Cerebral perfusion is not impaired in persons with moderate obstructive sleep apnoea when awake.

PURPOSE: It is well established that, together with a multitude of other adverse effects on health, severe obstructive sleep apnoea causes reduced cerebral perfusion and, in turn, reduced cerebral function. Less clear is the impact of moderate obstructive sleep apnoea (OSA). Our aim was to determine if cerebral blood flow is impaired in people diagnosed with moderate OSA. METHODS: Twenty-four patients diagnosed with moderate OSA (15 ≤ apnoea-hypopnea index (AHI) < 30) were recruited (aged 32-72, median 59 years, 10 female). Seven controls (aged 42-73 years, median 62 years, 4 female) with an AHI < 5 were also recruited. The OSA status of all participants was confirmed at baseline by unattended polysomnography and they had an MRI arterial-spin-labelling scan of cerebral perfusion. RESULTS: Neither global perfusion nor voxel-wise perfusion differed significantly between the moderate-OSA and control groups. We also compared the average perfusion across three regional clusters, which had been found in a previous study to have significant perfusion differences with moderate-severe OSA versus control, and found no significant difference in perfusion between the two groups. The perfusions were also very close, with means of 50.2 and 51.8 mL/100 g/min for the moderate-OSAs and controls, respectively, with a negligible effect size (Cohen's d = 0.10). CONCLUSION: We conclude that cerebral perfusion is not impaired in people with moderate OSA and that cerebral flow regulatory mechanisms can cope with the adverse effects which occur in moderate OSA. This is an important factor in clinical decisions for prescription of continuous positive airway pressure therapy (CPAP).

Development and outcomes of a primary care-based sleep assessment service in Canterbury, New Zealand.

Prior to 2007, increasing demand for sleep services, plus inability to adequately triage severity, led to long delays in sleep assessment and accessing continuous positive airway pressure. We established a community sleep assessment service carried out by trained general practices using a standardised tool and overnight oximetry. All cases were discussed at a multi-disciplinary meeting, with four outcomes: severe obstructive sleep apnoea treated with continuous positive airway pressure; investigation with more complex studies; sleep physician appointment; no or non-severe sleep disorder for general practitioner management. Assessment numbers increased steadily (~400 in 2007 vs. 1400 in 2015). Median time from referral to assessment and multi-disciplinary meeting was 28 and 48 days, respectively. After the first multi-disciplinary meeting, 23% of cases were assessed as having severe obstructive sleep apnoea. More complex studies (mostly flow based) were required in 49% of patients, identifying severe obstructive sleep apnoea in a further 13%. Thirty-seven percent of patients had obstructive sleep apnoea severe enough to qualify for funded treatment. Forty-eight percent of patients received a definitive answer from the first multi-disciplinary meeting. Median time from referral to continuous positive airway pressure for 'at risk' patients with severe obstructive sleep apnoea, e.g., commercial drivers, was 49 days, while patients with severe obstructive sleep apnoea but not 'at risk' waited 261 days for continuous positive airway pressure. Ten percent of patients required polysomnography, and 4% saw a sleep specialist. In conclusion, establishment of a community sleep assessment service and sleep multi-disciplinary meeting led to significantly more assessments, with short waiting times for treatment, especially in high-risk patients with severe obstructive sleep apnoea. Most patients can be assessed without more complex studies or face-to-face review by a sleep specialist. SLEEP DISORDERS: MORE ASSESSMENTS, SHORTER WAITS WITH COMMUNITY SLEEP SERVICE: A community-based service for common sleep disorders can provide rapid and easily accessed sleep assessment and treatment. A team led by Michael Hlavac and Michael Epton from Christchurch Hospital describe the creation of a sleep assessment service within the Canterbury district of New Zealand, in which initial assessments are conducted throughout the community by general practice teams under guidance and advice from sleep specialists at the region's largest hospital. Before the service, there were around 300 sleep assessments per year in all of Canterbury, a region with a population of around 510,000. Now, that number has more than tripled, with shorter waiting times for treatment, especially for people with severe sleep apnoea. The authors conclude that most patients can be assessed for a suspected sleep disorder without needing to visit a hospital's sleep unit.

The effects of hypoxia on load compensation during sustained incremental resistive loading in patients with obstructive sleep apnea.

