Between tidal volume and minute ventilation, which shows the larger percent increase by term?

Between tidal volume and minute ventilation, which shows the larger percent increase by term?

• A. Tidal volume increases 30-40%
• B. Minute ventilation increases 30-50%
• C. Both increase equally
• D. Only tidal volume increases

Answer: (B)

During pregnancy the respiratory system adapts to meet higher metabolic demands. Progesterone increases the central drive to breathe, so breathing becomes deeper and more efficient. Tidal volume rises about 30–40%, reflecting greater inspiratory depth. Minute ventilation, which is tidal volume times respiratory rate, increases even more because the rate also climbs modestly. The combined effect yields roughly a 30–50% increase in minute ventilation, larger than the increase in tidal volume alone. So the larger percent increase is seen in minute ventilation. The idea that only tidal volume increases isn’t correct, since the rate contributes as well and the two changes don’t rise equally.

During pregnancy the respiratory system adapts to meet higher metabolic demands. Progesterone increases the central drive to breathe, so breathing becomes deeper and more efficient. Tidal volume rises about 30–40%, reflecting greater inspiratory depth. Minute ventilation, which is tidal volume times respiratory rate, increases even more because the rate also climbs modestly. The combined effect yields roughly a 30–50% increase in minute ventilation, larger than the increase in tidal volume alone. So the larger percent increase is seen in minute ventilation. The idea that only tidal volume increases isn’t correct, since the rate contributes as well and the two changes don’t rise equally.