younger individuals, with values decreasing from about 100 mmHg in youth to around 80 mmHg at age 90.
What is the concept of dead space ventilation?
Dead space ventilation refers to the portion of inspired air that does not participate in gas exchange, typically the last 150 cc’s of an inspired breath or first 150cc’s of an expired breath.
- The specific calculation for deadspace is 1cc/lb IBW
What is the definition of anatomical dead space?
Anatomical dead space is the volume of the conducting airways where gas exchange does not occur.
- Approimately 150cc’s or 1cc/lb IBW
What is alveolar dead space?
Alveolar dead space occurs when ventilated alveoli are not perfused with blood, preventing gas exchange.
What is minute ventilation?
Minute ventilation is the total volume of air inhaled or exhaled from the lungs in one minute, consisting of both dead space ventilation and alveolar ventilation.
What is the normal minute alveolar ventilation?
Normal minute alveolar ventilation is 4.2 liters per minute.
What is the total minute ventilation for an average individual?
Total minute ventilation is approximately 6 liters per minute.
What is the net filtration pressure in the pulmonary capillaries?
The net filtration pressure in the pulmonary capillaries is 1 mmHg.
- 𝝿cap=28mmHg
- Pcap=7mmHg
- Pisf=-8mmHg
- 𝝿isf=14mmHg
So NFP=14+8+7-28
NFP=1mmHg
How does gravity affect lung perfusion?
Gravity causes more blood flow to the lower regions of the lung, ensuring better ventilation-perfusion matching.
What is hypoxic pulmonary vasoconstriction?
Hypoxic pulmonary vasoconstriction is a process where low oxygen levels (primary) or high CO2 levels (secondary) in the alveoli cause vasoconstriction in upstream pulmonary vessels, redirecting blood flow to better-ventilated areas.
True or False: General anesthetics can interfere with hypoxic pulmonary vasoconstriction.
True
- Volatile anesthetics open K+ channels in vascular smooth muscle beds that lead to vasodilation instead of vasoconstriction.
- This can effectively lead to continued bloodflow to poorly ventilated areas of the lung which can directly compromise gas exchange!
What happens to lung volumes under general anesthesia?
General anesthesia and muscle relaxation can significantly reduce lung volumes, especially in the supine position.
What is the expected PO2 in pulmonary venous blood compared to systemic arterial blood?
Pulmonary venous blood PO2 should be slightly higher (104mmHg) than systemic arterial blood PO2 (100mmHg) due to bronchiolar admixture.
What is the effect of aging on lung function?
Lung function begins to deteriorate around age 20, leading to decreased gas exchange efficiency and increased dead space.
Fill in the blank: The last 150cc of an inspired or the first 150cc of expired breath that is not used for gas exchange is referred to as _______.
[dead space ventilation]
Technically this is 1cc/lb of IBW deadspace but 150cc is the average healty 20yr old number.
What is the significance of the pleural pressure gradient?
The pleural pressure gradient directs fresh air to the base of the lung where blood flow is higher.
What factors can disrupt fluid balance in the lungs?
- Capillary permeability
- Increased blood pressure
- Decreased oncotic pressure
What is the term used to refer to both types of Dead Space in the lung?
Physiologic Dead Space
Physiologic Dead Space includes both anatomical and alveolar dead space.
What is the typical anatomical dead space for a 20-year-old?
150 cc
Anatomical dead space refers to the volume of air that does not participate in gas exchange.
How does age affect alveolar dead space?
Increases with age
Older individuals may have more areas of the lungs that are not functioning optimally.
What is the relationship between health status and alveolar dead space?
More healthy = less alveolar dead space; more unhealthy = more alveolar dead space
Healthy lungs typically have less dead space for gas exchange.
What is the consequence of increasing alveolar dead space?
Increased ventilation needed
More ventilation is required to compensate for areas where gas exchange is not occurring.
What is the tidal volume (Vt) used in the equation discussed?
500 cc
This volume consists of both dead space and alveolar ventilation.
What does the abbreviation V̇A represent?
Alveolar ventilation
V̇A refers to the volume of air entering the alveoli for gas exchange.
