94 Questions
What is the term for the energy required to increase the kinetic energy of molecules and overcome intermolecular forces?
Latent heat
What is the process by which heat energy is transferred through direct molecule-to-molecule contact?
Conduction
What is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases?
Vapor pressure
What is the amount of heat required to raise the temperature of 1 kg of a substance by 1 K?
Specific heat capacity
What occurs when a gas is cooled and its particles slow down to form a liquid?
Condensation
What is the term for the process by which a gas changes state to a liquid?
Condensation
What is the term for the point at which a liquid condenses at a particular pressure?
Saturated vapor pressure
What type of flow is characterized by a straightforward flow with the greatest flow in the middle?
Laminar flow
What is the relationship between laminar flow and hydrostatic pressure gradient?
Flow is directly proportional to hydrostatic pressure gradient
What predicts whether the fluid flow would be laminar or turbulent?
Reynolds number
What is the characteristic of a fluid that determines its tendency to occupy more space?
Density
What is the result of the Bernoulli effect in a Venturi mask?
Entrainment of ambient air to mix with oxygen
What is the purpose of a constriction in a Venturi mask?
To create a pressure drop and entrain ambient air
What is the characteristic of a fluid that determines its resistance to flow?
Viscosity
What is the effect of the Coanda effect on a fluid?
It entrains surrounding gas into the fluid
What is the characteristic of a tube that promotes turbulent flow?
High flow rates, changes in diameter, branches
What is the principle used to calculate pulmonary blood flow from oxygen uptake?
Fick Principle
What is the name of a device used to measure gas flow?
Pitot tube
What is the term for the internal force generated by a structure?
Tension
What is the equation for the pressure gradient in a tube?
Pressure gradient = tension/radius
What is the reason for the absence of an increased A-a gradient in patients with hypoventilation or high altitude?
Concurrent decrease in both the 'A' and the 'a' values
What are van der Waals forces?
Weak intermolecular forces between neutral molecules
What is the definition of heat in physics?
The transfer of energy from one body to another due to a difference in temperature
What is the definition of cold in physics?
The absence of heat
What is temperature?
The tendency of an object to gain or lose heat
How do you convert from Celsius to Kelvin?
Add 273.15 to the temperature in Celsius
What are the four ways heat is transferred?
Conduction, Convection, Radiation, and Evaporation
What is the SI unit of heat?
Joule (J)
What is the relationship between a calorie and a joule?
1 calorie is equal to 4.184 joules
What is the definition of 1 calorie?
The amount of heat required to raise the temperature of 1 gram of water by 1°C
Temperature is a measurement of the quantity of heat
False
What is heat capacity?
The units of heat per unit change in temperature
What is the most common type of heat loss during surgical cases?
Radiation
What type of surgical cases can increase heat loss?
Major abdominal surgeries
What are the properties of an ideal gas?
It has volume, but no mass or molecular interactions and molecules are constantly in motion.
What is vapor pressure?
The pressure exerted by a vapor in equilibrium with its solid or liquid (condensed) phase
What is STP in terms of temperature and pressure?
0°C and 1 atm
What is absolute zero?
The lowest possible temperature, 0 K (-273.15°C or -459.67°F)
What is Boyle's Law algebraically?
P1V1 = P2V2
What does Boyle's law indicate about the relationship between volume and pressure?
As pressure increases, volume decreases.
What is Charles' Law algebraically?
V1 / T1 = V2 / T2
What does Charles' Law state?
The volume of a gas is directly proportional to the temperature of the gas.
What is Guy-Lussac's Law algebraically?
P1/T1 = P2/T2
What does Guy-Lussac's law state?
At constant volume, the pressure of an ideal gas is directly proportional to absolute temperature
What is Avogadro's hypothesis?
A scientific principle that states under conditions of constant pressure and temperature, equal volumes of gases contain equal numbers of molecules
What does Avogadro's Law state?
Under conditions of constant pressure and temperature, there is a direct relationship between the volume and number of moles for an ideal gas
What is the molar volume of a gas at standard temperature and pressure (STP)?
22.4 L/mol
What is Dalton's Law of Partial Pressures?
The law that states that the total pressure of a mixture of gases is equal to the sum of the partial pressures of each individual gas.
What is Amagat's Law?
A law that states the volume of a gas mixture is equal to the sum of the volumes of all its constituents
What is Graham's Law?
A law that states the rate of diffusion of a gas is inversely proportional to the square root of its molecular weight.
What is the alveolar gas equation?
PAO2 = (PB-Pwater vapor)FIO2-PACO2(1.25)
What is the a-a gradient?
The difference in oxygen partial pressure between alveolar air and arterial blood
What can cause an increased alveolar-arterial (a-a) gradient?
