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Biomedical subjects

W T McNicholas

Publications and source records attributed to W T McNicholas.

At least 19 recordsLinked to original sources
PubMed1999

Subjective efficacy of nasal CPAP therapy in obstructive sleep apnoea syndrome: a prospective controlled study.

The response to nasal continuous positive airways pressure (nCPAP) of a wide variety of symptoms recognized to be associated with obstructive sleep apnoea syndrome (OSAS) was examined. Fifty-six consecutive patients with OSAS, confirmed by polysomnography (mean (SD) apnoea-hypopnoea index (AHI) 49.6 (22.6) events x h(-1), Epworth score 15.4 (5.0)), were asked to complete paired symptom evaluation questionnaires, before treatment and again after 4 months of nCPAP. The response rate was 80%. A control group of 21 consecutive OSAS patients of similar age, body mass index (BMI), AHI and Epworth score to the treated group but managed with conservative measures, completed the same questionnaires on two occasions, 4 months apart. The nCPAP-treated group showed significant reductions (Wilcoxon matched pairs test) in the symptoms of daytime sleepiness, restless sleep, heartburn, nocturia, enuresis, headache and nocturnal sweating, whereas controls showed no significant changes in these symptoms. There were no changes in BMI, smoking, alcohol consumption or exercise habits in either group. It was concluded that, in addition to improvements in symptoms of daytime sleepiness and restless sleep, a wide range of other symptoms may improve significantly with nasal continuous positive airways pressure therapy.

Case-Control Studies↗
PubMed1998

Efficacy of nasal continuous positive airway pressure therapy in chronic heart failure: importance of underlying cardiac rhythm.

BACKGROUND: Some previous reports have indicated beneficial cardiac effects of nasal continuous positive airway pressure (NCPAP) in patients with severe congestive heart failure (CHF), but others have reported deleterious cardiac effects, particularly among patients in atrial fibrillation (AF). The aim of this study was to determine if differences in cardiac rhythm influence the acute cardiac response to NCPAP. METHODS: Eleven consecutive patients with CHF were recruited, six in atrial fibrillation (AF) and five with sinus rhythm (SR). Cardiac index was measured during awake NCPAP application by the thermodilution technique during cardiac catheterisation. NCPAP was applied in a randomised sequence at pressures of 0, 5, and 10 cm H2O with three 30 minute applications separated by 20 minute recovery periods without NCPAP. RESULTS: Significant differences were found between the AF and SR groups for cardiac index responses to NCPAP (p = 0.004, ANOVA) with a fall in cardiac index in the AF group (p = 0.02) and a trend towards an increase in the SR group (p = 0.10). Similar differences were seen between the groups in stroke volume index responses but not in heart rate responses. Changes in systemic vascular resistance were also significantly different between the two groups (p < 0.005, ANOVA), rising in the AF group but falling in the SR group. CONCLUSIONS: These data indicate an important effect of underlying cardiac rhythm on the awake haemodynamic effects of NCPAP in patients with CHF.

Aged↗
PubMed1998

Resolution of obstructive sleep apnoea with growth in the Robin sequence.

A 12 year old female with the Robin sequence presented with a one year history of snoring, witnessed apnoeas and daytime sleepiness. Surgery in early childhood had consisted of cleft palate repair, tonsillectomy and adenoidectomy and, later, revision palatoplasty. Overnight polysomnography (PSG) demonstrated severe obstructive sleep apnoea syndrome with an apnoea/hypopnoea index (AHI) of 49 events x h(-1), and repetitive oxygen desaturations below 50%. Nasal continuous positive airway pressure (nCPAP) effectively controlled her sleep abnormalities. After 3 yrs of nCPAP therapy, she requested discontinuation and was fully reassessed. PSG without nCPAP revealed an AHI <5 events x h(-1) with no desaturations below 90% and normal sleep quality. A repeat lateral cephalometrogram showed increased mandibular length and posterior airway space and reduced soft palate length. The patient remains asymptomatic 9 months following nCPAP discontinuation. This case indicates that nasal continuous positive airway pressure is an effective nonsurgical therapy in children with obstructive sleep apnoea syndrome and the Robin sequence. It is likely that mandibular growth, increase in mandibular length and enlargement of the posterior airway space was responsible for the resolution of obstructive sleep apnoea syndrome in this case.

Cephalometry↗
PubMed1998

Implications of pathophysiology for management of the obstructive sleep apnoea syndrome.

The pathophysiology of obstructive sleep apnoea syndrome (OSAS) is complex and incompletely understood, but is principally based on an imbalance between the collapsing forces of the upper airway (UA) during inspiration and the counteracting dilating forces of the UA dilating muscles. A narrowed UA is very common among OSAS patients, which is usually due, in adults, to nonspecific factors such as fat deposition in the neck or abnormal bony morphology of the UA. Functional impairment of the UA dilating muscles is particularly important in the development of OSAS, and patients have a reduction in both tonic and phasic contraction of these muscles during sleep when compared to normal subjects. Arousal plays an important role in the termination of each apnoea, but may also contribute to the development of further apnoea because of a reduction in respiratory drive related to the hypocapnia which results from postapnoeic hyperventilation. A cyclical pattern of repetitive obstructive apnoeas may result. A better understanding of the integrated pathophysiology of obstructive sleep apnoea syndrome should help both in the choice of optimum therapy for each individual patient and also in the development of new therapeutic techniques.

