Respiratory system: anatomy & physiology

Kaiu Prikk 2009 autumn

The respiratory system

: TWO LUNGS, CONDUCTING AIRWAYS Upper airways: nose, mouth, larynx, pharynx Lower airways: trachea, right & left main bronchi, secondary bronchi, bronchioles, alveoli

Basic functions of respiratory system: 1. Air distributor 2. A gas exchanger O

2

, CO

2,

humidifying warming and 3. Acid-base balance 4. Phonation 5. Pulmonary defence & metabolism Respiration is an important homeostatic mechanism

Defense Mechanisms of respiratory system

The average person (moderately active) during the daytime breathes about 20,000 liters air/ 24 ho

urs

•small particles < 3 to 5 microns in diameter penetrate to the deep lung.

Lung defence mechanisms:

1. Structural protection: hears in the nose, cilia in the upper and lower airways (trap and remove foregin bodies form airways) 2. Mucosal lining fluid upper and lower airways: warms and humidifies air 3. Irritant receptors in the (recognize injurious agenst reflex nose  and airways sneeze or cough 4. Immune protection: respiratory tract mucosa and macropahges in alveoli

Pulmonary ventilation & Control of Breathing

Respiratory rate at rest is 15/per minute Pulmonary ventilation is the

exchange of air between the atmosphere and the lungs

.

Breathing process: -automatic -controlled subconsciously by the respiratory center at the base of the brain. People control their breathing for example during speech, singing, or voluntary breath holding. For example: an increased concentration of carbon dioxide is the strongest stimulus to breathe more deeply and more frequently. Conversely, when the carbon dioxide concentration in the blood is low, the brain decreases the frequency and depth of breaths

Respiratory Centers

1. The primary respiratory center: medulla Function: stimulation of basic inspiration for about 3 seconds and then basic expiration for about 2 seconds (5 sec/breath= 12 breaths/min).

2. Secondary respiratory center: pons contains 1) the pneumotaxic respiratory center; 2) the apneustic respiratory center. Function: Secondary respiratory center

:

modifies the basic respiratory rate The pneumotaxic respiratory center inhibits inspiratory time and increases breaths per minute. The apneustic respiratory center has not been clearly defined, (is postulated to prolong inspiratory time and reduces breaths per minute).

Respiratory centers in the brain stem

Respiration: 1. External respiration

alveoli and the

blood

is gas exchange between the lung of the pulmonary circulation. This process depends on: 1) gas partial pressure differences; 2) the integrity of lung membranes, 3) blood flow in and out of the lungs.

2. Internal respiration

is the exchange of gas between the blood and the cells of the body.

This process generally depends on the same factors as external respiration Movement of gases between the alveoli, blood and cells depends on the partial pressure difference of a gas across these regions. According to the Law of Diffusion, gases always move from a region of high partial pressure to a region of low partial pressure. If your lungs have a higher gas pressure than your blood, then the gas will move into your blood and visa versa

Respiration:

.

1. Quiet A.Quiet inspiration

: The

diaphragm contracts: volume decrease in

 causes an

increase in

of the thorax and the lungs  which causes a pressure of the thorax and lungs  air to enter the lungs, moving down its pressure gradient.

B. Quiet expiration

: The diaphragm relaxes  The elasticity of the muscle tissue and of the lung stroma causes recoil  returns the lungs to their volume before inspiration  the reduced volume causes the pressure in the lungs to increase  air leaves the lungs due to the pressure gradient.

2. Forced A. Forced inspiration

: Other muscles aid in the increase in thoracic and lung volumes.

The

scalenes

- pull up on the first and second ribs.

The

sternocleidomastoid muscles

pull up on the clavicle and sternum.

The

pectoralis minor

pulls forward on the ribs.

The

external intercostals

are especially important because they spread the ribs apart, thus increasing thoracic volume. It's these muscles whose contraction produces the "costal breathing" during rapid respirations

B. Forced Expiration

: The muscles aid in reducing the volume of the thorax and lungs: The

internal intercostals

- these compress the ribs together The

abdominus rectus

and

abdominal obliques: internal obliques, external obliques-

these muscles push the diaphragm up by compressing the abdomen.

