Neuroergonomic and psychometric evaluation of full-face crew oxygen masks respiratory tolerance: a proof-of-concept study

INTRODUCTION

Preventing in-flight hypoxia in pilots is typically achieved by wearing oxygen masks. These masks must be as comfortable as possible to allow prolonged and repeated use. The consequences of mask-induced facial contact pressure have been extensively studied, but little is known about mask-induced breathing discomfort. Because breathlessness is a strong distractor and engages cerebral resources, it could negatively impact flying performances.

METHODS

Seventeen volunteers (age 20-32) rated respiratory discomfort while breathing with no mask and with two models of quick-donning full-face crew oxygen masks with regulators (mask A, mask B). Electroencephalographic recordings were performed to detect a putative respiratory-related cortical activation in response to inspiratory constraint (experiment 1, n=10). Oxygen consumption was measured using indirect calorimetry (experiment 2, n=10).

RESULTS

With mask B, mild respiratory discomfort was reported significantly more frequently than with no mask or mask A (experiment 1: median respiratory discomfort on visual analogue scale 0.9 cm (0.5-1.4), experiment 1; experiment 2: 2 cm (1.7-2.9)). Respiratory-related cortical activation was present in 1/10 subjects with no mask, 1/10 with mask A and 6/10 with mask B (significantly more frequently with mask B). Breathing pattern, sigh frequency and oxygen consumption were not different.

CONCLUSIONS

In a laboratory setting, breathing through high-end aeronautical full-face crew oxygen masks can induce mild breathing discomfort and activate respiratory-related cortical networks. Whether or not this can occur in real-life conditions and have operational consequences remains to be investigated. Meanwhile, respiratory psychometric and neuroergonomic approaches could be worth integrating to masks development and evaluation processes.

Residual sleepiness in obstructive sleep apnoea: phenotype and related symptoms

The characteristics of residual excessive sleepiness (RES), defined by an Epworth score >10 in adequately treated apnoeic patients, are unknown. 40 apnoeic patients, with (n = 20) and without (n = 20) RES, and 20 healthy controls underwent clinical interviews, cognitive and biological tests, polysomnography, a multiple sleep latency test, and 24-h sleep monitoring. The marked subjective sleepiness in the RES group (mean ± sd score 16.4 ± 3) contrasted with moderately abnormal objective measures of sleepiness (90% of patients with RES had daytime sleep latencies >8 min). Compared with patients without RES, the patients with RES had more fatigue, lower stage N3 percentages, more periodic leg movements (without arousals), lower mean sleep latencies and longer daytime sleep periods. Most neuropsychological dimensions (morning headaches, memory complaints, spatial memory, inattention, apathy, depression, anxiety and lack of self-confidence) were not different between patients with and without RES, but gradually altered from controls to apnoeic patients without and then with RES. RES in apnoeic patients differs markedly from sleepiness in central hypersomnia. The association between RES, periodic leg movements, apathy and depressive mood parallels the post-hypoxic lesions in noradrenaline, dopamine and serotonin systems in animals exposed to intermittent hypoxia.

Inspiratory capacity predicts mortality in patients with chronic obstructive pulmonary disease

BACKGROUND

Chronic obstructive pulmonary disease (COPD) severity is usually graded upon the FEV(1) reduction and FEV(1) has been considered the most important mortality predictor with age in COPD. Recent studies suggest other factors as more powerfully related to mortality than FEV(1) in COPD patients.

AIM

To assess the impact of inspiratory capacity (IC) on mortality and morbidity in COPD patients during a 5-year follow-up period.

METHODS

We recruited 222 patients with mild-to-moderate COPD from January 1995 to December 2001 with an average follow-up period of 60 months (range 30-114 months). Among different respiratory parameters measured in stable conditions FEV(1), FEV(1)/FVC%, IC and PaO(2), PaCO(2) and BMI were chosen and their relationships with all-cause and respiratory mortality and with morbidity were assessed.

