Sustained isocapnic hypoxia suppresses the perception of the magnitude of inspiratory resistive loads

• Published in: Journal of applied physiology (1985) 2000-07, Vol.89 (1), p.47-55
• Main Authors: Orr, R. S, Jordan, A. S, Catcheside, P, Saunders, N. A, McEvoy, R. D
• Format: Article
• Language: English
• Subjects: Adult; Airway Resistance - physiology; Anatomy & physiology; Arousal - physiology; Biological and medical sciences; Carbon Dioxide - blood; Fingers - physiology; Humans; Hypoxia - physiopathology; Male; Medical sciences; Non tumoral diseases; Otorhinolaryngology. Stomatology; Oxygen - administration & dosage; Perceptions; Psychophysics; Respiratory Mechanics - physiology; Respiratory system; Sensory Thresholds - drug effects; Sensory Thresholds - physiology; Sleep Apnea, Obstructive - physiopathology; Sleep disorders; Space life sciences; Upper respiratory tract, upper alimentary tract, paranasal sinuses, salivary glands: diseases, semeiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.2000.89.1.47

1  Sleep Disorders Unit, Repatriation General Hospital, Daw Park, 5041; and 2  School of Medicine, Flinders University, Bedford Park, South Australia 5042 Australia The sensation of increased respiratory resistance or effort is likely to be important for the initiation of alerting or arousal responses, particularly in sleep. Hypoxia, through its central nervous system-depressant effects, may decrease the perceived magnitude of respiratory loads. To examine this, we measured the effect of isocapnic hypoxia on the ability of 10 normal, awake males (mean age = 24.0 ± 1.8 yr) to magnitude-scale five externally applied inspiratory resistive loads (mean values from 7.5 to 54.4   cmH 2 O · l 1 · s). Each subject scaled the loads during 37 min of isocapnic hypoxia (inspired O 2 fraction = 0.09, arterial O 2 saturation of ~80%) and during 37 min of normoxia, using the method of open magnitude numerical scaling. Results were normalized by modulus equalization to allow between-subject comparisons. With the use of peak inspiratory pressure (PIP) as the measure of load stimulus magnitude, the perception of load magnitude ( ) increased linearly with load and, averaged for all loaded breaths, was significantly lower during hypoxia than during normoxia (20.1 ± 0.9 and 23.9   ± 1.3 arbitrary units, respectively; P  = 0.048).  declined with time during hypoxia ( P  = 0.007) but not during normoxia ( P  = 0.361). Our result is remarkable because PIP was higher at all times during hypoxia than during normoxia, and previous studies have shown that an elevation in PIP results in increased . We conclude that sustained isocapnic hypoxia causes a progressive suppression of the perception of the magnitude of inspiratory resistive loads in normal subjects and could, therefore, impair alerting or arousal responses to respiratory loading. obstructive sleep apnea; psychophysics; arousal