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Biomedical subjects

R M Cayton

Publications and source records attributed to R M Cayton.

At least 19 recordsLinked to original sources
PubMed2003

Combined index of heart rate variability and oximetry in screening for the sleep apnoea/hypopnoea syndrome.

Many sleep centres employ a preliminary screening test in order to reduce the number of polysomnographies required in the routine diagnosis of the sleep apnoea/hypopnoea syndrome (SAHS). We investigated the combination of heart rate and oximetry information as a means of performing this test. A retrospective study of 100 patients with suspected SAHS was made. All patients had in-hospital polysomnography on one night. We estimated the number of respiratory event-related arousals by counting the number of autonomic arousals (assessed on the basis of changes in the heart interbeat interval) that were coincident with a rise in oximetry. The hourly index of such events was denoted the "cardiac-oximetry disturbance index" (CODI). The median apnoea/hypopnoea index (AHI) was 16.5 (range 1.0-93.6) h-1. The CODI correlated significantly with the AHI (Spearman correlation coefficient rs = 0.88, P < 0.01), and the area (+/- standard error) under the receiver operating characteristic (ROC) was 0.94 +/- 0.05. Oximetry alone (based on 4% dips) was a less effective screening test (rs = 0.80, P < 0.01; area under ROC 0.83 +/- 0.06). Using 2% dips in oximetry offered comparable performance with the CODI (rs = 0.91, P < 0.01; area under ROC 0.93 +/- 0.04). The CODI was better correlated with the electroencephalograph arousal index (rs = 0.84, P < 0.01) than was oximetry (2% dips, rs = 0.57, P < 0.01). The CODI algorithm also offers an informal measure of self-validation: a large discrepancy between the number of autonomic arousals and the number of rises in oximetry indicates the presence of autonomic arousals without changes in oximetry (or vice versa). This self-validation mechanism identified several patients in this study, and may be useful in identifying sleep disruption due to chronic pain or other causes.

Adult↗
PubMed2002

Health utilities in evaluating intervention in the sleep apnoea/hypopnoea syndrome.

Formulating a rational health policy necessitates the ability to compare between different healthcare interventions and disease scenarios. Continuous positive airway pressure (CPAP) therapy with a conservative lifestyle strategy in sleep apnoea/hypopnoea syndrome (SAHS) was evaluated using health utility and quality-adjusted life years (QALYs) as outcome measures. A total 71 SAHS (apnoea/hypopnoea index > or = 15 h(-1)) patients completed a randomised, parallel group study over 3 months using utilities derived by the standard gamble approach (Usg) and European quality of life questionnaire (Euroqol) (Ueq). The severely impaired health status at baseline improved by 23% (Usg 0.32 to 0.55) adding 8 QALYs in the CPAP group, compared to a 4% improvement with 4.7 QALYs added in the lifestyle group (Usg 0.31 to 0.35). The Ueq showed a marginal change with CPAP (0.73 to 0.77) but did not demonstrate any improvement with lifestyle intervention. The health status impairment in sleep apnoea/hypopnoea syndrome patients is markedly improved by continuous positive airway pressure compared to a modest improvement with conservative lifestyle strategies using the standard gamble utility, which may be incorporated in effectiveness and economic analyses. The European quality of life questionnaire did not reflect a similar degree of impact and is probably not useful in this population.

Health Behavior↗
PubMed2001

The sleep apnoea/hypopnoea syndrome depresses waking vagal tone independent of sympathetic activation.

