To what extend human body is similar to a machine ? • Human body must have an energy source in both phases, electrical and mechanical • Human body consists of billions of engines (Cells) • Cardiovascular system acts as a transport ways between these engines to supply them with fuel and exclude wastes

Fuel cycle within the machine : 1- Food is digested in the digestive system 2 - Digested food is combined with oxygen (O2) 3- Oxygenated digested food is immersed to the cells and combustion takes place to produce fuel Why 80 % of air is nitrogen not oxygen ?

Air is inhaled through the nose or mouth and then through the pharynx, larynx, and the trachea. The trachea divides into the right and left bronchus, each of which continues to bifurcate into smaller and smaller bronchi and terminal bronchioles until they form alveoli

Alveoli are the actual operating units of the lungs

1- Perfusion: getting the blood to the pulmonary capillary bed. 2- Ventilation: getting the air to the alveolar surface Human Body Blood

Perfusion

Atmosphere

Air

Ventilation

where p is the partial pressure of the solute in the gas above the solution, c is the concentration of the solute and kH is a constant with the dimensions of pressure divided by concentration.

Gas transfer velocity

α

Bubbles from liquids of low surface tension last longer than those of higher surface tension, Why ? Because liquids with higher surface tension form bubbles with high pressure inside so rupture of these bubbles are easier. Alveoli are lined with a liquid called surfactant, therefore they have tendency to get smaller due to surface tension of the surfactant. Surfactant is a unique liquid because it is unlike all liquids, it has not a constant surface tension. Surface tension of the surfactant is mainly depends on the alveoli surface area.

Receiving various signals from the nervous system, the diaphragmatic muscles contract and the diaphragm moves downward. As the diaphragm depresses, it creates vacuum in the lungs and air rushes into the lungs to fill it. As the diaphragm relaxes, it pushes the molecules closer together, increasing the internal pressure in the lungs. The air flows from the lungs into the lower pressure outside the body.

160 Oxygen Partial Pressure (PO2) mmHg

120

Resting 100

60

Exercising

40

Time

CO has a very secure attachment with the same sites that oxygen binds with in the blood molecules. This combination is 250 times higher than the oxygen so it blocks them. CO victims are placed in oxygen chamber to enhance their PO2 with 3 atm that enhance the PO2 by a factor 15. This treatment is not long tern treatment because higher O2 is toxic.

The volume of the lungs during different stages of normal and deep breathing is a good diagnostic of lung functionality. A relatively simple instrument, called the spirometer is used to measure airflow into and out of the lungs and record it on a graph of lung volume (L) versus time (sec).

During normal breathing at rest, this is referred to as the tidal volume (TV) at rest . In other words TV is “The amount of gas inspired or expired with each breath”.

During heavy exercise, the tidal volume (TV) is considerably larger. At the end of a normal inspiration it is possible with some effort to further fill the lungs with air. The maximum amount of additional air taken in is called inspiratory reserve volume (IRV). Similarly, at the end of a normal expiration we can force more air out of the lungs and the maximum volume of additional expired air is called expiratory reserve volume (ERV).

A modern spirometer

An incentive spirometer

A traditional and modern spirometer used to measure a lot of parameters which deal with the lungs performance. The airflow in and out of the lungs is recorded on a rotating chart. Water is used as an air-tight seal to keep air within the counterbalance drum. Note: The information collected by the spirometer spirogram.

printed out on a chart called a

Tidal Volume

TV

Volume of air inspired and then expired during breathing in rest

Inspiratory Reserve Volume

IRV

Volume of air a person can inspire above tidal volume

Expiratory Reserve Volume

ERV

Volume of air a person can exhale below resting expiratory volume

Inspiratory Capacity

IC

Volume of a person can inspire above the resting expiratory volume

Residual Volume

RV

Volume of air left in lung after maximum expiratory effort

Functional Residual Capacity

FRC

Air remains in lung after normal expiration

Vital Capacity

VC

Maximum volume of air that can be inspired and then expired

Forced Vital Capacity

FVC

The same VC but under maximum expiratory force

Respiratory Volumes -

Tidal Volume(TV) Inspiratory Reserve Volume (IRV) Expiratory Reserve Volume (ERV) Residual Volume (RV)

-

Respiratory Capacities

Vital Capacity (VC) Inspiratory Capacity(IC) Functional Residual Capacity (FRC) Total Lung Capacity (TLC)

This is the area of the respiratory system (trachea and bronchi) in which air is not exposed to blood. (150 cm3)

This is the area of alveoli by act of some diseases cannot perfuse the blood to O2.

