Sleep-related changes in the human 'neuromuscular' ventilatory response to hypoxia

Ventilatory neural drive in chronically hypercapnic patients with COPD: effects of sleep and nocturnal noninvasive ventilation

Sleep brings major challenges for the control of ventilation in humans, particularly the regulation of arterial carbon dioxide pressure (P _aCO2 ). In patients with COPD, chronic hypercapnia is associated with increased mortality. Therefore, nocturnal high-level noninvasive positive-pressure ventilation (NIV) is recommended with the intention to reduce P _aCO2 down to normocapnia. However, the long-term physiological consequences of P _aCO2 "correction" on the mechanics of breathing, gas exchange efficiency and resulting symptoms (i.e. dyspnoea) remain poorly understood. Investigating the influence of sleep on the neural drive to breathe and its translation to the mechanical act of breathing is of foremost relevance to create a solid rationale for the use of nocturnal NIV. In this review, we critically discuss the mechanisms by which sleep influences ventilatory neural drive and mechanical consequences in healthy subjects and hypercapnic patients with advanced COPD. We then discuss the available literature on the effects of nocturnal NIV on ventilatory neural drive and respiratory mechanics, highlighting open avenues for further investigation.

Pulmonary management of the patient with muscular dystrophy

Pulmonary involvement is common in patients with muscular dystrophy, and routine screening for evidence of respiratory muscle dysfunction should be performed. Testing for respiratory muscle strength, as well as an assessment for sleep-disordered breathing, should be obtained in consultation with a specialist. Adequate airway clearance and correction of impaired ventilation are the key components of pulmonary management in this group of patients. Also, special emphasis on airway clearance is recommended during upper respiratory infections, as well as in the postoperative period. Early initiation of ventilatory support has been shown to result in longer life expectancy.

Respiratory chemosensitivity during wake and sleep in harbour seal pups (Phoca vitulina richardsii)

In this study, we examined the cardiorespiratory patterns of harbour seal pups under normoxic/normocarbic (air), hypoxic/normocarbic (15%, 12%, and 9% O2 in air), and normoxic/hypercarbic (2%, 4%, and 6% CO2 in air) conditions while awake and sleeping on land. Animals were chronically instrumented to record electroencephalogram (EEG), electromyogram (EMG), and electrocardiogram (EKG) signals, which, along with respiration (whole-body plethysmography) and oxygen consumption (VO2), were recorded from animals breathing each gas mixture for 2-4 h on separate days. Our results show that for animals breathing air, VO2 was not significantly lower during slow-wave sleep (SWS; 7.71 +/- 0.39 mL O2 min(-1) kg(-1); all measurements are mean +/- SEM) than during wakefulness (WAKE; 8.80 +/- 0.25 mL O2 min(-1) kg(-1)) and was unaffected by changes in respiratory drive. Although there was no significant fall in VO2 associated with a decrease in arousal state, breathing frequency (f(R)) did decrease (from 18.80 +/- 1.50 breaths min(-1) in WAKE to 10.40 +/- 0.49 breaths min(-1) in SWS), while the incidence of long apneas (>20 s) increased (12.76 +/- 4.06 apneas h(-1) in WAKE and 31.95 +/- 2.37 apneas h(-1) in SWS). Breathing was rarely seen during rapid eye movement (REM) sleep. Tachypnea was present at all levels of increased respiratory drive; however, hypoxia induced a dramatic bradycardia regardless of arousal state, while hypercarbia produced a tachycardia in SWS only. The hypoxic and hypercarbic chemosensitivities of harbour seal pups were similar to those of terrestrial mammals; however, unlike terrestrial mammals, where hypoxic and hypercarbic sensitivities are often reduced during SWS, the sensitivity of harbour seal pups to hypoxia and hypercarbia remained unchanged during the decrease in arousal state from WAKE to SWS.

Pulmonary complications of chronic neuromuscular diseases and their management

Chronic neuromuscular diseases may affect all major respiratory muscles groups including inspiratory, expiratory, and bulbar, and respiratory complications are the major cause of morbidity and mortality. Untreated, many of these diseases lead inexorably to hypercapnic respiratory failure, precipitated in some cases by chronic aspiration and secretion retention or pneumonia, related to impairment of cough and swallowing mechanisms. Many measures are helpful including inhibition of salivation, cough-assist techniques, devices to enhance communication, and physical therapy. In addition, ventilatory assistance is an important part of disease management for patients with advanced neuromuscular disease. Because of its comfort, convenience, and portability advantages, noninvasive positive pressure ventilation (NPPV) has become the modality of first choice for most patients. Patients to receive NPPV should be selected using consensus guidelines, and initiation should be gradual to maximize the chances for success. Attention should be paid to individual preferences for interfaces and early identification of cough impairment that necessitates the use of cough-assist devices. For patients considered unsuitable for noninvasive ventilation, invasive mechanical ventilation should be considered, but only after a frank but compassionate discussion between the patient, family, physician, and other caregivers.