M6(1) Ventilation Mechanics and the Flow-Volume Loop

respiratory events

there are four main events to respiration

1. pulmonary ventilation

2. external respiration

3. respiratory gas transport

4. internal respiration

pulmonary ventilation

exchange of air between the atmosphere and the lungs

external respiration

exchange of O2 and CO2 between the lungs and the blood

respiratory gas transport

O2 and CO2 are transported by the blood

internal respiration

exchange of O2 and CO2 between the blood and cells

simple diffusion

passive transport where molecules move from an area of higher concentration to an area of lower concentration

• no energy needed

• high pressure to low pressure

Boyle’s law

states that pressure is inversely proportional to volume

• when temp and amount of gas are kept constant

Boyle’s law examples

pressure inversely proportional to volume

• if volume increases, pressure decreases

• if volume decreases, pressure increases

inspiratory muscles

primarily the diaphragm and external intercostals

expiratory muscles

primarily the abdominal muscles and internal intercostal

• only majorly active during exercise (during active expiration)

diaphragm

primary muscle of respiration, and it plays a central role in breathing, especially during inspiration

• contracts during inspiration

medullary respiratory center

controls inspiration

• sends signals to diaphragm and external intercostal muscles

• involved in forced breathing (inspiration + expiration) during exercise

inspiration mechanics

MRC sends signal to inspiratory muscles (diaphragm + intercostal muscles)

• intrapulmonary pressure drops below atmospheric pressure

  • air sucked into lungs along pressure gradient

expiration mechanics at rest

at rest, there is passive recoil of the lungs and chest wall

• intrapulmonary pressure goes above atmospheric pressure

  • air pushed out of lungs

expiration during exercise

during exercise, expiration becomes active with the recruitment of additional muscles

• intrapulmonary pressure increases above atmospheric pressure

  • air pushed out of lungs even more

to help get rid of CO₂ faster

residual volume

the amount of air that remains in the lungs after a maximal exhalation

• prevents lung collapse

flow volume loop

a graph that shows the relationship between airflow (y-axis) and lung volume (x-axis) during a maximal inspiration and expiration

• X-axis (horizontal): Lung Volume (from Residual Volume → Total Lung Capacity)

• Y-axis (vertical): Airflow (positive = expiration, negative = inspiration)

phases of loop

Phases of the Loop:

1. Starting Point – Residual Volume (RV):

2. Inspiration (below the x-axis):

3. Expiration (above the x-axis):

starting point on loop

represents the Residual Volume

• loop begins at lowest lung volume (after full exhalation)+

inspiration on loop

looks like a symmetrical parabola

• flow rises smoothly to Peak Inspiratory Flow then returns to 0 L/s at Total Lung Capacity (TLC)

expiration on loop

looks like a sail on a boat

• starts at TLC and rises sharply to Peak Expiratory Flow before returning to 0 gradually at Residual Volume

young adult flow volume loop

max VO₂ = 42 ml/kg/min

peak V_E = 100 L/min

young athlete flow volume loop

max VO₂ = 73 ml/kg/min

peak V_E = 170 L/min

differences between athlete and adult

overall loop width wider

max VO₂ is higher in athlete (73 ml/kg/min vs 42 ml/kg/min)

peak V_E is higher in athlete (170 L/min vs 100 L/min)

tidal volume is higher

TLC is slightly higher

minute ventilation

total volume of air moved in and out of the lungs per minute during normal breathing

maximum voluntary ventilation

(MVV) maximum amount of air a person can move in and out of the lungs per minute when breathing as fast and deep as possible

• represents the “upper limit” of how much air the lungs and respiratory muscles can move

• generally higher in athletes (180-220 L/min vs 140-180 L/min)

overlapping

in the expiratory portion of the curve, overlapping can be seen on the gradual descent downwards with lower intensity loops

• airway diameter better maintained from submaximal to maximal intensity exercise

expiratory flow limitation

at high levels of fitness or exercise intensity, ventilation (VE) can reach near-maximal levels.

• respiratory system reaches mechanical limits, despite increased effort (e.g. via expiratory flow muscles), expiratory flow does not increase further

• limits expiratory flow

parabola shape

inspiratory portion of loop looks like a parabola

• airway diameter actually increases during inspiration ,

• airflow changes gradually and symmetrically, forming that smooth, rounded, parabolic curve

sail shape

expiratory portion of loop looks like a sail

• high elastic recoil (help of internal intercostals during exercise → sharp jump

• airway diameter decreases during expiration → gradual descent down