physiological adaptations of respiration

What happens to blood gases during exercise despite increased oxygen consumption?

Despite 20-fold increase in oxygen consumption during exercise, arterial blood gases (PCO2, PO2, pH) remain close to resting concentrations.

What are the main contributors that increase ventilation during exercise?

1. Primary/secondary motor cortices activity

2. Joint receptor stimulation (proprioceptors)

3. Local muscle hypoxia

4. Higher cortical input (learned response)

What is the Respiratory Exchange Ratio (RER)?

RER = VCO2 expired/VO2 inspired, measured at the lungs using indirect calorimetry. Indicates which macronutrients are being used for energy.

What are the typical RER values and what do they indicate?

Rest/light exercise (0.7-0.85): Primarily fat metabolism

• Moderate (0.85-0.95): Mix of fats and carbs

• High intensity (0.95-1.0+): Primarily carbohydrates

• 1.0: Supramaximal exercise with lactic acid buffering

What is the normal VO2max range for different populations?

Middle-aged adults: 30-40 mL O2/(min × kg)

• People with respiratory/heart disease: 10-20 mL O2/(min × kg)

• Elite endurance athletes: 80-90 mL O2/(min × kg

What is the Hering-Breuer reflex?

A protective reflex that prevents over-inflation of lungs during inspiration. Triggered when tidal volume exceeds 1.5 liters in humans.

What causes nitrogen narcosis in diving?

Increased pressure at depth raises nitrogen partial pressure, causing more nitrogen to dissolve in neural tissue, disrupting neural function. Symptoms begin around 120 feet depth.

What causes decompression sickness ("the bends")?

Rapid ascent causes dissolved nitrogen to form bubbles in tissues and blood as pressure decreases, leading to vascular blockage, joint pain, and potential neurological symptoms.

What are the primary adaptations to high altitude?

1. Increased red blood cell production

2. Increased lung diffusing capacity

3. Increased cardiac output

4. Enhanced mitochondrial oxygen extraction

What unique adaptations do native high-altitude populations show?

1. Large "barrel" chests

2. Decreased total body size

3. Left-shifted hemoglobin dissociation curve

4. Better oxygen binding at lower ambient PO2

How does atmospheric pressure change with diving depth?

For every 33 feet below surface, atmospheric pressure increases by one atmosphere (760 mmHg). At 33 feet depth = 2 atmospheres (1520 mmHg).

What is hyperbaric oxygen toxicity?

A condition caused by high PO2 at depth that can cause convulsions, disorientation, and long-term brain damage from free radical formation.

How do helium-oxygen mixtures help prevent diving complications?

Helium replaces nitrogen because it:

1. Has smaller molecules that equilibrate/eliminate faster

2. Is less dense, reducing breathing work

3. Minimizes narcosis and bubble formation risk

What is acute mountain sickness and its early symptoms?

Condition from rapid ascent to altitude. Early symptoms:

1. Shortness of breath with mild exertion

2. Quick muscle fatigue

3. Reduced hemoglobin saturation

What happens during hyperventilation at altitude?

Hyperventilation lowers arterial CO2 but doesn't improve oxygen pressure, leading to hypocapnia and increased plasma pH, causing nausea.

What is the relationship between exercise and respiratory control?

Exercise increases ventilation before blood gas changes occur through motor cortex activity, joint receptors, and learned responses

How does recompression therapy work for decompression sickness?

Patient is placed in hyperbaric chamber, pressure raised to diving depth, then slowly reduced over hours allowing safe nitrogen off-gassing.

What happens to gas exchange during exercise?

Resting O2 consumption (300 ml/min) can increase to 3,000 ml/min in fit individuals and up to 6,000 ml/min in elite athletes.

What limits VO2max?

The point where O2 transport systems can no longer keep pace with increasing power output demands, causing O2 uptake to plateau.

How does the Hering-Breuer reflex mechanism work?

1. Pulmonary stretch receptors detect lung expansion

2. Signal travels via vagus nerve to medulla

3. Inspiratory neurons are inhibited

4. Inspiration terminates, expiration begins

What are the dangers of staying at very high altitudes?

Extended exposure leads to:

1. Increased blood viscosity from high hematocrit

2. Cardiac ventricle hypertrophy

3. Increased cardiac workload against resistance

How does atmospheric pressure affect PO2 at extreme altitude?

At Mount Everest (29,000 feet):

• Atmospheric pressure = 253 mmHg

• PO2 of inhaled air = 51 mmHg (vs 150 mmHg at sea level)

How does RER change during recovery from exercise?

Initially remains elevated due to continued H+ buffering

• Gradually returns to normal as oxygen debt is repaid

• Eventually shifts back to primarily fat oxidation

What is the chemical equation for lactic acid buffering during intense exercise?

H+ + HCO3− → H2CO3 → CO2 + H2O

What makes breathing more difficult during diving?

Increased pressure compresses the lungs, requiring more effort to inhale against external pressure to keep lungs inflated.

What is the recommended decompression time for deep dives?

For a one-hour dive at 50 feet depth, approximately 3 hours of decompression is required.

How do peripheral chemoreceptors respond differently at altitude versus exercise?

