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Biomedical subjects

G F Rafferty

Publications and source records attributed to G F Rafferty.

At least 19 recordsLinked to original sources
PubMed2006

Respiratory function of very prematurely born infants at follow up: influence of sex.

OBJECTIVE: To test the hypothesis that male compared with female prematurely born infants would have worse lung function at follow up. DESIGN: Prospective follow up study. SETTING: Tertiary neonatal intensive care units PATIENTS: Seventy six infants, mean (SD) gestational age 26.4 (1.5) weeks, from the United Kingdom oscillation study. INTERVENTIONS: Lung function measurements at a corrected age of 1 year. MAIN OUTCOME MEASURES: Airways resistance (Raw) and functional residual capacity (FRC(pleth)) measured by whole body plethysmography, specific conductance (sGaw) calculated from Raw and FRC(pleth), and FRC measured by a helium gas dilution technique (FRC(He)). RESULTS: The 42 male infants differed significantly from the 34 female infants in having a lower birth weight for gestation, requiring more days of ventilation, and a greater proportion being oxygen dependent at 36 weeks postmenstrual age and discharge. Furthermore, mean Raw and FRC(pleth) were significantly higher and mean sGaw significantly lower. After adjustment for birth and current size differences, the sex differences in FRC(pleth) and sGaw were 15% and 26% respectively and remained significant. CONCLUSION: Lung function at follow up of prematurely born infants is influenced by sex.

Airway Resistance↗
PubMed2005

Plethysmograph and interrupter resistance measurements in prematurely born young children.

BACKGROUND: Airways obstruction in premature infants is often assessed by plethysmography, which requires sedation. The interrupter (Rint) technique does not require sedation, but has rarely been examined in children under 2 years of age. OBJECTIVE: To compare Rint results with plethysmographic measurements of airway resistance (Raw) in prematurely born, young children. DESIGN: Prospective study. SETTING: Infant and Paediatric Lung Function Laboratories. PATIENTS: Thirty children with a median gestational age of 25-29 weeks and median postnatal age of 13 months. INTERVENTIONS AND MAIN OUTCOME MEASURES: The infants were sedated, airway resistance was measured by total body plethysmography (Raw), and Rint measurements were made using a MicroRint device. Further Raw and Rint measurements were made after salbutamol administration if the children remained asleep. RESULTS: Baseline measurements of Raw and Rint were obtained from 30 and 26 respectively of the children. Mean baseline Rint values were higher than mean baseline Raw results (3.45 v 2.84 kPa/l/s, p = 0.006). Limits of agreement for the mean difference between Rint and Raw were -1.52 to 2.74 kPa/l/s. Ten infants received salbutamol, after which the mean Rint result was 3.6 kPa/l/s and mean Raw was 3.1 kPa/l/s (limits of agreement -0.28 to 1.44 kPa/l/s). CONCLUSION: The poor agreement between Rint and Raw results suggests that Rint measurements cannot substitute for plethysmographic measurements in sedated prematurely born infants.

Airway Obstruction↗
PubMed2005

Dampened ventilatory response to added dead space in newborns of smoking mothers.

BACKGROUND: Term newborns can compensate fully for an imposed dead space (tube breathing) by increasing their minute ventilation. OBJECTIVE: To test the hypothesis that infants of smoking mothers would have an impaired response to tube breathing. DESIGN: Prospective study. SETTING: Perinatal service. PATIENTS: Fourteen infants of smoking and 24 infants of non-smoking mothers (median postnatal age 37 (11-85) hours and 26 (10-120) hours respectively) were studied. INTERVENTIONS: Breath by breath minute volume was measured at baseline and when a dead space of 4.4 ml/kg was incorporated into the breathing circuit. MAIN OUTCOME MEASURES: The maximum minute ventilation during tube breathing was determined and the time constant of the response calculated. RESULTS: The time constant of the infants of smoking mothers was longer than that of the infants of non-smoking mothers (median (range) 37.3 (22.2-70.2) v 26.2 (13.8-51.0) seconds, p = 0.016). Regression analysis showed that maternal smoking status was related to the time constant independently of birth weight, gestational or postnatal age, or sex (p = 0.018). CONCLUSIONS: Intrauterine exposure to smoking is associated with a dampened response to tube breathing.

Female↗
PubMed2004

Exhaled nitric oxide in chronically ventilated preterm infants.

Exhaled nitric oxide (eNO) levels were measured in eight ventilated infants, mean gestational age 25.8 (SD 1.7) weeks and postnatal age 55 (SD 39) days, before and after three days of dexamethasone treatment. The eNO levels fell from a mean of 6.5 (SD 3.4) to 4.2 (SD 2.6) parts per billion (p = 0.031) and the mean supplementary oxygen levels from 62% to 45% (p = 0.0078).

