Respiratory Mechanics and Gas Exchange · USMLE Step 1

How does increasing tidal volume compare to increasing respiratory rate in improving alveolar ventilation in a hypercapnic patient?

  1. Increasing tidal volume is more efficient than increasing rate
  2. Increasing rate is more efficient than increasing tidal volume
  3. Both are equally efficient
  4. Neither helps because dead space is fixed
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Correct answer: Increasing tidal volume is more efficient than increasing rate

Because alveolar ventilation = respiratory rate × (tidal volume – dead space), increasing tidal volume reduces the proportion lost to dead space and more effectively increases alveolar ventilation than increasing rate.

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