1/14. Factors determining the onset and course of hypoxemia during apnea: an investigation using physiological modelling.We used the Nottingham physiology Simulator to examine the onset and course of hypoxemia during apnea after pulmonary denitrogenation. The following factors, as possible determinants of the hypoxemia profile, were varied to examine their effect: functional residual capacity, oxygen consumption, respiratory quotient, hemoglobin concentration, ventilatory minute volume, duration of denitrogenation, pulmonary venous admixture, and state of the airway (closed versus open). Airway obstruction significantly reduced the time to 50% oxyhemoglobin saturation (8 vs 11 min). Provision of 100% oxygen rather than air to the open, apneic patient model greatly prolonged time to 50% oxyhemoglobin saturation (66 vs 11 min). Hemoglobin concentration, venous admixture, and respiratory quotient had small, insignificant effects on the time to desaturation. Reduced functional residual capacity, short duration of denitrogenation, hypoventilation, and increased oxygen consumption significantly shortened the time to 50% oxyhemoglobin saturation during apnea. IMPLICATIONS: Reduction in oxygen levels during cessation of breathing is dangerous and common in anesthetic practice. We used validated, mathematical, physiological models to reveal the impact of physiological factors on the deterioration of oxygen levels. This study could not be performed on patients and reveals important information.- - - - - - - - - - ranking = 1keywords = hypoventilation (Clic here for more details about this article) |
2/14. Hypersomnia with periodic breathing (an acromegalic Pickwickian).The syndromes of Pickwickian, Ondine's curse, and primary alveolar hypoventilation are respiratory disorders manifesting increased sleepiness and irregular respiratory rhythms. These disorders are currently grouped as hypersomnia with periodic breathing (HPB). Polygraphic techniques have lead to a reasonable hypothesis as to the pathophysiology of the multiple variants of HPB. Discernible causes of HPB have been attributed to both central and peripheral factors. Peripheral factors encompass those conditions relating to upper airway obstruction. An acromegalic person suffering the HPB syndrome secondary to laryngeal stenosis is described.- - - - - - - - - - ranking = 1keywords = hypoventilation (Clic here for more details about this article) |
3/14. Periodic apnea, exercise hypoventilation, and hypothalamic dysfunction.Periodic apnea and exercise hypoventilation were observed in a 14-year-old boy. hyperphagia, obesity, serum hyperosmolality without diabetes insipidus or appropriate thirst, and retardation of growth and sexual development indicated a hypothalamic disorder. Neurologic evaluation was normal except for electroencephalographic changes induced by apnea. Pulmonary function tests, resting arterial blood gases in the wakeful state, and ventilatory response to inhaled CO2 were also normal. Acute hypoxemia and respiratory acidosis occurred with apnea during sleep and with insufficient ventilation during exercise. The central origin of sleep apneas was shown by esophageal pressure monitoring. The hypothalamic dysfunction and exercise hypoventilation distinguish this patient from others with obesity and periodic apnea.- - - - - - - - - - ranking = 6.0015098295435keywords = hypoventilation, obesity (Clic here for more details about this article) |
4/14. Central hypoventilation during quiet sleep in two infants.Expired ventilation (VE), tidal volume (VT), frequency (f), and alveolar PCO2 (PACO2) were examined in six normal infants at 41 to 52 weeks post-conceptional age and in two infants who were apneic at birth. Their response to breathing 5% carbon dioxide in air and to 100% oxygen in quiet sleep were compared to those in rapid eye movement (REM) sleep. VE in normal infants was 259 ml/kg/min in REM and 200.2 ml/kg/min in quiet sleep with the difference being due to decreased carbon dioxide production and to decreased dead space. VE increased 34.4 ml/kg/min/mm Hg of PCO2 elevation with 5% carbon dioxide breathing during REM and was not significantly different during quiet sleep. During oxygen breathing VE fell by 32.7% at 30 seconds before increasing again. In the affected infants, VE and PACO2 during REM at 1 and 4 months were normal. At 1 month, during quiet sleep, each infant became apneic and PACO2 rose 9 and 8 mm Hg/min respectively. At this time mechanical ventilation was begun. At 4 months, during quiet sleep, VE was 0.064 and 0.063 ml/kg/min at PACO2 of 66 mm Hg in each infant. The change was due entirely to a decrease in VT to 2.3 and 2.5 ml/kg. At this time 5% carbon dioxide breathing given during normal ventilation in REM produced an abrupt fall in VT to 2.0 and 2.2 ml/kg with no change in frequency. Oxygen breathing during REM at one month had no effect but at 4 months produced apnea requiring mechanical ventilation after one minute. The findings suggest that the ventilatory response to carbon dioxide is (1) important in initiation of extrauterine ventilation and (2) in sustaining ventilation particularly in quiet sleep. It is not necessary in sustaining ventilation awake or in REM sleep and it represents a balance between the stimulatory and depressant effects of carbon dioxide on the central nervous system.- - - - - - - - - - ranking = 4keywords = hypoventilation (Clic here for more details about this article) |