Anti-Inflammatory Agents↗
PubMed2004

Effect of salmeterol on respiratory muscle activity during exercise in poorly reversible COPD.

BACKGROUND: Some patients with irreversible chronic obstructive pulmonary disease (COPD) experience subjective benefit from long acting bronchodilators without change in forced expiratory volume in 1 second (FEV(1)). Dynamic hyperinflation is an important determinant of exercise induced dyspnoea in COPD. We hypothesised that long acting bronchodilators improve symptoms by reducing dynamic hyperinflation and work of breathing, as measured by respiratory muscle pressure-time products. METHODS: Sixteen patients with "irreversible" COPD (<10% improvement in FEV(1) following a bronchodilator challenge; mean FEV(1) 31.1% predicted) were recruited into a randomised, double blind, placebo controlled, crossover study of salmeterol (50 micro g twice a day). Treatment periods were of 2 weeks duration with a 2 week washout period. Primary outcome measures were end exercise isotime transdiaphragmatic pressure-time product and dynamic hyperinflation as measured by inspiratory capacity. RESULTS: Salmeterol significantly reduced the transdiaphragmatic pressure-time product (294.5 v 348.6 cm H(2)O/s/min; p = 0.03), dynamic hyperinflation (0.22 v 0.33 litres; p = 0.002), and Borg scores during endurance treadmill walk (3.78 v 4.62; p = 0.02). There was no significant change in exercise endurance time. Improvements in isotime Borg score were significantly correlated to changes in tidal volume/oesophageal pressure swings, end expiratory lung volume, and inspiratory capacity, but not pressure-time products. CONCLUSIONS: Despite apparent "non-reversibility" in spirometric parameters, long acting bronchodilators can cause both symptomatic and physiological improvement during exercise in severe COPD.

Aged↗
PubMed2004

Pulmonary function abnormalities in children with sickle cell disease.

BACKGROUND: Adults with sickle cell disease (SCD) have restrictive lung function abnormalities which are thought to result from repeated lung damage caused by episodes of pulmonary vaso-occlusion; such episodes start in childhood. A study was therefore undertaken to determine whether children with SCD have restrictive lung function abnormalities and whether the severity of such abnormalities increases with age. METHODS: Sixty four children with SCD aged 5-16 years and 64 ethnic matched controls were recruited. Weight and sitting and standing height were measured, and lung function was assessed by measurement of lung volumes and forced expiratory volume in 1 second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF) before and after bronchodilator. RESULTS: Compared with the control subjects, the children with SCD had lower mean (SD) sitting height (69 (6.3) cm v 73 (7.7) cm; p=0.004), sitting:standing height ratio (0.50 (0.02) v 0.51 (0.01); p<0.0001), weight (33 (10.9) kg v 41 (14.9) kg; p=0.001), functional residual capacity measured by a helium gas dilution technique (1.2 (0.3) l v 1.3 (0.4) l; p=0.04), FEV1 (1.5 (0.5) l v 1.9 (0.7) l; p=0.0008), FVC (1.7 (0.6) l v 2.1 (0.8) l; p=0.001), and PEF (3.9 (1.3) l/s v 4.8 (1.5) l/s; p=0.0004). The effect of age on lung function differed significantly between the children with SCD and the controls for total lung capacity and vital capacity measured by plethysmography and functional residual capacity measured by helium gas dilution. CONCLUSION: Lung function differs significantly in children with SCD compared with ethnic matched controls of a similar age. Our results suggest that restrictive abnormalities may become more prominent with increasing age.

Adolescent↗
PubMed2003

Effect of posture on respiratory function and drive in preterm infants prior to discharge.

Our objective was to determine the effect of posture on respiratory function and drive in prematurely born infants immediately prior to discharge. Twenty infants (6 oxygen-dependent), median gestational age 29 weeks (range, 25-32), were studied at a median postconceptional age (PCA) of 36 weeks (range, 33-39). On 2 successive days, infants were studied both supine and prone; each posture was maintained for 3 hr. The order on each day in which postures were studied was randomized between infants. At the end of each 3-hr period, tidal volume (Vt), inspiratory (Ti) and expiratory (Te) time, respiratory rate, and minute ventilation were measured. In addition, respiratory drive was assessed by measuring the pressure generated in the first 100 msec of an imposed airway occlusion (P(0.1)), and respiratory muscle strength was assessed by recording the maximum inspiratory pressure (Pimax) generated against an occlusion which was maintained for at least five breaths. Overall, tidal volume was higher (P < 0.05), but respiratory rate (P < 0.05), P(0.1) (P < 0.05), and Pimax (P < 0.05) were lower in the prone compared to the supine position. There were no significant differences in Ti or Te between the two postures. In oxygen-dependent infants only, minute volume was higher in the prone position (P < 0.05). In conclusion, posture-related differences in respiratory function are present in prematurely born infants studied prior to neonatal unit discharge.