The modest daytime hypertension and sympathetic upregulation associated with the sleep apnoea/hypopnoea syndrome (SAHS), does not explain the relatively large increased risk of cardiac morbidity and mortality in the SAHS patients population. Therefore, efferent vagal and sympathetic activity was evaluated during wakefulness in SAHS subjects and matched healthy controls, in order to determine if vagal downregulation may play a role in the aetiology of cardiac disease in the SAHS. The awake autonomic nervous system function of 15 male subjects, with mild-to-moderate SAHS was compared to that of 14 healthy controls matched for age, body mass index, gender and blood pressure. All subjects were free from comorbidity. Vagal activity was estimated from measurements of heart rate variability high frequency power (HF) and sympathetic activity was measured from urine catecholamine excretion. The %HF power was significantly (p < 0.03) reduced in SAHS patients (10+/-1.6 (mean+/-SEM)) as compared to controls (17 +/- 3). In addition, HF power correlated with the apnoea/hypopnoea index in the SAHS subjects (R = -0.592, p = 0.02). There was no statistically significant difference in the daytime excretion of nonadrenaline between control (242 +/- 30 nmol x collection(-1)) and SAHS (316 +/- 46 nmol x collection(-1)) subjects (p = 0.38). In these sleep apnoea/hypopnoea syndrome patients there was limited evidence of increased waking levels of urine catecholamines. The principal component altering waking autonomic nervous system function, in the sleep apnoea/hypopnoea syndrome subjects, was a reduced daytime efferent vagal tone.

Adult↗
PubMed1999

Evaluation of frequency and time-frequency spectral analysis of heart rate variability as a diagnostic marker of the sleep apnoea syndrome.

The sleep apnoea/hypopnoea syndrome (SAHS) elicits a unique heart rate rhythm that may provide the basis for an effective screening tool. The study uses the receiver operator characteristic (ROC) to assess the diagnostic potential of spectral analysis of heart rate variability (HRV) using two methods, the discrete Fourier transform (DFT) and the discrete harmonic wavelet transform (DHWT). These two methods are compared over different sleep stages and spectral frequency bands. The HRV results are subsequently compared with those of the current screening method of oximetry. For both the DFT and the DHWT, the most diagnostically accurate frequency range for HRV spectral power calculations is found to be 0.019-0.036 Hz (denoted by AB2). Using AB2, 15 min sections of non-REM sleep data in 40 subjects produce ROC areas, for the DFT, DHWT and oximetry, of 0.94, 0.97 and 0.67, respectively. In REM sleep, ROC areas are 0.78, 0.79 and 0.71, respectively. In non-REM sleep, spectral analysis of HRV appears to be a significantly better indicator of the SAHS than the current screening method of oximetry, and, in REM sleep, it is comparable with oximetry. The advantage of the DHWT over the DFT is that it produces a greater time resolution and is computationally more efficient. The DHWT does not require the precondition of stationarity or interpolation of raw HRV data.

Adult↗
PubMed1998

Long-term nasal intermittent positive pressure ventilation in patients with cystic fibrosis and hypercapnic respiratory failure (1991-1996).

In patients with cystic fibrosis (CF), nasal intermittent positive pressure ventilation (NIPPV) is currently used as a short-term bridge to transplantation but its precise role has yet to be determined. Patients were offered a therapeutic trial of NIPPV when candidates for lung transplantation, with respiratory failure unresponsive to medical treatment. Twelve patients, six male of mean age of 26 +/- 1.4 years, had a trial of NIPPV. At recruitment the mean percentage predicted forced expired volume in one second (FEV1) was 15.1% +/- 1.2%, arterial carbon dioxide (PaCO2) 8.7 +/- 0.6 kPa, arterial oxygen (PaO2) with variable FiO2 7.4 +/- 0.6 kPa and arterial bicarbonate (HCO3-) 40.1 +/- 1.6 mmol l-1. Ten cases tolerated NIPPV for 1-15 months, mean 5.1 +/- 1.4 months, with subjective improvement in headache and quality of sleep. At 3 months, there was significant improvement in forced vital capacity, PaCO2 and arterial HCO3- and there was a reduction in the number of hospital inpatient days (P < 0.05). Subsequently three cases had lung transplantation, four died on the active list and three are awaiting organs. Two patients failed to tolerate NIPPV owing to abdominal bloating and increasing hypercapnia. In conclusion, NIPPV, if tolerated, was a useful adjunct in the treatment of CF patients with hypercapnic respiratory failure awaiting transplantation. Further prospective studies are required to determine the optimum time to commence NIPPV and to clarify its precise role.

