Pulmonary Ventilation

Pulmonary Structure and Function

Pulmonary Ventilation –

Process by which ambient air is moved into and exchanges with air in the lungs

…Different from oxygen consumption

Figure 12.1

Pulmonary Structure and Function

Gas exchange (O2 and CO2) occurs in the alveoli

O2 transfers from alveolus to capillary blood

CO2 transfers from capillary blood to alveolus

Fig 12.1

Each minute at rest 250 ml of O2 and 200 ml of CO2 diffuse in opposite directions

Pulmonary Structure and Function

Fig 12.1

Lungs contain 600 million alveoli

Extremely thin-walled sacs (0.3 mm thick)

Lie side by side with thin walled capillariesAlveoli receive largest blood supply of any organ in the body

Pulmonary Structure and Function

Lungs – Extremely large surface area for gas exchange

Lungs provide the gas exchange surface separating blood from alveolar gases

Figure 12.2

Adult lung weighs 1 kg and hold 4-6 L of air

Pulmonary Structure and Function

Pulmonary ventilation functions primarily to maintain a constant and favorable concentration of O2 and CO2 in the alveoli during rest and exercise

Adequate pulmonary ventilation ensures complete gas exchange before blood leaves lungs for transport to tissues

Pulmonary Structure and FunctionBreathing mechanics

Inspiration – diaphragm descends, ribs are raised, volume increases, intrapulmonic pressure decreases, air rushes in (chest cavity size increases)Contributing muscles: external intercostals, sternocleidomastoids, scalenes, spinal extensors

Fig 12.3

Pulmonary Structure and Function

Breathing mechanics

Expiration – Passive process

diaphragm relaxes, ribs lower, volume decreases, intrapulmonic pressure increases, air rushes out (chest cavity size decreases)Contributing muscles: rectus abdominus, internal intercostals, posterior inferior serratus

Fig 12.3

Pulmonary Structure and Function

Ventilatory System:

Conducting Zone – Trachea to Bronchioles

No alveoli

Air transport, warming, humidification, particle filtration

Anatomic "Dead" Space*Respiratory Zone – Bronchioles to Alveoli

Surface area for gas exchange

Fig 12.4

Pulmonary Structure and Function

Measuring Lung Volume:

Lung volumes measurements (static or dynamic) can help identify potential obstructive or restrictive lung diseases

Lung volumes vary with age, gender, body size, body composition and stature

Fig 12.6

Water-sealed, volume displacement recording spirometer

Pulmonary Structure and Function

Static Lung Volume Measurements: Provides record of ventilatory volume and breathing rate

Tidal Volume (TV) – volume inspired or expired per breath (600 ml)

Inspiratory Reserve Volume (IRV) – maximal inspiration at end of tidal inspiration (3000 ml)

Expiratory Reserve Volume (ERV) – maximal expiration at end of tidal expiration (1200 ml)

Force Vital Capacity (FVC) – maximal volume expired after maximal inspiration (TV+IRV+ERV; 4800 ml)

Fig 12.6

Pulmonary Structure and Function

Static Lung Volume Measurements:

Residual Lung Volume (RLV) – air volume remaining in lungs after maximal expiration (1200 ml)

-allows uninterrupted gas exchange between blood and alveoli

Functional Residual Capacity (FRC) – Volume in lungs after tidal expiration (ERV + RLV; 2400 ml)

Total Lung Capacity (TLC) – volume in lungs after maximal inspiration (FVC + RLV; 6000 ml)

Fig 12.6

Pulmonary Structure and FunctionDynamic Lung Volumes:

Adequate pulmonary ventilation depends on ability to sustain high airflow levels (not air movement in single breath)

Dynamic Ventilation depends on:

1) FVC (“stroke volume” of the lungs)

2) Breathing rate

High airflow levels (velocity) depends on lung compliance (ability to stretch or expand):

“loose” (high compliance) – emphysema, asthma

“stiff” (low compliance) – fibrosis

Pulmonary Structure and FunctionDynamic Lung Volumes

Forced Expiratory Volume (FEV) to FVC ratio:

FVC measured over 1 s (FEV1.0) – measures pulmonary airflow capacity, or overall resistance to air movement upstream in the lungs (normal value = 80-85% of FVC)

Fig 12.8

No Elastic Recoil (loose)

Too Much Elastic Recoil (stiff)

Pulmonary Structure and Function3. Minute Ventilation (VE):

•Volume of air moved in and out of respiratory tract per minute

•VE=Breathing Rate (BR) x TV

At rest VE = 12 breaths/min x 0.5 L/breathVE = 6 Lmin

Exercise VE = 30 x 2.5 VE=50 x 3.5VE = 75 Lmin VE=150 LminModerat

eVigorous

Pulmonary Structure and Function

Dynamic Lung Volumes:

• Measurements of dynamic lung function can indicate the severity of obstructive or restrictive lung diseases

• FEV/FVC - Normal or increased for restrictive lung disease (80% or greater)

• FEV/FVC - <70% indicates obstructive lung disease

Pulmonary Structure and Function

Aging and lifestyle affect lung volumes and pulmonary function Aging: Decreased lung compliance

FEV1.0 and FVC decrease after age 20

Diffusion capacity decreases

Partial Pressure of O2 decreasesDiaphragm muscles weakens by ~25%

Pulmonary Structure and Function

Dynamic Lung Volumes:Provide no information about aerobic fitness:

No difference in healthy vs olympic athletes

Not predictive of track or marathon performance, distance running

Pulmonary Structure and Function

Dynamic Lung Volumes:

• Important part of standard medical/health examination for “at risk” exercisers (smokers, asthmatics)

Pulmonary Structure and Function

By increasing rate and depth of breathing - increases alveolar ventilation

•TV increases at start of moderate exercise

•As intensity increases, TV plateaus at 60% of FVC

•Breathing rate provides alveolar ventilation at higher exercise intensities

How do we ensure sufficient air reaches the alveoli during exercise?

Fig 12.10

Pulmonary Structure and Function

Definitions:

Hyperventilation – increase in pulmonary ventilation that exceeds the O2 needs of metabolism (“overbreathing”)

Unloads CO2 excessively (which constricts arteries with less O2 to brain)

Can lead to unconsciousness.

Pulmonary Structure and Function

Definitions:

Dyspnea – shortness of breath or subjective distress in breathing (sense of inability to breathe)

Occurs in physical exertion (novel exercisers), at altitude, or with obstructive or restrictive pulmonary disorders

Result of elevated CO2 and H+ in blood from fatigue of poorly trained respiratory muscles (shallow, ineffective breathing)

Pulmonary Structure and Function

Definitions:

Valsalva Maneuver – Increases intrathoracic pressure that occurs when exhalation is forced against a closed glottis

Results:

Collapse of veins in thoracic region

Impaired venous return

Acute DROP in arterial blood pressure

Decreased blood supply to brain

"spots before the eyes" "fainting"

Pulmonary Structure and Function

Definitions:

Valsalva Maneuver

Fig 12.11

Acute drop in blood pressure

Blood pressure overshoot

Pulmonary Structure and Function

Valsalva Maneuver

Fig 12.11

*Valsalva Maneuver does NOT cause the acute rise in blood pressure with resistance training