Inspiratory load compensation is impaired in patients with obstructive sleep apnea (OSA), a condition characterized by hypoxia during sleep. We sought to compare the effects of sustained hypoxia on ventilation during inspiratory resistive loading in OSA patients and matched controls. Ten OSA patients and 10 controls received 30 min of isocapnic hypoxia (arterial oxygen saturation 80%) and normoxia in random order. Following the gas period, subjects were administered six incremental 2-min inspiratory resistive loads while breathing room air. Ventilation was measured throughout the loading period. In both patients and controls, there was a significant increase in inspiratory time with increasing load (P = 0.006 and 0.003, respectively), accompanied by a significant fall in peak inspiratory flow (P = 0.006 and P < 0.001, respectively). The result was a significant fall in minute ventilation in both groups with increasing load (P = 0.003 and P < 0.001, respectively). There was no difference between the two groups for these parameters. The only difference between the two groups was a transient increase in tidal volume in controls (P = 0.02) but not in OSA patients (P = 0.57) during loading. Following hypoxia, there was a significant increase in minute ventilation during loading in both groups (P < 0.001). These results suggest that ventilation during incremental resistive loading is preserved in OSA patients and that it appears relatively impervious to the effects of hypoxia.

Hypoxia impairs the arousal response to external resistive loading and airway occlusion during sleep.

STUDY OBJECTIVES: Sustained hypoxia is a neurocognitive depressant, which has been shown to impair respiratory load sensation. Hypoxia has also been shown to impair arousal in animal models, but the effects of sustained hypoxia on arousal in humans have not been studied. The aim of this study was to assess the effects of sustained hypoxia on arousal from sleep in normal subjects. DESIGN: Twelve normal male subjects (age, 24.3 +/- 1.2 years; body mass index, 24.8 +/- 1.4 kg/m2) were studied during stable stage 2 non-rapid eye movement sleep on 2 separate nights 1 week apart. SETTING: Sleep physiology laboratory. PARTICIPANTS: Normal healthy volunteers. INTERVENTIONS: Arousal responses to external resistive loads (18 cm H2O x L(-1) x sec(-1)) and occlusions were compared during room-air breathing following sustained normoxia and isocapnic hypoxia (SaO2 approximately 85%). MEASUREMENTS AND RESULTS: Time to arousal and minimum esophageal pressure preceding arousal were measured. Time to arousal was significantly increased following hypoxia compared with normoxia for resistive loads (24.6 + 4.4 seconds vs. 12.6 +/- 1.9 seconds, p = .007) but not occlusions. Minimum esophageal pressure prior to arousal was more negative following hypoxia for both external loads (-16.8 +/- 1.2 vs. -13.5 +/- 1.3 cm H2O, p = .035) and occlusions (-19.6 +/- 2.2 vs. -15.1 +/- 1.5 cm H2O, p = .029). CONCLUSIONS: We conclude that sustained isocapnic hypoxia delays arousal to inspiratory loading during sleep and increases the respiratory arousal threshold. This has implications for disorders characterized by sustained nocturnal hypoxia, such as neuromuscular weakness, chronic obstructive pulmonary disease, obesity-hypoventilation syndrome, and severe obstructive sleep apnea.

Acute sustained hypoxia suppresses the cough reflex in healthy subjects.

RATIONALE: An intact cough reflex is important to protect the lung from injurious substances and to clear excess secretions. A blunted cough reflex may be harmful or even fatal in respiratory disease. Hypoxia is common in respiratory disorders and has been shown to have depressant effects on respiratory sensation and ventilation. We hypothesized that it might also suppress the cough reflex. OBJECTIVES: To determine if acute hypoxia increases cough threshold and cough tachyphylaxis to inhaled capsaicin. METHODS: On two occasions, 16 healthy subjects inhaled a saline control followed by doubling doses of capsaicin aerosol (range, 0.49-500 microM) every minute for 15 s during controlled ventilation (approximately 190% baseline) with isocapnic hypoxia (SpO2, approximately 80%) or isocapnic normoxia, in random order. When a subject responded to a dose with five or more coughs, the next doubling dose of capsaicin was administered continuously for 60 s to assess acute tachyphylaxis. MAIN RESULTS: The capsaicin concentration required to elicit five coughs was significantly higher during isocapnic hypoxia compared with normoxia (29.6 +/- 16.0 vs. 23.4 +/- 15.6 microM, p = 0.01). During continuous capsaicin inhalation, significantly more coughs were evoked in the first 10 s compared with the last (2.3 +/- 0.3 vs. 1.3 +/- 0.3, p < 0.01), indicating cough tachyphylaxis. However, the decrease was the same during hypoxia and normoxia (-1.3 +/- 0.4 vs. -0.9 +/- 0.6, p = 0.54). CONCLUSIONS: Acute isocapnic hypoxia suppresses cough reflex sensitivity to inhaled capsaicin. This finding raises the possibility that the cough reflex may be impaired during acute exacerbations of hypoxic-respiratory disorders.

