Influence of Added Dead Space on Pulmonary Ventilation.

Abstract

Summary. Hyperventilation due to extra dead space did not cause any significant improvement in ventilatory efficiency as measured in nitrogen wash‐out experiments during oxygen breathing. In the experiments with extra dead space a significant increase in degree of uniformity of ventilation could be demonstrated. The subject's dead space increased, and the over‐all efficiency remained constant. The efficiency‐improving effect of a better distribution and the efficiency‐deteriorating effect of a larger dead space probably cancelled out. The better distribution is most probably explained by the effect of mixing of gas from different lung fractions in the large dead space. The experiments were performed with a nitrogen meter.

Informative Value of Simple Multibreath Nitrogen Washout Measurements for Clinical and Research Purposes

“…This observa tion is consistent with evidence suggesting a tendency toward more uniform inspired gas distribution with increasing Vx [7,15,27]. Because the Vp/Vx ratio can be ex pected to vary with Vx [3], our finding may also reflect the slowing effect of dead space on nitrogen clearance, predictable on the basis of theoretical and experimen tal data [5,29,32]. The observation of a similar, although quantitatively less im portant, relation between VTand LCl2%corr or MR (i.e.…”

“…LCI was well correlated with PCD (correlation coefficient: 0.687 for LCl2%and 0.712 for LCI 1.5%, p<0.01), suggesting that the two indexes provide basically similar information, although more marked discrepancies can occasion ally be observed. These discrepancies may be due to physiological factors; theoreti cally, for instance, a high Vd/V j ratio can be expected to increase LCI and to de crease PCD [5,29]. However, the discre pancies between LCI and PCD may also reflect the influence of technical factors; for example, compared with LCI, PCD may be more sensitive to the presence of a very slow component in the washout curve.…”

The Effect of Added Dead Space on the Pulmonary Response to Exercise

“…PETco2 also showed a progressive rise with increasing added volume and increasing work load. Several groups have studied the effects of an increase in dead space in healthy subjects at rest and have found similar increases in ventilation and alveolar Pco2 [5,14,15]. Barnett and P eters [4] also found increases in V t and Paco2 in mongrel dogs that breathed through lengths of tubing attached to a tracheostomy.…”

“…The magnitude of the changes were related to the sub ject's ventilatory response to CO2, as measured at rest. The level of exercise, CO2 output, or volume of dead space did not appear to have independent effects on the ventilatory response.The addition of an artificial dead space at the mouth leads to an increase in the alveolar Pco2, and in ventilation both in healthy subjects at rest [5] and in dogs subjected to tracheostomy [4], During exercise, the effect of an added dead space will be magnified due to the increase in C 0 2 output.We have studied the effect of adding dead space on the respiratory re sponse to exercise. Two different volumes of dead space were added and these were studied at 2 or 3 exercise loads in 4 subjects.…”

Gas‐mixing in the Lungs A Study of the Clinical Applicability of the So‐called Becklake‐index

“…In a later work Bouhuys et al (5) increased the tidal volume in another way, by adding an extra dead space in the experimental setup. I t could not be shown, however, that the wash-out was more efficient under these experimental conditions, but a marked tendency towards a more even ventilation was found.…”