Medical physiology
BREATHING
Aim and components of breathing: supply the cells in the body with O2 and get rid of the CO2 that is
produced in the cellular metabolism
Processes involved in breathing
- ventilation: transport of gasses in and out of the lungs
- gas exchange: diffusion between alveoli and blood
- ventilation/perfusion ratio: tuning ventilation and lung perfusion
- gas transport: transport of gasses in the blood
- gas exchange (or diffusion): exchange of gas between blood and cells
- cellular respiration: use of O2 and production of CO2 in cells
Anatomical death space: conducting zone (trachea, primary bronchi, smaller bronchi, bronchioles)
Spirometry:
- VT: tidal volume: volume inhaled and exhaled
during quiet breathing
- IRV: inspiratory reserve volume: maximum
volume above tidal volume that we can inhale
into our lungs
- ERV: expiratory reserve volume: maximum
volume that we can exhale from our lungs at
the end of a normal breath
- RV: residual volume: volume of air remaining
in the lungs after a full expiration
- FRC: functional residual capacity: air already
in the lungs before inhalation (start volume) =
ERV + RV
- IC: inspiratory capacity = VT + IRV
- VC: vital capacity: maximal amount of air you
can breathe in and out = IC + ERV
- TLC: total lung capacity: all air that is possible for the lungs to contain = VC + RV
Ventilation
- Boyle’s law: P * V = constant → ventilation causes pressure changes in the lung
Inhalation
- diaphragm contracts → thoracic volume ↑ → pressure lungs ↓
- external intercostal muscles contract → inhalation
Exhalation
- diaphragm relaxes → thoracic volume ↓
- internal intercostal muscles contract → exhalation
Forces to be overcome during breathing
1. Elastic forces (‘static’)
- retraction forces lung
- retraction forces thorax wall
2. Resistance forces (‘dynamic’)
,- airway resistance
- tissue resistance
,Lungs want to be small, but they cannot, because of the little fluid between the pulmonary and
parietal pleura
Thorax wants to be big, sticks to the lungs
Static (or relaxation) volume-pressure curve
- pneumothorax: collapsed lungs, big thorax
- at FRC: Plungs = Pthorax
Compliance: volume change that occurs with a
certain pressure change
- steepness of the static V/P-curve gives
information about the compliance
→ less steep: hard to expand lungs
→ more steep: easy to expand lungs
- factors determining the lung compliance
1. Elastin- and collagen fibres: in life you lose
elastin → stiffness ↑
2. Surface tension of the alveoli: layer of fluid in
alveolar membrane → wants to pull together →
lung wants to be smaller
- strong retraction force of lungs in total
- collapse of smaller alveoli into bigger ones
- type 2 pneumocytes in alveoli: release
surfactant → surface tension↓
- more pneumocytes in smaller alveoli
Airway resistance: caused by friction of gasses in the airways
- 80-90% of the resistance that has to be overcome
- radius ↓ → massive resistance ↑
Dynamic volume-
pressure relationship
- intrapleural pressure at
start of inspiration: - 5
cm H2O
- breathe in: 0.5 L of air
- intrapleural pressure at
end of inspiration
Work of breathing = area
under the curve
- necessary to expand the
lungs
- energy released by
recoiling of the lung
overcomes the R during
expiration → expiration =
free
, Shortness of breath /
dyspnoea: increased work
of breathing compared to
normally under those
circumstances
1. R↑: more effort to
inhale and exhale (extra
inspiratory and expiratory
muscle required)
2. Compliance ↓: more
stiffness
3. Compliance ↑:
breathing in is
easy, but
breathing out
does not go for
free
- emphysema:
lose walls
between alveoli
→ bigger alveoli
→ smaller
surface tension
→ easy to
expand the lungs → less recoiling → breathe out is harder
Forced expiration
- R↑ → forced expiration goes slower FEV1/FVC = 47%
instead of 80%
- airway obstruction
- FVC = forced vital capacity
- FEV1 = expired volume in the first second after maximal
inspiration
Air-trapping: due to forced expiration the pressure in the
intrapleural space and in the alveoli is positive → air leaves
the lungs → pressure in bronchiole drops quickly →
pressure over the lung wall is suddenly negative → bronchiole pushed close
- can be prevented by lip-pursing
Respiratory minute volume (RMV): volume inhaled or exhaled from a person’s lungs per minute
- with a constant RMV and changing respiratory frequency: 12-20 breaths per min → least effort
- physiological dead space (VD): anatomical and alveolar dead space (high alveoli are not perfused) =
150 ml (if not otherwise specified)
- O2 is less soluble than CO2 → less O2 free dissolved than CO2 in blood
Partial pressure of a gas in a fluid = partial pressure of that gas in the air mixture to which the fluid is
