Flashcards in CBT2 Ventilation and gas exchange Deck (119)
Define Tidal volume (TV or V small T)
The volume of air inspired and expired during regular breathing (i.e. gentle normal breathing not deep breathing)
Define Inspiratory reserve volume (IRV)
The volume of air that can be inspired after a tidal inspiration
Define Expiratory reserve volume (ERV)
The volume of air that can be expired after a tidal expiration
Define Residual volume (RV)
The volume of air that cannot be emptied from the lungs, no matter how hard you expire. This is ﬁxed because of the lung-chest wall interface
How do you calculate the total lung capacity? (TLC)
RV + IRV + TV + ERV
How do you calculate the functional residual capacity (FRC)
RV + IRV. The volume of air in the lungs following a tidal expiration at rest. This capacity represents the “default” volume of the lungs, when the lung recoil (inwards) and chest recoil (outwards) are in equilibrium
How do you calculate inspiratory capacity (IC)
TV + IRV. The maximum volume of air the lungs can draw in from the equilibrium FRC point
How do you calculate vital capacity (VC)
TLC – RV; or, TV + IRV + ERV. The volume of air between the maximum and minimum achievable volumes (range)
What factors affect all the different breathing and lung volumes?
Height is the most influential, but others include:
- developmental exposure to altitude
What does dead space describe? (V small D)
Generic term that describes parts of the airways that do not participate in gas exchange (e.g. conducting and respiratory airways)
What are the three types of dead space?
1) Anatomical dead space
2) Alveolar dead space
3) Physiological dead space
Describe Anatomical dead space
This includes the entirety of the conducting airways and the upper respiratory tract (oral/nasal cavity, pharynx and larynx). This value cannot be measured using standard spirometry. It requires a dilution test with a known volume of inert gas (e.g. helium)
Describe Alveolar dead space
This includes respiratory tissues unable to participate in gas exchange, usually due to an absent or inadequate blood ﬂow. In healthy individuals, this volume is effectively zero
Describe Physiological dead space
This is the sum of anatomical and alveolar dead space volumes
How many generations are there in the conducting zone?
Typically how many ml are there in the anatomical dead space?
150ml in adults at FRC
What are non-perfused parenchyma?
Alveoli without a blood supply
How many generations is the respiratory zone?
How many ml is the respiratory zone in adults? (referred to as alveolar ventilation)
What is the amount of air moving in and out of the lungs per minute referred to?
pulmonary ventilation (V small E)
How is pulmonary ventilation calculated?
TV x breathing frequency
What is the primary function of breathing?
Ventilation of the alveolar tissue
What is alveolar ventilation?
The amount of air per minute reaching the gas exchange surface
How do you calculate alveolar ventilation during tidal breathing?
It is equal to the difference between tidal volume and dead space multiplied by breathing frequency (V small alv = ((VT - VD) x Rf).
Typically, for every generation further down the airway there is a divergence in the path associated with a _____ decrease in the pressure and velocity of airﬂow.
At rest, how are the mechanical forces of the lungs balanced?
How can the balance of mechanical forces be distorted, in order to stimulate ventilation?
Increasing pressure outside of the lung, or decreasing pressure inside the lung
What is positive-pressure breathing?
Increasing pressure outside of the lung (e.g. a patient on a ventilator)
Explain negative-pressure breathing, i.e. inhalation under normal conditions
The respiratory muscles decreases intrathoracic pressure (diaphragm contracts downward towards the abdomen and the external intercostal muscles pull the ribcage outwards and upwards) by creating a partial vacuum; the lung as an elastic expandable tissue stretches to ﬁll the space which sucks air in from the outside the body to normalise the pressure.