Test 3: Wk11: 6 Dynamic Properties of Lungs and Alveolar Ventilation - Dasgupta Flashcards
At the top of the chest, gravity acts to — making the pleural pressure
pull lung tissue away from the chest wall
more negative
At the bottom of the thorax, gravity — making the pleural pressure
presses lung tissue against the chest wall
less negative
Pleural pressure is most
negative at the —, and is least negative in the —
uppermost part of the thorax
lowermost part of the thorax
Differences in pleural pressure affect the way alveoli are
ventilated in different
parts of the lung.
Inspired air is not distributed evenly in the lungs. This is the result of (2)
1) the gradient in pleural pressure
2) the non-linear compliance curve of the lungs
the change in volume is greatest for the units at the —of the lung
and least for the units at the —
bottom
top
The lowest part of the lung is ventilated — than the uppermost part
more
the bottom part of the lung is — ventilated than the top.
always better
compliance is better at
the bottom of the lung
areas with different compliance are ventilated
differently
DALTON’S LAW OF PARTIAL PRESSURES
THE TOTAL PRESSURE OF A
MIXTURE OF GASES IS THE SUM OF THE PARTIAL PRESSURES OF
INDIVIDUAL GASES
PO2
partial pressure O2
160mmHg
PN2
partial pressure N2
600 mmHg
In room air, the fraction of O2 is —. The fraction of N2 in air is —.
- 21
0. 79
when room air is drawn into airways another species of gas is added
water vapor
at body temperature partial pressure of water vapor is
47mmHg
in the airways PO2 PN2 and PH2O
PO2 150mmHg
PN2 563 mmHg
PH2O = 47 mmHg
partial pressures in alveoli change because of
gas exchange
Gas exchange in alveoli removes — O2 and adds — CO2
250 ml O2
200ml CO2
— mL of air inspired
3600
after gas exchange alveoli contain — mL O2, — mL N2, — mL CO2
O2 506 mL
N2 2844 mL
CO2 200 mL
total 3550 mL
50 mL H2O excreted was liquid
The rate of alveolar ventilation depends on (3)
1) Respiratory Rate
2) Tidal Volume
3) Dead Space Volume
Rate of Total Ventilation (Minute Ventilation) =
VE = Frequency x VT
VA stands for
alveolar ventilation per minute
VD stands for
dead space volume
TV stands for
tidal volume
VA =
VA = Frequency (VT - VD)
Respiratory exchange ratio (R) =
R = Rate of CO2 output / Rate of O2 uptake
Anatomical dead space
Volume of air left in conducing airways.
For a normal adult, anatomical dead space = 150 ml
Alveolar dead space
is the volume of air left in unperfused alveoli.
The alveolar dead space is very small in a normal adult.
Physiological Dead Space
is the summation of alveolar dead space and
anatomical dead space.
VDtotal = VDanatomical + VDalveolar
Bohr Equation for Dead Space
VD/VT = (PaCO2 - PECO2) / PaCO2
PeCO2
Partial pressure of CO2 mixed in expired gase
PaCO2
Partial pressure of arterial CO2
if VA* is halved (i.e. hypoventilation), but CO2 production remains the same, the alveolar (A) and arterial (a) PCO2 will
double.
if VA * is doubled (i.e. hyperventilation), but CO2 production remains the
same, the alveolar (A) and arterial (a) PCO2 will
be halved.
Alveolar Gas Equation
PAO2 = FIO2 (PB-PH2O) - PaCO2 / 0.8)
normal arterial pH
normal venous pH
- 35 - 7.45
7. 34 - 7.37
Normal arterial PO2
Normal Venous PO2
80-100 mmHg
38-42 mmHg
Normal Arterial PCO2
Normal Venous PCO2
35-45 mmHg
44-46 mmHg
Normal Arterial HCO3
Normal Venous HCO3
22-26 meg/ml
24-30 meg / ml
normal oxygen saturation
95-100%
Hypoxemia
low partial pressure of oxygen in arterial blood.
Hypercapnia
high partial pressure of carbon dioxide in arterial blood.
