Master of Nursing Science
Dr Nick Allcock
Introduction and Worksheet 1
The four worksheets in this series reviewing the physiology of the respiratory system
each starts with the description of a patient with an altered respiratory system. In
order to understand the care that this patient will require an understanding of
respiratory physiology is required. Working through the worksheets will give you the
necessary knowledge to answer the questions about the cases. These questions will be
the basis of tutorials so don’t worry if you are finding them difficult, come to the tutorial
ready to discuss them. If you are having any problems with the worksheets contact the
Module leader to seek extra help / tutorials. References throughout the package refer to
the Marieb (2001)1 unless otherwise stated.
Essential to the functioning of all cells in the body is a supply of oxygen, without an
adequate supply of oxygen cells and tissues are damaged and will die. 250ml of O2 per
minute is required at rest and this can increase 30 fold during exercise. During
metabolic processes 200ml per minute of CO2 is produced. The exact balance depends
on the energy substrates used in metabolism and defined by the Respiratory Quotient
E.g. if using carbohydrate:
C6 H12 O6 + 602 6CO2 + 6H2 0 = R.Q. = 602 / 6CO2 = 1.0
The system responsible for the supply of oxygen and the removal of CO 2 is the
Respiratory System. In order that O2 can be supplied to cells and CO2 removed a
number of processes occur which together are referred to as respiration.
Define each of the following
1. Pulmonary ventilation
2. External ventilation
3. Transportation of respiratory gases
4. Internal respiration
The four worksheets will discuss these processes as well as the way these processes are
It is important that you have an understanding of the anatomical structure of the
thorax, the airways and the lungs. Review your notes from the session on anatomy of
the respiratory system and read pages 835-850. By the end of this and your anatomy
session you should be able to: draw and label a simple diagram of the gross anatomy of
the respiratory system e.g. fig 23.1, understand the role of different
Marieb E (2001) Human Anatomy and Physiology (fifth edition). Addison Wesley Longman. San Francisco.
Mechanics of Breathing
John Law is a tall thin 28-year-old welder who has generally experienced good health.
On his way to work one morning he experience severe chest pain that gradually got
worse causing him difficulty in breathing (dyspnoea). Admitted to hospital his chest X-
ray revealed a collapsed right lung. He was diagnosed as suffering from a spontaneous
pneumothorax (a condition in which air escapes into the pleural cavity). An underwater
sealed drain was inserted which enabled the lung to re-expand and relieved the
dyspnoea he was experiencing.
Aims and objectives
This worksheet and the introduction cover the objectives 1-13 listed under the
respiratory system in the Biological Sciences Module Handbook.
In order to understand what has happened in John’s case an understanding of
respiratory mechanics is needed. To understand how gases are moved in and out of the
lungs we need to understand how gases behave and therefore we need to consider the
conventional notation associated with quantities in respiratory physiology.
In 1952 a conventional notation
for expressing quantities in respiratory physiology was internationally agree. It is
Standard symbols Q = volume of blood ( l ) V = gas volume ( l )
f = breath frequency (min -1) F = fractional composition
Qualifiers a = of arterial blood A = of alveolar gas
v = of venous blood E = of expired gas
I = of inspired gas D = of dead space
T = of tidal volume O2, CO and N2 as usual
A dot above the symbol indicates "rate of" eg. V = gas flow.
Using these conventions, we combine the symbols thus :-
Q = cardiac output (l.min-1) VA = alveolar ventilation (l.min-1)
FIO = fraction of oxygen in inspired gas.
The way that gases behave is described by a number of the gas laws.
Boyle’s law: The volume of a given mass of gas is inversely proportional to the
pressure to which it is subject, provided the temperature is constant. (P 1 V1 = P2 V2).
Read the section on page 851 and answer the following:
If the volume in which a gas is contained is increased the pressure will decrease
If the volume in which a gas is contained is decreased the pressure will increase
In the human body temperature is not always constant and therefore we have to take
this into account by considering:
Charles’ law: The volume of a given mass of gas is directly proportional to its absolute
temperature provided the pressure remains constant. (V 1 T 1= V 2 T2).
We therefore have to consider these laws together and combining them gives us the
general gas law: P1 V1 / T1= P2 V2 / T2
Pressure relations in the thorax
Changes in the volume in which gases are contained therefore affect the pressures of
the gases contained within them. These principles can be applied to the thoracic cavity.
