Physiology of the Respiratory System

Pleural linkage at rest

Lungs = somewhat expanded

Thorax = somewhat compressed

resting lung volume

the amount of air in the lungs at rest position

Lung Volumes

tidal volume, inspiratory reserve volume, expiratory reserve volume, residual volume

how to measure lung volume

spirometry

what is tidal volume and its normal volume

volume of air moved during quiet inhalation or exhalation. M 600mL, F 450mL

what percent of tidal volume is in anatomical dead space and alveoli respectively?

30% in anatomical dead space

70% in alveoli

what is anatomical dead space?

conducting portion of the lung that does not take part in exchanging gas

what is inspiratory reserved volume and its normal value?

amount of air that can be inhaled above tidal volume, about 2500ml

what is expiratory reserved volume and its normal value?

amount of air that can be exhaled below tidal volume, about 1000ml

what is residual volume and its normal value?

amount of air left in the lung after forceful exhalation, about 1100ml

list the lung capacities

Inspiratory capacity

Functional residual capacity

Vital capacity

Total lung capacity

what is inspiratory capacity and its normal value?

tidal volume + inspiratory reserved volume

500ml + 2500ml = 3000ml

what is functional residual capacity and its normal value?

expiratory reserved volume + residual volume

1000ml + 1200ml = 2200ml

what is vital capacity and its normal value?

IRV + ERV + tidal volume

2500+1000+500= about 4000ml

what is total lung capacity and its normal value?

total amount of air in the lung after maximal inspiration

about 6000ml in man, slightly less in woman

what are the main muscle for inhalation and exhalation?

Inhalation: diaphragm, external intercostal muscle

Exhalation: abdominal muscle, internal intercostal muscle

what is the difference between activity of inhalation and exhalation?

Inhalation is an active process and exhalation is passive process due to elastic recoil of the lung and thoracic cage

list the respiratory cycle

Rest → Inhalation → Exhalation → Rest

Specific Pressures for Speech and nonspeech Functions

Alveolar pressure

Intrapleural pressure

Subglottal pressure

Intraoral pressure

How to measure lung pressure?

Manometery

atmospheric pressure

the pressure exerted by atoms and molecules in the atmosphere surrounding Earth (760 mm Hg/ or 1,033 cm H2O)

alveolar pressure

pressure within the individual alveolus

intrapleural pressure

pressure within the pleural cavity

subglottal pressure

pressure below the vocal folds

intraoral pressure

the air pressure within the oral cavity

Boyle's Law

inverse relationship between volume and pressure.

P = 1/V

describe the resting phase of breathing cycle

Atmospheric = intraoral = alveolar when at rest

Atmospheric pressure = 760 mm HG or 1,033 cm H20

Intrapleural pressure is -3 to -5 cm H20 at rest

All respiratory muscle at rest

describe the lung during inhalation

Space between pleurae increases

Intrapleural pressure becomes a larger "negative" (pressure "increases" up to -10 cm H20)

uThis expands each alveolus

Alveolar, subglottal, intraoral pressures becomes negative re: atmospheric (~-2 cm H20)

Air enters the lungs

describe the lung during exhalation

Intrapleural pressure becomes less negative

Alveolar pressure becomes positive relative to atmosphere

Subglottal & intraoral pressure become positive re: atmosphere

Air leaves the lungs

what is pleural pressure and what causes it?

It is the pressure between parietal and visceral pleura. It is always negative and less than intrapulmonary pressure. It is formed by the lung and chest wall. The lung wants to collapse and the chest wall wants to expand

what are the 4 components of the control system for breathing?

1. chemoreceptor

2. mechanoreceptor

3. control center in medulla and pons

4. respiratory muscles

list the control center for breathing and their location

*Brain Stem

Cerebral cortex

describe cerebral cortex's voluntary control on breathing

Can temporarily over ride brain stem. We can hyper or hypoventilate. Hyperventilation decrease PaCO2 and increase pH, can induce unconsiousness. Hypoventilation increase PaCO2 and decrease pH. Both are strong drive for ventilation.

Relaxation pressure

The pressure produced entirely by nonmuscular forces of the respiratory apparatus

Relaxation Pressure Diagram

Relationship between breathing and pressure

The more you have inspired, greater is the positive pressure generated

The more you have expired, the greater is the negative pressure generated

At relaxation of the muscles of inspiration and expiration, this proportion remains in the lungs.

38% of VC

Above 38% VC

Inspiratory process is active, exp. is passive

Chest wall recoil generates a positive pressure (are attempting to make thorax smaller)

Below 38% VC

Expiratory process is active, insp. is passive

Restoring forces generates a negative pressure (are attempting to make thorax larger)

For non-speech respiration

40% of the respiratory cycle is inhalation, 60% is exhalation

For speech respiration

10% of cycle is inhalation and 90% is exhalation

Tidal breathing rate

12 cycles per minute

Minimum subglottal pressure required to drive vocal folds

3-5 cm H20

Subglottal pressure required for quiet conversational speech

7-10 cm H20

Checking action

using the muscles of inspiration to impede the outflow of air during expiration

What does happen when the subglottal pressure drop below 50% of VC?

Muscles of expiration will be enlisted