Drive↗
PubMed2003

Non-volitional assessment of skeletal muscle strength in patients with chronic obstructive pulmonary disease.

BACKGROUND: Although quadriceps weakness is well recognised in chronic obstructive pulmonary disease (COPD), the aetiology remains unknown. In disabled patients the quadriceps is a particularly underused muscle and may not reflect skeletal muscle function as a whole. Loss of muscle function is likely to be equally distributed if the underlying pathology is a systemic abnormality. Conversely, if deconditioning and disuse are the principal aetiological factors, weakness would be most marked in the lower limb muscles. METHODS: The non-volitional technique of supramaximal magnetic stimulation was used to assess twitch tensions of the adductor pollicis, quadriceps, and diaphragm muscles (TwAP, TwQ, and TwPdi) in 22 stable non-weight losing COPD patients and 18 elderly controls. RESULTS: Mean (SD) TwQ tension was reduced in the COPD patients (7.1 (2.2) kg v 10.0 (2.7) kg; 95% confidence intervals (CI) -4.4 to -1.4; p<0.001). Neither TwAP nor TwPdi (when corrected for lung volume) differed significantly between patients and controls (mean (SD) TwAP 6.52 (1.90) N for COPD patients and 6.80 (1.99) N for controls (95% CI -1.5 to 0.97, p=0.65; TwPdi 23.0 (5.6) cm H(2)O for COPD patients and 23.5 (5.2) cm H(2)O for controls (95% CI -4.5 to 3.5, p=0.81). CONCLUSIONS: The strength of the adductor pollicis muscle (and the diaphragm) is normal in patients with stable COPD whereas quadriceps strength is substantially reduced. Disuse may be the principal factor in the development of skeletal muscle weakness in COPD, but a systemic process preferentially affecting the proximal muscles cannot be excluded.

Aged↗
PubMed2002

Reproducibility of twitch and sniff transdiaphragmatic pressures.

Twitch transdiaphragmatic pressure (Tw Pdi) measured with magnetic stimulation of the phrenic nerve is used to follow up patients and to assess the effect of clinical treatments on diaphragm function. However the reproducibility of Tw Pdi on different occasions has been little studied. We investigated 32 normal subjects, measuring Tw Pdi elicited by bilateral magnetic stimulation of the phrenic nerves on two to 14 occasions. Sniff transdiaphragmatic pressure (sniff Pdi) was also measured. The mean value of Tw Pdi and sniff Pdi were 28+/-5 and 134+/-24 cm H(2)O, respectively. The within subjects coefficient of variation was 11% for both Tw Pdi and sniff Pdi. We conclude that there is a variability of Tw Pdi and the variability of Tw Pdi is the same as that of sniff Pdi.

Diaphragm↗
PubMed2002

Airway resistance estimation by best fit analysis in very premature infants.

Plethysmographic measurement of airway resistance (R(aw)) has been determined by single-point analysis, usually at 50% of maximum inspiratory flow (MIF). Computer-assisted (best fit) analysis, however, allows R(aw) to be calculated by applying a regression line to any portion of the plethysmograph pressure-flow loop. We determined whether the results of best fit analysis using a computer program, sampling at 200 Hz, were influenced by the portion of the inspiratory loop analysed and if best fit or single-point analysis gave more reproducible results. Twenty infants of median gestational age 26 (range 24-28) weeks, were studied at a median age of 12 (12-14) months corrected for prematurity. R(aw) was calculated by best fit analysis between 0 and 33% MIF, 0 and 50% MIF and 0 and 67% MIF and single-point analysis at 50% of MIF. Similar mean R(aw) values were obtained by best fit analysis between 0 and 33% MIF (2.79 kPa/(l/s)) and 0 and 50% MIF (3.01 kPa/(l/s)) and single-point analysis at 50% MIF (2.86 kPa/(l/s)), but best fit analysis between 0 and 67% gave higher results (3.60 kPa/(l/s)), p < 0.0001. Within the linear portion of the inspiratory loop, the mean intrasubject coefficient of variation was lowest for best fit analysis between 0 and 50% MIF. Best fit computerized analysis between 0 and 50% MIF is recommended as the analysis of choice.