5/14. Diaphragmatic pacing: an alternative to long-term mechanical ventilation.Electrical percutaneous stimulation of the phrenic nerves was first employed in 1948 by Sarnoff to provide temporary artificial ventilation in patients with respiratory failure. However, the technique was limited by development of infection around the electrode. Short-term radiofrequency stimulation of the phrenic nerves was first utilised by Glenn in 1964 and adapted to long-term use in patients with central hypoventilation in 1968 and with traumatic quadriplegia in 1972. The technique employed alternate pacing of each hemidiaphragm with high frequency stimulation (25-30 Hz) with a respiratory rate of 12 to 17 per minute which, in a series of 17 quadriplegic adults, although initially successful, was self-limiting because of eventual damage to the nerves and diaphragms. More recently, continuous bilateral simultaneous low frequency (up to 8 Hz) stimulation with a respiratory rate of 5 to 9 per minute has not induced myopathic changes. This phenomenon has been attributed to: 1. the conversion of the mixture of slow and fast twitch fibres in the diaphragm to a uniform population of fatigue resistant fibres induced by low frequency stimulation, and 2. the reduction in the total current necessary to achieve adequate gas exchange when both diaphragms contract simultaneously with the less frequent stimulation at lower energy. Diaphragmatic pacing has been applied to infants and children with emphasis on the selection of patients and optimum setting of stimulus parameters. This communication presents a case report of diaphragmatic pacing in a child with a review of the principles of application. The advantages and disadvantages compared to mechanical ventilation are also discussed.- - - - - - - - - - ranking = 1keywords = hypoventilation (Clic here for more details about this article) |
6/14. Primary alveolar hypoventilation managed by negative-pressure ventilators.A girl who had a history of repeated apnea was found to have absent chemical drive to ventilation and, on sleep monitoring, both central and obstructive types of apnea. She is currently undergoing successful mechanical ventilation at night with negative-pressure ventilators.- - - - - - - - - - ranking = 4keywords = hypoventilation (Clic here for more details about this article) |
7/14. retrognathia and sleep apnea. A life-threatening condition masquerading as narcolepsy.The association of sleep apnea with daytime hypersomnolence without obesity, and its potentially lethal cardiopulmonary sequelae, make it crucial that this condition be distinguished from narcolepsy. A patient with retrognathia who had been diagnosed as a narcoleptic for 15 years had the primary complaint of excessive daytime sleepiness. sleep laboratory evaluation showed severe hypoxemia and a mean of 366 upper airway obstructions per night. The patient was treated with a tracheotomy; this resulted in relief of the sleep-related upper airway obstructions, hypoxemia, and hypersomnolence.- - - - - - - - - - ranking = 0.00075491477176061keywords = obesity (Clic here for more details about this article) |
8/14. meningeal carcinomatosis in breast cancer presenting as central hypoventilation: a case report with a brief review of the literature.meningeal carcinomatosis can appear with a variety of neurologic signs and symptoms. Alterations in respiratory control have not been reported in this syndrome or in neurologic syndromes associated with systemic cancer. The authors report on a case of documented leptomeningeal carcinoma from breast cancer presenting as apnea; they note its successful treatment with radiation and intrathecal chemotherapy. The authors conclude that respiratory failure can be considered as part of the syndrome of leptomeningeal carcinomatosis.- - - - - - - - - - ranking = 4keywords = hypoventilation (Clic here for more details about this article) |
9/14. Partial upper airway obstruction and sleep apnoea.An unusual case is described in which partial upper airway obstruction led to a sequence of events characterized by sleep disturbance, enuresis, somnolence and cardio-respiratory collapse. The upper airway obstruction was not immediately apparent as the cause of subsequent clinical events. attention is drawn to the general medical problems which may be produced by upper airway obstruction, with particular reference to those accompanying obesity and abnormal stature.- - - - - - - - - - ranking = 0.00075491477176061keywords = obesity (Clic here for more details about this article) |
10/14. Transcutaneous gas tension monitoring in the management of intraoperative apnea.Periods of apnea or severe hypoventilation may occur during procedures which involve the airway or during thoracic operations. Routine vital signs and ECG monitoring of these situations are incapable of quantitating the severe tissue hypoxia and acidosis which develop under these circumstances; rather, they only reflect the morbid complications of hypoxia and acidosis (i.e., bradycardia, ectopy, and hypotension). Transcutaneous oxygen and carbon dioxide sensors directly measure tissue gas tensions with a short sensor response time. This report documents the efficacy of transcutaneous gas tension monitoring in the management of these high-risk situations.- - - - - - - - - - ranking = 1keywords = hypoventilation (Clic here for more details about this article) |
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