Adult↗
PubMed1998

A case of systemic pseudo-pseudoxanthoma elasticum with diverse symptomatology caused by long-term penicillamine use.

A 47 year old man presented with a two year history of increasing cervical dysphagia, dyspnoea, and cutaneous signs. He had been diagnosed 27 years previously with Wilson's disease and was treated with penicillamine (1.5 g daily). Systemic abnormality of elastic fibres was confirmed by light and electron microscopy following biopsy of skin, lung, oesophageal muscle, gum, pharyngeal tissue, and cervical connective tissue. Dysphagia was relieved by cricopharyngeal myotomy. Substitution of trientene dihydrochloride for penicillamine relieved cutaneous and systemic manifestations. This is possibly the first case demonstrating an association between prolonged penicillamine use and biopsy proved systemic pseudo-pseudoxanthoma elasticum. The presenting symptoms may have resulted from the abnormal numbers and properties of elastic fibres, and the changes were caused by penicillamine use, rather than by idiopathic, inherited pseudoxanthoma elasticum.

Chelating Agents↗
PubMed1997

Psychological morbidity and coping skills in patients with brittle and non-brittle asthma: a case-control study.

BACKGROUND: An association between psychological morbidity and asthma is well recognized and an increase in negative psychosocial factors in brittle asthma has been previously reported. Such factors, apart from affecting patient perceptions, may alter patients' self-management of their condition. METHODS: We have undertaken a case-control study on 29 well characterized brittle and non-brittle asthmatics in the West Midlands Region to assess their level of psychological morbidity, using the General Health Questionnaire (GHQ) and the living with asthma questionnaire, and their responses to changes in asthma symptoms, using the Asthma Symptom Checklist and a taped interview. RESULTS: Significant differences in GHQ (mean score brittle 19.5 vs non-brittle 7.2, P = 0.0002) and living with asthma (mean score brittle 1.30 vs non-brittle 1.00, P = 0.002) reinforced the presence of psychological factors in this group of patients with severe asthma. Interviews regarding responses to hypothetical asthma attacks showed that patients with brittle asthma delayed seeking medical attention more often than those with non-brittle asthma and instead preferred to self-administer beta-agonist medication. Sixteen (55.2%) of the 29 patients with brittle asthma would have delayed 7 days before seeking medical attention in a slow onset attack compared with 6/29 (20.7%) in the non-brittle group. In a fast onset attack 14 (48.3%) patients with brittle asthma would not have summoned help, despite finding it difficult to walk to the kitchen for a drink whereas in the non-brittle group 24 out of 29 (82.8%) would have summoned help. Levels of family support tended to be lower in patients with brittle asthma (mean family APGAR 7.3 vs 8.65 P = 0.09). CONCLUSIONS: Brittle asthma is associated with greater psychological morbidity and altered strategies for coping with deteriorating asthma symptoms. Attention should be paid to the presence of such factors in the management of patients with brittle asthma.

Adrenergic beta-Agonists↗
PubMed1996

Potential effects of correction of inaccuracies of the mini-Wright peak expiratory flow meter on the use of an asthma self-management plan.

BACKGROUND: Patient self-management plans for asthma use peak expiratory flow (PEF) meter readings for decisions on adjusting asthma treatment. PEF meters have been shown to be inaccurate and the effect of this inaccuracy on such treatment plans has been determined. METHODS: PEF measurements were made by 127 severe asthmatic patients at least twice a day for at least two weeks using a mini-Wright meter. The daily variation from "best" PEF and the within day PEF variability were calculated before and after correction for the meter's known inaccuracy. The effect of this data correction on the number of days when trigger points were reached for changing asthma therapy was then determined. RESULTS: Continuous PEF readings were available from 114 subjects with a median of 157.5 days of data per subject (range 15-489 days). Correction of the PEF data led to the number of days of satisfactory asthma control being reduced in 72% of subjects with just one subject showing an increase in satisfactory control. Data correction reduced the percentage of total days of satisfactory control from 46% to 36% of days, and increased the days requiring more inhaled steroids from 33% to 36%. The days on which a course of oral corticosteroids was required increased from 16% to 23%. CONCLUSIONS: The accuracy of PEF meters significantly influences the interpretation of currently used asthma self-management plans. Managing asthma with the corrected PEF data would have increased the amount of treatment received by these patients since the severity of the asthma was underestimated by the raw data.

