Gas laws and partial pressures

Supple O2 to tissues via circulation

Eliminate CO2 produced by tissue metabolism

Regulate blood pH and acid-base balance

What are the respiratory functions of the lungs

Central nervous system- has to generate signal to breathe

Phrenic and intercostal motor nerves

Respiratory muscles

Intact pleural space

Patent airways

Normal lung parenchyma with high compliance

What systems are required for effective respiration

Alveolar ventilation

Bidirectional diffusion of O2 and CO2

Perfusion of metabolizing tissues

What 3 processes are required for normal gas exchange in the lungs

Inspiration- ribs expand, diaphragm contracts

Expiration- ribs contract, diaphragm relaxes

Post-expiration- period between breaths

What are the phases of the respiratory cycle

Mean: 95 mmHg

(80-110)

What is the normal PaO2

Mean: 40 mmHg

(35-45)

What is the normal PaCO2

Mean: 7.4

(7.35-7.45)

What is the normal arterial pH

Mean: 24 mEq/L

(22-28)

What is the normal arterial concentration of HCO3-

760 mmHg

How much is barometric pressure

Bulk flow

Non-random movement from high total pressure to low total pressure independent of the composition of the gas

Non-random movement from high total pressure to low total pressure independent of the composition of the gas

Movement of air into and out of lungs during ventilation

PA < PB on inspiration

What is bulk flow

Diffusion

Random movement from high partial pressure to low partial pressure dependent on the composition of the gas

Random movement from high partial pressure to low partial pressure dependent on the composition of the gas

Diffusion of O2 across the alveolar-capillary barrier

PAO2 > PvO2

What is diffusion

Ventilation

The exchange of air between the atmosphere and alveoli

The exchange of air between the atmosphere and alveoli by bulk flow

What is ventilation

Gas exchange

The exchange of O2 and CO2 between alveolar air and alveolar capillary blood

The exchange of O2 and CO2 between alveolar air and alveolar capillary blood OR between tissue capillary blood and cells

What is gas exchange

F (bulk flow)= (PB-PA)/R

Alveolar pressure cycles below and above atmospheric

PA altered by change in VL by inspiratory muscles

Inhalation: PB>PA-> air comes in

Exhalation: PA>PB-> air rushes out

Describe how air goes in and out of the lungs via bulk flow

The hypothetical pressure that a particular gas in a mixture would exert if it was present along at a given volume

Partial pressure of gas X in atmosphere:

(PX)= PB x FX (fraction of gas in mixture)

What is a partial pressure of a gas

0.21

What is the fraction of O2 in atmospheric air

160 mmHg

What is the partial pressure of O2 in atmospheric air

PAO2= 105 mmHg

Lower PAO2 than inspired air (160) as some O2 leaves alveoli and enters capillaries

What is the normal partial pressure of O2 in the alveoli

PACO2= 40 mmHg

Higher PACO2 than inspired air (0.3) as CO2 enters alveoli from pulmonary capillaries

What is the normal partial pressure of CO2 in the alveoli

Can measure PACO2 from PaCO2 because CO2 is highly-diffusable- blood and alveolus equilibriate by the distal end of capillary

Cannot measure PAO2 from PaO2 because it's not as diffusable- not enough time to reach full equilibrium

How can/can't arterial pressure of CO2 and O2 be used to measure their alveolar pressures

PAO2= (Pb- PH2O) x FiO2 - PaCO2/ RQ

RQ= The ratio between the amount of CO2 entering the alveoli from the blood, and the amount of O2 entering blood from alveoli= ~0.8-0.9

Normal PH2O at animal body temperature= 50 mmHg

PAO2= (760-50) x 0.21 - 40/0.8 or 0.9= 100-105 mmHg

How is PAO2 calculated

PIO2 of inspired air

Rate of alveolar ventilation

Rate of body's O2 consumption

Cardiac output and perfusion

The overall rate of O2 consumption to alveolar ventilation

What factors determine PAO2

Decreased PIO2= decreased PAO2

Inhale less O2-> less O2 reaches alveoli

Generally remains constant unless altitude changes

How does PIO2 affect PAO2

Decreased V*A reduces PAO2- less fresh air enters alveoli per unit of time

Less O2 entering= less O2 in alveolus

How does rate of alveolar ventilation affect PAO2

If the body is using more O2, PAO2 decreases- larger amount of inspired O2 will diffuse immediately into the bloodstream to replenish tissues

How does the rate of bodily O2 consumption affect PAO2

Decreased cardiac output and perfusion will decrease PAO2

Decreased CO means more O2 is taken out of blood, meaning PaO2 returning to lungs is low, increasing the pressure gradient and causing O2 to leave the lungs into the bloodstream

How does cardiac output affect PAO2

Rate of alveolar ventilation

Rate of body CO2 production

Overall ratio of CO2 generation to alveolar ventilation

What factors determine PACO2

Decreased V*A (hypoventilation) increases PACO2

Less fresh air coming in-> cannot dilute the CO2 already present

How does alveolar ventilation reate affect PACO2

If the body is making more CO2, PACO2 increases

More CO2 is entering the alveoli from the blood stream per unit of time

How does rate of bodily CO2 production affect PACO2

Inversely related

If CO2 generation is constant and alveolar ventilation decreases, then PaCO2 must increase

