Tidal and Minute
At rest, a normal breath is approximately: 500 mL – the tidal volume (VT).
This is divided into:
- Anatomical dead-space (150 mL) limited to the conducting airways, gas exhaled unchanged
- Alveolar ventilation (350 mL) reaches the lower airways, gas takes place in respiratory exchange
Multiplying VT by the respiratory rate (around 14 L/min) gives the minute volume (Vmin).
VT x RR = Vmin
500 x 14 = 7000 mL/min (7 L/min)
Inspiration normally lasts half as long as expiration: an I:E ratio of 1:2.
Question: What is the alveolar minute volume?
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At rest, a normal breath is approximately: 500 mL – the tidal volume (VT).
This is divided into:
- Anatomical dead-space (150 mL) limited to the conducting airways, gas exhaled unchanged
- Alveolar ventilation (350 mL) reaches the lower airways, gas takes place in respiratory exchange
Multiplying VT by the respiratory rate (around 14 L/min) gives the minute volume (Vmin).
VT x RR = Vmin
500 x 14 = 7000 mL/min (7 L/min)
Inspiration normally lasts half as long as expiration: an I:E ratio of 1:2.
Question: What is the alveolar minute volume?
Answer: Alveolar ventilation x respiratory rate
350 x 14 = 4900 mL/min (~ 5 L/min).