- Tidal volume
- Normal, quiet breathing involves inspiration and expiration of a tidal volume (VT).
- Normal tidal volume is approximately 500 mL(MCQ)
- tidal volume includes the volume of air that fills the alveoli plus the volume of air that fills the airways.(MCQ)
- inspiratory reserve volume
- The subject is asked to take a maximal inspiration, followed by a maximal expiration
- The additional volume that can be inspired above tidal volume is called the inspiratory reserve volume(MCQ)
- approximately3000 mL(MCQ)
- expiratory reserve volume
- The additional volume that can be expired below tidal volume is called the expira- tory reserve volume
- approximately1200 mL.(MCQ)
- residual volume
- The volume of gas remaining in the lungs after a maximal forced expiration is the residual volume (RV),
- It is approximately 1200 mL(MCQ)
- It cannot be measured by spirometry (MCQ)
- inspiratory capacity (IC)
- composed of the tidal volume plus the inspiratory reserve volume
- approximately3500 mL (500 mL +3000 mL). (MCQ)
- functional residual capacity (FRC
- composed of the expiratory reserve volume (ERV) plus the residual volume
- it is approximately 2400 mL (1200 mL +1200 mL). (MCQ)
- FRC is the volume remaining in the lungs after a normal tidal volume is expired
- It is the equilibrium volume of the lungs.
- Vital capacity (VC)
- composed of the inspiratory capacity plus the expiratory reserve volume
- it is approximately 4700 mL (3500 mL +1200 mL)(MCQ)
- Vital capacity
- volume that can be expired after maximal inspiration
- Its value increases with (MCQ)
- body size
- male gender,
- physical conditioning
- Its value decreases with age(MCQ)
- Total lung capacity (TLC)
- includes all of the lung volumes
- It is the vital capacity plus the residual volume,(MCQ)
- It is 5900 mL (4700 mL +1200 mL).(MCQ)
- What are the lung capacities that cannot be measured by spirometry ?
- Since residual volume cannot be measured by spirometry, lung capacities that include the residual volume also cannot be measured by spirometry
- FRC and TLC cannot be measured (MCQ)
- the volume remaining in the lungs after a normal expiration
- it is the resting or equilibrium volume of the lungs.(MCQ)
- There are two methods used to measure FRC (MCQ)
- helium dilution method
- Dead space
- volume of the airways and lungs that does not participate in gas exchange.
- Anatomic Dead Space
- The anatomic dead space is the volume of the con- ducting airways, including the nose (and/or mouth), trachea, bronchi, and bronchioles.
- It does not include the respiratory bronchioles and alveoli.(MCQ)
- The volume of the conducting airways is approximately 150 mL(MCQ)
- To sample alveolar air, one must sample end-expiratory air(MCQ)
- Physiologic Dead Space
- Physiologic dead space includes the anatomic dead space of the conducting airways plus a functional dead space in the alveoli.
- The functional dead space can be thought of as ventilated alveoli that do not participate in gas exchange.
- The most important reason that alveoli do not partici- pate in gas exchange is a mismatch of ventilation and perfusion,
- In normal persons, the physiologic dead space is nearly equal to the anatomic dead space.
- The ratio of physiologic dead space to tidal volume provides an estimate of how much ventilation is “wasted” (either in the conducting airways or in nonperfused alveoli).
- Partial pressure of CO2 (PCO2) of mixed expired air (PECO2)
- Used to estimate volume of the physiologic dead space(MCQ)
- based on three assumptions:
- All of the CO2 in expired air comes from exchange of CO2 in functioning (ventilated and perfused) alveoli
- there is essentially no CO2 in inspired air
- thephysiologic dead space (non- functioning alveoli and airways) neither exchanges nor contributes any CO2.
- If physiologic dead space is zero, then PECO2 will be equal to alveolar PCO2 (PACO2).
- if a physiologic dead space is present, then PECO2 will be “diluted” by dead space air and PECO2 will be less than PACO2 by a dilution factor. (MCQ)
- Therefore, by comparingPECO2 with PACO2, the dilution factor (i.e., volume of the physiologic dead space) can be measured.