Airway Resistance↗
PubMed2002

The importance of using ethnically appropriate reference ranges for growth assessment in sickle cell disease.

Height and weight were measured and body mass index (BMI) calculated in 56 sickle cell disease (SCD), 57 Caucasian (CC), and 63 African/Caribbean (AC) 3-9 year old children. The SCD children were taller, but had similar weight and BMI to the CC controls. The SCD group had lower weight and BMI than the AC controls. The AC controls were of greater height, weight, and BMI than CC controls. These data highlight the importance of using ethnically appropriate reference ranges.

Aging↗
PubMed2002

Prediction of extubation failure in preterm infants.

OBJECTIVE: To identify whether the results of assessment of respiratory muscle strength or respiratory load were better predictors of extubation failure in preterm infants than readily available clinical data. PATIENTS: Thirty six infants, median gestational age 31 (range 25-36) weeks and postnatal age 3 (1-14) days; 13 were < 30 weeks of gestational age. METHODS: Respiratory muscle strength was assessed by measurement of maximum inspiratory pressure generated during airway occlusion, and inspiratory load was assessed by measurement of compliance of the respiratory system. RESULTS: Overall, seven infants failed extubation-that is, they required reintubation within 48 hours. These infants were older (p < 0.01), had a lower gestational age (p < 0.01), and generated lower maximum inspiratory pressure (p < 0.05) than the rest of the cohort. Similar results were found in the infants < 30 weeks of gestational age. Overall and in those < 30 weeks of gestational age, gestational age and postnatal age had the largest areas under the receiver operator characteristic curves. CONCLUSION: In very premature infants, low gestational age and older postnatal age are better predictors of extubation failure than assessment of respiratory muscle strength or respiratory load.

Age Factors↗
PubMed2002

Effect of posture on oxygenation and respiratory muscle strength in convalescent infants.

OBJECTIVE: To determine if differences in respiratory muscle strength could explain any posture related effects on oxygenation in convalescent neonates. METHODS: Infants were examined in three postures: supine, supine with head up tilt of 45 degrees, and prone. A subsequent study was performed to determine the influence of head position in the supine posture. In each posture/head position, oxygen saturation (SaO2) was determined and respiratory muscle strength assessed by measurement of the maximum inspiratory pressure (PIMAX). PATIENTS: Twenty infants, median gestational age 34.5 weeks (range 25-43), and 10 infants, median gestational age 33 weeks (range 30-36), were entered into the first and second study respectively. RESULTS: Oxygenation was higher in the prone and supine with 45 degrees head up tilt postures than in the supine posture (p<0.001), whereas PIMAX was higher in the supine and supine with head up tilt of 45 degrees postures than in the prone posture (p<0.001). Head position did not influence the effect of posture on PIMAX or oxygenation. CONCLUSION: Superior oxygenation in the prone posture in convalescent infants was not explained by greater respiratory muscle strength, as this was superior in the supine posture.

Female↗
PubMed2002

Postprandial effects on twitch transdiaphragmatic pressure.

Twitch transdiaphragmatic pressure (Pdi,tw), measured following magnetic stimulation of the phrenic nerves, is used to assess diaphragm strength, contractility and fatigue. Although the effects of posture, lung volume and potentiation on Pdi,tw are well described, it is not known whether the degree of gastric filling affects the measurement. Pdi,tw was recorded in seven healthy volunteers on two occasions with antero-lateral magnetic stimulation of the phrenic nerves. On the first occasion, the subjects had fasted for at least 8 h, whilst on the second occasion, measurements were made after each subject had eaten a substantial meal sufficient to produce a feeling of satiation. Mean postprandial unpotentiated and potentiated Pdi,tw were significantly greater than corresponding fasting Pdi,tw in all seven volunteers (29.8 versus 25.7 cmH2O and 38.9 versus 34.4 cmH2O, respectively). This was due to a significantly increased gastric pressure component (1.10 versus 0.84 and 0.94 versus 0.78, respectively), and reduced abdominal compliance (36 versus 62 mL x cmH2O(-1)). Twitch oesophageal pressure was preserved (15.0 versus 15.4 cmH2O). The postprandial state increases twitch transdiaphragmatic pressure, and this should be taken into account when using twitch transdiaphragmatic pressure to follow-up patients or to assess the effects of interventions on diaphragm contractility.

Abdomen↗
PubMed2001

Effect of maturity on maximal transdiaphragmatic pressure in infants during crying.

