Journal of applied physiology
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Randomized Controlled Trial Comparative Study
Mechanisms of nasal high flow on ventilation during wakefulness and sleep.
Nasal high flow (NHF) has been shown to increase expiratory pressure and reduce respiratory rate but the mechanisms involved remain unclear. Ten healthy participants [age, 22 ± 2 yr; body mass index (BMI), 24 ± 2 kg/m(2)] were recruited to determine ventilatory responses to NHF of air at 37°C and fully saturated with water. We conducted a randomized, controlled, cross-over study consisting of four separate ∼60-min visits, each 1 wk apart, to determine the effect of NHF on ventilation during wakefulness (NHF at 0, 15, 30, and 45 liters/min) and sleep (NHF at 0, 15, and 30 liters/min). ⋯ In the nasal cavity model, NHF increased expiratory but decreased inspiratory resistance depending on both the cannula size and the expiratory flow rate. The mechanisms of action for NHF differ from those of CPAP and are sleep/wake-state dependent. NHF may be utilized to increase tidal breathing during wakefulness and to relieve respiratory loads during sleep.
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Editorial Comment
Rebuilding the lung: signals for a complex architectural task.
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Randomized Controlled Trial
Interindividual relationships between blood pressure and cerebral blood flow variability with intact and blunted cerebrovascular control.
The relationships between blood pressure variability (BPV) and cerebral blood flow variability (CFV) across individuals in the presence of intact and blunted cerebrovascular control are poorly understood. This study sought to characterize the interindividual associations between spontaneous BPV and CFV under conditions of normal and blunted [calcium channel blockade (CCB)] cerebrovascular control in healthy humans. We analyzed blood pressure and flow velocity data from 12 subjects treated with CCB (60 mg oral nimodipine) and 11 subjects treated with a placebo pill. ⋯ Compared with placebo, CCB reduced very-low-frequency MAP (P < 0.05) and MCAv(mean) power (P < 0.01) and the low-frequency cross-spectral phase angle (P < 0.05). The magnitude of change in MAP and MCAv(mean) power with CCB (i.e., change scores) was positively related in the very-low-frequency range. Collectively, these findings indicate that CFV may be an explanatory factor in the association between elevated BPV and adverse cerebrovascular outcomes and support the possibility of using CCB to improve hemodynamic stability under resting conditions.
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Methods to classify activity types are often evaluated with an experimental protocol involving prescribed physical activities under confined (laboratory) conditions, which may not reflect real-life conditions. The present study aims to evaluate how study design may impact on classifier performance in real life. Twenty-eight healthy participants (21-53 yr) were asked to wear nine triaxial accelerometers while performing 58 activity types selected to simulate activities in real life. ⋯ Walking time was systematically overestimated, except for lower back sensor data (range: 7-757%). In conclusion, classifier performance under confined conditions may not accurately reflect classifier performance in real life. Future studies that aim to evaluate activity classification methods are warranted to pay special attention to the representativeness of experimental conditions for real-life conditions.
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Hyperbaric oxygen (HBO(2)) stimulates presumptive central CO2-chemoreceptor neurons, increases minute ventilation (V(min)), decreases heart rate (HR) and, if breathed sufficiently long, produces central nervous system oxygen toxicity (CNS-OT; i.e., seizures). The risk of seizures when breathing HBO(2) is variable between individuals and its onset is difficult to predict. We have tested the hypothesis that a predictable pattern of cardiorespiration precedes an impending seizure when breathing HBO2. ⋯ Breathing HBO2 induced an early transient increase in V(min) (Phase 2) and HR during the chamber pressurization, followed by a second significant increase of V(min) ≤8 min prior to seizure (Phase 3). HR, which subsequently decreased during sustained hyperoxia, showed no additional changes prior to seizure. We conclude that hyperoxic hyperpnea (Phase 3 of the compound hyperoxic ventilatory response) is a predictor of an impending seizure while breathing poikilocapnic HBO(2) at rest in unanesthetized rats.