Lecture 3- Properties of Gases

What is pressure?

Force per unit area.

What is the total pressure?

sum of all partial pressures

As the number of gas molecules increases what happens to the pressure?

It also increases

How does a mercury barometer work?

Air pressure pushes down on the surface of the mercury opposite to gravity, making some rise up the tube. The greater the air pressure, the higher the mercury rises.

What is the pressure at sea level?

760 mmHg

What is the pressure at Mt. Everest?

228 mmHg

What happens to the number of oxygen molecules as the elevation rises?

The gas molecule dimish

As elevation rises, what happens to the % composition of gases in the air?

They stay the same

What is the partial pressure of a gas equal to?

Patm times the % of gas in the atmosphere

At a warmer temperature, what happens to the pressure?

Pressure decreases as humidity increases

What happens once pressure is measured in humidity not dry air?

The pressure decreases once humidity is included

What is the ideal gas law?

PV=nRT

When nRT is constant in the ideal gas law, and it is a closed system, what can the ideal gas law conclude?

Pressure is inversely proportional to volume

What is Boyle's Law?

P1V1=P2V2

What does Boyle's law explain?

The basis for pulmonary vetilation

What does Boyle's law conclude?

1) Changes in volume create changes in pressure

2) Changes in pressure cause gas to flow towards the lower pressure

If the volume in the lung increases, what happens to the pressure in the lung?

It decreases

What does expiration do in terms of volume and pressure?

Decreases volume, increases pressure, causing air to ,move out of the lung

When does inspiration occur?

When alveolar pressure is less than atmospheric pressure.

When does expiration occur?

When alveolar pressure is greater than atmospheric pressure

When interplural pressure is negative during inspiration, what is alveolar pressure?

Zero

interplural pressure is always...

sub-atmospheric (negative)

When is interpleural pressure most negative?

During inspiration

What happens to thoracic volume as inspiration occurs?

It increases

In what direction do gasses flow?

From high pressure to low pressure

What is ventilation a direct function of?

Differences in gas pressure and resistance to flow

What is the flow of gas directly proportional to?

Pressure differences

What is the flow of gas inversely proportional to?

Resistance to flow

What is the flow of an airway equal to?

(Palveoli- Patm) times r^4

What determines airway resistance?

airway diameter

What does Poiseuille's Law describe?

The resistance to fluid flow through a tube

What factor affects airway resistance?

The diameter of airways

What changes the tube diameter of airways?

The bronchioles

What does the branching of airways do?

Increases the total cross-sectional area, decreasing the air flow velocity

As the cross-sectional area increases, what happens to airflow velocity?

It decreases

What is Coal worker's pneumoconiosis?

A respiratory condition in which particles of coal dust get stuck in the lung, developing a fibrosis as the lung gets stiffer

What happens to a patient with CWP?

Their lungs lose the ability to drag things along and the lung is unable to expand as easily, putting a heavier load on the heart

What does Henry's Law state?

At a constant temperature, the amount of gas dissolved in a liquid is proportional to its partial pressure in the gas phase

What does Henry's law describe?

The solubility of gases in an aqueous environment

What does Henry's law conclude?

The solubility of CO2 in water is about 20 times greater than the solubility of water in O2

What is spirometry?

The measurement of breathing

What is a spirometer?

instrument used to measure respiratory volumes and capacities

How does a spirometer work?

-patient breathes into tube
-floating bell moves up and down as the patient breathes
-pen recorder, then graph the changes in lung volume

When the subject inhales and air moves into the lung, what happens to the volume of the bell and the pen?

The volume of the bell decreases while the pen rises on the tracing

When a patient exhales, what happens to the bell and the tube?

The bell goes up while the pin goes down

What is tidal volume?

amount of air inhaled and exhaled during a normal breathing cycle.

What is expiratory reserve volume?

Amount of air that can be forcefully exhaled after a normal tidal volume exhalation

What is inspiratory reserve volume?

Amount of air that can be forcefully inhaled after a normal tidal volume inhalation

What are the 3 volumes that can be measured with a spirometer?

Tidal volume, ERV, and IRV

What is residual volume?

Air in lungs after maximal expiration.

What is total lung capacity?

vital capacity + residual volume

What is vital capacity?

the volume of air that the patient can exhale after a maximal inhalation.

How is the vital capacity calculated?

Expiratory reserve volume + tidal volume + inspiratory reserve volume

What is inspiratory capacity?

tidal volume + inspiratory reserve volume

What is functional residual capactiy?

The total amount of air in the lungs at the lowest point of tidal volume

How is FRC calculated?

FRC = ERV + RV

What is FRC normally?

2.5 L

What does the FRC point represent?

The point in the breathing cycle where the inward lung tissue elastic recoil and chest wall expansion are balanced and equal

What can residual volume NOT be measured by?

Simple spirometry

How do you measure function residual capacity?

Helium Dilution

What is helium dilution?

Charging up system then adding a known quantity of helium

What is the first step in helium dilutions?

Add a known quantity of helium to a known volume of gas, giving an initial concentration, C1

As the volume of gas increases, what happens to the concentration of helium?

The concentration of helium decreases to C2

What can be calculate from a helium dilution?

The change in volume given the quantity of helium has stayed the same

What does V2 equal?

FRC

How does a helium dilution work as a whole?

1) The quantity of helium does not change

2) C2 < C1 because V1 + V2

3) V2 = V1 (C1/C2-1)

What does V2 represent FRC?

At the end of normal respiration ONLY

What best describes the vital capacity of the lung?

The maximum amount of gas that can be expired after a maximum inspiration

What best describes that tidal volume of the lung

The volume of gas inspire or expired in an unforced respiratory cycle

Whole body plethysmography is based upon Boyle's Law and most often used to measure what?

residual volume

If someone inhales as much air as possible and then exhales maximally, the total amount of air exhaled from the lungs is called:

vital capacity

When the abdominal and intercostal muscles contract, what happens?

The pleural pressure becomes less negative

What gas law describes the cause of bends?

Henry's law