To understand this we need to understand the pressure relationships within the thoracic
Label the diagram below and make notes on the factors generating the following
1. Atmospheric pressure
2. Intrapleural pressure
3. Intrapulmaonary pressure (intra-alveolar pressure)
Read and make notes on the section on pages 851-853 on inspiration. In particular note
1. What are the two main respiratory muscles responsible for inspiration?
The two main sets of muscles are the diaphragm and the external
intercostal muscles although the diaphragm is the more important.
2. Expansion of the thorax leads to expansion of the lung- why? Think about the role of
The two layers of the pleura are normally kept in contact due to the
properties of the pleural fluid. Expansion of the chest leads to expansion of
the lungs and therefore a reduction in intrapleural pressure. Air therefore
passess into the lungs from the atmosphere.
3. How do the Intrapleural and Intrapulmonary pressures change during the respiratory
See figure 23.14. on page 853
4. What is the role of the accessory muscles and when are these used?
Accessory muscles, the scalenes, the sternocleidomastoid and pectoralis
minor all contribute to deep or forced inspirations by raising the ribs even
more than is normal during quiet respiration.
5. The use of accessory muscles is a useful sign when assessing a patient’s respiratory
function- what do you think it signifies?
It signifies that the patient has a higher demand for oxygen than quiet
respiration can deliver either due to a high demand or due to poor
In contrast to inspiration, quiet expiration is a passive process that results from the
relaxation of the inspiratory muscles, the volume of the thoracic cavity therefore
decreases leading to an increased intrathoracic pressure and thus expiration. Read the
section on expiration page 816 to ensure you understand this.
Pressure volume relationships
Changes in volume in the thoracic cavity, as we have seen, lead to pressure changes
that result in changes in airflow. There are however a number of factors that influence
the flow of air in response to these pressure differences. Read and make notes about
the following factors (pg. 853-854).
1. Airway resistance
2. Alveolar surface tension
3. Lung compliance
The amount of air moved in or out of the lungs by ventilation therefore depends on a
number of factors. Assessment of these volumes can tell us a lot about an individual’s
health and therefore assessment of these volumes using instruments such as the
vitalograph and spirometer is commonly performed by nurses. You will be carrying out
this type of assessment during a practical session later in the module.
Combining these volumes can also give us measures called respiratory capacities.
Read about the volumes on pg. 855-856 and fill in the diagram below.
By comparing these values with normal we can use these measures to assess an
individual’s respiratory function. By asking a subject to inhale deeply and exhale as
quickly and as far as possible we can, using a vitalograph, measure the amount of air
expired in one second FEV1 (forced expiratory volume in one second) and the total
exhaled FVC (forced vital capacity).
By dividing these FEV1/FVC we can calculate the amount of FVC that an individual can
expire in one second which is normally 0.8. In individuals experiencing an obstructive
disease such as Asthma, FEV1/FVC is decreased whereas in restrictive diseases such as
pulmonary fibrosis it is increased.
The nursing care of patients with respiratory problems can often involve advising and
encouraging patients to adopt effective respiratory patterns. So what is the most
To answer this we need to consider the concept of dead space. Read the section on pg.
Fill in the blank spaces in the table below to identify, which is the most effective
respiratory pattern, slow deep ventilation or fast shallow? (AVR = (TV-dead space) x
Breathing Dead space Tidal Respiratory Minute Alveolar
pattern ml Volume Rate respiratory ventilation
ml /min volume rate
Normal 150 500 20 10,000 7000
Slow / deep 150 1000 10 10,000 8500
Rapid / 150 250 40 10,000 4000
The above calculations should prove to you that deep slow breaths are more effective.
If you are not convinced read the section on pg. 857 on alveolar ventilation rate.
Questions about the case
Re-read the case study presented at the beginning of the work sheet and using the
knowledge gained working through the sheet answer the following cases.
1. What is a pneumothorax?
2. Why does John’s lung collapse?
3. Why does only one of John’s lungs collapse?
4. Why can’t John’s right lung expand when he tries to inspire?
5. What would happen if we inserted a drain open to the air?
6. Below is a diagram of an underwater sealed drain- how does this allow the lung to
7. What type of respiratory pattern would you encourage John to adopt and how could
you encourage him to breathe in this way?
Come to the seminar with answers to the above questions and any questions you have
about the work covered by the worksheet. In preparation it would be a good idea to
review the objectives given in your BFH handbook and prepare questions.