Adolescent↗
PubMed1995

The performance of Mini Wright peak flow meters after prolonged use.

The accuracy of 84 new and 35 old Mini Wright peak flow meters were tested using a servo-controlled pump system. The 95% confidence limits for flow measurement across the range of the new meters was between +/- 151 min-1 at the lower end of the range and +/- 28 l min-1 at the top of the range. The readings for 22 (63%) of the old meters (age range 1-13 yr) were within these 95% confidence limits. For the remaining 13 old meters (age range 1-13 yr) whose readings were not within these limits, there were 11 meters with readings falling below and two meters with readings above these limits. Twelve of these old meters were washed and retested and there was no significant change in their readings. Twenty of the new meters were retested after 1 yr of continuous use and their readings were significantly higher with a median value of 5 l min-1 across the range, although only two of these 20 meters had readings outside the 95% confidence limits set from the 84 new meters. It is concluded that whilst Mini Wright meters aged up to 14 yr can give readings which are as good as new meters, some meters demonstrate significant changes in readings after only 1 yr and washing did not correct this change. It is recommended that clinicians prescribing peak expiratory flow (PEF) meters should be responsible for checking the patient's meter as well as their PEF readings at clinic visits.

Disinfection↗
PubMed1995

Validation of British Thoracic Society guidelines for the diagnosis of the sleep apnoea/hypopnoea syndrome: can polysomnography be avoided?

BACKGROUND: The British Thoracic Society report on the diagnosis and treatment of the sleep apnoea/hypopnoea syndrome (SAHS) suggests that, if the pulse oximetry baseline oxygen saturation is above 90%, then 15 4% oxygen desaturation/hour in bed will diagnose SAHS requiring treatment. The diagnostic outcome of applying these guidelines has been studied. METHODS: One hundred patients referred to a district general hospital sleep clinic were recruited. After initial clinical assessment, overnight pulse oximetry measurements were performed, followed by full polysomnography at the regional laboratory. RESULTS: Sixty nine patients underwent both pulse oximetry and polysomnography. All 10 patients with more than 15 4% desaturations/hour on pulse oximetry had SAHS confirmed on polysomnography (specificity = 100%). Twenty two patients with SAHS were misdiagnosed using pulse oximetry alone (sensitivity = 31%). These patients had low apnoea scores but high hypopnoea scores. CONCLUSIONS: The BTS pulse oximetry criteria are highly specific when positive (specificity = 100%), but may miss patients with the SAHS who have hypopnoeic episodes which cause arousal but not significant oxygen desaturation (sensitivity = 31%). It should be emphasised that pulse oximetry alone does not always give sufficient information to discriminate between those patients with or without SAHS. Patients with "negative" pulse oximetry and symptoms of SAHS should undergo polysomnography or multi-channel recording.

False Negative Reactions↗
PubMed1994

Rates of change in peak expiratory flow and in diurnal variation in peak flow in patients recovering from acute severe asthma.

