Lung Physiology Flashcards
Requirement of respiratory pump
To move 5 litres/minute of inspired gas
(Cardiac output 5 litres/min)
How does respiratory pump operate
Generation of negative intra-alveolar pressure
Inspiration active requirement to generate flow
Bones, muscles, pleura, peripheral nerves and airways all involved
Function of bony structures in respiratory pump
Bony structures support respiratory muscles and protect lungs
Rib movements; pump handle and water handle
Muscles of inspiration
Largely quiet and due to diaphragm (C3/4/5) contraction
External intercostals (nerve roots at each level)
Muscles of expiration
Passive during quiet breathing
Pleura
2 layers- visceral and parietal
Potential space only between these (few millilitres of fluid)
Respiratory pump nerves
Sensory: sensory receptors assessing flow, stretch, e.t.c
C fibres
Afferent via vagus nerve (10th cranial nerve)
Autonomic sympathetic, parasympathetic balance
Static lungs
Both chest wall and lungs have elastic properties and a resting (unstressed) volume
Changing this volume requires force
Release of this force leads to a return to the resting volume
Pleural plays an important role linking chest wall and lungs
Just above functional residual capacity
Gas exchange ventilation
Bulk flow in the airways allows;
O2 and CO2 movement
Large surface area required, with minimal distance for gases to move across.
Total combined surface area for gas exchange 50-100 m2
300,000,000 alveoli per lung
Gas exchange perfusion
Adequate pulmonary blood supply needed
Total combined surface area for gas exchange
50-100 m^2
Alveolar ventilation- dead space
Dead space
Volume of air breathed in not contributing to ventilation
Last volume of air remains in conducting airways (or small amount not used in alveoli)
Anatomical: approx. 150mls
Alveolar: approx. 25mls
Physiological (anatomic + alveolar) = 175 mls
Anatomic dead space
150 mls
Alveolar dead space
25 mls
Physiological dead space
175 mls
Arterial bronchial circulation
Branches of bronchial arteries
Paired branches arising laterally to supply bronchial and peri-bronchial tissue and visceral pleura
Systemic pressure (I.e. LV/aortic pressures)
Relaxed diaphragm shape
Domed
Contracted diaphragm
Lowers and flattens
Diaphragm nerve origins
C3,C4,C5
Venous drainage of bronchi
Bronchial veins drain ultimately into superior vena cava
Functional residual capacity
Minimum amount of air in lungs
Arterial pulmonary circulation
Left and right pulmonary arteries run from right ventricle
Low(er) pressure system (I.e. RV/ pulmonary artery pressures)
17 orders of branching
How many orders of branching in pulmonary circulation
17
Broncho-vascular bundle
Pulmonary artery and bronchus run parallel
Number of capillaries per alveolus
1000
Alveolar perfusion
Each erythrocyte may come into contact with multiple alveoli
Erythrocyte thickness an important component of the distance across which gas has to be moved
At rest, 25% the way through capillary, haemoglobin is fully saturated
At rest what percentage of way through capillary is haemoglobin fully saturated
25%
What does perfusion of capillaries depend on
Pulmonary artery pressure
Pulmonary venous pressure
Alveolar pressure
Ventilation and perfusion
Matching ventilation and perfusion important
Hypoxic pulmonary vasoconstriction
Pulmonary vessels have high capacity for cardiac output
- 30% of total capacity at rest
Recruiting of alveoli occurs as a consequence of exercise
PaCO2
Arterial CO2
PACO2
Alveolar CO2
PiO2
Pressure of inspired oxygen
FiO2
Fraction of inspired oxygen (0.21)
Constant at all altitudes
VA
Alveolar ventilation
VCo2
CO2 production
Hypoxic pulmonary vasoconstriction
Constrict blood vessels going to areas of lungs with low oxygen concentrations
CO2 elimination
PaCO2 = kVCO2 /VA
PaCO2 is inversely proportional to alveolar ventilation
Normal PaCO2
4-6 kPa
3 ways in CO2 carried
Bound to haemoglobin
Plasma dissolved
