TY - JOUR
T1 - Cardiorespiratory Responses to Voluntary Hyperventilation During Normobaric Hypoxia
AU - Haddon, Alexander
AU - Kanhai, Joel
AU - Nako, Onalenna
AU - Smith, Thomas G
AU - Hodkinson, Peter D
AU - Pollock, Ross D
N1 - Publisher Copyright:
© Reprint and copyright by the Aerospace Medical Association, Alexandria, VA
PY - 2023/2/1
Y1 - 2023/2/1
N2 - BACKGROUND: Unexplained physiological events (PE), possibly related to hypoxia and hyperventilation, are a concern for some air forces. Physiological monitoring could aid research into PEs, with measurement of arterial oxygen saturation (S
po
2) often suggested despite potential limitations in its use. Given similar physiological responses to hypoxia and hyperventilation, the present study characterized the cardiovascular and respiratory responses to each. METHODS: T en healthy subjects were exposed to 55 mins of normobaric hypoxia simulating altitudes of 0, 8000, and 12,000 ft (0, 2438, and 3658 m) while breathing normally and voluntarily hyperventilating (doubling minute ventilation). Respiratory gas analysis and spirometry measured end-tidal gases (P
ETo
2 and P
ETo
2) and minute ventilation. S
po
2 was assessed using finger pulse oximetry. Mean arterial, systolic, and diastolic blood pressure were measured noninvasively. Cognitive impairment was assessed using the Stroop test. RESULTS: Voluntary hyperventilation resulted in a doubling of minute ventilation and lowered P
ETo
2, while altitude had no effect on these. PET o2 and S
po
2 declined with increasing altitude. However, despite a significant drop in PET o2 of 15.2 mmHg from 8000 to 12,000 ft, S
po
2 was similar when hyperventilating (94.7 ± 2.3% vs. 93.4 ± 4.3%, respectively). The only cardiovascular response was an increase in heart rate while hyperventilating. Altitude had no effect on cognitive impairment, but hyperventilation did. DISCUSSION: For many cardiovascular and respiratory variables, there is minimal difference in responses to hypoxia and hyperventilation, making these challenging to differentiate.
AB - BACKGROUND: Unexplained physiological events (PE), possibly related to hypoxia and hyperventilation, are a concern for some air forces. Physiological monitoring could aid research into PEs, with measurement of arterial oxygen saturation (S
po
2) often suggested despite potential limitations in its use. Given similar physiological responses to hypoxia and hyperventilation, the present study characterized the cardiovascular and respiratory responses to each. METHODS: T en healthy subjects were exposed to 55 mins of normobaric hypoxia simulating altitudes of 0, 8000, and 12,000 ft (0, 2438, and 3658 m) while breathing normally and voluntarily hyperventilating (doubling minute ventilation). Respiratory gas analysis and spirometry measured end-tidal gases (P
ETo
2 and P
ETo
2) and minute ventilation. S
po
2 was assessed using finger pulse oximetry. Mean arterial, systolic, and diastolic blood pressure were measured noninvasively. Cognitive impairment was assessed using the Stroop test. RESULTS: Voluntary hyperventilation resulted in a doubling of minute ventilation and lowered P
ETo
2, while altitude had no effect on these. PET o2 and S
po
2 declined with increasing altitude. However, despite a significant drop in PET o2 of 15.2 mmHg from 8000 to 12,000 ft, S
po
2 was similar when hyperventilating (94.7 ± 2.3% vs. 93.4 ± 4.3%, respectively). The only cardiovascular response was an increase in heart rate while hyperventilating. Altitude had no effect on cognitive impairment, but hyperventilation did. DISCUSSION: For many cardiovascular and respiratory variables, there is minimal difference in responses to hypoxia and hyperventilation, making these challenging to differentiate.
KW - Humans
KW - Carbon Dioxide
KW - Hyperventilation
KW - Hypoxia
KW - Oximetry
KW - Altitude
UR - http://www.scopus.com/inward/record.url?scp=85147724704&partnerID=8YFLogxK
U2 - 10.3357/AMHP.6163.2023
DO - 10.3357/AMHP.6163.2023
M3 - Article
C2 - 36755012
SN - 2375-6314
VL - 94
SP - 59
EP - 65
JO - Aerospace medicine and human performance
JF - Aerospace medicine and human performance
IS - 2
ER -