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Biomedical subjects

J Stocks

Publications and source records attributed to J Stocks.

At least 91 records · Page 5Linked to original sources
PubMed1995

A critical assessment of uncalibrated respiratory inductance plethysmography (Respitrace) for the measurement of tidal breathing parameters in newborns and infants.

We have compared results obtained with an uncalibrated respiratory inductance plethysmograph (RIP) with those of a face mask and pneumotachograph (PNT) for the computerized measurement of the time to reach peak tidal expiratory flow as a ratio of total expiratory time (tPTEF:tE). Simultaneous measurements were made in 32 healthy neonates aged 0-3 weeks, 35 healthy infants aged 5-82 weeks, and 28 infants aged 15-94 weeks with physician diagnosed recurrent wheeze. The group mean (+/- SD) values of tPTEF:TE determined using a PNT were 0.455 (+/- 0.129), 0.263 (+/- 0.077), and 0.232 (+/- 0.089) for the neonates, healthy infants and infants with recurrent wheeze respectively. RIP gave mean (+/- SD) values that were 0.055 (+/- 0.044) and 0.025 (+/- 0.104) lower than the PNT in healthy neonates and infants with recurrent wheeze respectively; RIP values were 0.002 (+/- 0.073) higher in the healthy infants over 4 weeks of age than measurements by PNT. Although the difference between the two measurements was not related to the thoracoabdominal phase angle, as measured from Lissajous figures, examination of the RIP ribcage and abdominal signals revealed that many healthy subjects, while appearing clinically in phase, had ribcage and abdominal signals that differed markedly from each other in terms of convexity/concavity during early expiration. This may explain the lack of agreement between the two methods. We conclude that uncalibrated RIP should be used with caution for the determination of tPTEF:tE, even in subjects whose ribcage and abdomen appear to move synchronously. The measurement of tPTEF:tE did not differentiate between the healthy infants and infants with recurrent wheezing.

Data Interpretation, Statistical↗
PubMed1995

Effect of neck rotation on the timing and pattern of infant tidal breathing.

While neck flexion and extension are known to influence the patency of the upper airway, far less information is available regarding the effects of neck rotation. The effect of neck rotation on respiratory rate (RR), expiratory time (tE), and phase angle (phi) was assessed in 17 healthy infants aged between 1 and 4 months. An inclinometer was used to measure neck rotation and uncalibrated Respiratory inductive Plethysmography to measure the dependent variables while the infants were in natural, quiet sleep. Baseline measurements were made with the head positioned centrally (0 degree rotation); further measurement positions included 30 degrees, 60 degrees, 90 degrees rotation, and repeat measurement at 0 degree (0r degree) in randomized order. Mean RR, tE, and phi were determined for each infant in each position. Using the paired t-test, RR at 0 degree rotation was significantly higher than that at 0r degree rotation (mean difference, 5 bpm; 95% CI, 2.1, 8.1; P = 0.0023); mean tE at 0 degree rotation was significantly shorter than at 0r degree rotation (mean difference, -0.18s; 95% CI, -0.27, -0.07; P = 0.002); whereas phi remained similar (mean difference, 10 degrees; 95% CI, -2.2, 22.3; P = 0.10. These changes probably reflect the slowing of metabolism that occurs after the onset of quiet sleep, and they emphasize the importance of randomization. Measurements at 0r degree were randomized and hence were most likely to reflect the true basal condition of the infant with the head in a neutral position. Consequently, these data, rather than those collected at 0 degree at the onset of quiet sleep, were used for comparisons with all subsequent positional changes. When comparing the positions whose order was randomized, neck rotation did not significantly affect RR (P = 0.445), tE (P = 0.272), or phi (P = 0.169). However, two infants demonstrated marked changes in respiratory pattern with decreases in RR and increases in tE at 90 degrees rotation, suggesting that some infants may be susceptible to obstruction in this position.

Humans↗
PubMed1995

Oxygen saturation in children in the postoperative period.