As carbonic acid
Is fraction of inspired oxygen same at all altitudes
0.21 for all altitudes
Differences in pressure affects amount of air inspired
Physiological causes of high CO2
V’A reduced: reduced minute ventilation
V’A reduced: increase dead space ventilation by rapid shallowing breathing
V’A reduced: increase dead space by ventilation/ perfusion mismatching (V/Q)
Increased CO2 production
Alveolar gas equation
PAO2 = PiO2 - PaCO2/R
R= respiratory quotient (ratio of vol CO2 released/ vol O2 absorbed- assume = 0.8)
Respiratory quotient
ratio of Vol CO2 released/Vol O2 absorbed, assume = 0.8
Causes of low PaO2 (hypoxaemia)
Alveolar hypoventilation
Reduced PiO2
Ventilation/perfusion mismatching (V/Q)
Diffusion abnormality
Hb dissociation curve
Sigmoid shape
- As each O2 molecule binds, it alters the conformation of haemoglobin, making subsequent binding easier (cooperative binding)
Varying influences:
2,3 diphosphoglyceric acid
H+
Temperature
CO2
Varying influences of Hb dissociation curve
2,3 diphosphoglyceric acid
H+
Temperature
CO2
Acid-base control
Body maintains close control of pH to ensure optimal function (eg enzymatic cellular reactions)
Dissolved CO2/carbonic acid/respiratory system interface crucial to the maintenance of this control
AA difference
Difference between PAO2 and PiO2
Indication of how sick a patient is
Normal pH
7.40
(7.36-7.44)
Normal H+ concentration
40 nmol/l (34-44 nmol/l)
What can be measured on a arterial blood gas
PaCO2
PaO2
pH
HCO3-
Buffers
Blood and tissue buffers important
Carbonic acid / bicarbonate buffer in particular
CO2 under predominant respiratory control (rapid)
HCO3- under predominant renal control (less rapid)
The respiratory system is able to compensate for increased carbonic acid production, but;
Elimination of fixed acids requires a functioning renal system
CO2 acid base control
Predominantly respiratory control
HCO3- acid base control
Predominately renal control
Carbonic acid equilibrium
Carbonic anhydride
CO2 + H20 <-> H2CO3 <-> H+ + HCO3-
Henderson-Hasselbalch equation
pH = 6.1 + log10[[HCO3-]/[0.03 x PCO2]]
Henderson-Hasselbalch equation- in order to keep pH at 7.40, log of the ratio must equal…
1.3
As PaCO2 rises (respiratory failure)
HCO3- must also rise (renal compensatory mechanism) to allow this
4 main acid-base disorders
Respiratory acidosis, respiratory alkalosis, metabolic acidosis, metabolic alkalosis
Respiratory acidosis
increased PaCO2, decreased pH, mild increased HCO3-
Respiratory alkalosis
decreased PaCO2, increased pH, mild decreased HCO3-
Metabolic acidosis
reduced bicarbonate and decreased pH
Metabolic alkalosis
increased bicarbonate and increased pH
pH equation
-log10[H+]
Where is the greatest resistance to airflow?
The greatest point of resistance is the segmental bronchi, because the lower and smaller airways are much more numerous, so collectively have a greater cross-sectional area and therefore offer less resistance.
Inspiration
• the diaphragm contracts and flattens, increasing the vertical length of the thoracic cavity
• The external intercostal muscles contract (and the internal intercostal muscles relax) causing the ribs to move up and out, increasing the lateral length of the thoracic cavity
• As a result, the volume of the thoracic cavity increases
• As the lungs are held against the inner thoracic wall by the pleural seal, they also undergo an increase in volume.
• an increase in lung volume results in a decrease in thepressurewithin the lungs- the pressure of the environment external to the lungs is now greater than the environment within the lungs, meaning air moves into the lungs down the pressure gradient.
Describe the anatomical structure air will pass through as it travels from the nose to the alveoli.
Upper airways:
• The air passes through the nares into the nasopharynx. It then continues through the oropharynx and laryngopharynx before entering the larynx and then the trachea.
