Biophysics of Breathing Jan Jaku

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Biophysics of Breathing Jan Jaku


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Breathing is a vital function of the body, a
periodic and rhythmic process of inspiration
and expiration that co-vers the metabolic
demands of body for O2 and CO2.- must assure
the intake of O2 250 ml / min, and the
expenditure of CO2 200 ml / min. - can be
interrupted or increased volun-tarily (from the
cortex) - is governed by respiratory
centre, localized within the brainstem
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• Anatomy of Breathing
• Upper Airways - nose, nasopharynx, larynx
• Lower Airways - trachea, bronchial tree,
• Lungs (right left) -
  alveoli
• Respiratory muscles

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Breathing (Respiration) - External (the air
exchange at the level of lungs)- Internal
(the O2 and CO2 exchange at the tissue level)
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External and Internal BreathingAtmosphere
Lung Blood - Heart Extracel. liquid
Cells Oxygen
CO2
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Respiratory and Cardiovascular Relationships
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External Breathing 1. VENTILATION - cyclic
air exchange during breathing caused by the
respiratory pump muscles - diaphragm, external
and internal intercostals, abdominal, and
auxiliary muscles.2. DISTRIBUTION - mixing of
inhaled air with an air that remains within the
airways after expiration (150 ml-death
volume).3. DIFFUSION - transfer of O2 and CO2
through the alveol-ar-capillary membrane along
the partial pressure gradients (Ficks Law)4.
PERFUSION- gas transport in blood between lungs
and tissues by heart and vessels
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Ventilation - the role of respiratory
musclesDiaphragm moves downward at
inspiration and upward during
expiration (60 of volume changes in
thorax)Intercostal muscles - external
(inspiratory), and inte-rnal (expiratory) muscles
Auxiliary musles (of neck, thorax, abdomen)-
help to main respiratory muscles
(Paralelogram- see Practicals)
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Ventilation - types (in adults)

• Minute ventilation (MV) VT .fb 0.5.12 6
  (l/min)
• (VT tidal volume (0.5 l), fb breathing rate)
• Alveolar ventilation (AV) 0.35.12 4.2 (l/min)
• Comparing to Minute ventilation, the value of
• Alveolar ventilation is reduced, because the
• death volume (0.15 l ) must be substracted from
• VT

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Origine of Breathing.Action
potentials from respiratory centre drive
respiratory muscles. These, in turn are
contracted and create pressure changes. Pressure
changes enable pressure gradient and this leads
to a flow of air. Then lungs are filled (or
emptied) with air volumes.(Herings model of
breathing - see practicals)Remember these
changes A / AT REST QUIET INSPIRATION
(active process) contraction of diaphragm
external intercostals ? fall of pleural pressure
(PPl - 0.8 kPa) ? fall of intrapulmonary (Pp
- 0.1 kPa ) ? Pressure gradient ? inspiratory
airflow (VI 0.4 l/s) ? inspiratory tidal
volume (VT 0.5 l)
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OUIET EXPIRATION (mostly passive process)
recoil forces (i.e elasticity of the thoracic
wall and lung tissue passive movement of the
diaphragm upward ? slightly negative Ppl -
0.1kP, and to slightly positive intrapulmonay
pressure PP 0.5 kPa ? pressure gradient ?
expiratory airflow (VE - 0.4 l/s) ? expiratory
volume ( VT 0.5 l ) empties the lungs
B/ AT WORK FORCEFUL INSPIRATION consists of
the same processes as shown above contraction
of external intercostals auxiliary muscles
result in higher pressure gradients, and to
higher values of Ppl, PP, VE and VT
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FORCEFUL EXPIRATION (e.g. in cough, sneeze,
strong voluntary expiration) It starts sudenly
with contraction of abdominal muscles
(expiratory), creating high abdominal pressure
(PAB), very high PPl and PP pressures, also very
high pressure gradient, and thus extremely strong
expiratory airflow (velocity like tornado) and
very high expiratory volume
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Mechanics of breathing - means concomitant
changes of respiratory muscles (diaphragm,
intercostal and auxiliary muscles) creating
particular Ppl and PP, pres-sures, inspiratory
and expiratory airflows (V), and tidal volumes
(VT), resulting in some Work of breathing
(during inspiration and expiration).Work of
breathing is affected byLung compliance,
Airway resistance
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1/ Lung compliance distensibility (C) - is the
ratio between Volume of air (VT) / Pressure (P).
N 2 (l . kPa-1) Lung fibrosis C - the lung
tissue is thicker and thus its compliance
(distensibility) is lowerLung emphysema C-
lung tissue is thinner, and thus compliance
(distensibility) of the lungs is higher.
LOOP OF LUNG COMPLIANCE
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2/ Airway resistance Raw - is the relationship
between PRESSURE (P) / AIR FLOW (V)