What is the normal respiratory rate for a healthy 20-year-old?
12 breaths per minute
This is the expected respiratory frequency for a healthy individual.
Calculate the minute alveolar ventilation for a person taking 12 breaths per minute with an alveolar ventilation of 350 cc per breath.
4.2 liters per minute
This is calculated by multiplying breaths per minute by alveolar ventilation per breath.
What is the normal minute dead space ventilation for a healthy individual?
1.8 liters per minute
This is derived from 150 cc of dead space ventilation multiplied by 12 breaths per minute.
What is the total minute ventilation combining both dead space and alveolar ventilation?
6 liters per minute
This is the sum of minute alveolar ventilation and minute dead space ventilation.
What does the abbreviation V̇E stand for?
Minute total ventilation
This includes all expired air, both from dead space and alveolar ventilation.
At the end of an inspired breath, which gas composition is expelled first?
Dead space gas
The first portion of the expired breath corresponds to the air that was in the dead space.
What is the expected alveolar PO2 with normal ventilation?
About 104 mmHg
This is a typical value when blood flow and ventilation are normal.
What happens to alveolar PO2 if ventilation is increased?
Alveolar PO2 increases
Increased ventilation allows more fresh air to enter the lungs.
What is the normal alveolar PCO2 with normal ventilation?
40 mmHg
This is the expected level of carbon dioxide in the alveoli under normal conditions.
What is the pulmonary capillary pressure typically measured at?
7 mmHg
This value is lower than systemic circulation pressures.
What is the interstitial protein osmotic pressure in the pulmonary circulation?
14 mmHg
This is approximately double what it is in the systemic circulation.
What is the net filtration pressure in the pulmonary capillaries?
1 mmHg
This is a measure of fluid movement out of the capillary into the interstitium.
What role do lymphatics play in the lungs?
They remove excess fluid
Lymphatics help maintain fluid balance in the lungs.
True or False: Fluid in the lungs is beneficial for gas exchange.
False
Excess fluid in the lungs can obstruct gas exchange.
What is the left atrial pressure threshold that can lead to pulmonary edema?
Around 23 mmHg
This pressure can indicate a significant problem in fluid balance.
What is the significance of left atrial pressure in relation to edema formation in the lungs?
Left atrial pressure normally around 2 can rise to about 23 before causing significant problems
This indicates a safety factor for edema formation in the lungs.
What are two major risks that can lead to fluid buildup in the lungs?
- Loss of blood without replacement of colloids
- Left heart failure
These conditions can lead to increased pressures in the lungs and potential edema.
What does the filtration coefficient do in the context of fluid flow in the lungs?
It turns pressure into a fluid flow rate (Q)
Q stands for flow and is influenced by various filtration forces.
What can cause increased capillary permeability leading to pulmonary edema?
- Infections
- ARBs
- Inhaled toxins
- Oxygen toxicity
These factors can lead to protein leakage into the interstitium and fluid buildup.
How does left heart failure contribute to pulmonary edema?
It causes blood to back up in the lungs, increasing pressure and leading to edema
The inability of the left heart to pump effectively results in fluid accumulation.
Fill in the blank: The average pleural pressure in between breaths is _______.
negative five centimeters of water
This is a standard measurement that affects lung mechanics.
How does gravity affect blood flow in the lungs?
Lower regions of the lung receive more blood flow due to greater distension and lower resistance
Blood flow is gravity-dependent, with more perfusion at the lung base.
What happens to alveoli at the top and bottom of the lung during normal breathing (FRC)?
They are typically more full (about 60%) compared to those at the base (about 25%)
This affects where fresh air is directed during inhalation.
What happens to alveoli at the top and bottom of the lung during normal breathing (RV)?
They are typically more full (30%) at the the top compared with the bottom (20%).
- 20% is the lowest that alveolar air can get due to small airways collapsing before more air can be pushed out.
What can cause flash pulmonary edema in a patient with a closed airway?
Generating extremely negative thoracic pressure while trying to inhale
This can occur in young, fit individuals attempting to breathe against an obstruction.