Anatomical dead space can be measured using the Bohr equation. It is more commonly used to calculate the latter. Bohr equation states that the dead space (Vd) is calculated as follows:

Vd/Vt = PaCO2 – PeCO2 PaCO2

Where, Vd is dead space volume, Vt is tidal volume, PaCO2 is the partial pressure of carbon dioxide in the arterial blood, and PeCO2 is the partial pressure of carbon dioxide in the expired air.

Compliance Is a measure of the tendency of a hollow organ to resist recoil toward its original dimension upon removal of a distending or compressing force. It is a very important physical characteristic of the lungs Compliance

In adults

Liter/cm

=

compliance

Fibrosis in lung results in Stiff lungs Flabby lung

=

0.18 - 0.27 liter/cm

small volume change in large pressure Change large volume change in small pressure Change

Why infants with respiratory distress syndrome (RDS) have lungs with low compliance ? RDS is a respiratory disorder that affects premature infants born about 6 weeks or more before their due dates. In this situation, infant’s lungs cannot produce sufficient surfactant which the liquid coats the inside of lung to keep lungs open to breathe air once they are born. Oxygen insufficiency may be results in some physiological organs damage.

for electric circuit: V= IR then R = V/I (Volt/A) Airways resistance is given by the following equation:

R= ∆P/V

where V = ∆V/∆t

(rate of air flow )

The time constant (t) of the lung is related to the airway resistance (R) and the compliance (C= ΔV/ΔP)

t = RC

(sec)

Time constant of the lung is complicated since many parts of the lung are interconnected. If one part of the lung has a larger time constant than other parts, it will not get its share of the air and that part of the lung will be poorly ventilated. The amount of work done in normal breathing account for a small fraction of the total energy consumed by the body (about 2% at rest) but the work of breathing during heavy exercise may amount to 25% of the body's total energy.

1The destruction of lung tissue reduces the springiness of the lungs. The lungs become more compliant-a small change in pressure produces a larger than normal change in the volume [C=∆V/∆P]. Much of the work of breathing is done in overcoming the resistance of the airways R = ∆P/V In emphysema walls of the alveoli are damaged by inflammation, hence alveoli can lose their natural elasticity and become overstretched and ruptured. Their will be a reduced number and strength of the springs which result in expansion of the chest wall and narrowing of the major airways causing an increase in airway resistance. 1- The lungs become flabby and expands as the reduced tension allows the chest wall to expand. 2- The tissues do not pull very hard on the airways, permitting the narrowed airways to collapse easily during expiration.

The person who has emphysema could be tested by being unable to blow out a candle.

Asthma is another common obstructive disease, that causes the airways of the lungs to swell and narrow (its volume decreases). The basic problem is also expiratory difficulty due to the increased airway resistance [R= ∆P/V]. Some of this resistance is apparently due in part to swelling (edema) and mucus in the smaller airways, but much of it is due to contraction of the smooth muscles around the large airway. Lung compliance [C = ∆V/∆P ] is normal.

Functional residual capacity (FRC) [Lung volume after normal expiration] may be higher than normal, since the patient often starts to inspire before completing a normal expiration.

* Pet hair or dander * Dust * weather changes * Chemical Pollution * Pollen * Infections * Smoking Aspirin and other non-steroidal anti-inflammatory drugs (NSAIDs) provoke asthma in some patients. Many people with asthma have a personal or family history of allergies or eczema. Others have no history of allergies.