Some adult patients have periods of significant oxygen desaturation after surgery but, other than for immediately after surgery in the recovery room, few data are available in children. We monitored overnight paired preoperative and postoperative oxygen saturations in 19 children, and overnight postoperative saturations in 50 additional children to determine whether children have periods of desaturation in the postoperative period. The children underwent surgery usually associated with moderate to severe postoperative pain, and were treated with epidural, intravenous, or intramuscular opioids. In the group of 19 children mean (SD) preoperative oxygen saturation was 96.6% +/- 1.3%, and the mean postoperative saturation was 95.7% +/- 1.2%. The average change was 0.88% +/- 1.52%. The 95% confidence interval of the paired difference was 0.13% to 1.6%. There was no significant difference in the percent of monitored time that the patients spent with an oxygen saturation less than 95%, 90%, 85%, or 80%. In the 50 children monitored only in the postoperative period, mean (SD) saturation was 97.8% +/- 1.9%. The data show that, in contrast to some reports in adults, this group of children did not have multiple episodes of clinically significant oxygen desaturation in the postoperative period.

Adolescent↗
PubMed1995

Comparison of single-breath and plethysmographic measurements of resistance in infancy.

Single-breath technique (SBT) measurements of total respiratory resistance (Rrs) were compared with plethysmographic measurements of airway resistance (Raw) in healthy infants < or = 13 wk of age (Group 1; n = 49) and > 13 wk of age (Group 2; n = 37) and in infants > 13 wk of age with prior wheeze (Group 3; n = 49). A significantly higher percentage of Rrs (19%) than of Raw (2%) measurements were technically unsatisfactory, alinearity of the flow-volume curve accounting for 54% of Rrs failures. Although both Rrs and Raw were significantly higher in Group 3 infants, between-subject variability was wide in all groups. Rrs was significantly higher than initial expiratory (IE) Raw in all groups. Mean difference Rrs-IE Raw (95% CI) values were 1.98 (1.51, 2.48), 1.29 (0.96, 1.62), and 1.97 (1.56, 2.38) kPa.L-1.s for Groups 1, 2, and 3, respectively. Significant but smaller differences were seen for end-expiratory (EE) Raw in Groups 1 and 2 but not in Group 3. Mean difference Rrs-EE Raw (95% CI) values were 0.68 (0.11, 1.26), 0.55 (0.19, 0.92), and 0.31 (-0.06, 0.69) kPa.L-1.s for Groups 1, 2, and 3, respectively. Despite wide between-subject variability in Rrs and a relatively high failure rate, the SBT is simple to use, and it may be applicable to epidemiologic studies. However, clinical applications in individual infants may be limited by failure to detect the dynamic changes in resistance throughout the breath evident from plethysmographic studies.

Airway Resistance↗
PubMed1994

The relationship between tPTEF:tE and specific airway conductance in infancy.

This study examines the association between the time taken to achieve peak tidal expiratory flow as a proportion of total expiratory time (tPTEF:tE) and specific airways conductance (SGaw) in healthy infants and those with prior physician diagnosed, associated, lower respiratory illness with wheezing (prior LRI) during the first year of life. We compared tPTEF:tE and SGaw, the latter estimated during both initial inspiration (ll) and end-expiration (EE), in 168 infants (94 males), measured on 220 occasions. Mean (range) tPTEF:tE was 0.321 (0.150-0.522) in 73 healthy infants aged less than 3 months (mean, 7.8 weeks), in whom mean (range) EE SGaw and plethysmographic thoracic gas volume at functional residual capacity (FRCpleth) were 2.47 s-1 kPa-1 (0.6-5.8) and 141 mL (87-204), respectively. Both tPTEF:tE and EE SGaw were significantly lower in older infants with prior LRI (n = 79; mean age, 50.0 weeks) compared to a similarly aged group of healthy infants (n = 68; mean age, 48.5 weeks), the mean difference [95% confidence intervals (CI)] being -0.039 (-0.013, -0.064) and -0.48 s-1 kPa-1 (-0.24, -0.72), respectively. A significant but weak association between tPTEF:tE and EE SGaw was found among infants above 3 months of age, irrespective of prior wheezing status. However, this relationship was not significant in healthy younger infants, in whom a significant but weak association with FRCpleth was found. Further work is needed to elucidate the factors influencing tidal expiratory flow patterns in infancy.

Age Factors↗
PubMed1994

Hering-Breuer reflex and respiratory system compliance in the first year of life: a longitudinal study.

