Structure and Function of Pulmonology System

Conducting vs Gas Exchange Airways

conducting airways (CAs)

• don’t participate in gas exchange
  -dead space

gas exchange airways (GEAs)

• respiratory bronchioles

• alveolar ducts

• alveoli
  -surface area: tennis cour
  -300 million/lung

Respiratory Defense Mechanisms

upper respiratory tract mucosa

• maintain temperature+humidity

• traps particles/bacteria/gases

nasal hairs/turbinates

• traps particles

• traps bacteria

• traps gases

mucous blanket

• protects trachea+bronchi

• traps particles/bacteria in lower airways

cilia

• sends mucous blanket/particles to oropharynx

alveolar macrophages

• phagocytosis→ingest+remove bacteria from alveoli

surfactant

• enhances alveoli phagocytosis

• down-regulates inflammation

nares irritant receptors

• sneeze reflex

airways irritant receptors

• cough reflex
  -trachea
  -large airways

Breathing Resistance Factors

major vs accessory muscles

alveolar surface tension

surfactant

elastic properties
-compliance vs recoil

airway resistance

Compliance

ease of lung stretching

Recoil

ease of lung rebound post-inhalation stretching

inverse to compliance

Negative Pressure Maintenance Mechanisms

lungs need negative pressure to function

negative pressure maintained by pleura

no negative pressure→lungs collapse

factors
-lung tissue elasticity
-osmotic forces
-lymphatic pump

Respiration

exchange of oxygen and carbon dioxide

occurs at cellular level

Ventilation vs Diffusion vs Perfusion

ventilation

• mechanical movement of air/gas in+out of lungs

• respiration is not ventilation

diffusion

• movement of gas between air spaces in the lungs+bloodstream

perfusion

• movement of blood into/out of capillary beds

pulmonary system:
-ventilation
-diffusion

cardiovascular system:
-perfusion

Pulmonary vs Alveolar Ventilation

maintain CO2 elimination→normal arterial CO2+normal acid-base balance
DX→arterial blood gas (ABG)

pulmonary
total exchange of gases between atmosphere (outside air) and lungs

alveolar
exchange of gases within gas exchange portion of lungs

Respiratory Center+Respiratory Groups

located in the brainstem

dorsal respiratory group

sets up basic automatic rhythm

1. impulses from peripheral chemoreceptors in carotid+aortic bodies

2. detects PaCO2+oxygen amount in arterial blood

ventral respiratory group

contains inspiratory+expiratory neurons

• increased ventilation effort needed→activated

pneumotaxic+apneustic centers

located in the pons

• inspiratory depth+rate modification→medullary centers

Central Chemoreceptors vs Peripheral Chemoreceptors

central

• reflects PaCO2

• stimulated by hydrogen in CSF (increased pH)

• increases respiratory rate+depth

peripheral

• located in aorta+carotid bodies

• stimulated by hypoxemia (increased PaO2)

• arterial hypoxemia→increases ventilation

Lung Receptors

irritant receptors

• sensitive to noxious substances

• stimulation→cough/bronchioconstriction+increased respiratory rate

stretch receptors

• protect against excess lung inflation

• decreases ventilation rate+volume

juxtapulmonary capillary/J-receptors

• sensitive to increased pulmonary capillary pressure

Diffusion

occurs in respiratory portion of lung

driven by partial pressure gradients

affecting factors

• surface area

• membrane thickness

• partial pressure differences

• solubility of gases

Oxygen Transport

methods

PO2/partial pressure oxygen:
-how much oxygen is dissolved in plasma
-not efficient

combined with hemoglobin→oxyHb
-efficient
-oxygen removed from Hb→deoxygenated/reduced Hb

oxygen transport cycle

1. oxygen arrives from pulmonary alveolus into hemoglobin

2. oxygen binds on to hemoglobin

3. RBC carries oxygen from lungs to body tissue

4. RBC drops off oxygen into tissue+CO2 binds to hemoglobin

5. RBC brings CO2 back to lungs

Oxyhemoglobin Dissociation/2,3 DPG Graph

describes the relationship between hemoglobin saturation and partial pressure of arterial oxygen