Adult↗
PubMed1997

Reversible hypercapnia in chronic obstructive pulmonary disease: a distinct pattern of respiratory failure with a favorable prognosis.

PURPOSE: Hypercapnia is regarded as a poor prognostic indicator in chronic obstructive pulmonary disease (COPD), but many patients hospitalized with hypercapnia associated with an acute exacerbation of COPD revert to normocapnia during recovery. We wished to determine if this reversible hypercapnia represents a distinct pattern of respiratory failure in COPD, or simply a stage in the progression to chronic hypercapnia. We therefore compared the long-term clinical progression and survival of COPD patients with reversible hypercapnic respiratory failure (defined as type 2.1) to those with normocapnic (PaCO2 < 50 mm Hg; type 1) and also to those patients with chronic hypercapnic (PaCO2 > 50 mm Hg) respiratory failure (defined as type 2.2). PATIENTS AND METHODS: We prospectively followed for 5 years a cohort of 85 patients who had been admitted as emergencies during a 1-year period to the respiratory unit of a University teaching hospital with an exacerbation of COPD complicated by respiratory failure (PaO2 < 60 mm Hg). The main long-term outcome measures were survival and blood gas changes. RESULTS: Sixty-eight (80%) patients survived the initial admission, and 17 (27%) survived 5 years. PaCO2 rose substantially more during exacerbations in type 2.1 patients (mean 15.8 mm Hg), compared with type 2.2 (mean 6.8 mm Hg) and type 1 patients (mean 1.5 mm Hg). We analyzed 149 subsequent admissions among the survivors over the following 5 years. Type 2.1 patients had a better 5-year survival (28%) than type 2.2 (11% survival; P < 0.05), and similar to type 1 patients (33% 5-year survival). Only 24% of reversible hypercapnic patients developed chronic hypercapnia during long-term followup. CONCLUSIONS: The data support reversible hypercapnia being a distinct manifestation of respiratory failure in COPD, with a similar prognosis to that of normocapnic respiratory failure.

Aged↗
PubMed1997

Potassium and ventilation during exercise above and below the ventilatory threshold.

Increases in arterial plasma potassium during exercise may provide an important drive to ventilation. We examined the changes in arterialized venous plasma potassium concentration ([K +]av) and ventilation that occur during sustained exercise at workloads above and below the ventilatory threshold (Vt) in young health humans. After the onset of exercise at a workload below-Vt, [K +]av rose by 0.3 (+/- 0.1) mmol l-1 (mean +/- SEM). Following 30 min of exercise at this intensity [K +]av had fallen (P < 0.05, ANOVA) by an amount approximately equal to one third of the initial increase. While [K +]av fell, ventilation remained stable. At 5 min after the onset of sustained exercise above the Vt [K +]av had risen by 0.7 (+/- 0.1) mmol l-1 and thereafter remained constant. Ventilation slowly increased throughout the above-Vt protocol. These results show significant differences in the time course of the changes in [K +]av and ventilation. They do not support the hypothesis that changes in [K +]a during moderate exercise cause linearly related changes in ventilation.

Adult↗
PubMed1997

Malignant chondroid syringoma presenting as multiple pulmonary nodules.

Malignant chondroid syringoma, a very rare tumour, presenting with multiple pulmonary metastases in a 50 year old woman is described. Initial diagnostic confusion with pulmonary hamartoma occurred due to histopathological similarities. However, re-examination of a skin biopsy specimen taken 17 years previously from a hand lesion yielded the necessary information to identify the pulmonary lesions definitively as metastases from the original skin lesion. The features of this very rare indolent tumour are described.

Adenoma, Pleomorphic↗
PubMed1997

A rapid desktop theophylline assay. Evaluation of use in clinical management.

STUDY OBJECTIVES: To assess the practicality and precision of a simple desktop theophylline assay (Biotrack 516TM) in comparison to a standard laboratory assay system (Abbott TDxTM). DESIGN: A prospective blinded paired sample study. SETTING: The respiratory ward and outpatient clinics, the pulmonary function and biochemistry laboratories of a university teaching hospital. PATIENTS: Sixty patients with asthma or COPD attending the respiratory service. MEASUREMENTS AND RESULTS: Paired specimens for theophylline assay were collected simultaneously for analysis. There was a highly significant (p < 0.001) correlation between the two assay systems for both the total range studied (1.2-39.1 micrograms/mL; r = 0.98), and the clinically important range of 5-15 micrograms/mL (r = 0.95). The limits of agreement for the data by the Bland and Altman method indicated a +/-2 micrograms/mL limit for the 5-15 micrograms/mL range and a +/-2.7 micrograms/mL limit for the total range studied. CONCLUSIONS: The Biotrack 516 is an easy-to-use system, which provides rapid and reasonably precise measurements of serum theophylline levels. The device should be of particular value in smaller centers without an on-site laboratory assay system.