exposed
BREATHING
Aim and components of breathing: supply the cells in the body with O2 and get rid of the CO2 that is
produced in the cellular metabolism
Processes involved in breathing
- ventilation: transport of gasses in and out of the lungs
- gas exchange: diffusion between alveoli and blood
- ventilation/perfusion ratio: tuning ventilation and lung perfusion
- gas transport: transport of gasses in the blood
- gas exchange (or diffusion): exchange of gas between blood and cells
- cellular respiration: use of O2 and production of CO2 in cells
Anatomical death space: conducting zone (trachea, primary bronchi, smaller bronchi, bronchioles)
Spirometry:
- VT: tidal volume: volume inhaled and exhaled
during quiet breathing
- IRV: inspiratory reserve volume: maximum
volume above tidal volume that we can inhale
into our lungs
- ERV: expiratory reserve volume: maximum
volume that we can exhale from our lungs at
the end of a normal breath
- RV: residual volume: volume of air remaining
in the lungs after a full expiration
- FRC: functional residual capacity: air already
in the lungs before inhalation (start volume) =
ERV + RV
- IC: inspiratory capacity = VT + IRV
- VC: vital capacity: maximal amount of air you
can breathe in and out = IC + ERV
- TLC: total lung capacity: all air that is possible for the lungs to contain = VC + RV
Ventilation
- Boyle’s law: P * V = constant → ventilation causes pressure changes in the lung
Inhalation
- diaphragm contracts → thoracic volume ↑ → pressure lungs ↓
- external intercostal muscles contract → inhalation
Exhalation
- diaphragm relaxes → thoracic volume ↓
- internal intercostal muscles contract → exhalation
Forces to be overcome during breathing
1. Elastic forces (‘static’)
- retraction forces lung
- retraction forces thorax wall
2. Resistance forces (‘dynamic’)
,- airway resistance
- tissue resistance
,Lungs want to be small, but they cannot, because of the little fluid between the pulmonary and
parietal pleura
Thorax wants to be big, sticks to the lungs
Static (or relaxation) volume-pressure curve
- pneumothorax: collapsed lungs, big thorax
- at FRC: Plungs = Pthorax
Compliance: volume change that occurs with a
certain pressure change
- steepness of the static V/P-curve gives
information about the compliance
→ less steep: hard to expand lungs
→ more steep: easy to expand lungs
- factors determining the lung compliance
1. Elastin- and collagen fibres: in life you lose
elastin → stiffness ↑
2. Surface tension of the alveoli: layer of fluid in
alveolar membrane → wants to pull together →
lung wants to be smaller
- strong retraction force of lungs in total
- collapse of smaller alveoli into bigger ones
- type 2 pneumocytes in alveoli: release
surfactant → surface tension↓
- more pneumocytes in smaller alveoli
Airway resistance: caused by friction of gasses in the airways
- 80-90% of the resistance that has to be overcome
- radius ↓ → massive resistance ↑
Dynamic volume-
pressure relationship
- intrapleural pressure at
start of inspiration: - 5
cm H2O
- breathe in: 0.5 L of air
- intrapleural pressure at
end of inspiration
Work of breathing = area
under the curve
- necessary to expand the
lungs
- energy released by
recoiling of the lung
overcomes the R during
expiration → expiration =
free
, Shortness of breath /
dyspnoea: increased work
of breathing compared to
normally under those
circumstances
1. R↑: more effort to
inhale and exhale (extra
inspiratory and expiratory
muscle required)
2. Compliance ↓: more
stiffness
3. Compliance ↑:
breathing in is
easy, but
breathing out
does not go for
free
- emphysema:
lose walls
between alveoli
→ bigger alveoli
→ smaller
surface tension
→ easy to
expand the lungs → less recoiling → breathe out is harder
Forced expiration
- R↑ → forced expiration goes slower FEV1/FVC = 47%
instead of 80%
- airway obstruction
- FVC = forced vital capacity
- FEV1 = expired volume in the first second after maximal
inspiration
Air-trapping: due to forced expiration the pressure in the
intrapleural space and in the alveoli is positive → air leaves
the lungs → pressure in bronchiole drops quickly →
pressure over the lung wall is suddenly negative → bronchiole pushed close
- can be prevented by lip-pursing
Respiratory minute volume (RMV): volume inhaled or exhaled from a person’s lungs per minute
- with a constant RMV and changing respiratory frequency: 12-20 breaths per min → least effort
- physiological dead space (VD): anatomical and alveolar dead space (high alveoli are not perfused) =
150 ml (if not otherwise specified)
- O2 is less soluble than CO2 → less O2 free dissolved than CO2 in blood
Partial pressure of a gas in a fluid = partial pressure of that gas in the air mixture to which the fluid is
exposed