1. The rates of change in mean peak expiratory flow and in diurnal variation in peak flow were compared in 14 patients recovering from acute severe asthma. 2. Peak expiratory flow was measured on hospital admission, and at 6-hourly intervals for the next 3 weeks. 3. Diurnal variation in peak flow was assessed by measuring the following: amplitude (the highest minus the lowest peak expiratory flow during any given 24 h period), amplitude % mean (the highest minus the lowest peak expiratory flow during any given 24 h period divided by the mean peak expiratory flow over that period) and residual amplitude (the maximum variation about the mean peak expiratory flow during any given 24 h period). 4. Plots of diurnal variation in peak flow and peak expiratory flow against time were constructed for each patient. To enable comparison of changes in peak expiratory flow and diurnal variation in peak flow the data were transformed. 5. The rate of change for mean peak expiratory flow and for the three measures of diurnal variation in peak flow was assessed by fitting an exponential function to each set of data, and calculating the slope of the exponential curve halfway through the period of observation (10.5 days). 6. Median (range) slope for peak expiratory flow was 0.055 (0-2.57). The comparable value for amplitude was -3.15 (-1.27 to -4.22) (absolute median values compared, P = 0.0029), for amplitude % mean was -1.87 (-0.18 to -5.95) (P = 0.012) and for residual amplitude was -1.43 (-0.62 to -3.09) (P = 0.033).(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1994

Does single dose salmeterol affect exercise capacity in asthmatic men?

The aim of this study was to investigate whether the long-acting beta-agonist salmeterol affects athletic performance in patients with asthma. The effect of 50 micrograms salmeterol on the cardiorespiratory responses to a progressive maximal cycle exercise test and on endurance capacity (defined as the exercise duration at 70% maximum oxygen uptake), was compared with 200 micrograms salbutamol and a matched placebo in eight asthmatic men. Both salmeterol and salbutamol improved pre- and postexercise forced expiratory volume in one second (FEV1) for maximal and endurance exercise. Following active treatment, patients exercised from a significantly high baseline FEV1, with both salmeterol (3.58(1.16)l) (mean (SD)) and salbutamol (3.55(1.24)l) compared with placebo (3.29(1.35)l). Similar improvements preceded endurance exercise. Cardiorespiratory, haemodynamic or subjective responses to the progressive maximum exercise tests were not different with salmeterol, salbutamol or placebo, nor did endurance capacity change with any treatment modality. Blood lactate levels, after 15 min exercise, were significantly higher with salbutamol (3.64 (1.83) mM), but not with salmeterol (3.03 (1.64) mM), compared with placebo (2.95 (1.69) mM). These results demonstrate the absence of significant cardiorespiratory or metabolic effects during exercise after a single dose of salmeterol, together with a lack-of ergogenic effect, as measured by maximal or endurance exercise performance, in patients with asthma.

Adult↗
PubMed1993

Endurance exercise capacity in adults with cystic fibrosis.

We have compared the maximal and endurance exercise capacities in 22 (15 male) adult cystic fibrosis (CF) patients with a resting oxygen saturation (SaO2) > or = 90%, with age and sex matched controls (CON). The maximum oxygen uptake (VO2max) and heart-rate were lower for the CF group whereas the maximum ventilation reached a higher percentage of predicted. Furthermore, for the CF group there was a relationship between the % predicted VO2max and measures of lung function, confirming a ventilatory limit to maximum exercise in patients with more severe disease and a near normal maximum exercise capacity in those with mild disease. Endurance capacity, defined as the duration of exercise at 80% of each individuals VO2max, was however similar for the two groups [CF: 22.21 (15.82) vs. CON: 24.94 (13.05) min]; despite the CF group exercising under less efficient ventilatory conditions. Endurance capacity was not related to the measurements of lung function. Of the seven CF patients desaturating at maximal exercise (SaO2 < 90%), five desaturated at a work load of 80% VO2max, whereas only one desaturated at 50% VO2max. This study confirms that with increasing severity of disease, maximal exercise capacity may be limited in adult CF patients, whereas endurance capacity (at the same relative work load) is unimpaired. Furthermore, CF patients who desaturate during a progressive maximal exercise test are likely to desaturate during constant work load exercise if the intensity is high but unlikely to do so if the intensity is low. The information from these exercise tests would be of value for prescribing individual training programmes and for evaluating the effects.

Adolescent↗
PubMed1992

The effect of ipratropium bromide on maximal exercise capacity in asthmatic and non-asthmatic men.