What are some factors that can decrease interstitial hydrostatic pressure?
- Rapid evacuation of pneumothorax
- Closed airway breathing attempts
These actions can create transient changes in pressure that affect fluid dynamics in the lungs.
True or False: High altitude can lead to pulmonary edema.
True
High altitude conditions are associated with fluid retention in the lungs, although the exact mechanisms are not fully understood.
What is the effect of insufficient lymphatic drainage on pulmonary edema?
It can lead to fluid accumulation in the lungs
Conditions such as tumors or scarring can impede lymphatic function.
What is the impact of increased blood pressure on pulmonary edema?
It can exacerbate left heart failure and increase lung pressures
This can lead to fluid leakage into the lungs.
What is the role of alveolar compliance in lung function?
It describes how easily alveoli can expand and fill with air
Higher compliance allows for easier air filling in less full alveoli.
What happens to blood flow and ventilation in the upright lung?
Blood flow is greater at the base, while ventilation is also directed towards areas with more blood flow
This results in an efficient V/Q ratio.
What is the alveolar fullness at the top of the lung at FRC? What about RV?
60% full at FRC and 30% full at RV
What is the alveolar fullness at the base of the lung at FRC?
25% full a FRC and 20% full at RV
- 20% is the lowest an alveoli can be due to small airway collapse
How does gravity affect air distribution in the lungs?
It directs more air to the base of the lung
What is transpulmonary pressure (PTP)?
Alveolar distending pressure
At FRC, what is the transpulmonary pressure at the base of the lung if alveolar pressure is zero and pleural pressure is -1.5?
1.5
What is the transpulmonary pressure at the top of the lung at FRC if pleural pressure is more negative (-8.5)?
8.5
What happens to the compliance of the lung as it approaches capacity?
It decreases, making it harder to add more air
What does a steep slope on the compliance curve indicate?
High compliance
What is the compliance behavior of the lung during inspiration compared to expiration?
What is this phenomenon called?
More compliant during expiration
- Hysteresis
The lung is more compliant on expiration than inspiration because during inspiration, the lung has already had to overcome the initial stretch resistance. Alveoli are now more open and “less stiff.”
What is the pleural pressure at the apex of the lung at RV in a healthy 20-year-old?
-2.2
What is the transpulmonary pressure at the base of the lung at RV if pleural pressure is 4.8?
-4.8
At what capacity do alveoli typically remain when airways collapse?
20%
What is the compliance of the top of the lung when it is 30% full?
High compliance
What happens to the alveoli at the base of the lung at RV?
They are typically collapsed
How does the filling of the top of the lung affect the base of the lung?
It makes the base more prone to accepting volume
All alveoli are connected so pullinf on the upper ones generates force to pull open the lower ones.
What is the result of not having fresh air directed to well-perfused areas of the lung?
Gas exchange is compromised
Fill in the blank: The lungs typically behave differently on _______ compared to _______.
inspiration; expiration
True or False: The airways at the top of the lung are typically collapsed.
False
What does the term ‘compliance’ refer to in the context of lung physiology?
The ease with which the lung expands
What happens to the alveoli during a deep inspiration?
They fill more fully and become more compliant
What happens to lung volumes when a patient is placed in a supine position under general anesthesia?
Lung volumes decrease significantly, often resulting in very low lung volumes due to body position and muscle relaxation.
This is primarily because abdominal contents push against the diaphragm, reducing functional residual capacity (FRC) from about 3 liters in the upright position to about 2 liters in the supine position.
What is the compliance of the top and base of the lungs, especially at RV?
The top of the lung is very compliant, while the base of the lung is not compliant at all.
Increased transpulmonary pressure at the top keeps alveoli distended, while collapsed small airways at the base prevent air from entering.
What is hypoxic pulmonary vasoconstriction?
It is the constriction of blood vessels upstream of poorly ventilated alveoli, redirecting blood flow to better-ventilated areas.
This mechanism is unique to the lungs; in other vascular beds, low oxygen levels typically cause relaxation of blood vessels.
What role does smooth muscle in pulmonary blood vessels play?
