Mechanics Flashcards
What is a normal inspiratory reserve volume?
1.9 to 2. 5 liters
What is a normal tidal volume?
0.4 to 0.5
What is a normal expiratory reserve volume?
1.1 to 1.5
What is a normal residual volume?
1.5 to 1.9
What is a normal total lung capacity?
4.9 to 6.4
What is a normal inspiratory capacity?
2.3 to 3.0
What is a normal functional residual capacity?
2.6 to 3.4
What is a normal vital capacity?
3.4 to 4.5
What are three important features of gases that can be derived from the Ideal Gas Law?
- a gas will exert a pressure or a force per unit area. 2. a gas occupies a volume, expressed in liters. 3. the volume of a gas is directly proportional to its temperature and inversely proportional to the pressure.
What is the re-written version of the ideal gas law, where concentration is written as a constant?
P = RTC
What is total pressure equal to in the gas fraction equation?
1.0 Sum of all partial pressures must equal one
What is Dalton’s Law?
PB=PN2+PO2+PCO2+PH2O
When is water vapor pressure included in the Dalton’s Law equation?
when calculating for saturated air, i.e. in the body.
What is the fractional gas concentration (Fg) equation?
Fg = Pg/PB Where Pg is the gas partial pressure sum and Pb is barometric pressure
What does BTPS stand for?
body temperature, ambient pressure and saturated with water vapor. Volumes of ventilated gas are typically expressed in BTPS conditions (e.g., pulmonary ventilation, tidal volume).
What does STPD stand for?
standard temperature (0 ̊C or 273 ̊K), standard pressure (760 mmHg) and dry (no water vapor present). Metabolic rates (oxygen consumption and carbon dioxide production) are expressed as gas volumes in STPD conditions since volumes at STPD are directly related to the number of millimoles of oxygen consumed or carbon dioxide produced (22.4 ml per mmole).
What does ATPS stand for?
ambient temperature, ambient pressure and saturated with water vapor. Many respiratory variables are measured in ATPS conditions and must be converted to BTPS or STPD conditions as appropriate.
Henry’s Law describes the concentration of a dissolved gas in solution (Cg). What is the equation?
Cg = K * Pg where K is the solubility constant (specific to a certain temperature, solvent and gas) and Pg is the gas pressure in contact with the solvent
What is tidal volume?
the change in volume with quiet inspiration and expiration
What is inspiratory reserve volume?
the additional air that can be inspired with additional effort (max)
What is residual volume?
the air that can never be expelled from thelung, no matter how much effort is expended
What is functional residual capacity?
The sum of the expiratory reserve volume and the residual volume, i.e. all the air in the lung left after quiet expiration
What is inspiratory capacity?
All the air that could go in the lung after quiet expiration, i.e. the sume of tidal volume and inspiratory reserve volume
What is vital capacity?
The total air that can move in and out of the lungs in physiologic conditions , ie. the sum of inspiratory capacity, expiratory residual volume and inspiratory residual volume
what is total lung capacity?
All the possible air that could fit into the lung if you ignored physiology, i.e. vital capacity plus residual volume
What effect does water pressure have on the partial pressures of other gases in a mixture?
PH20 in saturated air decreases the overall partial pressure attributable to other gases, i.e. it lowers PO2 by 10 mm Hg
Is water vapor pressure dependent on temperature or barometric pressure? why?
It is dependent on temperature because temperature is what determines how much water goes from liquid to gas form and barometric pressure is a negligible component of that phase change
Why do gases go down a partial pressure gradient and not a concentration gradient?
the sum of all fractional gas concentrations must equal to one, but the variables that determine these concentrations (mathematically) are pressure alone. In particular for the concentration of a gas in solution, it varies only by the solubility coefficient and partial pressure of the gases.
What is the simplest requirement for inspiratory flow, keeping in mind that gas flows down a pressure gradient?
Pb (mouth) > Pa (alveolar)
Same is true for the reverse flow
What causes changes in Pa?
movement of diaphragm and chest wall, which in turn change the pressure on the intrapleural space
What are two ways of measuring intrapleural pressure?
1) placing a small catheter connected to a pressure measuring device in the intrapleural region
2) placing a balloon in the thoracic esophagus and measuring intraesophegeal pressure
During pneumothorax, which releases the thorax from the lung, what happens to the lung?
it collapses.
The rib cage EXPANDS because it is no longer tethered to the lung
The functional residual capacity is a compromise of which two forces in the normal thorax?
outward force of chest wall v. inward recoil force of the lung
What is a normal intrapleural pressure in passive FRC? What is the NET effect on the lung and the rib cage?
-3 to -6 cm H20
Lung: expansion
Rib cage: collapse
What is transpulmonary pressure and how do you calculate it?
Transpulmonary pressure: the pressure acting to inflate the lungs is the (PA - Pip).
Usually negative - causes lung EXPANSION
When the glottis is open and Pa is at equilibrium with Pb, what is the transpulmonary pressure equal to?
- Pip
How do you calculate the transthoracic pressure?
the force acting on the thoracic wall (Pip - PB). Since pleural pressure is generally negative, it “sucks” the chest wall inward.
What is the transrespiratory pressure? When do you measure it?
the difference between alveolar and atmospheric pressure measured (PA - PB).
-with the glottis closed and with the respiratory muscles relaxed
When transrespiratory pressure is negative, where will gas flow? Positive?
- negative: gas will flow into the alveoli when the glottis is opened.
- positive: gas will flow out of the lungs when the glottis is open.
What is elastance?
the inverse of compliance
What happens to the opposing force exerted by a rubber band (or a lung) when it is stretched?
it increases as the distance it is stretched increases
i.e. like a spring
What is the slope at any point when plotting pressure v. volume of a lung?
compliance at that volume
the following cause compliance to increases or decrease? a) respiratory distress syndrome
b) edema
c) atelectasis (i.e., alveolar collapse)
d) fibrosis
Decrease