lung volumes & alveolar ventilation Flashcards
Define the term ‘tidal volume’
- the air inhaled and exhaled in normal respiration in one breath
What amount of air (**in ml*) is the tidal volume?
500ml is inhaled and 500ml is exhaled
Define** inspiratory reverse volume** (IRV)
- the amount of air** in excess of tidal inspiration** that can be inhaled with maximum effort
- ie the amount of air inhaled after tidal volume inspiration
Define expiratory reverse volume (ERV)
the amount of air** in excess of tidal expiration** that can be exhaled with max effort
* ie the forceful expiration of air beyond tidal volume exspiration
Define residual volume
- the amount of air** remaining in the lungs after maximum expiration**
- air has to remain in lungs because otherwise the lungs would collapse
What is the purpose / function of the residual volume?
- keeps the alveoli** inflated between breaths **and mixes with fresh air on next inspiration
Define vital capacity (VC)
- The amount of air that can be exhaled with max effort after max inspiration (ERV +TV +IRV)
What is vital capacity used to assess?
- it is used to** assess strength of thoracic muscles as well as pulmonary function**
Define inspiratory capacity
- the maximum amount of air that can be inhaled after a normal tidal expiration (TV + IRV)
Define functional residual capacity (FRC)
- the amount of air remaining in the lungs after a normal tidal exspiration
Define the total lung capacity (TLC)
- the max amount of air that the lungs can contain
what is spirometry?
the measurement of lungs volumes and flow
what is the function of a spriometer?
any device used to measure lung volumes or flow
* different types eg bellow spirometer
Why cant total lung capacity (TLC), **functional residual capacity **(FRC) and residual volume (RV) be measured on a spirometer?
- this is because a spirometer only measures the volumes that can be inhaled or exhaled
What is the purpose of pulmonary function test?
what does the test provide? what does it determine?
- this test provides information on a patients lung function
- it can sense any abnormalities and monitor disease progression
- it can also determine fitness for surgical procedures
What is** ventilation (Ve) **and what is its value in ml/min?
- total volume of air entering the lung each minute
- value is 7500ml/min
What is the **respiratory rate **in breaths/min?
**15 **breaths/min
What are the 3 types of ‘dead space’?
- anatomical dead space
- physiological dead space
- experimental dead space
what is the total ventilation calculation?
Ve= Vt (tidal volume) x F (respiratory rate)
therefore Ve = 500ml x 15 breaths/min=7500ml/min
what is the calculation for alveolar ventilation?
* Va= (Vt-Vd) xF
* NOTE Vd = dead space
* therefore, Va= (500ml- 150ml (in eg) x 15 breaths/min = 5250ml/min
Define anatomical dead space
- volume of air that** does not take place in gas exchange **
What is the value of the anatomical dead space equal to?
* approx equal to a person’s weight eg a 150lbs man has a anatomical dead space of 150ml of air
define the **physiological dead space **
the sum of the anatomical dead space and the alveolar dead space
what is the purpose of the alveolar gas equation?
this equation is used to calculate the partial pressure of oxygen in the alveoli
what is the difference between Pa and PA
PA= partial pressure in alveoli
Pa- partial aterial pressure
What is the alveolar gas equation?
PAO2= FiO2 x (Patm-Ph20)- PaCO2/R
note Patm = 760mmHg
PH20=47 mmHg (this is the molecules of h20 in the respiratory tract for moisture)
Fi= 0.21
what is the definition & value of R in the alveolar gas equation?
- the **respiratory co - efficient **- ie for how many oxygen molecules are consumed, how many carbon dioxide molecules are produced?
- value is 0.8
what is the bohr equation and what is it used for?
- to measure the physiological dead space & quantify the ratio of dead space to tidal volume
- VD/Vt= (PACO2- PECO2)/PACO2
- note PECO2= partial pressure of expired CO2
what is the range of % that is defined as a healthy physiological dead space
between 20-40%