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Respiratory Physiology

Lecture 1

Andreas W. Henkel, Ph.D.

Prehistory of breathing

Early animals (580 million years ago)

didn’t need lungs !

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Evolution of breathing

Evolution of breathing

Fish swim

bladder turns

into lungs

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Human breathing

What is respiration?

� Movement of gases

� Gas exchange

� Transport of gas (oxygen and carbon

dioxide) in blood

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The airways

Conducting zone:

nose, mouth

air pipe (trachea)

bronchial tree

terminal bronchioles

The airways

Conducting zone:

- Warming and humidifying of air

- Mucus expulsion (300 cilia per cell)

- Small particle removal by ciliated cells

Common diseases:

Asthma, bronchitis

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Respiratory zone

Alveoli

Numbers : 300.000.000

Size : 0.25 – 0.5 mm

Surface : 60 – 80 m3

Garbage disposal: Macrophages clean alveoli

Respiratory zone

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Mechanics of breathingTwo pleural membranes

Parietal membrane attached to rib case and visceral membrane attached to lung

Pneumothorax

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Mechanics of breathingPressures

� Atmospheric pressure = 760 mm Hg

� Intrapleural pressure = 754 mm Hg –

pressure between pleural layers

� Intrapulmonary pressure = 757 mm Hg–

varies, pressure inside lungs

Mechanics of breathing

� Quiet breathing

– Diaphragm and external and

internal intercostals muscles

� Forced breathing

- Accessory muscles

(Scalene, pectoralis minor and

sternocleidomastoid)

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Mechanics of breathing

Normal outside

air pressure:

760 mm Hg

Inhale:

Alveolar press.

-3 mm Hg

Exhale:

Alveolar press.

+ 3 mm Hg

-3

-6

Alveoli are 250 times softer and elastic than a rubber balloon

Mechanics of breathing

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Mechanics of breathing

Inspiration/Inhalation

� Diaphragm & External intercostal muscles

� Increases volume in thoracic cavity as

muscles contract

� Volume of lungs increases

� Intrapulmonary pressure decreases

(757 mm Hg)

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in rest during inhalation

Expiration/Exhalation

� Inhalation muscles relax

� Thoracic-, internal intercostal and

abdominal muscles contract

� Volume of thoracic cavity decreases

� Volume of lungs decreases

� Intrapulmonary pressure increases

(763 mm Hg)

� Forced expiration is active

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Pulmonary ventilation

Factors that influence pulmonary air flow

Diameter of airways, esp. bronchioles

controlled by

Sympathetic & Parasympathetic NS

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Pulmonary ventilation

Air pressure in alveoli is inversely

proportional to the alveolar volume

Enlarging volume

= lower pressure

Pulmonary ventilationBoyle’s law

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Pulmonary ventilationBoyle’s law

Boyle’s law: p = k / V

Example: inflating a rubber balloon

- difficult (blow hard) at the beginning

- easy after initial inflation

Pulmonary ventilationSurface Tension

� Lung collapse

� Surface tension tends to oppose alveoli

expansion

� Pulmonary surfactant reduces surface tension

� Surfactant = surface active agent

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Pulmonary ventilationLaplace’s law

tension * thicknessPressure = -----------------------

radius

tension = elastic resistance

(e.g. soft rubber – hard rubber)

Reduced by surfactants

Pulmonary ventilation

� Surfactants lower tension !

� Surfactants cover the inner side of alveoli

� Surfactant of the alveoli:

Dipalmitoyl-lecithin (10) – protein (1)

When the alveoli volume gets smaller :

� surfactant concentration gets higher

� tension gets lower

� inhalation becomes easier

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Spirometry

� Analyze and measure many lung parameters

� Useful for diagnostics of lung diseases

� Useful for sport medicine

Spirometry

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Lung Volumes & Capacitiesquiet breathing

� Tidal Volume (500 mls)

� Respiratory Rate (12 breaths/minute)

� Minute Respiratory Volume (6000 mls/min)

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Lung Volumes & Capacitiesforced inhalation

� Inspiratory Reserve Volume

(♂ 3000, ♀ 2100 ml)

� Inspiratory Capacity (TV + IRV)

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Lung Volumes & Capacitiesforced exhalation

� Expiratory Reserve Volume

(♂ 1200, ♀ 800 ml)

� Residual Volume (1200 ml)

� Functional Residual Capacity (ERV + RV)

– Air left in lungs after exhaling the tidal volume

quietly

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Lung Volumes & Capacities

� Vital Capacity

� IRV + TV + ERV = ♂ 4700, ♀ 3400ml

� Maximum amount of air that can be moved

in and out of lungs

Inspiratory Tidal Expiratory

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Lung Volumes & CapacitiesTraining effect

Lung Volumes & Capacities

� Total Lung Capacity (♂ 5900, ♀ 4400)

� Dead air volume (150 ml) –

air not in the alveoli

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Lung diseases

Dyspnea : subjective shortness of breath

Asthma: bronchiolar constriction, inflammation,

mucous secretion

Constriction: leucotriens + histamine

from mastcells (allergy)

Bronchiodilation : beta 2 receptors agonist:

terbutalin

beta 1+ 2 receptors agonist:

epinephrine (β1 in heart !)

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Lung diseases

Emphysema: destruction of alveolar tissue

Smoke stimulates macrophages to secrete

proteolytic enzymes

Genetic disease:

no anti α-trypsin inhibitor is produced

Lung diseasesChronic obstructive pulmonary disease (COPD)

Causes: bronchitis and/or emphysema,

inflammation other cause

Pulmonary fibrosis

To much fibrous connective tissue disrupts the

structure of the lung.

Causes: small particle inhalation, black lung coal

dust