RESPIRATORY PHYSIOLOGY

5 Functions of the Respiratory System

1. Provides extensive gas exchange surface area between air and circulating blood

2. Moves air to and from exchange surfaces of lungs

5 Functions of the Respiratory System

3. Protects respiratory surfaces from outside

environment

4. Produces sounds

5. Participates in olfactory sense

Components of the Respiratory System

Figure 23–1

Organization of the Respiratory System

• The respiratory system is divided into the upper respiratory system, above the larynx, and the lower respiratory system, from the larynx down

The Respiratory Tract

• Consists of a conducting portion:– from nasal cavity to terminal bronchioles

• Consists of a respiratory portion:– the respiratory bronchioles and alveoli

What is the difference between external respiration

and internal respiration?

Respiration

• Refers to 2 integrated processes: – external respiration– internal respiration

External Respiration

• Includes all processes involved in exchanging O2 and CO2 with the environment

Internal Respiration

• Also called cellular respiration

• Involves the uptake of O2 and production of CO2 within individual cells

What are the major steps involved in

external respiration?

3 Processes of External Respiration

1. Pulmonary ventilation (breathing)

2. Gas diffusion:– across membranes between alveolar air

spaces and alveoalar capillaries, and across capillary walls between blood and other tissues

3 Processes of External Respiration

3. Transport of O2 and CO2:

– between alveolar capillaries and capillary beds in other tissues

What physical principles govern the movement of air into the lungs?

Pulmonary Ventilation

• Is the physical movement of air in and out of respiratory tract

• Provides alveolar ventilation (movement of air into and out of the alveoli)

• Alveolar ventilation: prevents the buildup of carbon dioxide in the alveoli and ensures a continuous supply of oxygen

Atmospheric Pressure

• The weight of air:– has several important physiological effects

Gas Pressure and Volume

• At normal atmospheric pressures, gas molecules are much farther apart than the molecules in a liquid, so the density of the air is relatively low.

• The forces acting between gas molecules are minimal so an applied pressure can push them closer together.

Gas Pressure and Volume

Figure 23–13

Boyle’s Law

• Defines the relationship between gas pressure and volume:

P = 1/V

• In a contained gas:– external pressure forces molecules closer

together– movement of gas molecules exerts pressure

on container

Mechanisms of Pulmonary Ventilation

Pressure Difference

• Air flows from area of higher pressure to area of lower pressure

A Respiratory Cycle

• Consists of: – an inspiration (inhalation)– an expiration (exhalation)

Respiration

• Causes volume changes that create changes in pressure

• Volume of thoracic cavity changes:– with expansion or contraction of diaphragm or

rib cage

Compliance of the Lung

• An indicator of expandability

• Low compliance requires greater force

• High compliance requires less force

Factors That Affect Compliance

1. Connective-tissue structure of the lungs

2. Level of surfactant production

3. Mobility of the thoracic cage

Compliance of the lung

• Loss of supporting connective structure of the lung increases compliance (emphysema): easier to expand the lungs, although respiratory exchange surfaces are damaged

• Inadequate surfactant decreases compliance (respiratory distress syndrome, skeletal muscle disorders): more pressure of force required to fill the lungs

Gas Pressure

• Can be measured inside or outside the lungs

• Normal atmospheric pressure: – 1 atm or Patm at sea level: 760 mm Hg

Pressure and Volume Changes with Inhalation and Exhalation

Figure 23–15

Intrapulmonary Pressure

• Also called intra-alveolar pressure• Pressure inside the respiratory tract at the

alveoli• Is relative to Patm

• In relaxed breathing, the difference between Patm and intrapulmonary pressure is small:– about —1 mm Hg on inhalation or +1 mm Hg

on expiration

Maximum Intrapulmonary Pressure

• Maximum straining, a dangerous activity, can increase range:– from —30 mm Hg to +100 mm Hg

Intrapleural Pressure

• Pressure in space between parietal and visceral pleura

• Averages —4 mm Hg• Maximum of —18 mm Hg• Remains below Patm throughout respiratory cycle

due to the relationship between the lungs and the body wall. The elastic fibers continuously oppose the fluid bond and pull the lungs away from the chest wall and diaphragm, lowering the atmospheric pressure.

The Respiratory Pump

• Cyclical changes in intrapleural pressure operate the respiratory pump:– which aids in venous return to heart

* On inspiration, diaphragm lowers, raising pressure in abdomen and lowers pressure in thorax, which creates partial vacuum in thorax that favors venous return to right atrium.

Tidal Volume

• Amount of air moved in and out of lungs in a single respiratory cycle

• Average value: 500 cc

What are the origins and actions of the respiratory muscles responsible for respiratory movements?

