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Pulmonary Ventilation. Week 2 Dr. Walid Daoud A. Professor. Pulmonary Ventilation. Pulmonary ventilation is mass movement of air in and out of the lungs. Forces for Pulmonary Ventilation: Pressure gradient between alveoli and atmosphere.

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Pulmonary ventilation

Pulmonary Ventilation

Week 2

Dr. Walid Daoud

A. Professor

Pulmonary ventilation1
Pulmonary Ventilation

Pulmonary ventilation is mass movement of air in and out of the lungs.

Forces for Pulmonary Ventilation:

Pressure gradient between alveoli and atmosphere.

Inspiration occurs when pressure in atmosphere exceeds pressure in alveoli.

Intra alveolar pressure
Intra-alveolar Pressure

At sea level, atm. pressure is 760 mmHg and all pressures in the respiratory system are expressed relative to atmospheric pressure.

-During inspiration Palv. = - 1 mmHg

-During expiration Palv. = + 1 mmHg

-At ends of inspiration & expiration= 0 mmHg

Changes in intra-alveolar pressure are caused by changes in volumes of lungs.

Intra pleural pressure
Intra-pleural Pressure

It is the pressure inside pleural space.

It is always negative under normal conditions.

. At end of normal expiration= - 4 mmHg

. At end of normal inspiration= -6 to -8 mmHg

. During forced inpiration with glottis closed

= - 30 to - 40 mmHg (Muller experiment).

. During forced expiration with glottis closed

= + 50 mmHg (Valsalva experiment).

Importance of negative intra pleural pressure
Importance of negative intra-pleural pressure

- It helps lung expansion.

- It helps venous and lymphatic return to the


- It is a measure of lung elasticity (recoil


Transpulmonary pressure
Transpulmonary Pressure

It is difference between intralveolar and intrapleural pressures.

= Palv. – Ppl

= 0 – (-4 ) = 4 mmHg

Transpulmonary pressure is called distending pressure which is the force acting to expand the lung against elastic recoil of the stretched lung.

Causes of negative intrapleural pressure
Causes of Negative Intrapleural pressure

The negativity is due to continuous tendency

of lungs to recoil inward against continuous tendency of chest wall to expand outward to reach their relaxation volume.

Causes of recoil tendency of lungs:

1- Elastic tissues of lungs

2- Surface tension of fluid lining the alveoli.

Pulmonary surfactant
Pulmonary Surfactant

A detergent -like substance secreted by

type II alveolar cells.


Complex mixture of phospholipid dipalmitoyl lecithin, apoproteins and calcium ions.


- Facilitation of lung expansion.

- Prevention of alveolar collapse during exp.

- Prevention of pulmonary edema.

Surfactant deficiency
Surfactant Deficiency

1- Respiratory distress syndrome (RDS).

2- Long-term inhalation of 100% oxygen.

3- Occlusion of one pulmonary artery.

4- Cigarette smoking.

5- Hypothyroidism.

6- Hypocoticism.

7- Hyperinsulinism.

Mechanism of respiration
Mechanism of Respiration

. Inspiration.

Active process.

. Expiration.

Resting expiration is a passive process

while forced expiration is an active one.



Itis a device to measure lung volumes and capacities.


Itis the used technique .


Itis the recording.

Pulmonary volumes
Pulmonary Volumes

1- Tidal volume (VT).

2- Inspiratory reserve volume (IRV).

3- Expiratory reserve volume (ERV).

4- Residual volume (RV).

RV can not be measured by spirometry

but can be calculated by helium-dilution method.

Pulmonary capacities
Pulmonary Capacities

1- Inspiratory capacity (IC).

2- Vital capacity (VC).

3- Functional residual capacity (FRC).

4- Total lung capacity (TLC).

FRC and TLC can not be measured by spirometry.

Factors affecting vital capacity
Factors affecting vital capacity

Physiological variations:

1- VC increases in:

Males, athletes and standing position.

2- VC decreases in:

Females, pregnancy and recumbent


Factors affecting vital capacity1
Factors affecting vital capacity

Clinical significance of VC:

VC is an index of lung function and strength

of respiratory muscles:

1- Paralysis or myositis of resp. muscles.

2- Bone deformities e.g, kyphosis or scoliosis.

3- Loss of lung elasticity e.g, emphysema.

4- Restrictive lung diseases e.g, lung fibrosis.

5- Obstructive lung diseases e.g, asthma.

6- Abdominal tumors.

Timed vital capacity
Timed Vital capacity

- Forced expiratory volume in first second (FEV1).

- Forced vital capacity (FVC).

Normally FEV1 = 80% of FVC

In diseases:

-Restrictive lung diseases: lung fibrosis:

. Both FEV1 & FVC are reduced.

. FEV1/FVC % is normal.

-Obstructive lung diseases: brochial asthma.

. FEV1 is reduced more than FVC

. FEV1/FVC % is low.