Lung volumes, loops, V and Q Flashcards
FEV1
IRV
ERV
RV
Vt
FEV1 - forced expiatory vol in 1 second
IRV - inspiratory reserve vol.
ERV - expiratory reserve vol
RV - residual vol
Vt - tidal vol
FVC
IC
FRC
VC
Pst
FVC - forced vital capacity
IC - inspiratory capacity
FRC - functional residual capacity
VC - vital capacity
Pst - Static pressure of lung
Normal lung volume diagram
Normal and abnormal FEV1/FVC
N: .8 or 100% predicted Abnormal: .75 in young, .7 in old, or <88%
Definition of obstruction
FEV1/FVC <.70 in old. Can become hyper inflated because hard to get air out. TLC higher, Residual vol higher, longer to empty
Definition of Restriction
Decreased TLC (tot. lung cap.) A decreased vital capacity or FVC does not always indicate restriction
FRC details
functional residual capacity. Determined by the balance of lung elastic recoil and chest wall recoil
Normal flow volume loop
voila
Breakdown of flow volume loop
pic
Flow volume loops for restrictive and obstructive
Obstructive = large vol, bowed look on expiration Restriction = steep expiration, narrow base
What affects flow most at low volumes?
Just airway resistance. Pt effort less important.
V and Q
Ventilation (the rate at which gas enters or leaves the lung)
Perfusion (the process of delivery of blood to a capillary bed)
V/Q ratio
a measurement used to assess the efficiency and adequacy of the matching of these two variables in the lung
change in alveoli diameter and ventilation from top to bottom of lung
Top ones more distended at baseline (gravity) than bottom. So the bottom ones can expand more than the top, so more ventilation happens in the base of lung than apex.
How does perfusion change from top to bottom of lung?
not uniform. more pulm. aa. and vv. pressure at bottom than top. Veins lower pressure than aa.
3 pressures to consider in lung vessels
P1 is the inflowing pressure, P2 is the pressure which must be reached by P1 before fluid will flow through the tube (ie so vessels don’t collapse), and P3 is the pressure downstream from the tube (veins).
Always ∆P = P1 - P2 or P3 (whichever is greater)
Going top to bottom, how does ventilation and perfusion change?
ventilation increases, and perfusion increases but at different rates
High V/Q ratio at top.
Low V/Q at bottom.
Anatomic and physiologic shunts
An anatomic shunt occurs when venous blood flows back to the circulation downstream from the lung – ie; the bronchial circulation
An intrapulmonary shunt occurs when venous blood flows through:
- Unventilated lung
- Heart defects
- Shunt channels in lung
What are interpulmonary shunts? What purpose do they serve?
Small vessels that allow R-L shunts around alveoli. Heavy exercise increases pulm. a. pressure, intrapulmonary shunts relieve it w/o causing pulm. edema.
What is Dead space? What is it good for?
V/Q = infinite. ie. air in trachea (no exchange) or in poorly/non-perfused alveoli.
Benefits:
CO2 retained (buffer possible)
air reaches body temp
humidified (better for mucous)
Define and give values for
mPAP
PCWP
PVR
mPAP = mean pulm. a. pressure, 14 +/- 3.5 mmHg
PCWP = pulm capillary wedge pressure, 2-15 mmHg
PVR = pulm. vascular resistance = (mPAP – PCWP) / CO
What is hypoxic vasoconstriction? Purpose?
Vessels constrict when exposed to low O2 or high CO2 to shift flow away from these areas to better ventilated
What is the relationship b/w dead space, shunt and V/Q mismatch?
Continuum: Shunt → V/Q mismatch → dead space