Figure 23–16a, b

The Respiratory Muscles

The Respiratory Muscles

Figure 23–16c, d

The Respiratory Muscles

• Most important are:– the diaphragm – external intracostal muscles of the ribs– accessory respiratory muscles :

activated when respiration increases significantly

The Mechanics of Breathing

• Inhalation:– always active

• Exhalation:– active or passive

3 Muscle Groups of Inhalation

1. Diaphragm:– contraction draws air into lungs– 75% of normal air movement

3 Muscle Groups of Inhalation

2. External intracostal muscles:– assist inhalation– 25% of normal air movement

3 Muscle Groups of Inhalation

3. Accessory muscles assist in elevating ribs:

– sternocleidomastoid– serratus anterior– pectoralis minor– scalene muscles– internal intercostals– external and internal oblique– rectus abdominis

Muscles of Active Exhalation

1. Internal intercostal and transversus thoracis muscles:

– depress the ribs

2. Abdominal muscles:– compress the abdomen– force diaphragm upward

Modes of Breathing

• Respiratory movements are classified:– by pattern of muscle activity– into quiet breathing and forced breathing

Quiet Breathing (Eupnea)

• Involves active inhalation and passive exhalation

• Diaphragmatic breathing or deep breathing: is dominated by diaphragm

• Costal breathing or shallow breathing:is dominated by ribcage movements

Elastic Rebound

• When inhalation muscles relax:– elastic components of muscles and lungs

recoil– returning lungs and alveoli to original position

Forced Breathing

• Also called hyperpnea

• Involves active inhalation and exhalation

• Assisted by accessory muscles

• Maximum levels occur in exhaustion

Respiratory Rates and Volumes

• Respiratory system adapts to changing oxygen demands by varying:– the number of breaths per minute (respiratory

rate); adult: 12-18/min; children: 18-20/min– the volume of air moved per breath (tidal

volume)

Respiratory Minute Volume(VE)

• Amount of air moved per minute

• Is calculated by:respiratory rate (f) tidal volume (VT)

(normal: 6 L/min)

• Measures pulmonary ventilation (how much air is moving into and out of the respiratory tract)

Anatomic Dead Space(VD)

• Only a part of respiratory minute volume reaches alveolar exchange surfaces

• Volume of air remaining in conducting passages is anatomic dead space

Alveolar Ventilation(VA)

• Amount of air reaching alveoli each minute

• Calculated as:(tidal volume — anatomic dead space)

respiratory rate (f)

Alveolar Ventilation

• A typical inhalation pulls about 500 cc of air into the respiratory system (VT)

• The first 350 cc enters the alveolar spaces• The last 150 cc does not reach the alveolar

spaces and thus not participate in gas exchange. This represents the anatomical dead space.

• The alveolar ventilation rate is more important than the respiratory minute volume because it determines the rate of oxygen delivery to the alveoli, not just the total air moved per minute.

Alveolar Gas Content

• Air in the alveoli contain less O2, more CO2 than atmospheric air:

– because air mixes with exhaled air

Alveolar Ventilation Rate

• Determined by respiratory rate and tidal volume:*for a given respiratory rate:

• increasing tidal volume increases alveolar ventilation rate

*for a given tidal volume:• increasing respiratory rate increases alveolar

ventilation

Respiratory Volumes and Capacities

Figure 23–17

Lung Volume

• Total lung volume is divided into a series of volumes and capacities useful in diagnosis

4 Pulmonary Volumes

1. Resting tidal volume:– in a normal respiratory cycle

2. Expiratory reserve volume (ERV):– The amount of air you can force out after a

normal quiet respiratory cyle

4 Pulmonary Volumes

3. Residual volume:– The amount of air remains in the lungs after

maximal exhalation– minimal volume (in a collapsed lung): the

amount of air that would remain in a collapsed lung (30-120 ml)

4. Inspiratory reserve volume (IRV):– Amount of air you take in over and above

the tidal volume

4 Calculated Respiratory Capacities

1. Inspiratory capacity: the amount air that you can draw into your lungs after you have completed a quiet respiratory cycle

tidal volume + inspiratory reserve volume

2. Functional residual capacity (FRC): the amount of air remaining in your lungs after you have completed a quiet respiratory cycle

expiratory reserve volume + residual volume

4 Calculated Respiratory Capacities

3. Vital capacity: the maximum amount of air that you can move into or out of your lungs in a single respiratory cycle

expiratory reserve volume + tidal volume + inspiratory reserve volume

4. Total lung capacity: vital capacity + residual volume

Pulmonary Function Tests

• Measure rates and volumes of air movements