The airway occlusion technique for measuring passive respiratory mechanics in infants relies on an ability to evoke the Hering-Breuer lung inflation reflex (HBR). However, there is conflicting evidence regarding the persistence of the HBR beyond the early newborn period. This study was designed to assess maturational changes in HBR activity and passive total respiratory system compliance (Crs) in healthy infants during the 1st yr of life. The strength of the HBR was assessed from the relative change in expiratory time (TE) after brief end-inspiratory airway occlusions compared with resting TE during spontaneous breathing. Crs was measured using the multiple-occlusion technique. Paired measurements of HBR activity and Crs were obtained during sedated sleep in 30 infants at 4-8 wk and at 1 yr of age. Significant HBR activity during tidal breathing persisted throughout the 1st yr of life, with TE increasing during occlusion by at least 26% in every infant. However, the relative strength of the reflex response decreased from a mean of 88.3% (range, 34-160%) at approximately 6 wk to 50.3% (range, 26-125%) by 1 yr of age (P < 0.001). All infants showed an increase in Crs with age, with mean Crs increasing from 60.1 +/- 8.9 (SD) to 149.0 +/- 20.6 ml/kPa between 6 wk and 1 yr. However, there was no apparent relationship between the magnitude of decline in HBR response and the age-related changes in Crs.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1994

DNA variants at the LPL gene locus associate with angiographically defined severity of atherosclerosis and serum lipoprotein levels in a Welsh population.

Coronary artery disease (CAD) patients (n = 235), comprising minimal (CAD-, n = 124) and severe (CAD+, n = 111) CAD, were recruited on the basis of their angiographic scores. Male control subjects (n = 123) were selected randomly from the Caerphilly Heart Study cohort. Subjects were genotyped for the Ser447-Ter mutation and HindIII/Pvu II restriction fragment length polymorphisms of the lipoprotein lipase gene and investigated for associations with severity and development of CAD and lipid and lipoprotein levels. The Ser447-Ter mutation showed no significant associations with CAD or dyslipidemia but was related to favorable lipid and lipoprotein profiles. The H2H2 genotype (P < .05) and H2 allele (P = .05) were significantly more frequent in CAD+ versus CAD- and control subjects versus CAD-. H2H2 subjects, among the entire male cohort, had significantly higher levels of apolipoprotein B (P = .0002), total cholesterol (P < .004), and triglycerides (P < .04) than alternative genotypes. P2P2 associated with significantly lower high-density lipoprotein cholesterol levels (P < .01). The H2 allele had most significant associations with raised apolipoprotein B levels compared with other biochemical parameters. Our data suggest that the H2 allele may be a linkage marker for an etiologic mutation for dyslipidemia and the severity and development of atherosclerosis; this is not the Ser447-Ter mutation.

Alleles↗
PubMed1994

Analysis of tidal breathing parameters in infancy: how variable is TPTEF:TE?

During recent years there has been increasing interest in the measurement of tidal breathing parameters, such as the time to reach peak tidal expiratory flow as a proportion of total expiratory time (TPTEF:TE), and their application to population-based studies of the determinants of early respiratory morbidity. However, little is known about factors influencing the within and between-subject variability of these parameters. This study examines the influence of sedation on TPTEF:TE, estimates the optimal number of breaths and breath epochs required to measure TPTEF:TE, and assesses short-term repeatability of this parameter during the first year of life, taking account of age-related differences. Measurements were made in 266 healthy infants and young children (1 d to 19 mo old). Mean (SD) TPTEF:TE fell from 0.49 (0.11) in the first 2 wk of life to 0.34 (0.09) by 5 to 8 wk, remaining similar thereafter. Sedation with triclofos sodium (75 mg/kg) had no significant effect on TPTEF:TE, which was 0.33 (0.10) in 23 unsedated 6-wk-old infants and 0.32 (0.08) in 49 sedated infants of similar age and weight (95% CI for the difference: -0.05, 0.04). At least 10 breaths in each of two separate epochs from each infant were required to provide a representative estimate of TPTEF:TE. The mean (SD) difference between repeat measurements made 5 to 108 min apart was 0.02 (0.08) in 34 infants younger than 6 wk of age (95% limits of agreement: -0.15, 0.18) and -0.01 (0.04) (95% limits of agreement -0.09, 0.08) in 30 infants 6 wk and older.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1994

A comparison of respiratory function in Afro-Caribbean and Caucasian infants.