All of the above
How do you calculate the estimated normal arterial-alveolar gradient?
(Age/4)+4
What is the Hagen-Poiseuille Equation and its significance to air flow?
A equation used to describe the relationship between pressure, fluid resistance, and flow rate in laminar flow
In laminar flow, what is the flow inversely proportional to?
Viscosity and tube length
What is the Reynolds number used for?
To predict the nature of flow in a pipe
What is the main difference between a tube and an orifice in terms of length and diameter?
A tube has a longer length and smaller diameter, while an orifice has a shorter length and larger diameter.
What Reynolds number indicates laminar flow?
Re < 2000
What does the Bernoulli's effect state?
Pressure is inversely proportional to the velocity when flow occurs through a constriction
What is the Coanda effect?
The ability of a gas/fluid to attach to a surface after passing through an asymmetric narrowing, exerting force on neighboring gas/fluid
After passing a constriction, what happens to a fluid at a bifurcation?
It sticks to one side of the branch, causing maldistribution
Laminar flow is dictated by what factor?
Viscosity of the fluid
Density is crucial in which type of flow?
Turbulent
Hagan Poiseuille Equation = flow (Q) = piPr^4/8nl P=pressure r=radius n = viscosity l = length
True
Flow through an orifice is typically laminar
False
Why is helium useful in promoting gas flow in cases of severe respiratory obstruction?
It makes oxygen less dense and allows it to travel to the lungs easier
In a venturi mask, what effect does the entrainment of air have on air flow?
Increased flow at a predictable FiO2
What are examples of devices used to measure gas flow?
All of the above
Low flow Thorpe tubes are tubular in nature and dependent on viscosity
True
High flow Thorpe tubes are orificial in nature and dependent on viscosity
False
What is a Bourdon gauge used for?
Measuring pressure
Where would you see orificial flow?
All of the above
What law states that pressure is equal to 2 times the tension divided by the radius?
Laplace's Law
According to Laplace's law, what happens to a smaller alveolus compared to a larger alveolus of equal surface tension?
It experiences a larger intra-alveolar pressure
What is the result of unequal surface tension in alveoli of different sizes?
The smaller alveolus collapses as air passes from the smaller to the larger alveolus
What is the relationship between the radius of a sphere and the intra-alveolar pressure according to Laplace's law?
The smaller the radius, the higher the intra-alveolar pressure
What causes air to pass into the larger alveolus, causing the smaller alveolus to collapse?
A larger inter-alveolar pressure in the smaller alveolus
Small alveoli (i.e. collapsed and nearly collapsed) are more difficult to inflate then large alveoli; this contributes to the low compliance seen at small lung volumes
True
Smaller alveoli will promote their own collapse by emptying into larger neighboring alveoli
True
What is the universal gas law?
P1V1/T1=P2V2/T2
High flow Thorpe tubes are orificial in nature and dependent on density
True
What is the primary form of heat loss in surgical patients?
Radiation
What type of heat loss may be greater in rooms with laminar air flow
Convection
How does evaporation cause heat loss during surgical procedures?
It occurs through the latent heat of vaporization of water from open body cavities and the respiratory tract
Owing to the high surface area/body mass ratio, infants are especially vulnerable to heat loss by radiation
True
According to the Hagen-Poiseuille equation, how does doubling the radius of a pipe affect the flow rate?
It increases the flow rate by a factor of 16
According to the Hagen-Poiseuille equation, how does tripling the radius of a pipe affect the flow rate?
The flow rate increases by a factor of 81
Low flowmeters are tubular and characterized by laminar flow
True
What is the effect of coronary steal?
Blood flow to unhealthy organs is diverted to healthy ones
Why are smaller alveoli more prone to collapse?
Smaller alveoli have a higher pressure gradient due to their smaller radius
How does the Bernoulli effect contribute to the functioning of Venturi masks?
It decreases pressure, which entrains air to mix with oxygen.
What is the purpose of a constriction in a Venturi mask?
To create a pressure drop (i.e. negative pressure) and entrains ambient air to mix with oxygen flow
In contrast to the Thorpe tube, which has a constant pressure, but a variable orifice, the Bourdon tube has a constant orifice, but a variable pressure.
True
Study Notes
Laplace's Law for a Sphere
- Laplace's law states that unequal-sized alveoli with equal surface tension have differing intra-alveolar pressures, with the smaller alveolus experiencing a larger pressure.
- This pressure difference causes air to pass from the smaller to the larger alveolus, leading to the collapse of the smaller alveolus.
- Pulmonary surfactant prevents the collapse of the smaller alveolus by decreasing its surface tension.
- Decreased surface tension in the smaller alveolus results in equal pressure in both alveoli.
- Transmural pressure difference (P) and sphere radius (r) are important variables in understanding Laplace's law.
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