Lower airways:
• The trachea then bifurcates into the right and left main bronchi. The left main bronchi splits into 2 lobar bronchi and the right main bronchi into 3 lobar bronchi, which then further subdivide into 10 segmental bronchi per lung. The air then travels through the terminal bronchioles (which are the last structure of the conducting airways) into the respiratory bronchioles, before entering the alveolar ducts and alveoli.
Expiration
• the diaphragm relaxes and returns to its resting position, reducing the superior/inferior dimension of the thoracic cavity
• The internal intercostal muscles contract (and the external intercostal muscles relax), depressing the ribs and sternum, reducing the anterior/posterior dimension of the thoracic cavity
• This decreases the volume of the thoracic cavity
• The elastic recoil of the lung tissue allows them to return to their normal size
• This results in an increases in pressure within the lungs. Pressure inside the lungs is now greater than in the external environment, so air moves out of the lungs down the pressure gradient
Accessory muscles involved in active inspiration
• Scalenes - elevates the upper ribs.
• Sternocleidomastoid - elevates the sternum.
• Pectoralis major and minor - pulls ribs outwards.
• Serratus anterior - elevates the ribs (when the scapulae are fixed).
• Latissimus dorsi - elevates the lower ribs.
Accessory muscles involved in active expiration
• Anterolateral abdominal wall - increases the intra-abdominal pressure, pushing the diaphragm further upwards into the thoracic cavity.
• Internal intercostal - depresses the ribs.
• Innermost intercostal - depresses the ribs.
In tissues where CO2 concentrations are high, what happens to affinity of haemoglobin for oxygen and the corresponding P50
Oxygen affinity is decreased
Increased P50
P50
the oxygen tension when hemoglobin is 50 % saturated with oxygen. When hemoglobin-oxygen affinity increases, the oxyhemoglobin dissociation curve shifts to the left and decreases p50. When hemoglobin-oxygen affinity decreases, the oxyhemoglobin dissociation curve shifts to the right and increases p50
What is the effect of carbon monoxide on the relationship between oxygen and haemoglobin
Causes haemoglobin to have an increased affinity for oxygen
CO binds to haemoglobin so still causes conformational change allowing more oxygen to bind
What is haemoglobin saturation at 40mmHg in the capillaries
75% (other 25% is released for respiring tissues)
Production of lactic acid and carbonic acid from respiring tissues encourages release of oxygen for respiring tissues. Why?
Decreased pH decreases haemoglobin’s affinity for oxygen
Alveolar ventilation equation
(Tidal volume - dead space) x respiratory rate
What kind of molecule is surfactant
Phospholipid
What kind of molecule is surfactant
Phospholipid
Where is the least resistance to airflow
Terminal bronchioles
Trans pulmonary pressure
Always positive relative to atmospheric pressure
Alveolar pressure - intrapleural pressure
Intrapleural pressure
Always positive due to elasticity:
- lungs tend towards collapse
- chest wall tends towards enlarging
FiO2 is ALWAYS
0.21
PiO2 at sea level?
100Kpa x 0.21 = 21KPa
Lung expansion is limited by compliance- determined by
Amount of elastic tissue
Surface tension in alveoli- decreased by surfactant
CADET- shifts O2-Hb curve to the right
CO2
Acidity
DPG
Exercise
Temperature
The diaphragm plays a major role in breathing.
Which nerve supplies motor function to the diaphragm?
Phrenic Nerve
The Vagus Nerve and its branches have both motor and sensory functions.
Which of the following structures receives its voluntary motor function from the vagus nerve and its branches?
Larynx
How would the resistance of an airway change if its radius was halved
16 times higher
Which control centre is responsible for controlling basic respiratory rhythm
Dorsal respiratory group
Lowest surface marking of the lungs
Anteriorly = 6th rib
Mid-axillary - 8th rib
Posteriorly- 10th rib
Expiration or exhalation is the process of letting air out of the lungs during the breathing cycle. Which mechanism is primarily responsible for this process?
Elastic recoil of lung