RESULTS

All these variables were associated with mortality at the univariate analysis. However, in a multivariate regression analysis (Cox proportional hazards model) for all-cause mortality age (year), IC (%pred.) and PaO(2) (mmHg) remained the only significant, independent predictors (HR=1.056, 95%CI: 1.023-1.091; HR=0.981, 95%CI: 0.965-0.998; HR=0.948, 95%CI: 0.919-0.979, respectively). According to the same analysis, IC (%pred.) and PaO(2) (mmHg) were significant independent predictors for respiratory mortality (HR=0.967, 95%CI: 0.938-0.997; HR=0.919, 95%CI: 0.873-0.969) together with FEV(1)/FVC% and BMI (kg/m(2)) (HR=0.967, 95%CI: 0.933-1.022; HR=0.891, 95%CI: 0.807-0.985, respectively). IC (%pred.), FEV(1)/FVC%, and PaO(2) (mmHg) were also significantly related to morbidity, as independent predictors of hospital admissions because of exacerbations (OR=0.980, 95%CI: 0.974-0.992; OR=0.943, 95%CI: 0.922-0.987; OR=0.971, 95%CI: 0.954-0.996, respectively).

CONCLUSION

IC (%pred.) is a powerful functional predictor of all-cause and respiratory mortality and of exacerbation-related hospital admissions in COPD patients.

Effects of upper airway anaesthesia on respiratory-related evoked potentials in humans

Cortical potentials evoked by mid-inspiratory occlusion arise from numerous receptors, many of which are probably within the upper airway. Their precise nature is not known. The aim of the current study was to improve knowledge of this by studying the effects of topical upper airway anaesthesia on respiratory-related evoked potentials. Respiratory-related evoked potentials were described through the averaging of electroencephalogram (EEG) epochs following mid-inspiratory occlusions (C3-CZ; C4-CZ). A total of 21 healthy volunteers (13 male, aged 22-52 yrs) were studied during mouth breathing, before and after topical upper airway anaesthesia (lidocaine). Moreover, 15 subjects were studied during nose breathing with and without anaesthesia. Six subjects were studied whilst inhaling L-menthol. Typical potentials were present in all the subjects, their components featuring normal amplitudes and latencies. The route of breathing and upper airway anaesthesia did not modify the EEG responses to inspiratory occlusions, qualitatively or quantitatively, during mouth or nose breathing. L-menthol had no effect. Upper airway receptors sensitive to topical anaesthesia are unlikely to contribute significantly to mid-inspiratory occlusion-evoked potentials. On the contrary, deeper receptors, such as joint and muscle receptors, could contribute dominantly to these potentials.

Upper airway dynamics during negative expiratory pressure in apneic and non-apneic awake snorers

Background

The ability of negative expiratory pressure (NEP) technique to differentiate between awake snorers with and without obstructive sleep apnea-hypopnea (OSAH) was investigated.

Methods

Forty-eight subjects with sleep disordered breathing (SDB) and 7 healthy subjects, as non-snorer controls, underwent the NEP application of -5 and -7 cmH₂O in the seated and supine position during wakefulness, after performing a sleep study. The upper airway collapsibility was assessed by computing the volume exhaled during the first 0.5 sec. (V,NEP_0.5) and 1 sec. (V,NEP₁) following the NEP start.

Results

Patients with severe (AHI ≥ 30) (n = 19) and mild-to-moderate (AHI <30 and >5) (n = 15) OSAH had lower V,NEP_0.5 (340 ± 88 ml) as compared to snorers (AHI ≤ 5) (n = 14) (427 ± 101 ml; p < 0.01) and controls (n = 7) (492 ± 69 ml; p < 0.001) in the supine position with NEP -5 cmH₂O. Less significant differences among the different groups were observed for V,NEP_0.5 in the seated position with NEP -5 cmH₂O and in both positions with NEP -7 cmH₂O (only OSAH patients vs controls, p < 0.001). Similar results were obtained for V,NEP₁ in either position by using both NEP -5 cmH₂O and -7 cmH₂O. In spite of this, a substantial overlapping of V,NEP_0.5 and V,NEP₁ between snorers and OSAH patients did not allow to identify a reliable diagnostic cut-off level. An inverse correlation with AHI was found for V,NEP_0.5 in the supine position with NEP -5 cmH₂O (r_s = -0.46, p < 0.05) in severe OSAH patients.

Conclusion

The awake OSAH patients exhibit values of V,NEP_0.5 and V,NEP₁ lesser than those of awake snorers. The NEP technique, however, appears to have a limited usefulness as clinical tool for routine screening of the OSAH patients during wakefulness.