Lecture 5: Pressure and gases

Question 1

Pressure equation

Answer 1

P = F/A

Question 2

Pressure unit?

Answer 2

N/m2

Question 3

kPa

Answer 3

kilopascal - used to express pascal units of pressure (very small)

Question 4

Real life usage?

Answer 4

Syringe

Question 5

Syringe use

Answer 5

pressure is higher from smaller syringes - important when administering intravenous drugs

Question 6

Pressure measurements in healthcare

Answer 6

mmHg
cmH2O
Psi

Question 7

mmHg (mm, Hg = mercury)

Answer 7

measuring blood pressure, inspiratory and expiratory pressures (connected to atmospheric pressure)

Question 8

cmH2O (cm, water)

Answer 8

Measurement of central venous pressure

Question 9

Psi (pounds per square inch)

Answer 9

Measure pressure to compressed gases & direct pressure on an object

Question 10

Pressure and liquid

Answer 10

Static liquid
Fluid in Containers
Bernoulil effect/Venturi barrel

Question 11

Static liquid

Answer 11

Evenly distributed pressure in all directions

Question 12

Fluid in Containers

Answer 12

subject to effects related to volume and atmospheric pressure/gravity

Question 13

Bernoulil effect/Venturi barrel

Answer 13

principle of entrainment

Question 14

Bernoulil effect

Answer 14

The principle that states that as the speed of a moving fluid (liquid or gas) increases, the
pressure within the fluid decreases.

Question 15

Pressure and Liquid: clinical application

Answer 15

IV fluids
nebuliser

Question 16

IV fluids

Answer 16

the higher the fluid container (IV bag)
the faster the outward flow of the fluid to the patient

Question 17

Blood flow and pressure (Heart contracts)

Answer 17

Heart contracts and relaxes – creating pressure within vessels (blood pressure).

Question 18

Blood flow and pressure (Vessel diameter)

Answer 18

Vessel diameter, vessel length and blood viscosity determine resistance to blood flow and therefore the pressure.

Question 19

Blood flow and pressure (Measuring)

Answer 19

Measuring the pressure - sphygmomanometer (blood pressure monitor)

Question 20

Blood flow & pressure: Clinical application

Answer 20

Constricted vessels can reduce flow and can increase blood pressure.
◦ Dilated vessels can increase flow and can reduce blood pressure.
◦ Pumping efficiency of the heart can also effect blood pressure

Question 21

Gas laws

Answer 21

Has no definite shape or volume of its own.
* A gas fills any container it occupies.
* Is easy to compress (basis of gas laws)
* Has a low density

Question 22

Gas laws are

Answer 22

are related to kinetic theory.
Kinetic theory that states matter is composed of tiny particles in constant random motion. (sometimes referred to as ‘Brownian’ motion)

Question 23

Boyle’s Law 1st Ideal Gas law

Answer 23

As the volume occupied
increases pressure decreases
* As the volume occupied
decreases pressure increases

Question 24

Boyle’s Law 1st Ideal Gas law

Answer 24

The absolute pressure (P)
exerted by a given mass of an ideal gas is inversely

proportional to the volume (V)

it occupies if the temperature (T)
and amount of gas remain unchanged within a closed
system.

Question 25

Why do we need to know Boyle's law?

Answer 25

Pressure is essential in breathing

Question 26

Daltons Law (in a mixture)

Answer 26

In a mixture of gases, the total pressure exerted is equal to the sum of the partial pressures of the individual gases.

Question 27

Daltons Law (The partial pressure)

Answer 27

The partial pressure of a gas in a mixture is the pressure that gas would exert if it occupied the total volume of the mixture.

Question 28

Daltons Law (This law)

Answer 28

This law explains that the sum of all partial pressures of gas in a mixture should equal the barometric pressure.

Question 29

Daltons law (clinical application)

Answer 29

Partial pressures within respirators rely on this law for safety in ensuring oxygen input and carbon dioxide output remains stable and gas mix is compatible with life.

Question 30

Daltons law: clinical application (diving bends)

Answer 30

Diving Bends – pressure effecting the concentrations of gases at depth. Decompression required to equalize the pressures within the body.

Question 31

Henry's law

Answer 31

The mass of a gas that will dissolve in water at a given temperature is proportional to the partial pressure of the gas and to its solubility coefficient

Question 32

Henry's law: so what does that mean?

Answer 32

Every cell depends on oxygen to survive – the intake and transport of oxygen around the body and removal of waste carbon dioxide is critical to our survival both O2 and CO2 are dissolved in the blood to be transported around the body for use within the cells

Question 33

How does Henry’s Law apply?

Answer 33

Gas exchange * Alveolar air composition * Concentration gradients

Question 34

How does Henry’s Law apply? (in a nutshell)

Answer 34

Oxygen in the bloodstream has a lower partial pressure than atmospheric oxygen, therefore it is able to diffuse into the blood along a pressure gradient. While a small percent is dissolved in plasma, most binds to haemoglobin for transport around the body, so that the oxygen can diffuse into the interstitial fluid and then cells down pressure gradients.

Question 35

Henry's law (clinical application)

Answer 35

Saturation level Oxygen therapy nebuliser

Question 36

Saturation level

Answer 36

measurement of the amount of haemoglobin molecules with oxygen attached and an indicator of respiratory function and potential anaemia.

Question 37

Oxygen therapy

Answer 37

As we inhale concentrated oxygen we change the alveolar air composition thus increasing the oxygen partial pressure. And therefore oxygen availability for diffusion. Note: not all masks are the same

Question 38

nebuliser

Answer 38

pressurised gas is used to creat a Bernoulli effect inside a mask to administer fluids in droplet form