BS2014: Respiratory Control during exercise

What is minute ventilation, Ve

the volume of air inspired or expired in 1 minute

What is Ve measured in

L/min

Equation for Ve

minute ventilation (Ve) = tidal volume (Vt) x breathing rate

Typical values of breathing rate, tidal volume, and minute ventilation at rest

• breathing rate — 12 breaths/min

• tidal volume — 0.5 L/min

• minute ventilation — 6 L/min

Typical values of breathing rate, tidal volume, and minute ventilation during moderate exercise

• breathing rate — 30 breaths/min

• tidal volume — 2.5 L/min

• minute ventilation — 75 L/min

Typical values of breathing rate, tidal volume, and minute ventilation during intense exercise

• breathing rate — 50 breaths/min

• tidal volume — 3.0 L/min

• minute ventilation — 150 L/min

What nerve is stimulated to increase breathing rate

the phrenic nerve

How does the nervous system increase breathing rate

• stimulates phrenic nerve to cause the diaphragm to contract more

• activates the intercoastal nerve to stimulate external intercoastal muscles to rapidly elevate the ribcage

Partial pressures of oxygen & carbon dioxide in oxygenated and deoxygenated blood

• oxygenated: PO₂ = 100, PCO₂ = 40

• deoxygenated: PO₂ = 40, PCO₂ = 46

What happens in phase 1 of our breathing during exercise and quickly into exercise does this occur

RAPID increase in breathing rate from rest in the first 15s

What happens in phase 2 of our breathing during exercise and quickly into exercise does this occur

a single exponential increase after the first 15s, which lasts up to 4 mins

What happens in phase 3 of our breathing during exercise

breathing rate plateaus

What is the ventilatory/anaerobic threshold

the exercise intensity at which minute ventilation increases disproportionately to oxygen consumption

What is the lactate threshold

the exercise intensity at which lactate begins accumulating in the bloodstream faster than it can be removed

What is LT1

when blood lactate increases above 1 mmol/L

What is OBLA (onset of blood lactate accumulation)

when blood lactate reaches above 4 mmol/L

What is hyperthermia induced hyperventilation

when breathing rate and tidal volume increase disproportionately to metabolic needs when body core temperature rises

How is oxygen transported in the blood

• 2% dissolved in the blood

• 98% bound to haemoglobin in the blood

What effect does exercise have on the O2-dissociation curve

it shifts it to the right

What is the name of the rightward shift of the O₂-dissociation curve

the Bohr effect

What is the Bohr effect

the decrease in haemoglobin’s affinity for oxygen (due to increase in CO₂ levels and low pH) to increase oxygen delivery to the working tissues

Why does the O2-dissociation curve shift to the right after exercise

• due to increased heat, lactate and H⁺ in working tissues

• more unloading of O₂ in working tissues

How is CO2 transported in the blood

• 60-70% dissolved in blood as bicarbonate ions

• 7-10% dissolved in blood (as CO2)

• up to 20% bound to haemoglobin

How much oxygen in the arteries during rest

20 ml O₂ per 100 ml blood

How much oxygen in the arteries during intense aerobic exercise

20 ml O₂ per 100 ml blood

How much oxygen in the veins during rest

15 ml O₂ per 100 ml blood

How much oxygen in the veins during intense aerobic exercise

20 ml O₂ per 100 ml blood

What is (a-v)O₂

difference in oxygen content between arterial and venous blood, which measures how much oxygen tissues are extracting

What is the effect of exercise on the (a-v)O₂

exercise increases it

Why does myoglobin have a steep saturation curve

so O₂ is delivered to the mitochondria even at low pO₂ levels

What is the limiting factor for exercising at altitude

reduced partial pressure of O₂ in the atmosphere

Henry’s Law

at a constant temperature, the amount of oxygen in the bloodstream is directly proportional to the partial pressure in alveolar air

Oxygen deficit

temporary shortage of oxygen that occurs at the start of exercise when the body's demand for ATP exceeds the oxygen supply available through aerobic metabolism

EPOC (Excess Post-exercise Oxygen Consumption)

the increased rate of oxygen intake by the body to recover from intense exercise

What occurs in the fast component of EPOC

• resaturation of blood with haemoglobin

• resaturation of myoglobin with oxygen

• replenishment of PCr within the muscle and replacement of ATP

How long does the fast component of EPOC last

usually 15s

How long may the slow component of EPOC last

30 mins → 24 hours depending on the duration and intensity of exercise

What occurs in the slow component of EPOC

• lactate clearance

• thermoregulation (reduction in body heat)

• tissue repair

• ion homeostasis

Ways to remove lactic acid

• transport to liver for gluconeogenesis

• excretion via sweat and urine

• dissociation into carbon dioxide and water