- Normal Tidal Breathing
- Diaphragm and intercostal muscles contract to increase the size of the thorax.
This results in increase in negative pressure in pleura. The gradient between atmosphere
and alveoli causes air to enter lung - inspiration. During this process elastic
recoil forces increase. Once the inspiration is stopped the elastic recoil forces in the
lung causes expiration. Expiration is passive and no muscles contract to produce
- Accessory Inspiratory Muscles
- When one takes a deep breath, accessory muscles of respiration are brought into
action (Scalene, sternomastoid and trapezium ). Scalene
is the first muscle to start contracting and gradually other two muscles are brought into
When these muscles contract for tidal breathing - it is
abnormal. It is easy to recognize contraction of sternomastoid and trapezium but is a late
phenomenon. Routinely one should feel the scalenus muscle during quiet breathing. Stand
behind the patient, lay your fingers over the scalenus behind the sternomastoid in the
supraclavicular fossa. When the muscle contracts it can be recognized as narrow band of
If the accessory inspiratory muscles are contracting for quiet breathing most
likely FEV volume is close to 30% and is between 1 - 1.5 liters. If a patient is
complaining of shortness of breath one should always be able to feel scalene muscle
contraction during quiet breathing. In psychogenic or anxiety induced shortness of breath
one would not feel the contraction of accessory muscles.
If accessory muscles are hypertrophied, it indicates that the process is
- Accessory Expiratory Muscles
- Normal tidal expiration is passive and there is no muscle contraction. Expiratory
muscle contraction is always accessory. When you force expiration, expiration muscles come
into play. Abdominal muscles and intercostals are expiratory muscles. If a patient
is contracting abdominal muscles for quiet respiration it is abnormal and he is attempting
to force expiration.
- Forced Expiration
- Only peak flows can be increased by forced expiration. The flow rates
cannot be increased for most of expiratory phase by forcing expiration. The increasing
positive pressure in pleura compresses airway and further decreases airway size thus
countering the increased force to expire.
In patients with increased
airway resistance patients attempt to increase airflow. They have two options either to
adopt a rapid shallow breathing or to use pursed lip breathing to counter
auto-peep and enhance emptying of lung. When airways are severely narrowed, air trapping
occurs and patient may breath with a very high FRC and the only way he can breath is to
adopt a rapid shallow breathing.
- Negative Pleural Pressure Assessment
- To take a deep inspiration one has to increase the negative pressure in pleura.
You can clinically detect increased negative pressure in pleura by watching for retraction
of supraclavicular fossa, intercostal spaces and downward movement of trachea.
these features are noted for quiet breathing obviously patient is making extra effort to
increase negative pressure in pleura to accomplish tidal breathing, which is abnormal.
- Position and Inspiratory Muscles Contribution to Function
- In erect position for tidal breathing diaphragm contributes 70% and intercostal
30%. In supine position contribution of diaphragm increases to 90%. Hence patients with
diaphragmatic paralysis become severely short of breath in supine position.
inspiratory muscles work optimally in erect position. They are inefficient in supine
position. This is one of the reasons why asthmatics like to stand or sit up with acute
- Position and Expiratory Muscles Contribution to Function
- The effect of expiratory muscles on diaphragm is optimal in erect position. When
abdominal muscles contract, it increases intra-abdominal pressure and passively pushes the
diaphragm up to empty air from lungs. In supine position the diaphragm is already high in
thorax and there is not much room to push it higher with forced expiration.
- Position, Lung, and Airway Size: Effect of Gravity
- The size of the lung is large in erect position, decreases in supine
position and becomes further smaller in lateral decubitus position (dependent lung).
phenomenon should be taken advantage of, in patients with partial airway obstruction. If
an asthmatic has no rhonchi in standing position, listen to his chest in supine and in the
dependent lung in lateral decubitus position. If there is occult airway narrowing this
maneuver will bring out the rhonchi. This is also one of the main reasons why asthmatics
may not want to lay supine as their airways become narrowed.
In patients with unilateral partial airway obstruction decubitus exam is very
- Position and Breath Sounds
- In the erect position breath sounds (and thus ventilation) is harsh in
bases. In lateral decubitus position the breath sounds are harsher
in the dependent lung. This is a gravity induced phenomenon. The resting (FRC) alveolar
size is smaller and is in the steep part of compliance curve. As a result larger volume
change occurs for a given change in negative pressure.
lung disease breath sounds will not increase when the deceased lung is dependent.
- Thoraco-Abdominal Partition
- Normal males have dominant abdominal component, while women have dominant
thoracic component. If there is acute abdomen, breathing will become primarily thoracic.
