What question did this study set out to answer?

To examine the transient effects of relieving arterial chemoreceptor stimulation on heart rate and ventilatory responses under hypoxic conditions in conscious humans.

December 1, 1977The Journal of PhysiologyOpen Access

Arterial chemoreceptors, ventilation and heart rate in man.

Q: What is the clinical evidence from this study?

Population: Healthy (n=3). Intervention: Transient relief of arterial chemoreceptor stimulation (O2 or CO2 tests) vs. Pre-test steady state (normo- or slightly hypercapnic hypoxia). Primary outcome: Changes in heart rate and ventilation.

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Key result

Transient withdrawal of arterial chemoreceptor stimulation primarily caused early tachycardia (in 81 of 104 tests), with ventilation decreasing significantly after a mean latency of 5.2 seconds.

Why the study?

Does transient relief of arterial chemoreceptor stimulation alter heart rate and ventilation in healthy subjects?

Population

3 healthy subjects

Comparison

Breathing a CO2-free mixture for two breaths to… vs Pre-test steady state of normo- or slightly…

Follow-up

Immediate (seconds)

Authors

DDDaniel B. DrysdaleUniversity of Oxford EPE S PetersenChristie (Canada)

Discussion

Member takes

Implication

Hypothesis-generating for chemoreflex control in health; should not yet inform clinical chemoreflex assessment in disease.

Key Points

To examine the transient effects of relieving arterial chemoreceptor stimulation on heart rate and ventilatory responses under hypoxic conditions in conscious humans.
Tested 3 healthy subjects maintained at steady-state normo- or slightly hypercapnic hypoxia (PA,CO2 38–46 torr, PA,O2 50–60 torr).
Transiently unloaded chemoreceptors using two-breath test mixtures of pure O2 or low O2 without CO2 under free-breathing and consciously controlled-breathing protocols across 104 trials.
Measured ventilatory changes, heart rate responses, and lung-to-ear circulatory transit time using an ear oximeter.
Ventilation decreased significantly after a mean latency of 5.2 seconds during free-breathing tests, closely tracking the average lung-to-ear circulation time of 4.9 seconds.
Heart rate increased significantly above baseline in 81 of 104 trials at a latency identical to ventilatory decline.
Secondary bradycardia developed 5–6 seconds later in free-breathing tests and controlled-breathing O2 tests, but was absent in controlled-breathing CO2 tests.

Structured PICO

Does transient relief of arterial chemoreceptor stimulation alter heart rate and ventilation in healthy subjects?

Population

3 healthy subjects undergoing transient changes in alveolar gas composition to assess arterial chemoreceptor stimulation.

Intervention

Breathing a CO2-free mixture for two breaths (either pure O2 or a low O2 mixture) to transiently relieve arterial chemoreceptor stimulation from a steady state of normo- or slightly hypercapnic hypoxia

Comparator

Pre-test steady state of normo- or slightly hypercapnic hypoxia

Outcome

Transient changes in heart rate and ventilationsurrogate

The primary effect of withdrawing arterial chemoreceptor stimulation in conscious humans is tachycardia, while secondary bradycardia is likely driven by lung reflexes.

Cite This Study

Drysdale et al. (1977) studied Healthy (n=3). Transient relief of arterial chemoreceptor stimulation (O2 or CO2 tests) vs. Pre-test steady state (normo- or slightly hypercapnic hypoxia) was evaluated on Changes in heart rate and ventilation. Transient withdrawal of arterial chemoreceptor stimulation primarily caused early tachycardia (in 81 of 104 tests), with ventilation decreasing significantly after a mean latency of 5.2 seconds.

synapsesocial.com/papers/6a9fe502603ff62333618d5a https://doi.org/10.1113/jphysiol.1977.sp012084

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