What is the relationship between alveolar ventilation and PaCO2

Central and peripheral NS- medulla is central control point

Musculoskeletal system: nasal mm, IC mm of chest wall, diaphragm, mm of abdominal wall, ribs

What are the 2 components of the respiratory pump system

Pressure of a fixed amount of gas/liquid (P) in a container is inversely proportional to the container's volume (V)

Bigger container= lower pressure

Smaller container= higher pressure

What is Boyle's law

Pressure difference between the inside and outside of the lungs (given relative to the inside of the lungs)

PTP= PA- PIP

PIP at rest is slightly neg so PTP at rest is slightly positive

Pos PTP= lungs expand

Neg PTP= lungs collapse

What is transpulmonary pressure

Lungs want to collapse. Chest wants to expand

Functional residual capacity= balance position at which those forces are equal- creases vacuum

What is the force balance of the lungs

intercostal muscles contract and the diaphragm flattens

Chest volume increases

High volume= low pressure. PIP decreases

PTP increases (think of equation)

Increased PTP sucks lungs outwards. VL increases

High volume= low pressure. PA decreases

PB> PA so air flows into the lungs down pressure gradient

Explain the pressure and volume changes that result in air entering the lungs during inspiration

Neural signal causes contraction of inspiratory IC mm (ribs move up and out) and of diaphragm (flattens- most important respiratory muscle)

Results in active increase in thoracic volume-> triggers pressure and volume changes that result in air entering lungs by bulk flow

End of inspiration: PA=PB

Inflated lungs exert greater elastic recoil. Equals the elevated PTP and VL stabilizes

Nerves to IC mm and diaphragm cease to fire

What is the process of inspiration starting at the neural signal

Usually passive

Nerve stimuli to diaphragm and IC mm cease- relaxation (ribs move down and in. Diaphragm domes up)

Chest wall has elastic recoil- starts to recoil inwards- triggers volume and pressure differences that result in passive forcing of air out of the lungs

What is the process of expiration at rest beginning with neural control

IC mm and diaphragm relax

Chest wall is elastic and recoils inward. Chest volume decreases

Low volume= high pressure. Increases PIP

PTP decreases (remember equation)

Low PTP pushes lungs inwards. VL decreases

Low volume= high pressure. PA increases

PA> PB-> air flows out of lungs down pressure gradient

Explain the pressure and volume changes that result in air leaving the lungs during expiration

Expiration of larger air volumes achieved by contraction of:

-secondary set of expiratory IC mm- actively pull ribs down and in

-abdominal muscles- increase intra-abdominal pressure and force diaphragm upwards into the thorax

End result is an active decrease in thoracic volume

What changes in expiration during periods of exercise

Tidal volume (VT)

The volume of air entering and leaving the lungs during a normal inspiration and subsequent expiration

The volume of air entering and leaving the lungs during a normal inspiration and subsequent expiration

Part of volume fills dead space (VD)

Part fills respiratory zone (VA)

What is tidal volume

Inspiratory reserve volume (IRV)

The maximal amount of air (above VT) that can be inspired on the deepest inspiration

The maximal amount of air (above VT) that can be inspired on the deepest inspiration

What is inspiratory reserve volume

Functional residual capacity (FRC)

The volume of air remaining in the lungs after expiration of resting VT

The volume of air remaining in the lungs after expiration of resting VT

Determined by balance between elastic recoil forces of chest wall and lung

What is functional residual capacity

Expiratory reserve volume (ERV)

The maximal volume of air (after VT) that can be expired on a forced expiration

The maximal volume of air (after VT) that can be expired on a forced expiration

What is expiratory reserve volume

Residual volume (RV)

The volume of air remaining in the lungs after forced expiration and expulsion of the expiratory reserve volume

The volume of air remaining in the lungs after forced expiration and expulsion of the expiratory reserve volume (cannot get that air out at all)

RV= FRC- ERV

Determined by strength of respiratory mm, lung compliance, chest wall stiffness, airway patency

What is residual volume

Vital capacity (VC)

The maximal volume that can be expired after a maximal inspiration

The maximal volume that can be expired after a maximal inspiration

VC= VT + IRV + ERV (still won't get rid of residual volume)

Useful clinical index of lung function

What is vital capacity

Total lung capacity

The total air volume of both lungs at the end of maximal inspiration

The total air volume of both lungs at the end of maximal inspiration

TLC= VT + IRV + ERV + RV

What is total lung capacity

Anatomic dead space

Alveolar dead space

What are the 2 types of dead space volume

The volume of air in the conducting airways that does not participate in gas exchange

What is anatomic dead space

The volume of alveoli that should be but are not exchanging gas

Abnormal in mammals and mainly due to disease

What is alveolar dead space

Anatomic + alveolar dead space

Quantified as the volume of the lung that is not producing CO2

In a normal healthy animal, should be equivalent to the anatomic dead space (should not have any alveolar dead space)

What is physiological dead space