Role of carotid chemoreceptors and pulmonary vagal afferents during helium-oxygen breathing in ponies.
Abstract: Our purpose was to assess compensatory breathing responses to airway resistance unloading in ponies. We hypothesized that the carotid bodies and hilar nerve afferents, respectively, sense chemical and mechanical changes caused by unloading, hence carotid body-denervated (CBD) and hilar nerve-denervated ponies (HND) might demonstrate greater ventilatory responses when decreasing resistance. At rest and during treadmill exercise, resistance was transiently reduced approximately 40% in five normal, seven CBD, and five HND ponies by breathing gas of 79% He-21% O2 (He-O2). In all groups at rest, He-O2 breathing did not consistently change ventilation (VE), breathing frequency (f), tidal volume (VT), or arterial PCO2 (PaCO2) from room air-breathing levels. During treadmill exercise at 1.8 mph-5% grade in normal and HND ponies, He-O2 breathing did not change PaCO2 but at moderate (6 mph-5% grade), and heavy (8 mph-8% grade) work loads, absolute PaCO2 tended to decrease by 1 min of resistance unloading. delta PaCO2 calculated as room air minus He-O2 breathing levels at 1 min demonstrated significant changes in PaCO2 during exercise resistance unloading (P less than 0.05). No difference between normal and HND ponies was found in exercise delta PaCO2 responses (P greater than 0.10); however, in CBD ponies, the delta PaCO2 during unloading was greater at any given work load (P less than 0.05), suggesting finer regulation of PaCO2 in ponies with intact carotid bodies. During heavy exercise VE and f increased during He-O2 breathing in all three groups of ponies (P less than 0.05), although there were no significant differences between groups (P greater than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Publication Date: 1987-03-01 PubMed ID: 3106307DOI: 10.1152/jappl.1987.62.3.1020Google 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 study investigates the effect of decreased airway resistance on the breathing patterns of ponies, specifically focusing on the roles of carotid bodies and hilar nerve afferents in detecting and responding to these changes.
Research Objectives and Hypothesis
- The main objective of the research was to understand the compensatory breathing responses in ponies when there is a decrease in airway resistance. It also seeks to identify the roles of carotid bodies and hilar nerve afferents in sensing these changes.
- The hypothesis under investigation is that ponies with denervated carotid bodies (CBD) and hilar nerves (HND) might display greater changes in ventilation when airway resistance is decreased (or “unloaded”).
Methods
- The experiment studied the effect of reducing airway resistance by around 40% in normal, CBD, and HND ponies. This was achieved by the ponies breathing in a mix of 79% helium and 21% oxygen (He-O2), at rest and during treadmill exercise.
- The parameters monitored were ventilation (VE), breathing frequency (f), tidal volume (VT), and arterial CO2 pressure (PaCO2).
Results
- During rest, helium-oxygen breathing did not consistently change the monitored parameters in any of the groups compared to normal room air-breathing levels.
- Different observations were made during treadmill exercise. In normal and HND ponies at a light workload, PaCO2 remained unchanged with helium-oxygen breathing but tended to decrease at moderate and heavy workloads.
- No significant difference was seen in the response to unloading during exercise (delta PaCO2) between normal and HND ponies. However, the difference in PaCO2 during unloading was greater in CBD ponies at any given workload, suggesting that intact carotid bodies may help in regulating PaCO2.
- During heavy exercise, an increase in ventilation and breathing rate was observed in all three pony groups during helium-oxygen breathing, with no significant difference between the groups.
Conclusion
- The study shows that airway resistance unloading does not consistently change breathing parameters at rest, but different responses are observed during exercise. The responses are not significantly different between normal and HND ponies.
- Greater differences in delta PaCO2 in CBD ponies indicate that carotid bodies may help in more finely regulating PaCO2. This might be important in understanding responses to airway resistance changes in species such as horses which have relatively high-breathing workloads during exercise.
Cite This Article
APA
Pan LG, Forster HV, Bisgard GE, Lowry TF, Murphy CL.
(1987).
Role of carotid chemoreceptors and pulmonary vagal afferents during helium-oxygen breathing in ponies.
J Appl Physiol (1985), 62(3), 1020-1027.
https://doi.org/10.1152/jappl.1987.62.3.1020 Publication
Researcher Affiliations
MeSH Terms
- Afferent Pathways / physiology
- Animals
- Carbon Dioxide / blood
- Carotid Arteries / physiology
- Chemoreceptor Cells / physiology
- Denervation
- Helium
- Horses / physiology
- Hydrogen-Ion Concentration
- Lung / innervation
- Oxygen
- Partial Pressure
- Respiration
- Vagus Nerve / physiology
Grant Funding
- 25739 / PHS HHS
- 5-F32-HL-06899-02 / NHLBI NIH HHS
Citations
This article has been cited 2 times.- Maillard D, Delpuech C, Hatzfeld C. Ventilatory adjustments during sustained resistive unloading in exercising humans. Eur J Appl Physiol Occup Physiol 1990;60(2):120-6.
- Donaldson LL. A review of the pathophysiology of exercise-induced pulmonary haemorrhage in the equine athlete. Vet Res Commun 1991;15(3):211-26.
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