Single-Breath Determination of Functional Dead Space and Mean Alveolar Gas

Bargeton, D; Florentin, E; Florentin, Diego

doi:10.1159/000395112

Cited by 2 publications

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“…), only slightly contaminated alveolar gas may be sampled at this time. Indeed, the condition that VT be equal or higher than 10% of vital capacity, postulated by BARGIITON and eo-workers [7] in order to have, at R (t).=Rr. an expired volume composition not contaminated 1 by dead space, was satisfied in our patients.…”

Section: Discussionmentioning

confidence: 99%

“…From the practical point of view, our results suggest that the widely used end-tidal gas concentrations may be very misleading in patients with CAO. The increased availability of automated techniques [7,20,21] should make possible the substitution of end-tidal determinations with the more accurate measurements. Since predictive formulae may overestimate anatomic dead space in patients with CAO, either Vo is measured or Rahn's approach UJtt t which does not require knowledge of its size, is used.…”

Section: Discussionmentioning

confidence: 99%

“…Stratified diffusive ventilation may add to this unevenness [1,4,5). During tidal breathing, sampling of alveolar gas is dependent on the size of VT [6,7,8], anatomical dead space [9,10], and asynchronous emptying of air spaces [11]. All these conditions influence to various degrees the methods used for obtaining alveolar gas concentrations.…”

mentioning

confidence: 99%

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Estimates of mean alveolar gas in patients with chronic airways obstruction

Giannella-Neto¹,

Paoletti²,

Fornai³

et al. 1989

Eur Respir J

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Alveolar to arterial differences (AaD) may be computed from representative alveolar gas pressures (PA). These are particularly difficult to obtain in patients with chronic airways obstruction (CAO) and severe inhomogeneity of the ventilation/perfusion (VA/Q) ratio. In 25 such patients, using a computerized mass spectrometer, representative values of alveolar gas were obtained: 1. as end-tidal concentrations (ET); 2. using the alveolar air equation with PACO2 derived from Bohr's equation (BE); 3. putting PACO2 = PACO2 into the alveolar air equation to compute ideal O2 alveolar pressure (ID); 4. applying Rahn's definition of "mean" alveolar gas (RD), i.e. taking within each jth breath, the alveolar pressures corresponding to the moment when the instantaneous gas exchange ratio R(t)j equals the overall exchange ratio for that breath Rj. During quiet breathing, the point where R(t)j equals Rj occurred at 71% of tidal volume (VT). Alveolar pressures by BE and RD resulted in similar values (115.5 +/- 6.9 and 115.5 +/- 6.6 mmHg for O2 and 30.3 +/- 5.7 and 30.8 +/- 5.7 mmHg for CO2, respectively), but they were significantly different from those by ET and ID (106.2 +/- 9.5 and 95.6 +/- 13.5 mmHg for O2 and 36.3 +/- 7.7 and 48.2 +/- 11.2 mmHg for CO2, respectively). These findings may be explained considering that PA(BE) and PA(RD) represent both high and low VA/Q units, whereas PA(ET) and PA(ID) represent mainly low VA/Q units. AaDCO2 by RD and BE appeared proportional to the severity of CAO as estimated from VT. Automated techniques make it possible to substitute end-tidal determinations with more accurate estimates either by measuring anatomical dead-space and using Bohr's equation or by applying Rahn's definition.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Estimates of mean alveolar gas in patients with chronic airways obstruction

Giannella-Neto¹,

Paoletti²,

Fornai³

et al. 1989

Eur Respir J

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Series dead space for inert gases in healthy subjects

et al. 1985

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In ten normal subjects, series dead space was determined for six intravenously infused inert gases (SF6, ethane, cyclopropane, fluothane, ether, acetone) from their expired and alveolar concentrations. The method for sampling alveolar gas was based on the criterion of identity of mean alveolar and expired gas exchange ratios. Inert gases were analysed chromatographically. Acetone, the most soluble gas, yielded the lowest dead space, the difference to the other gases being about 4.5%. This is probably due to the non-infinite value of the series dead space ventilation-perfusion ratio (VA/Q) which was estimated at about 2,000. The diffusivity, inversely related to the molecular weight, also played a role, the heaviest gas (fluothane) having a greater dead space than the lightest (ethane). The underestimation of the dead space from acetone is expected to be greater in subjects with low tidal volume and high bronchial blood flow, i. e. in some patients with respiratory disease.

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Single-Breath Determination of Functional Dead Space and Mean Alveolar Gas

Cited by 2 publications

References 0 publications

Estimates of mean alveolar gas in patients with chronic airways obstruction

Estimates of mean alveolar gas in patients with chronic airways obstruction

Series dead space for inert gases in healthy subjects

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