The work of breathing is done by the diaphragm, intercostal muscles, the muscles in the neck, and the abdominal muscles.

When the diaphragm contracts and moves lower, the chest cavity enlarges, reducing the pressure outside the lungs. To equalize the pressure, air enters the lungs. When the diaphragm relaxes and moves back up, the elasticity of the lungs and chest wall pushes air out of the lungs

Muscles of inspiration and expiration

Gas exchange

Air movement into and out of the lungs results: 1) differences in pressure brought about by changes in lung volume. Inspiration: intrapulmonary pressue < atmospheric presssue Changes in lung volume occur due to muscle contractions in the thorax and diaphragm Ventilation is influenced by the physical properties of the lungs: • compliance • elasticity • surface tension

Compliance

: the tendency of the lungs to expand, is due to the pulling action exerted by the pleural membranes.

Expansion is also facilitated by the action of surfactant in preventing the collapse of the alveoli.

Surface tension

: action of surfactant

Elasticity

or recoi

l:

is the process by which the lungs return to their original or resting volume. Elasticity is due to the elastic stroma of the lungs and the series elastic elements of the respiratory muscles, particularly the diaphragm.

Ventilation - Inspiration

Ventilation - Expiration

Alveolus and gas exchange

Respiratory regulation: Normal values

exchange rates of O 2 and CO 2 at the tissues and in the lungs must be equal: •High pCO 2 levels increase O 2 tissues •Low pO 2 dissociation in peripheral causes alveolar capillaries to constrict & send blood to lobules with high pO 2 •High pCO 2 levels cause bronchodilation to occur increasing airflow, reverse Changes in depth and rate of respiration are regulated by brain centers

Normal Blood Gases Arterial pH 7.35 - 7.45

PaO2

80 to 100 mm Hg dissolved in arterial blood) (The partial pressure of oxygen that is

PaCO2

35-45 mm Hg (The amount of carbon dioxide dissolved in arterial blood. Measured. Partial pressure of arterial CO2.)

SaO2 B.E.

95% to 100% (The arterial oxygen saturation)

–2 to +2 mEq/lite

(The base excess indicates the amount of excess or insufficient level of bicarbonate in the system. A base excess > +3 = metabolic alkalosis a base excess < -3 = metabolic acidosis

HCO3

22 to 26 mEq/liter (21 –28 mEq/L ) The calculated value of the amount of bicarbonate in the bloodstream

Hypoventilation

: the state in which a reduced amount of air enters the alveoli in the lungs  resulting in decreased levels of oxygen and increased levels of carbon dioxide in the blood. Hypoventilation can be due to breathing that is too shallow (hypopnea) or too slo w (bradypnea) or to diminished lung function.

Hyperventilation

: is excessive ventilation of the lungs, beyond what is required to achieve normal arterial blood gases For example: Rapid or deep breathing in infection, bleeding, or heart attack Hyperventilation: -has little effect on arterial pO 2 - no effect on oxygen saturation - main effect is to lower pCO 2 and produce a respiratory alkalosis and secondary hypocalcaemia Causes of hyperventilation: 1. Disordered blood chemistry with normal homeostatic response to stimulate the brain's respiratory centre, increasing rate and depth of breathing.

2. Voluntary and conscious act.

3. Psychological response to anxiety or stress, with little awareness.

Dyspnea:

Difficult breathing; shortness of breath.

Dyspnea is a sign of serious disease of the airway, lungs, or heart.

(Resting) Tidal Volume (TV):

This is the volume of air taken into the lungs when you inhale. Tidal volume increases with exercise or activity.

Residual Volume (RV):

is the volume of air left in the lungs at the end of maximal expiration (ie. the volume of air which you cannot voluntarily exhale from your lungs).

Vital Capacity (VC):

is the volume of air expelled from the lungs during a maximal forced expiration strating after a maximal forced inspiration.

Total Lung Capacity (TLC):

The residual volume (air you cannot expire) + vital capacity (total volume available for use) = total lung capacity.