Evaluation Studies as Topic↗
PubMed1997

Bed partners' assessment of nasal continuous positive airway pressure therapy in obstructive sleep apnea.

STUDY OBJECTIVE: This study aimed to evaluate the effects of nasal continuous positive airway pressure (nCPAP) therapy on sleep and daytime symptoms of bed partners and patients with obstructive sleep apnea (OSA). DESIGN: A cross-sectional questionnaire survey. SETTING: The sleep laboratory of a university teaching hospital. PATIENTS: Ninety-one consecutive OSA patients within 2 to 12 months of being prescribed nCPAP. RESULTS: Eighty-five replies (93% of sample population) were received. Twelve patients (14% of replies) had discontinued nCPAP therapy; two patients had not yet been supplied with an nCPAP device. Seventy-one patients continued nightly nCPAP therapy. Bed partners of these patients (n = 55) answered a separate questionnaire assessing improvements in their own sleep quality, daytime alertness, mood and quality of life (questions 1 to 4), and evaluated the same parameters for the patients (questions 5 to 8). Possible scores ranged from -1 (worse) to +3 (marked improvement). Questions 1 to 4 yielded median scores of 2, 1, 1, and 2, respectively, and scores of 3, 3, 2, and 3 for questions 5 to 8. A ninth question addressing perceived changes in the quality of their relationship resulted in a median score of 2. Mean (SD) Epworth sleepiness scores improved from 14.3 (5.8) to 5.2 (4.3) in patients receiving therapy (p < 0.005). CONCLUSIONS: These data indicate that bed partners of OSA patients treated with nCPAP experience important improvements in symptoms and personal relationships. The findings are of practical clinical use when counseling patients with OSA and their partners on the likely impact of nCPAP therapy on their quality of life.

Affect↗
PubMed1997

Impact of sleep in respiratory failure.

Sleep has a physiological influence on respiration, which can have major adverse effects on gas exchange in patients with respiratory insufficiency. These effects relate largely to a reduction in various stimulant inputs to the brainstem respiratory centre. Conditions that may be associated with sleep-related respiratory insufficiency range from pulmonary disorders (such as chronic obstructive pulmonary disease (COPD)), to central respiratory insufficiency (such as central alveolar hypoventilation), neurological and neuromuscular disorders (such as polio and muscular dystrophy), and thoracic cage disorders (such as kyphoscoliosis). All these conditions have in common the finding of hypoxaemia and hypercapnia, which become more pronounced during sleep. The relative hypoventilation, which is common to each condition, is due to varying combinations of an inadequate respiratory drive and an increase in the work of breathing. Management of respiratory insufficiency during sleep should be directed first at optimizing the underlying disorder, then at correcting hypoxaemia with controlled low-flow supplemental oxygen. Pharmacological therapy may be effective in some instances, but the choice of agent varies with the underlying disorder. Assisted ventilation is an important part of the management of advanced cases, and the recent development of intermittent positive pressure ventilation by nasal mask (NIPPV) has been an important advance in this area. Use of NIPPV during the night is associated with beneficial effects during the day, particularly improved awake gas exchange and respiratory muscle strength, in addition to less dyspnoea and improved quality of life. Electrophrenic pacing of the diaphragm is helpful in highly selected cases, particularly patients with central respiratory insufficiency and high quadriplegia, but is frequently complicated by the development of obstructive sleep apnoea.

Humans↗
PubMed1997

Clinical diagnosis and assessment of obstructive sleep apnoea syndrome.

Obstructive sleep apnoea (OSA) syndrome is very common, affecting up to 4% of adult males. The pathophysiology of OSA is complex and incompletely understood, but upper airway (UA) obstruction appears to be the net result of an inability of the UA dilating muscles to maintain a patent oropharyngeal airway during sleep. A narrowed UA is common among OSA patients, and in adults this is usually due to nonspecific factors, such as fat deposition in the neck, or abnormal bony morphology of the UA. The present criteria for the diagnosis of OSA are not well-defined, and different centres use different thresholds of apnoea and hypopnoea frequency during sleep to diagnose the clinical syndrome. The advent of many simplified diagnostic systems, some of which are portable and suitable for use in the patient's home, represents a major advance, but many of these systems are poorly validated, and there is no uniformity of measured variables among the various systems, apart from arterial oxygen saturation (Sa,O2). The established prevalence of OSA among the general population implies that most patients with suspected OSA should be initially assessed outside major sleep laboratories, in many cases by clinicians who may not have as detailed an understanding of the syndrome as clinicians who have undertaken specific training in sleep medicine. It is important, therefore, that clear-cut guidelines and criteria be established for the assessment and management of patients with suspected OSA.

Adult↗