Section 4 Flashcards
What is the tidal volume (VT), and what does it represent?
Tidal volume (VT) is the volume of air entering or leaving the lung during a single breath. At rest, this is typically around 500 ml.
Define inspiratory reserve volume (IRV) and provide its typical value at rest.
Inspiratory reserve volume (IRV) is the extra volume of air that can be maximally inspired above the resting tidal volume. At rest, this is typically around 3000 ml.
What is inspiratory capacity (IC), and how is it calculated?
Inspiratory capacity (IC) is the maximal volume of air that can be inhaled starting from the end of a normal expiration at rest. It is typically calculated as IC = VT + IRV, with a value of around 3500 ml.
Define expiratory reserve volume (ERV) and provide its typical value at rest.
Expiratory reserve volume (ERV) is the maximal volume of air that can be expelled starting at the end of a typical tidal volume. At rest, this is typically around 1000 ml.
What is residual volume (RV), and how is it indirectly measured?
Residual volume (RV) is the volume of air remaining in the lungs after maximal expiration. It cannot be directly measured by spirometry but is indirectly measured by the inspiration of a tracer gas such as helium, with a typical value of around 1200 ml.
Define Functional Residual Capacity (FRC) and provide its typical value.
Functional Residual Capacity (FRC) is the volume of air in the lungs at the end of normal passive expiration. It is typically around 2200 ml (FRC = ERV + RV).
What is Vital Capacity (VC), and how is it calculated?
Vital Capacity (VC) is the maximum volume of air that can be expelled during a single breath following a maximal inspiration. It is typically around 4500 ml (VC = IRV + VT + ERV).
Define Total Lung Capacity (TLC) and provide its typical value.
Total Lung Capacity (TLC) is the maximum volume of air the lungs can hold. It is typically around 5700 ml (TLC = VC + RV).
What does Forced Expiratory Volume in One Second (FEV1) represent, and how is it expressed?
Forced Expiratory Volume in One Second (FEV1) is similar to TLC but is derived from only the first second of expiratory effort. It is normally expressed as a ratio (FEV1/FVC) or converted to a percentage. At rest, this value is typically around 80%.
What are the two categories of respiratory dysfunction, and how do they differ in terms of lung volumes?
Obstructive Lung Disease: In individuals with obstructive lung disease, the FEV1 is lower, FRC and RV are greater, and VC is smaller compared to a healthy individual. This is due to difficulty exhaling as much air.
Restrictive Lung Disease: Restrictive lung disease is characterized by low lung volumes. While the absolute amount of air that can be exhaled in 1 second (FEV1) is reduced because the lungs are smaller, the proportion of the Forced Vital Capacity (FVC) that can be exhaled (FEV1/FVC) is normal since there is no obstruction to airflow.
VT - Tidal Volume:
Definition: The volume of air entering or leaving the lung during a single breath.
IC - Inspiratory Capacity:
Definition: The maximal volume of air that can be inhaled starting from the end of a normal expiration at rest.
ERV - Expiratory Reserve Volume:
Definition: The maximal volume of air that can be expelled starting at the end of a typical tidal volume.
VC - Vital Capacity:
Definition: The maximum amount of air a person can expel from the lungs after a maximum inhalation. It is equal to the sum of inspiratory reserve volume, tidal volume, and expiratory reserve volume.
IRV - Inspiratory Reserve Volume:
Definition: The extra volume of air that can be maximally inspired above the resting tidal volume.
RV - Residual Volume:
Definition: The volume of air remaining in the lungs after maximal expiration.
FRC - Functional Residual Capacity:
Definition: The volume of air in the lungs at the end of normal passive expiration.
TLC - Total Lung Capacity:
Definition: The maximum volume of air the lungs can hold.
What is more commonly used during pulmonary function testing, expiratory data, or inspiratory data?
Expiratory data is more commonly used during pulmonary function testing.
In a normal person, when does the flow peak during forced expiration, and how does it decrease?
In a normal person, flow peaks around 7 L/s during forced expiration and decreases in a linear fashion.
How does a person with obstructive lung disease differ in terms of flow rates and residual volume compared to a non-diseased person?
A person with obstructive lung disease starts at a higher lung volume, cannot achieve normal peak flow rates, and ends up at a higher residual volume.
What characterizes the flow-volume curve of a person with restrictive lung disease in terms of lung volume and peak flow rates?
A person with restrictive lung disease starts off at a lower lung volume, cannot reach normal peak flow rates, and ends up at a lower residual volume.
What type of curve is seen during forced expiration, and how can flow rate be calculated from this curve?
During forced expiration, the curve seen is a flow-volume curve. Mathematically determining the slope at any given time allows the calculation of flow rate.