- Function of Lung
- Is to provide oxygenation, get rid of CO2 the metabolic end product and maintain
pH. When the lungs fails to perform adequately patients can become hypoxic, retain CO2 and
develop respiratory acidosis. Hypoxia leads to central cyanosis. Central cyanosis can be
detected if conjunctive, mucous membrane of tongue, lips, nose, and fingers are blue. The
hands will be warm, fingers may be clubbed. Erythrocytosis could be detected in
conjunctive in chronic hypoxic states.
CO2 retention in extreme state
can be recognized by papilledema
pH changes are not easily detectable. Our ability to clinically detect hypoxia,
CO2 retention and pH changes is very poor and should not be relied on. Blood gases is
the best way to assess pulmonary function.
- Respiratory Rate
- Normal baseline respiratory rate is between 10-14 per minute. Rate should be
counted after patient is comfortable and without his knowledge. Decreased rate would
suggest suppression of respiratory center. (sedatives, raised intracranial tension)
Tachypnea is also abnormal and can be seen in a variety of disorders.
- Pattern of Breathing
- Normal respiration is regular with occasional sighing. Abnormal patterns are
Kussmaul's, biot's, Cheyne-Stokes etc. Multiple sighs would suggest anxiety state.
- Pattern of Breathing in Sleep
- In normal, the rate slows but is regular. In patients with sleep apnea
syndrome, one gets cyclical respiration. Pattern varies depending whether it is
obstructive or central type.
- Size of Thorax
- The size of thorax is determined by the balance between elastic recoil of lungs
and chest wall compliance. In normal, the FRC position is usually at 60% of the TLC. At
this position muscle length tension curve is optimal for muscle contraction. If the
elastic recoil of lung decreases the resting position of thorax will be larger, it maybe
80% of the TLC position. This position is very inefficient to generate force by muscles
and leads to shortness of breath.
- Symmetry of Hemithorax
- Both sides are equal in size and asymmetry is abnormal. Unilateral lung or
pleural disease alters negative pressure in pleura, affecting the resting size of
hemithorax. e.g. In pneumothorax the negative pressure in pleura is lost and there is
nothing to hold chest wall down. Hemithorax on that side will assume TLC position. In
patients with atelectasis the negative pressure in pleura increases and the size of
hemithorax will become smaller.
It is best to assess
symmetry of hemithorax with patient laying flat in bed without pillows. Stand either
at head or foot end and look tangentially at the thorax level to assess asymmetry.
- Has intra and extra thoracic components. The extra thoracic component narrows
during inspiration and widens during expiration. The intrathoracic component narrows
during expiration and widens during inspiration. If there is obstruction it gets worse
during the phase of inspiration, when the airway size is smaller.
- AP Diameter of Thorax
- The AP diameter of the thorax is usually less than transverse diameter in resting
state i.e.; in FRC position. If one takes a deep breath and attains the TLC position, AP
diameter is equal to transverse diameter giving the barrel shape. In patients with COPD
where the FRC is elevated they end up having barrel shape to thorax in resting position.
As we age and loose some elastic recoil to lungs similar situation arises.
- Chest Expansion
- Chest expansion can be measured with a tape
encircling around nipple in males and under breast in women. Normal chest expansion from
complete expiration to inspiration varies between 3 to 5 cms. In patients where the FRC is
high and in disease states of lung, pleural or chest wall the chest expansion will be
Chest expansion is symmetrical. Asymmetrical chest
expansion is abnormal. The hemithorax with decreased expansion is the abnormal side.
- Expiration Time
- Expiration time is measured by listening with stethoscope over Trachea.
Expiration even though is physiologically longer than inspiration, on auscultation over
lung fields it will be shorter. The air moves away from alveoli towards central airway
during expiration, hence you can hear only early third of expiration. However over Trachea
the entire duration of expiration can be heard. The normal forced expiration time
is less than 5 seconds. In patients with obstructive lung disease forced expiration time
is prolonged and is longer than 5 seconds.
- Expiratory Force
- Force of expiration is crudely measured by the ability to blow a lit matches at a
length of 12" from mouth. This corresponds to peak expiratory flow. Inability
to blow the matches at this length would imply decreased peak flows.
- Shortness of Breath
- Exercise, FRC... effort, position of comfort, lack of ... effort and CO2
- Changes with Aging
- As we age, the thorax tends to assume a barrel shape. The lung gradually looses
elastic recoil resulting in higher FRC. The cartilages calcify and the
compliance of the chest wall decreases. Osteoporosis results in kyphosis. All of
these factors contribute to barrel shaped chest and decreased chest expansion. Expiratory
force decreases as result of decreased elastic recoil of lungs. Arteriosclerotic
changes occur to cerebrovascular system. This results in alteration of the respiratory
center and can lead to Cheyne stokes respiration.