Which of the following statements best characterizes the pattern of ventilation

Question

Which of the following statements best characterizes the pattern of ventilation in the lungs during quiet breathing? A) surfactant keeps each region of the lung equally distended and ventilated B) gravity in the erect individual keeps the base of the lung more poorly expanded and it receives less ventilation than the apex C) gravity in the erect individual keeps the base of the lung more poorly expanded but it receives more ventilation than the apex D) gravity in the erect individual keeps the base of the lung more expanded and ventilated than the apex E) gravity in the erect indivdual keeps the base of the lung more expanded and less ventilated than the apex Explain your answer

Explanation / Answer

A) surfactant keeps each region of the lung equally distended and ventilated Surfactant increases the uniformity of lung aeration. Surfactant deficiency is a major cause of respiratory failure in newborns. We have investigated the roles of surfactant and positive end-expiratory pressure (PEEP) in the development of a functional residual capacity (FRC) and the distribution of ventilation at birth. Preterm rabbit pups (28 d GA) were delivered and received either saline or surfactant and then ventilated with (3PEEP) or without (0PEEP) 3 cm H2O PEEP (groups: saline/0PEEP, surfactant/0PEEP, saline/3PEEP, surfactant/3PEEP). Lung gas volumes were measured using plethysmography, and the uniformity of ventilation was analyzed using phase contrast (PC) x-ray imaging. Surfactant/0PEEP pups had greater FRCs and the lungs were more uniformly ventilated than saline/0PEEP pups; FRC at inflation 19-21 was 2.46 ± 0.52 mL/kg versus 0.91 ± 0.95 mL/kg (p < 0.05). Saline/3PEEP pups developed an FRC of 7.54 ± 1.68 mL/kg at inflation 19-21 (p < 0.05), but the distribution of ventilation was initially nonuniform. Surfactant/3PEEP pups had an FRC of 8.50 ± 0.80 mL/kg (at inflation 19-21), and the distribution of ventilation was more uniform than with saline/3PEEP (p < 0.05). In ventilated preterm newborn rabbits, PEEP has a greater effect on FRC than surfactant, although the two are additive. Surfactant, administered at birth, markedly improved the uniformity of ventilation irrespective of whether PEEP was applied.

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