Home management of mild to moderately severe community-acquired pneumonia: a randomised controlled trial.

OBJECTIVE: To determine whether community management of mild to moderate community-acquired pneumonia (CAP) is as effective and acceptable as standard hospital management of CAP. DESIGN: Randomised controlled trial. SETTING: Christchurch, New Zealand, primary and secondary care. PARTICIPANTS: 55 patients presenting or referred to the emergency department at Christchurch Hospital with mild to moderately severe pneumonia, assessed using a validated pneumonia severity assessment score, from July 2002 to October 2003. INTERVENTIONS: Hospital treatment as usual or comprehensive care in the home delivered by primary care teams. MAIN OUTCOME MEASURES: Primary: days to discharge, days on intravenous (IV) antibiotics, patient-rated symptom scores. Secondary: health status measured using level of functioning at 2 and 6 weeks, patient satisfaction. RESULTS: The median number of days to discharge was higher in the home care group (4 days; range, 1-14) than in the hospital groups (2 days; range, 0-10; P = 0.004). There was no difference in the number of days on IV antibiotics or on subsequent oral antibiotics. Patient-rated symptom scores at 2 and 6 weeks, median change in symptom severity from baseline to 6 weeks, and general functioning at 2 and 6 weeks did not differ between the groups. Patients in both groups were satisfied with their treatment, with a clear preference for community treatment (P < 0.001). CONCLUSIONS: Mild to moderately severe CAP can be managed effectively in the community by primary care teams. This model of comprehensive care at home can be implemented by primary care teams with suitable funding structures.

Sustained hypoxia depresses sensory processing of respiratory resistive loads.

RATIONALE: The combination of acute hypoxia and increased respiratory load is encountered in several respiratory diseases including acute life-threatening asthma and sleep apnea. Hypoxia has been shown to inhibit respiratory load perception in healthy and asthmatic subjects, and could contribute to treatment delays and impaired function of protective reflexes. OBJECTIVES: Using respiratory-related evoked potentials (RREPs) this study aimed to determine the sensory processes mediating hypoxia-induced suppression of respiratory load sensation. METHODS: EEG was measured over the central and parietal cortical regions in 14 healthy subjects. RREPs were elicited by 500-ms midinspiratory resistive load stimuli during and after isocapnic normoxia or hypoxia (blood arterial O2 saturation approximately 80%). On a separate occasion, subjects rated the perceived magnitude of five externally applied inspiratory resistive loads (range, 8.6-43.7 cm H2O x L(-1) x s) under similar experimental conditions. In both experiments subjects voluntarily ventilated approximately 90% above baseline to match ventilatory output between gas conditions. RESULTS: RREP stimulus was matched between gas conditions in 11 subjects (minimum mask pressure -9.7 +/- 0.6 versus -9.2 +/- 0.4 cm H2O). P1 and P2 amplitudes were reduced during isocapnic hypoxia compared with normoxia (maximal at Cz: P1, 2.5 +/- 1.1 versus 3.9 +/- 1.2 microv, p = 0.03; P2, 10.0 +/- 2.2 versus 12.4 +/- 2.1 microv, p < 0.01, respectively). Perceived magnitude of externally applied resistive loads was also reduced during hypoxia compared with normoxia (17.1 +/- 1.1 versus 19.0 +/- 1.1 au, p < 0.01). CONCLUSIONS: These data confirm that isocapnic hypoxia suppresses respiratory load sensation. Decreased amplitude of the earlier (P1) RREP component suggests that this is mediated, at least in part, by suppression of respiratory afferent information before its arrival at the primary sensory cortex.