describes how oxygen in blood is affected by different partial pressures

CO2 Transport

removes CO2 from body through the lungs

impacts the body’s acid/base balance

methods

• dissolved plasma (PCO2)
  -10%

• bicarbonate (HCO3-)
  -60%

• carbaminohemoglobin
  -30%

Primary vs Secondary Circulation Functions

primary function

• provide blood flow to gas exchange portion of the lung

• facilitate gas exchange

secondary/other functions

• filters blood from right (deoxygenated)→left side (oxygenated) of circulation

• removes microthromboemboli

• reservoir of blood for left side of heart

Pulmonary vs Bronchial Circulation

pulmonary
gas exchange function

bronchial
oxygenated blood from systemic circulation
meets lung’s metabolic needs

both

• dual blood supply

• low resistance+pressure system compared to systemic circulation
  -normal pulmonary BP: 25/10 mmHg

• thinner vessel walls→less resistance to flow

Gas Transport

effective gas exchange
needs approximately even distribution of gas (ventilation)+blood (perfusion) in all portions of lungs

distribution of perfusion+ventilation

• depends on gravity+body position

• standing vs supine vs lying position

ventilation-perfusion ratio

• ventilation→apices of lungs

• perfusion→bases of lungs

V/Q Relationships+Dead Space Unit vs Shunt

v=ventilation
p=perfusion

relates distribution of air in lungs+perfusion in capillaries

effective gas transfer→v=q

normal→0.8

dead space unit

• normal ventilation

• no perfusion

shunt

• no ventilation

• normal perfusion

• low v/q

Physiologic vs Morphologic Pulmonary Assessment Tools/Dx Tests

physiologic

• spirometry

• pulmonary diffusion

• capacity

• oximetry

morphologic

• radiology

• bronchoscopy

• biopsy

• sputum

PFT

measures
ventilation function
or
gas diffusion

shows dx affect on function

allows for assessment of disease progression

Ventilatory Function Tests

measured by:
-spirometry
-formula calculations

types

• lung volume

• lung capacity

• diffusion capacity

dx

• restrictive dx→decreased lung expansion

• obstructive dx→respiratory flow problems

Spirometry

measures flow+volume of air inhaled+exhaled
-measured against time
-cause of respiratory abnormality
-evaluation of progression/resolution

process

1. pt takes deep breath

2. blows as hard+long as possible into spirometer

3. evaluate results for rest+during exercise

pt education

• avoid smoking

• avoid heavy meals

• vigorous exercise

• alcohol

• fragrances

• restrictive clothing before test

Ventilation Measurement Volumes

tidal volume (TV)

• amount of air inhaled/exhaled in 1 breath at rest

• normal breathing

• normal→500mL

inspiratory reserve volume (IRV)

• maximum amount of air inhaled above TV inhalation

• normal→3000-3300mL

expiratory reserve volume (ERV)

• maximum amount of air exhaled below TV expiration

• normal→1000-1200mL

residual volume (RV)

• amount of air left after maximum inhalation

• normal→1200mL

Lung Capacities

forced vital capacity (FVC): maximum amount of air exhaled after forced inhalation

forced expiratory volume at 1 second (FEV1): 1 second of FVC
-FEV1/FVC ratio→airway obstruction measurement

total lung capacity (TLC): maximum amount of air in lungs after maximum inhalation
-VC=respiratory volume (RV)

inspiratory capacity (IC): maximum amount of air inhaled after normal exhalation

functional reserve capacity (FRC): volume of air remaining in lungs after total volume exhalation

Pulse Oximetry vs Capnography

pulse oximetry

• measures Hgb oxygen saturation
  -DX: low PaO2

• poor peripheral circulation→decreased accuracy

capnography

• measures amount of CO2 in expired air

• estimates PaCO2

• prone to inaccuracy

Blood Gas Analysis Values

determines current gas exchange status
need arterial blood for DX

I: acute respiratory problems
hypoxemia
cardiac arrest

normal values

pH→7.35-7.45

PaCO2→25-45mmHg

PaO2→80-100mmHg

HCO3→22-23mEq/L