Hypoxic ventilatory response and breathlessness following hypocapnic and isocapnic hyperventilation.
OBJECTIVE
To investigate the etiology of posthyperventilation (post-HV) hypoxemia following voluntary hyperventilation (VHV), we examined the effects of hypocapnic (hypo-CO2) and isocapnic (iso-CO2) VHV on the hypoxic ventilatory response (O2-response) and on the sensation of breathlessness during the O2-response.


METHODS
O2-responses and visual analog scale (VAS) scores for estimating breathlessness in 10 normal subjects during the O2-response under iso-CO2 conditions and under hypo-CO2 conditions immediately following voluntary maximal HV of 3 min duration were examined.


RESULTS
Although there was no significant difference in the post-HV ventilation levels following hypo-CO2 vs iso-CO2 VHV, the VAS scores at the start of the O2-response following hypo-CO2 VHV (30.2+/-24.2 mm) were significantly higher (p<0.05) than the VAS scores at the start of the O2-response following iso-CO2 VHV (13.7+/-8.4 mm). However, VHV did not have a significant effect on the O2-response at 2 min after the VHV when the arterial O2 saturation (SaO2) was below 90%. The nonsteady-state hypo-CO2 induced by VHV greatly attenuated the O2-response below 90% SaO2 and VAS scores at 70% SaO2.


CONCLUSIONS
Elevated VAS scores immediately following the hypo-CO2 VHV, which might be independent of actual breathing levels, and the attenuation of the O2-response following the hypo-CO2 VHV were not due to input from lung and chest wall mechanoreceptors induced by the hyperpnea itself, but rather to the hypo-CO2 induced by hyperpnea.
Chin
K
K
Department of Clinical Physiology, Chest Disease Research Institute, Kyoto University, Sakyo-ku, Japan.
Ohi
M
M
Kita
H
H
Otsuka
N
N
Oku
Y
Y
Mishima
M
M
Kuno
K
K
D000328:Adult; D002245:Carbon Dioxide / Q000097:blood*; D004417:Dyspnea / Q000503:physiopathology*; D006801:Humans; D006985:Hyperventilation / Q000503:physiopathology*; D000860:Hypoxia / Q000209:etiology* / Q000503:physiopathology*; D008297:Male; D012123:Pulmonary Ventilation / Q000502:physiology*; D012677:Sensation / Q000502:physiology; D013997:Time Factors
D002245:Carbon Dioxide