Isocapnic and small hypercapnic single-breath stimuli: evidence for an inhibitory inflation reflex in conscious man.
We wished to find out if a deep inspiration had any influence on subsequent breathing which was mediated by neural rather than chemical stimuli. We therefore compared the effect on ventilation of a deep isocapnic breath with that of a similar breath containing 6% CO2, and with the effect of two successive tidal volume breaths of 6% CO2. We studied five normal subjects, each of whom repeated the three manoeuvres 20 times, and we used ensemble averaging to increase the signal-to-noise ratio. The isocapnic deep inspiration was followed by a significant inhibition of ventilation in the group in the second post-stimulus breath, and in 4 of the 5 subjects in first and second post-stimulus breaths. This was due to an increase in both inspiratory and expiratory time, with a variable effect on tidal volume. A similar initial ventilatory inhibition was seen in the response to a deep breath of 6% CO2. When the isocapnic response was subtracted from the hypercapnic response, the result was similar to that observed from two tidal volume breaths of 6% CO2. We conclude that a single deep inflation of the lungs in awake man inhibits subsequent ventilation by a neural mechanism, and that this may affect the CO2 response measured by single-breath techniques using such manoeuvres.
Fernando
S S
SS
Dept of Medicine, St George's Hospital Medical School, London, UK.
Saunders
K B
KB
D000328:Adult; D002245:Carbon Dioxide / Q000494:pharmacology*; D005260:Female; D006801:Humans; D008297:Male; D012018:Reflex / Q000502:physiology*; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume / Q000502:physiology
D002245:Carbon Dioxide