Pulmonary Ventilation and Spirometry Quiz

Pulmonary Ventilation

• Minute Ventilation (Ve): Volume of air moved in and out of the lungs per minute. Calculated as tidal volume multiplied by respiratory rate.
• Increases with exercise intensity (as VO2 rises), closely associated with CO2 production.
• Normal range is 4-15 L/min but varies with body size and gender (males typically higher).
• Peak exercise can reach 180 L/min in males, increasing 25-30 fold with maximal exercise.
• Linear increase in Ve with O2 uptake during exercise.

Alveolar Ventilation (Va)

• Portion of minute ventilation involved in gas exchange within the alveoli.
• Determines gas concentrations at the alveolar-capillary membrane.
• Volume of gas participating in gas exchange per minute.

Dynamic Lung Volume

• Maximum air volume movable in and out of lungs, plus the speed of this movement.
• Measured via spirometry tests (see below).

Spirometry

• Forced Vital Capacity (FVC): Maximum volume of air expired after maximal inspiration.
• Forced Expiratory Volume in 1 second (FEV1): Volume expired in the first second of forced expiration, reflecting expiratory power and lung resistance.
• FEV1/FVC Ratio: Percentage of FVC that can be exhaled in one second; usually around 80% in health, potentially decreasing to 40% in lung disease.
• Maximum Voluntary Ventilation (MVV): Measures ventilatory muscle capacity; individual hyperventilates for 12-15 seconds, and volumes are extrapolated to a one-minute period.

Special Considerations

• Hyperventilation: Increased rate and/or depth of breathing, decreasing arterial PaCO2 (exhaling CO2) and potentially inducing respiratory alkalosis. It does not affect PaO2 because blood is already ~98% saturated with O2. This allows for a longer breath-hold until respiratory drive increases again. Respiration is primarily triggered by high PaCO2, not O2 demand.
• Dyspnea: Difficult or labored breathing, can be caused by delayed/inadequate cardiorespiratory adjustment, insufficient warm-up, metabolite accumulation, or large meal.
• Second Wind: Initial respiratory distress (up to 3-4 minutes) during continuous exercise, followed by slowing of ventilation and relief of local muscle fatigue in a steady state. Early oxidation accumulation occurs prior to the steady state, where relief occurs.
• Stitch in the Side: Pain in diaphragm/abdominal area, potentially due to insufficient warm-up, inadequate blood flow, anaerobic metabolism, or post-meal exercise.
• Valsalva Maneuver: Forced exhalation against a closed glottis; can cause dramatic increases in blood pressure in some individuals (especially with cardiovascular disease), so it's best avoided during weight training.

Gas Exchange in Lungs

• Minute Ventilation (Ve): Crucial for air delivery.
• Alveolar Ventilation (Va): Crucial for gas exchange (portion of Ve mixing with alveolar air).
• Ventilation-Perfusion Ratio: Uneven across the lungs (top: high ventilation, poor perfusion; bottom: poor ventilation, high perfusion). As long as the ratio remains above 0.5, gas exchange is generally adequate.

Ventilatory Control

• Primarily regulated by blood chemistry (PaO2, PaCO2, acidity, temperature) at rest. Sensory neural units in the medulla and arterial systems respond to these variations.
• PaCO2 is the most important stimulus at rest.
• Cortical and peripheral influences impact ventilation during exercise.
• Ventilation control during exercise is multifactorial.

Ventilation During Steady-State Exercise

• Ve/VO2 Ratio: Volume of air ventilated per litre of O2 uptake, indicating ventilation efficiency (around 25 in young, healthy individuals; lower values = higher efficiency; max efficiency commonly achieved around ventilatory and lactate thresholds).
• Ve/VCO2 Ratio: Indicates chemoreceptor sensitivity, with a relatively constant value until the onset of metabolic acidosis or lactate threshold. Endurance training improves these equivalencies (beneficial for both lung/heart disease rehabilitation).

Ventilatory Threshold

• Point when pulmonary ventilation increases disproportionately with oxygen uptake during graded exercise.
• Implies imbalance between lactate appearance and disappearance rates.
• Usually occurs between 55-69% VO2 max in untrained individuals (higher in trained athletes - as high as 80% or more).
• Often coincides with lactate threshold.

Altitude

• Acute Exposure: Lightheadedness, nausea, headache, insomnia, dyspnea due to decreased barometric pressure, reduced O2 partial pressures, and arterial hypoxia.
• Acute Acclimatization: Hyperventilation (initial defense) to increase alveolar ventilation and O2 loading; cardiovascular responses (increased blood flow at rest and submaximal exercise); cooling/drying effects that can trigger dehydration (increased HR response at altitude); alterations in acid-base balance (with the lactate paradox occurring).
• Chronic Acclimatization: Cardiovascular responses (increased blood flow, higher resting HR during submaximal exercise); hematological and cellular adaptations (increase oxygen-carrying capacity via increased Hb and RBC concentration); and some impact on hyperventilation/acid-base balance (though the lactate paradox can persist).

Detection of COPD

• History: Wheezing, dyspnea, sputum production, smoking history, occupational exposures.
• Grading: Symptom severity scale. Diseases associated: chronic bronchitis, emphysema, asthma.
• Spirometry: For detecting low flow/volume rates, often showing progressive loss of breathing capacity with age and COPD progression. Diagnosis typically by FEV1 test.
• Severity Gauging: FEV1 relative to age and gender-matched healthy individuals.
• Treatment: Lifestyle modification, bronchodilators, expectorants, steroids (severe cases).

Breathlessness Disability Scale

• Grades 1-4 based on exertion-related breathlessness severity. Grade 4 is the most severe; individuals in the highest severity stages (3 & 4) are often on supplemental oxygen and are focused on efficiency and energy conservation when working.

Asthma Response to Exercise

• Airways tightening during exercise, increasing difficulty breathing due to inflammation and mucus formation. Exercise-induced asthma is triggered by exposure to cold/dry air, pollutants.