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1
S.M.A.R.T.
Dental Nursing Sedation
Applied respiratory anatomy & physiology
Day 2
Mr J. Henry
The airways have 3 main functions.



Oxygen delivery system (piping & tubing)
Protection of lungs from foreign matter
Warming and humidifying gases
Oxygen Delivery
i.e. The Plumbing / Piping
Which facilitate the delivery of atmospheric air to the lung alveoli
Airway Resistance
Resistance to air flow is altered by the diameter of the bronchi and
bronchioles
Increased airway resistance (narrowing) is the main problem in obstructive
airway diseases such as ASTHMA
Protection of the lungs
Air is partially filtered by nasal hairs
Bacteria and other particles, which escape this, are usually trapped in the
layer of mucous lining the airways. Cilia lining the trachea, bronchi and
bronchioles convey the mucous back up towards the larynx and out into the
pharynx were it is swallowed.
Epiglottis deflects food around laryngeal opening
Vocal folds prevent food foreign bodies entering the trachea (trigger cough
reflex)
Warming and humidifying gases
By the time the air reaches the alveoli it is warmed and humidified making gas
exchange much easier.
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Respiratory tract
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Muscles of Respiration
Normal Inspiration
(active process)
External intercostal muscles contract (pull ribs up and out)
Intercostal nerves T1-T12
Diaphragm contracts (dome of diaphragm pulled down)
Phrenic nerves, C345
Accessory muscles in the neck used during maximal inspiration (elevate
sternum and first 2 ribs)
Normal Expiration
(passive process)
Elastic recoil of stretched lungs and relaxation of the inspiratory muscles
Forced Expiration
(active process)
Internal intercostal muscles (actively pull ribs downwards and inwards)
Abdominal muscles (increase abdominal pressure, forcing diaphragm
upwards)
Lung Volumes
Volume of gas moved in and out the lungs is dependent on age, sex, body
build and level of fitness
Normal Tidal Volume 0.4 –0.5 L
Normal Respiratory Rate 12-16 breaths per minute
Respiratory minute volume = Tidal Vol x Resp Rate
=
0.5
X 12
=
6 L / min
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Dead Space
Not all the inspired air will actually reach the areas within the lungs where gas
exchange can takes place.
Anatomical Dead Space
Includes all the upper airway down to the bronchial level. No gas exchange
takes place in these areas. The air, which enters these areas during
inspiration, is expelled again during expiration without contributing to
pulmonary oxygenation.
Physiological Dead Space
Anatomical dead space plus alveoli in the lung, which are ventilated but
receive very little pulmonary perfusion. (Normally physiological dead space is
about 150ml)
Alveolar ventilation rate = (tidal volume –dead Space) x Respiratory rate
(
0.5
-
.15
) x
12
Alveolar ventilation rate = 4.2 L/min
Inspiratory Reserve Volume (IRV)
It is usually possible for a person to inhale a further 3 L of air over and above
the tidal volume, this is called the inspiratory reserve volume (IRV).
Expiratory Reserve Volume (ERV)
If at the end of a normal exhalation, as much air as possible is forcibly
expelled from the lungs, a further 1 L can be eliminated; this is called the
expiratory reserve volume.
Vital Capacity (VC)
The total volume of air that can be expired after a maximum inspiration (TV +
IRV + ERV) is known as the vital capacity. (VC) which is about 4.5 L for an
adult.
Residual Volume (RV)
After maximum respiratory expiration approximately 1.5 L of air, the residual
volume (RV), remains in the lungs.
Total Lung Capacity
The total lung capacity is around 6 L (TV + IRV + ERV + RV).
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Oxygen Transport
Vast majority O2 in blood is transported within RBC bound to
haemoglobin; the reminder is dissolved in plasma.
Each haemoglobin molecule has 4 globin elements, each attached to
separate pigmented haem element
Oxygen binds reversibly with the haem elements forming
oxyhaemoglobin. Single molecule of haemoglobin can carry up to four
O2 molecules
Carbon Dioxide Transport
60-70% CO2 is carried in the plasma as bicarbonate ions (HCO3-) (CO2
diffuses into RBC’s where it reacts with water and is converted into
bicarbonate ions by the action of carbonic anhydrase enzyme in RBC’s. The
bicarbonate ions then diffuse back out into the plasma)
20-30% CO2 is carried in the blood as carbamino groups (formed by a
reaction between CO2 and amino acid residues in plasma proteins)
10 % CO2 is carried in the blood as dissolved CO2
Control of Respiration
The rate and depth of respiration is controlled by the respiratory (ventilation)
centre, which is situated in the brain.
Breathing can be altered by chemical and nervous control.
There are chemoreceptors situated in the aorta and carotid arteries and the
respiratory centre.
They are sensitive to a rise in the level of circulating carbon dioxide (C0 2), a
drop in blood pH or reduced levels of circulating oxygen (02).
Stretch receptors, situated in the lungs and respiratory muscles, can stimulate
the vagus nerve to inhibit inspiration.
Emotions can also affect breathing by influencing the higher centers of the
brain.
An increased partial pressure of carbon dioxide (Paco2) (hypercapnia) is a
more significant and sensitive stimulus for respiration than hypoxia;
a low Pao2 will cause an increase in ventilation rate but this is far less
dramatic than the hypercapnic drive.
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The hypoxic drive is a back-up mechanism, but it may assume importance in
patients with chronic lung disease.
Factors, which might affect normal breathing
and Oxygen Delivery to lungs
Pulse Oximeter
Non-invasive electromechanical monitoring of arterial SaO2
Allows early detection of a drop in Oxygen Saturation SaO2,
If monitoring the patient clinically, may only notice clinical signs of hypoxia /
cyanosis if saturation drops to 75 %, by then it may be to late !!
Oxygen Dissociation curve
Under normal conditions blood is 97% saturated at the PO2 of systemic
Arterial blood (13 kPa).
Saturation falls to 75% on reducing the PO2 to 5.3 kPa , the value found in
systemic venous blood.
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Factors which might affect normal breathing and oxygen delivery to lungs
Anatomical Problems
Narrowing of Nasopharynx
- common cold, Nasal polyps, enlarged adenoids
Narrowing of Oropharynx
- large tongue, large soft palate, enlarged tonsils, sore throat, restricted
opening
Narrowing of Laryngopharynx
- laryngitis, build up of mucus or catarrh in smokers
Medical Problems
Respiratory disorders
Musculoskeletal disorders
Cardiovascular disorders
Haematological disorders
- Asthma , chest infection, bronchitis
- Multiple sclerosis, myasthesia gravis
- Heart failure, atherosclerosis
- Anaemia
Other Problems relevant to dentistry
Shared airway
- Dentist drill , suction, water, mirror, matrix bands all crammed in!!!.
Position of the patient
Lying back , chin down tends to close airway
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Patient upright
Patient Lying back
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What do you do if patient obstructs there airway??
 Clear blockage
 Head tilt
 Chin lift
Pulse
Common sites
Carotid Artery
Brachial Artery
RadialArtery
Assess
Rate (beats per minute)
Rhythm ( regular / irregular )
Volume (strong / weak)
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