Exercise: Don't detect significant blood gas changes

• Altitude: Activated by lowered arterial PO2, triggering increased ventilation

What determines successful altitude acclimatization?

1. Rate of ascent

2. Final altitude reached

3. Individual physiological adaptability

4. Time allowed for adaptation

What happens to pulmonary ventilation during initial altitude exposure?

Immediate hyperventilation occurs to compensate for lower O2, but this leads to respiratory alkalosis until acclimatization occurs.

What are the critical time periods for different diving-related conditions?

Nitrogen narcosis: Effects begin after ~1 hour at 120 feet

• Oxygen toxicity: Risk increases with depth and exposure time

• Decompression sickness: Risk increases with depth and bottom time

During exercise, oxygen consumption can increase by what factor compared to rest?

a) 5-fold

b) 10-fold

c) 20-fold

d) 30-fold

C

Which of the following is NOT a contributor to increased ventilation during exercise?

a) Primary motor cortex activity

b) Joint receptor stimulation

c) Changes in blood pH

d) Local muscle hypoxia

C

A Respiratory Exchange Ratio (RER) of 0.7-0.85 indicates:

a) Primarily carbohydrate metabolism

b) Primarily fat metabolism

c) Equal mix of fat and carbohydrate

d) Protein metabolism

B

The normal VO2max for mildly active middle-aged adults is:

a) 10-20 mL O2/(min × kg)

b) 30-40 mL O2/(min × kg)

c) 50-60 mL O2/(min × kg)

d) 80-90 mL O2/(min × kg)

B

The Hering-Breuer reflex in humans is triggered when tidal volume exceeds:

a) 0.5 liters

b) 1.0 liters

c) 1.5 liters

d) 2.0 liters

C

For every 33 feet of depth in water, atmospheric pressure increases by:

a) 0.5 atmospheres

b) 1 atmosphere

c) 1.5 atmospheres

d) 2 atmospheres

B

Nitrogen narcosis typically begins to show symptoms at what depth?

a) 60 feet

b) 90 feet

c) 120 feet

d) 150 feet

C

At the summit of Mount Everest, the atmospheric pressure is approximately:

a) 153 mmHg

b) 253 mmHg

c) 353 mmHg

d) 453 mmHg

B

Which is NOT an adaptation to high altitude?

a) Increased red blood cell production

b) Decreased cardiac output

c) Enhanced mitochondrial oxygen extraction

d) Increased lung diffusing capacity

B

During exercise at high intensity (RER > 1.0), the elevated RER is primarily due to:

a) Increased fat metabolism

b) Increased protein breakdown

c) Bicarbonate buffering of lactic acid

d) Decreased oxygen consumption

C

What is the recommended decompression time for a one-hour dive at 50 feet?

a) 1 hour

b) 2 hours

c) 3 hours

d) 4 hours

C

Native high-altitude populations show which adaptation?

a) Smaller chest capacity

b) Increased total body size

c) Right-shifted hemoglobin dissociation curve

d) Left-shifted hemoglobin dissociation curve

D

During recovery from intense exercise, RER remains elevated because:

a) Continued fat oxidation

b) Ongoing H+ buffering

c) Increased protein metabolism

d) Decreased oxygen consumption

B

Which gas is preferred to replace nitrogen in diving mixtures?

a) Carbon dioxide

b) Argon

c) Helium

d) Neon

C

Early symptoms of acute mountain sickness include all EXCEPT:

a) Shortness of breath

b) Muscle fatigue

c) Increased hemoglobin saturation

d) Reduced exercise capacity

C

The resting oxygen consumption of approximately 300 ml/min can increase in elite athletes to:

a) 2,000 ml/min

b) 4,000 ml/min

c) 6,000 ml/min

d) 8,000 ml/min

C

Hyperventilation at altitude results in:

a) Increased arterial PO2

b) Hypercapnia

c) Hypocapnia

d) Decreased plasma pH

C

The primary danger in diving occurs during:

a) Initial descent

b) Maximum depth

c) Ascent

d) Equipment preparation

C

Which statement about blood gases during exercise is correct?

a) PCO2 increases significantly

b) PO2 decreases significantly

c) pH changes dramatically

d) Values remain close to resting levels

D

Long-term residence at high altitude can lead to:

a) Decreased blood viscosity

b) Cardiac ventricle hypertrophy

c) Reduced hematocrit

d) Decreased pulmonary blood volume

B

The Hering-Breuer reflex is mediated by:

a) Glossopharyngeal nerve

b) Vagus nerve

c) Phrenic nerve

d) Hypoglossal nerve

B

At moderate exercise intensity, RER values typically range from:

a) 0.70-0.80

b) 0.85-0.95

c) 1.00-1.10

d) 1.15-1.25

B

Hyperbaric oxygen toxicity can cause all EXCEPT:

a) Convulsions

b) Decreased free radical formation

c) Brain damage

d) Disorientation

B

The primary purpose of recompression therapy is to:

a) Increase oxygen delivery

b) Allow safe nitrogen off-gassing

c) Reduce blood pressure

d) Increase CO2 elimination

B