(Unit is
kPa / l / s)In a disease like bronchial asthma
the airway resistance is high, because the
contraction of smooth muscles within the lower
airways decreases the diameter of airways. Thus,
the airflow is low, but work of muscles and
breathing is high.
LOOP OF AIRWAY RESISTANCE
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The Lung Volumes(Remember 4 main
breathing volumes and 4 capacities).Tidal volume
VT 0.5 lInspiratory reserve volume IRV 2.5
lExpiratory reserve volume ERV 1.5 lResidual
volume RV 1.2 l (consists of collapse volume
0.4 l minimal volume 0.8 l)
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The Lung CapacitiesVital
capacity VC VT IRV
ERV
Functional residual
capacity FRC ERV RVInspiratory capacity
IC VT IRVTotal capacity
TC VT IRV ERV RV
(See practicals)
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Morphology of Alveoli and Capillaries(Coupling
of Respiratory and Cardiovascular Systems)
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Partial Pressure of Gases - a drive for
diffusionATHMOSPHERIC AIR is a mixture of 21
of O2 0.04 CO2 78 of N2 ,and other
residual gases (e.g. Hellium, Neon, Argon)
Partial pressures of particular gases depend on
their concentration within the air. (DALTONS
LAW). The higher is of a gas within a gas
mix-ture, the higher is its partial pressure (and
vice versa).At normal value of barometric
pressure 101.3 kPa (760 torr,1atm) the partial
pressure of P02 is approx. 21 kPa and PCO2 is
0.04 kPa
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Remember Using DALTONS LAW one can count
partial pre-ssure of a gas according to formula
PO2 V O2 x ( PB - PH2O ) / 100 PO2
20.93 x (101.3 0.8) / 100 21.03 (kPa)PCO2
0.04 (kPa)PN2 79 (kPa)
This formula can be used for calculations of
parti-cular pressures of gases in the air, in
the airways or within the arterial and venous
blood. See next table.
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The values of GAS Volumes (in ) and their
Partial pressures (kPa), in the Atmospheric air,
Alveolar air, in the arterial and venous blood
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DIFFUSION is a transfer of gases (O2...)
through the Alveolar - capillary membrane along
the partial pressure gradients of O2 and CO2 or
N2 being governed by FICKS LAW Diffusion
rate V (P1 P2) . A . k
sP1 P2 partial
pressuresA diffusion surface (70 m2) s
thickness of Alv. - capillary membrane (0.8
um)k  diffusive constant -depends on a membrane
and gas propertiesDiffusion rate VO2 15 20
ml / min. Diffusion rate for CO2 is 20 - times
higher than for O2
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Diffusion through the alveolo - capillary membrane
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Dynamics of Diffusion
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PHYSICAL SOLUBILITY of O2 and CO 2 within the
blood plasma is under HENRYS LAW VO2 ? x
PO2 x 1000 3 ml O2 /1l arterial blood
PB VCO2 ? x
PCO2 x 1000 27 ml CO2 / 1l arter. blood
101 ?, ? - coefficients
for O2, and CO2 (respectively) PB -
atmospheric (barometric) pressureSolubility of
gases in liquids depends on their partial
pressures. Gases in liquids are in two forms
physically disolved in blood plasma, and
chemically bounded on Hemoglobine of the red
blood cells.1 l of arterial blood takes 200 ml of
O2. From this only 3 ml of O2 is physically
dissolved in plasma, and 197 ml O2 binds
chemically on Hemo-globine.
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Wishing You Pleasant Day