title: Cardio-respiratory measures following isocapnic voluntary hyperventilation.
abstract: In some individuals, breathing is greater than at rest following voluntary hyperventilation. Most previous investigations have employed short hyperventilation periods; here we examine the time course of cardio-respiratory measures before, during, and after a 5-min voluntary hyperventilation, maintaining isocapnia throughout. We examined the possible co-involvement of the cardiovascular system; hypothesising that post-hyperventilation hyperpnoea results from an increase in autonomic arousal. In four subjects (two males, two females) of 18 (nine males, nine females) we observed a post-hyperventilation hyperpnoea, characterised by a slow decline of ventilation toward resting levels with a time constant of 109.0 +/- 16.1s. By contrast, heart rate, and systolic and diastolic blood pressure were unchanged from rest during and after voluntary hyperventilation for all subjects. We concluded that males and females were equally likely to exhibit post-hyperventilation hyperpnoea, and suggest that they may be characterised by an increased resting heart rate and the choice of breathing frequency to increase ventilation during the voluntary hyperventilation. We further concluded that post-hyperventilation hyperpnoea is rare, but when present is a strong and lasting phenomenon, and that it is not the result of an increased autonomic arousal.
authors.affiliation: Department of Physiology, University of Toronto, Ontario, Canada M5S 1A8.
authors.forename: Safraaz
authors.initials: S
authors.lastname: Mahamed
authors.forename: Judy
authors.initials: J
authors.lastname: Tsai
authors.forename: James
authors.initials: J
authors.lastname: Duffin
mesh_terms: D000328:Adult; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000378:metabolism; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D006985:Hyperventilation / Q000150:complications / Q000503:physiopathology*; D008297:Male; D012119:Respiration; D015656:Respiratory Mechanics / Q000502:physiology*; D012737:Sex Factors; D013990:Tidal Volume / Q000502:physiology; D013997:Time Factors
chemical_list: D002245:Carbon Dioxide