Why is expiratory flow more useful in assessing pulmonary function than inspiratory flow?
Expiratory flow is more useful in assessing pulmonary function because the limits on ventilation are during expiration, not inspiration. This is evident in simple experiments where exhaling from total lung capacity to residual volume takes much longer than inhaling from residual volume to total lung capacity.
What is the minute ventilation, and how is it calculated?
The minute ventilation (VE) is the amount of gas breathed in one minute and is calculated by the equation: Tidal Volume (VT) x Respiratory Frequency (f) = Minute Ventilation (VE).
At rest, what is the typical minute ventilation for a person with a tidal volume of 500 ml and a ventilation rate of 12 breaths/minute?
At rest, with a tidal volume of 500 ml and a ventilation rate of 12 breaths/minute, the minute ventilation is 6 L/min.
Why does the minute ventilation not represent the amount of ventilation available for gas exchange?
The minute ventilation does not represent the amount of ventilation available for gas exchange due to anatomical dead space.
Define anatomical dead space and explain its impact on gas exchange.
Anatomical Dead Space is the volume of the airways that represents the inspired gas that is unavailable for exchange with pulmonary capillary blood. About 150 ml of the tidal volume remains in the airways and cannot be used for gas exchange, meaning that only 350 ml of air reaches the alveoli.
Using the formula for minute ventilation, in your opinion, is it better to increase frequency of
breathing or tidal volume in order to increase gas exchange in the alveoli?
As you’ve learned, during inspiration, some of the inspired air remains in the airways and never reaches the alveoli due to the anatomic dead space. The dead space volume has important consequences for alveolar ventilation. If the volume of gas a person breathes in with each breath (the tidal volume) is the same as the volume of the dead space, then the alveolar ventilation must be zero. In other words, all the inspired gas stays in the anatomic dead space.
To have an effective alveolar ventilation (in terms of gas exchange), tidal volume must exceed dead space volume. It would seem, therefore, that the ideal breathing pattern to maximize alveolar minute ventilation is one in which an individual uses a slow deep breathing pattern, when
tidal volume is much greater than dead space volume
What is the condition for ventilation to reach the alveoli, and how does it relate to tidal volume and anatomical dead space?
For ventilation to reach the alveoli, the tidal volume must be greater than the anatomical dead space. In other words, efficient ventilation occurs when tidal volume exceeds the anatomical dead space.
In terms of ventilation efficiency, what is emphasized - the depth of breaths or the speed of ventilation?
Ventilation is more efficient with “deeper” breaths rather than a faster ventilation rate.
What is the work of breathing, and how is it related to normal quiet breathing?
The work of breathing is the energy expended to inhale and exhale a breathing gas. During normal quiet breathing, the inspiratory muscles overcome the elastic recoil of the lung and airway resistance, while expiration is passive using the lung’s recoil.
What percentage of total body energy is typically expended during quiet breathing, and why is it so low?
Less than 3% of total body energy is expended during quiet breathing. This low percentage is due to the lung’s normal compliance and low airway resistance, requiring very little energy.
How are tidal volume and respiratory rate optimized to minimize the work of breathing during quiet breathing?
Tidal volume and respiratory rate are optimized during quiet breathing to minimize the work of breathing.
At lower respiratory rates, how is tidal volume affected, and what is the impact on the work of breathing?
At lower respiratory rates, increasing tidal volume is necessary to maintain alveolar ventilation, leading to the inspiratory muscles working harder and higher elastic work of the lung.
How does increasing respiratory rates affect tidal volume and the work of breathing?
Increasing respiratory rates can reduce tidal volume, reducing elastic work of the lung. However, it increases flow-resistive work of the lung since more air is moved.
Using what you have learned so far regarding the work of breathing and pulmonary diseases, what do you think would happen to tidal volume and respiratory frequency in the case of COPD? What about exercise?
What are the four conditions that increase the work of breathing, and what are the examples associated with each condition?
Decreased Compliance:
Example: Pulmonary fibrosis, where scarring of lung tissues decreases pulmonary compliance, leading to increased work required to expand the lungs.
Increased Resistance:
Example: COPD and asthma, where increased airway resistance requires more work to overcome flow resistance. There is a decrease in respiratory frequency, while tidal volume remains roughly the same.
Decreased Elastic Recoil:
Example: Emphysema, where a decrease in elastic recoil leads to increased work of breathing. Passive expiration alone cannot expel air from the lungs, so expiratory muscles are recruited. There is a decrease in respiratory frequency, while tidal volume remains roughly the same.
Increased Demand for Ventilation:
Example: During exercise, there is an increased need for ventilation, leading to increases in both tidal volume and respiratory rate, thereby increasing the work of breathing.