The effect of 0.5 mg nebulized ipratropium bromide (IB) on the cardio-respiratory responses to a progressive maximal cycle exercise test was compared with a matched placebo (P) in eight mild asthmatic and eight non-asthmatic men. The forced expiratory volume in l s (FEV1) in the asthmatic group was higher after ipratropium bromide both at rest [IB, mean 4.07 (SD 1.18) l versus P, 3.83 (1.29) l, P less than 0.05] and after exercise [IB, 3.64 (1.31) l versus P, 3.30 (1.40) l, P less than 0.02]. Since the percentage fall in the FEV1 after exercise was not significantly changed by ipratropium bromide [IB, -12 (11)% versus P, -16 (14)%], the improvement in the post-exercise FEV1 in the asthmatic group is attributable to the pre-exercise bronchodilatation. The resting and post-exercise FEV1 in the non-asthmatic group were also significantly higher after ipratropium bromide. However, neither group showed any differences in the cardio-respiratory, haemodynamic or subjective responses to the progressive maximum exercise test when ipratropium bromide was compared with placebo. These results demonstrate the absence of significant cardio-respiratory effects during exercise with this relatively high dose of ipratropium bromide, in patients with mild asthma and in non-asthmatic subjects. No ergogenic effect on maximal exercise performance was shown to question its use by asthmatic athletes engaged in high level competition.

Adult↗
PubMed1991

Cardio-respiratory responses to exercise following treatment of acute severe asthma.

Asthmatic patients are encouraged to adopt a normal and active life-style. However, following treatment of acute severe asthma, patients may ask for advice about taking exercise. Serial measurements of the cardio-respiratory responses to continuous work load exercise, were made in asthmatic patients convalescing following hospital treatment of an acute exacerbation. Eighteen asymptomatic patients, (seven male) aged 18-48 years, were studied. The first test was performed within 1 week of admission, when the mean (SD) peak expiratory flow rate (PEFR) was 88 (20)% predicted normal and the arterial oxygen tension (PaO2) was 13.1 (1.4) kPa. No significant differences in the mean cardio-respiratory responses, from the last minute of exercise, were found during the 4-week study. There were no significant differences in the four tests, between the resting PEFR, lowest post-exercise PEFR or % change in PEFR. Also, there were no significant differences in the pre-exercise, end of exercise and recovery (10 min after exercise) PaO2, between the four tests. However, taking the four tests as a whole, significant relationships were found between the recovery PaO2 and the lowest post-exercise PEFR, expressed in absolute terms (r = 0.515, P less than 0.001), and as a percentage of predicted normal (r = 0.533, P less than 0.001); and also between the recovery PaO2 and the % change in PEFR after exercise (r = 0.299, P less than 0.05). It is suggested that a formal exercise test should be performed in convalescent asthmatics wishing to participate in active sports. Patients with exercise-induced asthma may then be identified and treated appropriately.

Acute Disease↗
PubMed1991

The effect of sustained-release theophylline in nocturnal asthma.

Nocturnal symptoms are common and often disabling in asthmatic subjects. Furthermore, they often persist, in spite of appropriate dosages of inhaled beta 2-agonists and topical steroids. In such a clinical situation, theophylline preparations may have a therapeutic role. This double-blind, placebo-controlled, cross-over trial was designed to evaluate the effectiveness of a twice-daily Bioavail slow-release theophylline capsule in a group of out-patient asthmatics, with a history of nocturnal and/or early morning wheeze or chest tightness. Theophylline was initially prescribed and monitored in an 'open' phase to obtain the drug dosage required to achieve a serum level in the therapeutic range of 10-20 mg/l. In the ten patients who completed the study, serum theophylline levels were stable throughout. During active treatment there was an improvement in morning peak expiratory flow rate (PEFR), and a reduction in measurements of diurnal variation. In addition, the bronchodilator response to an inhaled beta 2-agonist was preserved. Bioavail theophylline has thus been shown to be an effective agent in the management of adults with nocturnal asthma.

Adult↗