It can constrict or relax to determine blood flow through pulmonary capillaries based on the ventilation status of the alveoli.
This allows for better matching of ventilation and perfusion in the lungs.
Fill in the blank: The tendency of airway smooth muscle is to tighten up in response to _______.
hyperoxia
Over time, hyperoxia can cause capillary swiss-cheese, so this is a protective mechanism for the lung.
How does general anesthesia affect the body’s ability to manage pulmonary blood flow?
General anesthetics open potassium channels in vascular smooth muscle, leading to relaxation and potentially allowing blood flow in poorly ventilated areas.
This interferes with the body’s normal compensatory mechanisms for managing ventilation and perfusion.
What happens to alveolar gas composition if blood flow through a capillary is stopped?
The alveolar gas composition will resemble the inspired gas mixture, with PO2 close to 150 and CO2 close to zero.
This occurs because without blood flow, there is no gas exchange happening in that part of the lung.
What is the significance of the compliance in different lung regions?
Compliance varies, affecting how air is distributed; air tends to go to areas with higher compliance.
This is crucial for effective ventilation during different body positions and conditions.
True or False: The alveoli at the top of the lung are typically smaller than those at the base.
False
What is a consequence of using 100% oxygen for an extended period?
It can lead to airway reactivity and potential tightening of small airways, complicating ventilation.
Prolonged exposure to high oxygen levels can cause adverse respiratory effects.
What happens to expiratory reserve volume (ERV) when a person moves from an upright to a supine position?
ERV decreases due to abdominal contents pushing against the diaphragm, involuntarily pushing air out of the lungs.
What is the primary controller of smooth muscle reactivity in the lungs?
Hypoxic pulmonary vasoconstriction is the most important reflex.
Other responses, such as airway tightening or reactions to CO2 levels, are secondary to this mechanism.
What happens to blood vessels in a collapsed part of the lung?
Blood vessels in that area constrict to redirect blood flow to healthier regions of the lung.
This helps maintain blood gas levels and overall lung function.
What occurs when there is a mismatch between ventilation and perfusion?
The body compensates by constricting blood vessels in poorly ventilated areas to optimize gas exchange elsewhere.
What is the expected change in vital capacity when a person transitions from upright to supine?
Trick question: Depending on the weight of abdominal contents, ERV can decrease significantly when moving supine due to some of the usual voluntary air reservoir being involuntarily pushed out.
- When our ERV decreases, our IRV increases so our maxium depth of inspiration isn’t affected.
- VC remains constant.
What happens to the Expiratory Reserve Volume (ERV) when moving into a supine position?
ERV is reduced when moving into a supine position
This reduction occurs because some of the volume that could be expired is involuntarily pushed out.
How does moving into a supine position affect vital capacity?
Vital capacity does not change
The depth of a maximal breath effort remains the same.
What happens to Inspiratory Reserve Volume (IRV) and Expiratory Reserve Volume (ERV) in a supine position?
IRV tends to expand, ERV tends to shrink
This shift occurs due to pressure from the base of the lung on the diaphragm.
What equipment is typically used to measure lung volumes and capacities?
Spirometer
An incentive spirometer is commonly used in pulmonary function labs.
Describe the basic function of a spirometer.
Measures air volume during inspiration and expiration
The device operates by displacing air in an upside-down container, tracing patterns based on air volume.
What does a normal breathing tracing on a spirometer represent?
Tidal volume
This is the volume of air inhaled or exhaled during normal breathing.
What is measured when a patient is instructed to expel all air from their lungs?
Expiratory Reserve Volume (ERV)
This is the additional air that can be forcibly exhaled after a normal expiration.
What is measured when a patient is instructed to inspire as much air as possible?
Inspiratory Reserve Volume (IRV)
This is the additional air that can be inhaled after a normal inspiration.
Fill in the blank: The old spirometer equipment resembled an upside-down _______.
water heater
This design was used to measure air volumes before modern computerized equipment.
What is the total lung capacity?
The maximum amount of air the lungs can hold
This includes all volumes: tidal volume, inspiratory reserve volume, and expiratory reserve volume.