The aim of this study was to determine the effect of maturation on diaphragmatic function. In addition, we investigated whether noninvasive assessment yielded similar results to invasive measurement. Twenty-eight infants, median gestational age (GA) 35.5 wk (range, 25 to 42 wk) and postconceptional age (PCA), 37.6 wk (range, 32 to 44 wk), were examined. Diaphragmatic function was assessed by measuring the maximal transdiaphragmatic pressure during crying (cPdi) using balloon catheters in the midesophagus (Pes) and the stomach (Pgas). In 14 of the infants, a noninvasive measurement of inspiratory muscle strength, maximal inspiratory pressure (PImax), was also made. cPdi and PImax were recorded during a crying effort with the airway occluded at end-expiration. The median cPdi and Pes during crying (cPes), but not Pgas during crying (cPgas), were significantly lower in those studied at a PCA of less than term compared with those studied at an older age (p < 0.05). cPdi and cPes, but not cPgas, correlated significantly with PCA (r = 0.44, p < 0.02; r = 0.43, p < 0.03; respectively) and gestational age (r = 0.46, p < 0.02 and r = 0.56, p < 0.01; respectively). In the 14 infants, the median PImax was lower, but it correlated significantly with cPdi (r = 0.79, p < 0.01). We conclude maturation does affect diaphragm function, and PImax may provide a noninvasive index of diaphragm strength.

Crying↗
PubMed2001

Whistle mouth pressure as test of expiratory muscle strength.

Expiratory muscle strength is a determinant of cough function. Mouth pressures during a maximal static expiratory effort (PE,max) are dependent on patient motivation and technique and low values are therefore difficult to interpret. This study hypothesized that a short, sharp and maximal expiration through a narrow aperture, a "whistle", might provide a complementary test of expiratory muscle strength. To obtain a maximal whistle, subjects (27 healthy volunteers and 10 patients with amyotrophic lateral sclerosis) were asked to perform a short, sharp blow as hard as possible, from total lung capacity, through a reversed paediatric inhaler whistle, connected to a flange-type mouthpiece. In both healthy subjects and patients, whistle mouth pressure (Pmo,W) was closely related to the pressure measured in the oesophagus and stomach during the same manoeuvre. In healthy subjects, Pmo,W and PE,max correlated with wide limits of agreement, although Pmo,W values were significantly higher than PE,max (131+/-31 cmH2O versus 101+/-27 cmH2O, p<0.0001). In patients, it was also found that Pmo,w and PE,max values were strongly related (r=0.937, p<0.0001). In healthy subjects, the intraclass correlation coefficient and the variation coefficient for Pmo,W repeated measurements were respectively 0.88 and 7.0%. However Pmo,W and PE,max were always smaller than the gastric pressure generated by a maximal cough. It is concluded that mouth whistle pressure, a noninvasive, reproducible and simple test, provides a reliable measure of expiratory muscle strength in healthy subjects that is acceptable to patients and can be used in a complementary fashion to maximal static expiratory effort.

Adult↗
PubMed2000

Sniff nasal inspiratory pressure in children.

Maximal static inspiratory pressure (P(IMAX)) generated at the mouth is one of the tests of inspiratory muscle strength in children. In adults, inspiratory muscle strength has also been assessed using sniff nasal inspiratory pressure (SNIP). This test is easier to perform than P(IMAX) and might therefore be applicable to children. To test this hypothesis, we measured P(IMAX) and SNIP in 116 children aged 4 to 11 years (54 girls, 62 boys). P(IMAX) was measured using a tube mouthpiece and SNIP using a tightly fitting plug in one nostril, while a sniff was performed through the other nostril. Both tests were performed from functional residual capacity (FRC). Pressure was measured with a differential pressure transducer and displayed in real time on a computer screen. Weight, standing height, sitting height, gender, and age were recorded. There was a significant difference (P < 0.01) in group mean (SD) data between SNIP (81.3 (27.4) cmH(2)O) and P(IMAX) (67.9 (28.1) cmH(2)O). Bland/Altman analysis demonstrated a mean difference of -13.5 cmH(2)O (SD 21.4) between the techniques. Regression analysis indicated highly significant relations (P < 0.01) between SNIP and P(IMAX), and between weight, standing and sitting height, and age for SNIP, and between weight, standing height, and age for P(IMAX). SNIP and P(IMAX) were greater in boys than girls (83.2 vs. 79.2 cmH(2)O SNIP; 72.9 vs. 62.0 cmH(2)O P(IMAX)), but this difference was only significant for P(IMAX) (P < 0.05). SNIP was significantly greater than P(IMAX) (P < 0.01) in both boys and girls. These data suggest that SNIP provides a simple, noninvasive additional test to P(IMAX) for assessing inspiratory muscle strength in children.

Child↗