Effect of reducing anatomic dead space on arterial PCO2 during CO2 inhalation.
Abstract: Carotid body-denervated (CBD) ponies have a less than normal increase in arterial PCO2 (PaCO2) when inspired CO2 (PICO2) is increased, even when pulmonary ventilation (VE) and breathing frequency (f) are normal. We studied six tracheostomized ponies to determine whether this change 1) might be due to increased alveolar ventilation (VA) secondary to a reduction in upper airway dead space (VD) or 2) is dependent on an upper airway sensory mechanism. Three normal and three chronic CBD ponies were studied while they were breathing room air and at 14, 28, and 42 Torr PICO2. While the ponies were breathing room air, physiological VD was 483 and 255 ml during nares breathing (NBr) and tracheostomy breathing (TBr), respectively. However, at elevated PICO2, mixed expired PCO2 often exceeded PaCO2; thus we were unable to calculate physiological VD using the Bohr equation. At all PICO2 in normal ponies, PaCO2 was approximately 0.3 Torr greater during NBr than during TBr (P less than 0.05). In CBD ponies this NBr-TBr difference was only evident while breathing room air and at 28 Torr PICO2. At each elevated PICO2 during both NBr and TBr, the increase in PaCO2 above control was always less in CBD ponies than in normal ponies (P less than 0.01). The VE-PaCO2, f-PaCO2, and tidal volume-PaCO2 relationships did not differ between NBr and TBr (P greater than 0.10) nor did they differ between normal and CBD ponies (P greater than 0.10). We conclude that the attenuated increase in PaCO2 during CO2 inhalation after CBD is not due to a relative increase in VA secondary to reducing upper airway VD.(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1986-08-01 PubMed ID: 3091574DOI: 10.1152/jappl.1986.61.2.728Google Scholar: Lookup
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- Journal Article
- Research Support
- U.S. Gov't
- Non-P.H.S.
- Research Support
- U.S. Gov't
- P.H.S.
Summary
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This research paper explores the effect of reducing anatomical dead space on arterial carbon dioxide levels (PaCO2) during carbon dioxide (CO2) inhalation in ponies which have had their carotid body denervated (CBD). The results suggest that the lower-than-normal rise in PaCO2 seen in these ponies during CO2 inhalation cannot be attributed to an increase in alveolar ventilation due to a reduction in upper airway dead space.
Objective and Methodology
- The objective of the research was to understand why CBD ponies demonstrate a lower than normal increase in arterial CO2 levels when breathing in CO2, even when their respiration rate and breathing frequency are normal.
- They examined this by studying six ponies who had tracheostomies (an incision in the windpipe to assist breathing). Of the six ponies, three were normal and three were chronic CBD ponies.
- The researchers investigated two possible explanations. They wanted to discover if this phenomenon occurred either due to increased alveolar ventilation as a result of reduced upper airway dead space or dependent on an upper airway sensory mechanism.
Findings
- The researchers found physiological dead space was lower during tracheostomy breathing (TBr) than when breathing through the nostrils (NBr). The researchers could not reliably calculate physiological VD under conditions of elevated inhaled CO2.
- In both types of ponies, arterial CO2 levels were slightly higher during nasal breathing than tracheostomy breathing. However, in the CBD ponies, this difference was only noticeable while breathing room air and at 28 Torr PICO2.
- At increased levels of PICO2, the increase in PaCO2 was less in the CBD ponies than in the normal ponies, regardless of the method of breathing employed (i.e., NBr or TBr).
- The relationship between ventilation rate and CO2 levels, the frequency of ventilation and CO2 levels, and the tidal volume (size of breath) and CO2 levels did not vary significantly between the two types of breathing or between normal and CBD ponies.
Conclusion
- The researchers concluded that the lesser rise in CO2 levels seen in ponies after CBD during CO2 inhalation cannot be attributed to an increase in alveolar ventilation due to a reduction in dead air space across the upper airway.
Cite This Article
APA
Forster HV, Pan LG, Bisgard GE, Flynn C, Hoffer RE.
(1986).
Effect of reducing anatomic dead space on arterial PCO2 during CO2 inhalation.
J Appl Physiol (1985), 61(2), 728-733.
https://doi.org/10.1152/jappl.1986.61.2.728 Publication
Researcher Affiliations
MeSH Terms
- Animals
- Arteries
- Carbon Dioxide / blood
- Carotid Body / physiology
- Denervation
- Horses
- Hypercapnia / physiopathology
- Nose
- Partial Pressure
- Respiration
- Respiratory Dead Space
- Tracheotomy
Grant Funding
- 25739 / PHS HHS
Citations
This article has been cited 2 times.- Burgraff NJ, Neumueller SE, Buchholz K, Langer TM 3rd, Hodges MR, Pan L, Forster HV. Ventilatory and integrated physiological responses to chronic hypercapnia in goats. J Physiol 2018 Nov;596(22):5343-5363.
- Cipulli F, Sanna A, Garberi R, Lassola S, Forcione M, Bellani G, Foti G, Rezoagli E. Dead space in critical care: a practical approach with clinical scenarios. J Anesth Analg Crit Care 2026 Jan 9;6(1):20.
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