Inspiratory Reserve Volume (IRV):

Total lung capacity minus the volume of air in the lung at the end of a normal inspiration.

Expiratory Reserve Volume (ERV):

.is the volume of gas that is expelled from the lungs during a maximal forced expiration that strats at the end of normal tidal expiration

Functional Residual Capacity:

is the total volume of air left in the lungs at the conclusion of normal, resting expiration. This value includes the expiratory reserve volume plus the residual volume

(ERV + RV)

.

Forced Expiratory Volume 1 (FEV1):

the volume of air that can be expired during the first second of expiration in a vital capacity determination.... generally about 80% of VC.

Forced Expiratory Volume 1 (%) or FEV1(%):

FEV1/VC, expressed as %, normal value >70% expressed as a percentage

ratio PEF -

peak expiratory flow rate - the peak flow rate during expiration

Lung function tests or PFTs

-evaluate how well your lungs work.

1.

Spirometry 2.

3.

Diffusion test Body plethysmography 4.

Inhalation challenge tests 5. Cardiopulmonary exercise test 6. Six-minute walk test 7. A peak flor meter or PEF (

A home lung function test uses a peak flow meter)

8. Blood Gas analysis

.

Spirometry:

-is the first lung function test done. - detect the presence of lung disease.

Spirometry is recommended as the “Gold Standard” for diagnosis of obstructive lung disease by: National Lung Health Education Program (NLHEP); National Heart, Lung and Blood Institute (NHLBI); World Health Organization (WHO)

The lung function values measured with spirometry are: Forced vital capacity (FVC)

. This measures the amount of air you can exhale with force after you inhale as deeply as possible.

Forced expiratory volume (FEV)

. This measures the amount of air you can exhale with force in one breath. The amount of air you exhale may be measured at 1 second

(FEV1),

2 seconds (FEV2), or 3 seconds (FEV3). FEV1 divided by FVC can also be determined.

Forced expiratory flow 25% to 75%.

an exhale (FVC). This measures the air flow halfway through

Peak expiratory flow (PEF)

. This measures how quickly you can exhale. It is usually measured at the same time as your forced vital capacity (FVC).

Slow vital capacity (SVC)

. This measures the amount of air you can slowly exhale after you inhale as deeply as possible

Spirogram

VC IN (L) FVC (L) FEV1 (L) FEV1 % VC MAX (%) PEF (L/S) Pred 2,94 2,96 2,52 79,41 6,27 Act1 2,17 1,99 1,40 64,20 4,76 %Soll 73,8 67,3 55,3 80,8 75,9

Body plethysmography

: To measure total lung capacity (TLC), RV, airway resistance

Diffusion test or transfer test:

measures how well your lungs transfer a small amount of carbon monoxide (CO) into the blood. Diffusing capacity provides an estimate of how well a gas is able to move from your lungs into your blood.

Atrerial blood gases analysis

: to determine the amount of oxygen and carbon dioxide in your bloodstream.

Cardiopulmonary exercise te sting is a non-invasive and objective method of evaluating both cardiac and pulmonary function

Airway obstruction & restriction

Airway obstruction

Forced expiratory volume (FEV 1 ) FEV 1 divided by FVC Forced expiratory flow 25% to 75% Lower with higher FEV 2 Lower < 70% Lower Peak expiratory flow (PEF) Total lung capacity (TLC) (V T ) Slow vital capacity (SVC) Functional residual capacity (FRC) Lower Normal or higher Normal or lower Higher Residual volume (RV) Higher Expiratory reserve volume (ERV) Normal or lower RV divided by TLC ratio Higher and FEV 3

Airway restriction Forced vital capacity (FVC) Lower than predicted value Forced expiratory volume (FEV 1 ) FEV 1 divided by FVC Forced expiratory flow 25% to 75% Peak expiratory flow (PEF) Normal or lower with higher FEV 2 and FEV 3 Normal or higher Normal or lower Normal or higher Total lung capacity (TLC) (V T ) Slow vital capacity (SVC) Lower Lower