SME
Human Anatomy & Physiology · Problem type
Minute and alveolar ventilation
Use this for “Tidal volume 500 mL, dead space 150 mL, 12 breaths a minute. What is the alveolar ventilation?”
Chart
Minute ventilation: VE = 6 L/min
Tidal volume VT = 500 mL
Dead space volume VD = 150 mL
Breathing rate f = 12 min⁻¹
This is an example. Type your own values to start a new problem.
VA (L/min)
=
(
VT (mL)
−
VD (mL)
)
×
f (min⁻¹)
VE
Minute ventilation
calculated · L/min
Vdead
Dead space ventilation
worked out (not typed) · L/min
Formulas
VE
=
VT
×
f
1,000
6
=
500
×
12
1,000
VA
=
(VT
−
VD)
×
f
1,000
4.2
=
(500
−
150)
×
12
1,000
Vdead
=
VD
×
f
1,000
1.8
=
150
×
12
1,000
Assumptions
•
Each breath moves the tidal volume; its first part only fills the airways, the dead space, where no gas is exchanged.
•
The rest of each breath reaches the alveoli, so alveolar ventilation is (VT − VD) times the breaths a minute.
•
The breaths are all the same size and evenly spaced; 1,000 mL make 1 L.
Step-by-step
WE KNOW
VT = 500 mL, VD = 150 mL, f = 12 min⁻¹
FIND
minute ventilation (VE), alveolar ventilation (VA), dead space ventilation (Vdead)
Step 1 · Find minute ventilation (VE)
Use VE = VT × f ÷ 1,000
Each
breath
moves
one
tidal
volume,
f
times
a
minute;
1,000
mL
make
1
L.
VE
=
500
×
12
1,000
VE
=
6,000
1,000
VE = 6 L/min
Step 2 · Find alveolar ventilation (VA)
Use VA = (VT − VD) × f ÷ 1,000
Only
the
part
of
each
breath
past
the
dead
space
reaches
the
alveoli,
f
times
a
minute.
VA
=
(500
−
150)
×
12
1,000
VA
=
350
×
12
1,000
VA
=
4,200
1,000
VA = 4.2 L/min
Step 3 · Find dead space ventilation (Vdead)
Use Vdead = VD × f ÷ 1,000
The
dead
space
fills
again
with
every
breath,
f
times
a
minute.
Vdead
=
150
×
12
1,000
Vdead
=
1,800
1,000
Vdead = 1.8 L/min
Check
Put the numbers back in. Both sides should match.
6
=
500
×
12
1,000
✓
4.2
=
(500
−
150)
×
12
1,000
✓
1.8
=
150
×
12
1,000
✓
Topic check
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