Characteristics of the washout dead space

Lewis, S. Mitchell; Martin, C. J.

doi:10.1016/0034-5687(79)90014-8

Cited by 10 publications

(6 citation statements)

References 20 publications

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“…The ratio of dead space to tidal volume increases during shallow breathing or when the total physiological dead space is raised because of an increase of alveolar dead space in conditions like emphysema, pulmonary embolism, or acute respiratory distress syndrome ( 9 , 13 ); this requires an increase of breathing frequency to maintain the same level of alveolar ventilation. For the above-mentioned conditions a small reduction of dead space would lead to a significant improvement in gas exchange resulting in the reduction of minute ventilation or/and the normalizing of blood gas parameters.…”

Section: Discussionmentioning

confidence: 99%

Nasal high flow reduces dead space

Möller

Feng

Domanski

et al. 2017

Journal of Applied Physiology

199

155

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Clearance of expired air in upper airways by nasal high flow (NHF) can be extended below the soft palate and de facto causes a reduction of dead space. Using scintigraphy, the authors found a relationship between NHF, time, and clearance. Direct measurement of CO2 and O2 in the trachea confirmed a reduction of rebreathing, providing the actual data on inspired gases, and this can be used for the assessment of other forms of respiratory support.

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Section: Discussionmentioning

confidence: 99%

Nasal high flow reduces dead space

Möller

Feng

Domanski

et al. 2017

Journal of Applied Physiology

199

155

View full text Add to dashboard Cite

show abstract

“…It is known that during normal breathing at rest approximately one-third of tidal volume is rebreathed from the anatomical dead space ( 11 ). At the end of expiration, the dead space is filled with gas depleted in oxygen (15–16% compared with 21% in ambient air) and rich in CO 2 (5–6% compared with 0.04% in ambient air).…”

Section: Discussionmentioning

confidence: 99%

“…The ratio of dead space to tidal volume (V D /V T ) increases during shallow breathing, which in turn requires an increase of breathing frequency to maintain an adequate level of alveolar ventilation. Physiological dead space can be significantly increased in conditions like emphysema in chronic obstructive pulmonary disease (COPD) or pulmonary embolism by the elevated alveolar dead-space volume ( 11 ) that would lead to a high V D /V T ratio, or in acute respiratory distress syndrome (ARDS) ( 9 ), which is associated with higher mortality. In these cases, even a small reduction of dead space would lead to a relatively high increase in alveolar volume.…”

Section: Discussionmentioning

confidence: 99%

Nasal high flow clears anatomical dead space in upper airway models

Möller

Celik

Feng

et al. 2015

Journal of Applied Physiology

249

156

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Recent studies showed that nasal high flow (NHF) with or without supplemental oxygen can assist ventilation of patients with chronic respiratory and sleep disorders. The hypothesis of this study was to test whether NHF can clear dead space in two different models of the upper nasal airways. The first was a simple tube model consisting of a nozzle to simulate the nasal valve area, connected to a cylindrical tube to simulate the nasal cavity. The second was a more complex anatomically representative upper airway model, constructed from segmented CT-scan images of a healthy volunteer. After filling the models with tracer gases, NHF was delivered at rates of 15, 30, and 45 l/min. The tracer gas clearance was determined using dynamic infrared CO2 spectroscopy and 81mKr-gas radioactive gamma camera imaging. There was a similar tracer-gas clearance characteristic in the tube model and the upper airway model: clearance half-times were below 1.0 s and decreased with increasing NHF rates. For both models, the anterior compartments demonstrated faster clearance levels (half-times < 0.5 s) and the posterior sections showed slower clearance (half-times < 1.0 s). Both imaging methods showed similar flow-dependent tracer-gas clearance in the models. For the anatomically based model, there was complete tracer-gas removal from the nasal cavities within 1.0 s. The level of clearance in the nasal cavities increased by 1.8 ml/s for every 1.0 l/min increase in the rate of NHF. The study has demonstrated the fast-occurring clearance of nasal cavities by NHF therapy, which is capable of reducing of dead space rebreathing.

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“…This can be compared with 180 ml for a group of clinic patients [4] and 199 ml for a group of 105 male patients with chronic airways disease [10]. Thus the dead space volume in our study is somewhat lower than the other two patient groups.…”

Section: Discussionmentioning

confidence: 72%

ICU monitoring of ventilation distribution

Mitchell¹,

Wilson²,

Sierra³

1986

International Journal of Clinical Monitoring and Computing

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The oxygen washin method has been shown to be a practical way to measure functional residual capacity (FRC) in the intensive care unit. The ventilator oxygen concentration is increased and measurements of respiratory flow and oxygen concentration at the mouth are made with the patient monitoring system. No additional personnel, bedside equipment or ventilator attachments are required. A feasibility study was performed to determine if this method could be used to estimate a continuous distribution of ventilation with respect to ventilation to volume ratio VA/V. Due to gas mixing in the ventilator, the inspired oxygen fraction does not increase instantaneously to its new value. An equation was derived which models the lung as 50 discrete compartments and accounts for the transient change in mean inspired oxygen fraction. A digital computer simulation demonstrated good distribution recovery for one and two mode ventilation distributions. Continuous distributions were computed for four post cardiac surgery patients at four levels of positive end expiratory pressure (PEEP). In these patients a linear increase in the amount of ventilation in the normal VA/V range occurred with increasing PEEP, i.e., slow and fast spaces tended to move centrally toward a more normal VA/V range. At zero PEEP 26% of the ventilation occurred in the normal range and this increased to 49% at 15 PEEP. Dead space fraction was poorly estimated and spurious modes occurred in the high VA/V range.

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Characteristics of the washout dead space

Cited by 10 publications

References 20 publications

Nasal high flow reduces dead space

Nasal high flow reduces dead space

Nasal high flow clears anatomical dead space in upper airway models

ICU monitoring of ventilation distribution

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