Pulmonary Pulmonary VentilationVentilation

And lung capacitylung capacity

BY BY RANA DASRANA DAS

External respiration can be divided into4 major functional events

1) Ventilation2) Diffusion3) Transport of O2 and CO2 in the

blood, body fluids, to and from the cells

4) Regulation of ventilation

PULMONARY VENTILATION BOYLE’S LAW Gas pressure in closed container is

inversely proportional to volume of container

Pressure differences and Air flows

Mechanics of pulmonary ventilation

Diaphragm – which increase and decrease the vertical diameter of the chest cavity.

Intercostal muscles – affect the anteroposterior diameter of the chest cavity by moving the ribs.

Internal intercostal muscle (downward and backward) lower the ribs and sternum reducing the anteroposterior diameter

External intercostal muscle (downward and forward) raise the ribs and sternum increasing the anteroposterior diameter of the thoracic cavity

ExpirationExpiration InspirationInspiration

Increased vertical Increased vertical diameterdiameter

Increased A-P Increased A-P diameterdiameter

External External intercostals intercostals contractedcontracted

Internal Internal intercostals intercostals relaxedrelaxed

Abdominals Abdominals contractedcontracted

Elevated Elevated rib cagerib cage

Diaphragmatic Diaphragmatic contractioncontraction

Inspiration/Inhalation

Diaphragm & Intercostal muscles Increases volume in thoracic cavity as

muscles contract Volume of lungs increases Intrapulmonary pressure decreases

(758 mm Hg)

Expiration/Exhalation

Muscles relax Volume of thoracic cavity decreases Volume of lungs decreases Intrapulmonary pressure increases

(763 mm Hg) Forced expiration is active

Factors that influence pulmonary air flow

F = P/R Diameter of airways, esp. bronchioles Sympathetic & Parasympathetic NS

Various pressure in the lungsPleural pressure – is the pressure of fluid in the narrow space between the visceral and parietal pleura, normally slightly negative pressure

The normal pleural pressure at the beginning of inspiration is –5cm of H2O (it reach about –7.5cm of H2O due to movement of the chest cage)

The pleural pressure at the beginning of expiration is–7.5cm of H2O to reach –5cm of H2O

Alveolar pressureAlveolar pressure: – is the pressure inside the lung alveoli

During inspiration: ↓ –1cm of H2O (this slight negative pressure is enough to move about 0.5 liter of air into the lungs in the first 2 second of inspiration)

During expiration: it rises to about +1cm of H2O (this forces 0.5 liter of inspired air out of the lungs during the 2 to 3 seconds of expiration

Inspiration and expiration

The work done in breathing

the work of inspiration can be divided into 3 fractions:

The work required to expand the lungs against its elastic forces called compliance work or elastic work.The work required to overcome the viscosity of the lung and chest wall structures called tissue resistance work.The work required to overcome airway resistance called airway resistance work.

Work energy required for respiration:during normal quiet respiration = 2 to 3% of the total work energy (↑ to 50 fold in exercise, ↑ airway resistance).

Pulmonary volumes and capacities

1) Tidal volume – is the volume of air inspired or expired with each normal breath = 500ml in young adult man.

2) Inspiratory reserve volume – is the extra volume of air that can be inspired over and beyond the normal tidal volume = 3000ml.

3) Expiratory reserve volume – is the extra amount of air that can be expired by forceful expiration after the end of a normal tidal expiration ~ 1100ml.

4) Residual volume – is the extra volume of air that still remain in the lungs after the most forceful expiration ~ 1200ml.

The pulmonary capacities

1) Inspiratory capacity – is the volume of air inspired by a maximal inspiratory effort after normal expiration = 3500ml = inspiratory reserve volume + tidal volume.

2) The functional residual capacity – is the volume of air remaining in the lungs after normal expiration = 2300ml = expiratory reserve volume + residual volume.

3) The vital capacity – is the volume of air expired by a maximal expiratory effort after maximal inspiration ~ 4600ml = inspiratory reserve volume + tidal volume + expiratory reserve volume.

4) Total lung capacity – is the maximum volume of air that can be accommodated in the lungs ~ 5800ml = vital capacity + residual volume.

5) Minute respiratory volume – is the volume of air breathed in or out of the lungs each minute = respiratory rate x tidal volume = 12 X 500ml = 6000ml/min.

All lung volume and capacity are about 20 to 25% less in women than in men and are greater in athletic persons than in small and asthenic persons.

Does Ventilation Limit Aerobic Capacity for Average Person?

If inadequate breathing capacity limited aerobic capacity, ventilatory equivalent for oxygen would decrease.

Actually, healthy person tends to over-breathe in relation to VO2.

In strenuous exercise, decreases arterial PCO2 & increase Alveolar PO2.

Work of Breathing Acute effects of 15 puffs

on a cigarette during a 5-minute period 3 fold increase in airway

resistance Lasts an average 35

minutes Smokers exercising at

80% Energy requirement of

breathing after smoking was 14% of oxygen uptake

Energy requirement of breathing no cigarettes was only 9%.

THANK YOU.