Landis E1, Loeffler L1, Kissel K1, Denis J1, Harris B1, Elias A2, Christiansen L2, Formiga M1, Cohen M1, Cahalin L1, Perez M2
1University of Miami Miller School of Medicine, Physical Therapy, Coral Gables, United States, 2The Miami Project to Cure Paralysis, Miami, United States
Background: Acute intermittent hypoxia (AIH) has a wide variety of therapeutic effects for individuals with spinal cord injuries, but there is limited research on its cardiovascular effects in the neurologically healthy population. Daily moderate AIH has been shown to reduce blood pressure, heart rate (HR), and peripheral vascular resistance in hypertensive patients. However, the effects of a single AIH session have not been reported, and a wide variety of protocols are utilized.
Purpose: The purpose of this study was to evaluate the effects of a single 30-minute AIH session on HR and arterial oxygen saturation (SaO2) in young healthy individuals and identify factors related to the cardiovascular response.
Methods: 16 healthy participants (8 men, 8 women) with mean±SD age, height, and weight of 24±2years, 170.5±9cm, and 69.8±16kg, respectively, randomly underwent one normoxic testing session and one hypoxic session at least one week apart. The AIH session involved 1-minute of inspired oxygen (FiO2) of 10% followed by 1-minute of FiO2 of 21% repeated for 30 minutes while the normoxic session continuously provided 21% FiO2. Baseline SaO2 and HR were obtained and were digitally recorded from a finger pulse oximeter every 4 seconds during intervention and for 60 minutes post-AIH. Subjects and investigators were blinded to trials.
Results: No adverse reactions occurred during AIH. The mean±SD HR and SaO2 at baseline during the AIH trial was 73.1±7.8 bpm and 96.9±1.5%, respectively, and were not significantly different from the normoxic trial. No significant change in SaO2 or HR was observed during the normoxic trial. However, during AIH, SaO2 decreased significantly (p 0.05) at 1-minute (92.3±1.5%) and remained significantly decreased throughout the session, returning to baseline within 1-minute of terminating AIH. During AIH, the HR increased significantly (p 0.05) at minute 1:20 and remained significantly increased throughout the session, followed by a post-AIH HR that was significantly lower than baseline throughout the 60-minute recovery. A significant relationship was observed between SaO2 and % change in HR from baseline to minute-2 post-AIH (r= -.54; p=.03). Also, participants who were able to maintain SaO2 above 85% during AIH had a significantly greater reduction in HR from both baseline and the end of the hypoxic session to minute-2 post-AIH (p 0.05). Chi-square analyses demonstrated that the number of participants who achieved at least a 10% reduction in HR from baseline to minute 2 post-AIH was significantly greater for the group who maintained SaO2 above 85% (p=0.01).
Conclusion(s): AIH elicits a sustained decreased HR post-treatment which mimics a training effect that is related to maintenance of SaO2. This is consistent with previous literature indicating that more severe levels of hypoxia can produce detrimental effects on the cardiovascular system. However, the results of this study have identified a target SaO2 level during AIH above which beneficial cardiovascular effects appear to be elicited.
Implications: Maintenance of SaO2 above 85% by titrating FiO2 during AIH may provide a more specific application of AIH to improve the cardiovascular response post-AIH; especially in individuals unable to exercise. Further research is warranted.
Keywords: Intermittent hypoxia, cardiorespiratory response, oxygen saturation
Funding acknowledgements: The Miami Project to Cure Paralysis
Purpose: The purpose of this study was to evaluate the effects of a single 30-minute AIH session on HR and arterial oxygen saturation (SaO2) in young healthy individuals and identify factors related to the cardiovascular response.
Methods: 16 healthy participants (8 men, 8 women) with mean±SD age, height, and weight of 24±2years, 170.5±9cm, and 69.8±16kg, respectively, randomly underwent one normoxic testing session and one hypoxic session at least one week apart. The AIH session involved 1-minute of inspired oxygen (FiO2) of 10% followed by 1-minute of FiO2 of 21% repeated for 30 minutes while the normoxic session continuously provided 21% FiO2. Baseline SaO2 and HR were obtained and were digitally recorded from a finger pulse oximeter every 4 seconds during intervention and for 60 minutes post-AIH. Subjects and investigators were blinded to trials.
Results: No adverse reactions occurred during AIH. The mean±SD HR and SaO2 at baseline during the AIH trial was 73.1±7.8 bpm and 96.9±1.5%, respectively, and were not significantly different from the normoxic trial. No significant change in SaO2 or HR was observed during the normoxic trial. However, during AIH, SaO2 decreased significantly (p 0.05) at 1-minute (92.3±1.5%) and remained significantly decreased throughout the session, returning to baseline within 1-minute of terminating AIH. During AIH, the HR increased significantly (p 0.05) at minute 1:20 and remained significantly increased throughout the session, followed by a post-AIH HR that was significantly lower than baseline throughout the 60-minute recovery. A significant relationship was observed between SaO2 and % change in HR from baseline to minute-2 post-AIH (r= -.54; p=.03). Also, participants who were able to maintain SaO2 above 85% during AIH had a significantly greater reduction in HR from both baseline and the end of the hypoxic session to minute-2 post-AIH (p 0.05). Chi-square analyses demonstrated that the number of participants who achieved at least a 10% reduction in HR from baseline to minute 2 post-AIH was significantly greater for the group who maintained SaO2 above 85% (p=0.01).
Conclusion(s): AIH elicits a sustained decreased HR post-treatment which mimics a training effect that is related to maintenance of SaO2. This is consistent with previous literature indicating that more severe levels of hypoxia can produce detrimental effects on the cardiovascular system. However, the results of this study have identified a target SaO2 level during AIH above which beneficial cardiovascular effects appear to be elicited.
Implications: Maintenance of SaO2 above 85% by titrating FiO2 during AIH may provide a more specific application of AIH to improve the cardiovascular response post-AIH; especially in individuals unable to exercise. Further research is warranted.
Keywords: Intermittent hypoxia, cardiorespiratory response, oxygen saturation
Funding acknowledgements: The Miami Project to Cure Paralysis
Topic: Cardiorespiratory
Ethics approval required: Yes
Institution: University of Miami
Ethics committee: Institutional Review Board
Ethics number: 997
All authors, affiliations and abstracts have been published as submitted.
