Danielle Alleyne

Lung capacities / volumes

The Spirometer

*an apparatus for measuring the volume of air inspired and expired by the lungs.

*records the amount of air and the rate of air that is breathed in and out over a specified period of time.

*Pt. is asked to breathe quietly. Normal, quiet breathing involves inspiration and expiration of a tidal volume (Vt).

(includes the volume of air that fills the alveoli plus the volume of air that fills the airways. )

*then, pt. is asked to take a maximal inspiration, followed by a maximal expiration. Allowing additional lung volumes to be revealed.

Pulmonary Volumes1.The tidal volume is the volume of air inspired or expired with each normal breath; (approx. 500 milliliters in the adult.)

2. The inspiratory reserve volume is the extra volume of air that can be inspired over and above the normal tidal volume when the person inspires with full force; (approx. 3000 milliliters.)

3. The expiratory reserve volume is the maximum extra volume of air that can be expired by forceful expiration after the end of a normal tidal expiration; (approx. 1100 milliliters.)

4. The residual volume is the volume of air remaining in the lungs after the most forceful expiration; (approx 1200 milliliters)

Pulmonary Capacities1. The inspiratory capacity equals the tidal volume plus the inspiratory reserve volume. This is the amount of air (about 3500 milliliters) a person can breathe in, beginning at the normal expiratory level and distending the lungs to the maximum amount.

2. The functional residual capacity equals the expiratory reserve volume plus the residual volume. This is the amount of air that remains in the lungs at the end of normal expiration (about 2300 milliliters).

3. The vital capacity equals the inspiratory reserve volume plus the tidal volume plus the expiratory reserve volume. This is the maximum amount of air a person can expel from the lungs after first filling the lungs to their maximum extent and then expiring to the maximum extent (about 4600 milliliters).

4. The total lung capacity is the maximum volume to which the lungs can be expanded with the greatest possible effort (about 5800 milliliters); it is equal to the vital capacity plus the residual volume

* .

VC = IRV + VT + ERV

VC = IC + ERV

TLC = VC + RV

TLC = IC + FRC

FRC = ERV + RV

*Dead space the volume of the airways and lungs that does not participate in gas exchange.

=

anatomic dead space of the conducting airways

+ physiologic dead space

* Anatomic Dead Space

∞the volume of the conducting airways, including the nose (and/or mouth), trachea, bronchi, and bronchioles.

∞does not include the respiratory bronchioles and alveoli.

∞volume of the conducting airways is approximately 150 mL.

* Physiologic Dead Space

∞the total volume of the lungs that does not participate in gas exchange.

∞includes the anatomic dead space of the conducting airways plus a functional dead space in the alveoli.

∞ In normal persons, the physiologic dead space is nearly equal to the anatomic dead space.

Mechanics of Breathing

Lungs can be expanded & contracted in two ways:-

1. by downward and upward movement of the diaphragm to lengthen or shorten the chest cavity

2. by elevation and depression of the ribs to increase and decrease the AP diameter of the chest cavity

During inspiration: Diaphragm contracts (pulls lower surfaces of lungs

downwards) External Intercostal & Accessory muscles raise the rib cage ↑ intra-thoracic volume

↓ intra-thoracic pressure

During expiration: Expiration is normally passive. Diaphragm relaxes (elastic recoil of lungs) As lungs recoil from the stretch of inhalation, air flows back

out until the pressures in the chest and the atmosphere reach equilibrium.

This is called a reverse pressure gradient. Internal Intercostal & Abdominal muscles pull the rib cage

downward during expiration

Pressures Pleural pressure is the pressure of the fluid in the thin

space between the lung pleura and the chest wall pleura.

there is normally a slight suction, which means a slightly negative pressure.

Alveolar pressure is the pressure of the air inside the lung alveoli.

Transpulmonary pressure is the difference between the alveolar pressure and the pleural pressure.

It is a measure of the elastic forces in the lungs that tend to collapse the lungs at each instant of respiration, called the recoil pressure.

Compliance

describes the distensibility of the system Hence, lung compliance refers to the extent of

expansion of the lungs for a given change in pressure.

The greater the amount of elastic tissue, the greater the tendency to "snap back," and the greater the elastic recoil force, but the lower the compliance.

The compliance of the lungs and chest wall is inversely correlated with their elastic properties

Compliance of Chest Wall Negative intra-pleural pressure is created by two opposing

elastic forces pulling on the intra-pleural space:

1. The lungs, with their elastic properties, tend to collapse2. The chest wall, with its elastic properties, tends to spring out

When these two opposing forces pull on the intra-pleural space, a negative pressure is created.

In turn, this negative intra-pleural pressure opposes the natural tendency of the lungs to collapse and the chest wall to spring out.

1. No longer a negative intra-pleural pressure to hold the lungs open2. no longer a negative intrapleural pressure to keep the chest wall from

expanding

Emphysema Condition associated with loss of elastic fibers in the lungs

The compliance of the lungs increases

At a given volume, the collapsing (elastic recoil) force on the lungs is decreased

The tendency of the lungs to collapse is less than the tendency of the chest wall to expand

Two forces no longer in balance

For balance to occur, volume must be added to the lungs to increase their collapsing force

Patients have a new higher Functional Residual Capacity

Fibrosis aka ‘restrictive disease’

Condition associated with stiffening of lung tissues and decreased compliance

The compliance of the lungs decreases

The tendency of the lungs to collapse is greater than the tendency of the chest wall to expand

The opposing forces no longer in balance

To re-establish balance, the lung and chest-wall system will seek a new lower Functional Residual Capacity