- Why is PCO2 of systemic arterial blood (PaCO2) is equal to the PCO2 of alveolar air (PACO2).
- Alveolar air cannot be sampled directly.
- Alveolar air normally equilibrates with pulmonary capillary blood (which becomes systemic arterial blood).
- Volume of physiologic dead space is calculated by the following equation:(MCQ)
- VD = Physiologic dead space (mL)
- VT =Tidal volume (mL)
- PaCO2 = PCO2 of arterial blood (mm Hg)
- PECO2 = PCO2 of mixed expired air (mm Hg)
- In words, the equation states that the volume of the physiologic dead space is the tidal volume (volume inspired with a single breath) multiplied by a fraction.
- The fraction represents the dilution of alveolar PCO2 by dead space air (which contributes no CO2).
- Ventilation rate is the volume of air moved into and out of the lungs per unit time.
- Minute ventilation
- total rate of air movement into and out of the lungs
- Minute ventilation = VT x Breaths/min(MCQ)
- Alveolar ventilation,
- corrects for the physiologic dead space. (MCQ)
ALVEOLAR VENTILATION EQUATION
- There is inverse relationshipbetween alveolar ventilation and alveolar PCO2 (PACO2).(MCQ)
- The alveolar ventilation equation is expressed as follows:
- ifCO2 production is constant, then PACO2 is determined by alveolar ventilation.
- For a constant level of CO2 production, there is a hyperbolic relationship between PACO2 and alveolar ventilation.
- Increases in alveolar ventilation cause a decrease in PACO2
- Decreases in alveolar ventilation cause an increase in PACO2.
- ifCO2 productiondoubles (e.g., during strenuous exercise), the hyperbolic relationshipbetweenPACO2 and alveolar ventilation shiftstothe right(MCQ)
- Under these conditions, the only way to maintainPACO2 atitsnormalvalue(approximately40mmHg) is for alveolar ventilation to double also.
- ifCO2 production increases from 200 mL/min to 400 mL/min, PACO2 is maintained at 40 mm Hg if, simultaneously, alveolar ventilation increases from 5 L/min to 10 L/min.
- FORCED EXPIRATORY VOLUMES
- Vital capacity
- volume that can be expired following a maximal inspiration(MCQ)
- Forced vital capacity (FVC)
- total volume of air that can be forcibly expired after a maximal inspiration,
- volume of air that can be forcibly expired in the first second is called
- Normally, the entire vital capacity can be forcibly expired in 3 seconds, so there is no need for “FEV4.”(MCQ)
- in a normal person, FEV1/FVC is approximately 0.8(MCQ)
- 80% of the vital capacity can be expired in the first second of forced expiration
- In a patient with an obstructive lung disease such as asthma(MCQ)
- both FVC and FEV1 are decreased
- FEV1 is decreased more than FVC
- FEV1/FVC is also decreased,
- In a patient with a restrictive lung disease such as fibrosis(MCQ)
- both FVC and FEV1 are decreased
- FEV1 is decreased less than FVC is.
- Thus, in fibrosis, FEV1/ FVC is actually increased
- Vital capacity
How does Lung Volume Change?
Learn about how muscle contraction and lung recoil actually help the lungs change their volume with every breath! Rishi is a pediatric infectious disease physician and works at Khan Academy.
Lung Volume Measurements
Disclaimer: the information in this video only represents the knowledge and property of the video’s authors- no one else. The information in this video is for entertainment / educational purposes only. Please visit your healthcare provider for any medical advice!
Pulmonary Function Tests (PFT): Lesson 3 – Lung Volumes
The methods of measuring lung volumes (e.g. helium dilution, nitrogen washout, body plethysmography), and a discussion of how the total lung capacity affects PFT interpretation, particularly the diagnosis of restrictive lung disease.
Respiratory Physiology: Spirometry, lung volumes and capacities
Introduction to spirometry, the four different lung volumes, and the four lung capacities.
Lung Volume Testing by Plethysmography
What happens when you come for a Lung Volume Test
Lung Volume reduction surgery