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Alterations in Ventilatory Pattern and Ratio of Dead-Space to Tidal Volume

1987; Elsevier BV; Volume: 92; Issue: 6 Linguagem: Inglês

10.1378/chest.92.6.1013

1931-3543

Richard W. Baker, N. K. Burki,

Emergency and Acute Care Studies

The effects of alterations in ventilatory pattern on the simultaneously measured physiologic and anatomic dead-spaces (Vdphys and Vdan, respectively) and the dead-space to tidal volume ratio (Vd-Vt) were studied in 17 healthy normal subjects (13 men, four women, ages 21 to 36 years). There were no significant changes in Vdan with increases in respiratory frequency (f) or tidal volume (Vt). The Vdphys increased (mean change + 0.153 L, p<0.05) with increase in Vt (mean increase +0.84 L, p<0.01), but did not alter significantly with a twofold increase in f, at control Vt. Increase in Vt significantly reduced Vd/Vt (mean change –10.4 percent, p<0.05), but increase in f, at control Vt, did not significantly alter Vd/Vt. These results indicate that in normal subjects, increase in Vt alters ventilation/perfusion matching in the lungs, whereas an increase in f, at constant Vt, has no effect on ventilation/perfusion matching. Increases in Vd/Vt cannot, therefore, be ascribed to alterations in ventilatory pattern where either Vt, or f, or both are increased. The effects of alterations in ventilatory pattern on the simultaneously measured physiologic and anatomic dead-spaces (Vdphys and Vdan, respectively) and the dead-space to tidal volume ratio (Vd-Vt) were studied in 17 healthy normal subjects (13 men, four women, ages 21 to 36 years). There were no significant changes in Vdan with increases in respiratory frequency (f) or tidal volume (Vt). The Vdphys increased (mean change + 0.153 L, p<0.05) with increase in Vt (mean increase +0.84 L, p<0.01), but did not alter significantly with a twofold increase in f, at control Vt. Increase in Vt significantly reduced Vd/Vt (mean change –10.4 percent, p<0.05), but increase in f, at control Vt, did not significantly alter Vd/Vt. These results indicate that in normal subjects, increase in Vt alters ventilation/perfusion matching in the lungs, whereas an increase in f, at constant Vt, has no effect on ventilation/perfusion matching. Increases in Vd/Vt cannot, therefore, be ascribed to alterations in ventilatory pattern where either Vt, or f, or both are increased.