Race is recognized as an important determinant of lung function in children and adults, but limited data exist for infants. Accurate interpretation of lung function tests during the neonatal period may depend on appropriate values for predicting normality. The aim of this study was to compare tidal breathing parameters, Hering-Breuer reflex (HBR) activity, and total respiratory compliance (Crs) in healthy newborn caucasian (white) and Afro-Caribbean (black) infants, to determine whether separate reference values were required for these two ethnic groups. Respiratory function was measured in 33 healthy black infants, 18 of whom were premature, and 33 healthy white infants matched for sex, gestational age, weight, postnatal age, and maternal smoking during pregnancy. There were no significant paired differences between black and white infants with respect to minute ventilation, respiratory frequency, the ratio of time to reach peak expiratory flow to total expiratory time, or HBR activity. Values of Crs were similar in black and white full-term infants (37.5 (SD 9.0) versus 35.0 (6.3) ml.kPa-1, respectively) suggesting that, in the immediate newborn period, separate reference values are not necessary for these parameters. However, Crs was somewhat lower in black than white preterm infants (26.0(5.2) versus 29.5(7.2) ml.kPa-1, this difference reaching statistical significance if results were expressed in relation to body weight (95% confidence interval of within-pair differences -4.0 to -0.02 ml.kPa-1 x kg-1; p < 0.05). We conclude that no separate reference values for tidal breathing, Hering-Breuer reflex activity or total respiratory compliance are required for white and black babies in the immediate newborn period.(ABSTRACT TRUNCATED AT 250 WORDS)

Black People↗
PubMed1994

Effect of continuous negative extrathoracic pressure on respiratory mechanics and timing in infants recovering from neonatal respiratory distress syndrome.

Changes in respiratory mechanics and timing produced by continuous negative extrathoracic pressure (CNEP) of -0.6 kPa were assessed in 18 infants recovering from neonatal respiratory distress syndrome. The median gestational age was 28 wk (range 24-36 wk). All infants were recruited before discharge from neonatal intensive care and were measured at a median postnatal age of 58 d (range 10-127 d) and a median weight of 2.67 kg (range 1.99-3.77 kg). All had been treated for respiratory distress syndrome; 11 were diagnosed as having chronic lung disease. At the time of the study, all infants were stable breathing room air. There was a significant decrease of the respiratory rate in all but one infant from 63.6 +/- 10.0 to 49.3 +/- 9.1 breaths per min (mean +/- SD) during CNEP. This was predominantly due to a marked prolongation of the expiratory time. Passive respiratory mechanics were assessed using airway occlusion techniques. Whereas respiratory system compliance (Crs) did not change in the infants with a normal baseline measurement, there was a significant improvement of Crs in the 11 infants with low Crs values in atmosphere: In the latter, all of whom were very-low-birth-weight infants, Crs assessed by the multiple occlusion technique (mean +/- SD) corrected for body weight increased from 7.9 +/- 1.5 to 9.4 +/- 1.9 mL.kPa-1.kg-1 in CNEP (p = 0.012). There was no consistent change in respiratory system resistance in this population of 18 infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1993

Variability of plasma apolipoprotein (apo) A-II levels associated with an apo A-II gene polymorphism in monozygotic twin pairs.

A dimorphic MspI RFLP (alleles M1 and M2) in an Alu unit 528 base pairs downstream from the apolipoprotein A-II gene on chromosome 1 was investigated for associations with dyslipoproteinaemia or coronary atherosclerosis. No significant differences were observed between the allele frequencies in healthy random controls (M2 = 0.850, n = 70) and patients with primary hypertriglyceridaemia (M2 = 0.846, n = 52) or severe coronary atherosclerosis (M2 = 0.819, n = 47). The apolipoprotein A-II gene may also contribute to the regulation of plasma levels or composition of HDL in response to environmental changes. To study the effect upon apolipoprotein A-II variability, 42 monozygotic twin pairs were genotyped for the MspI RFLP. Pairs with the genotype M2M2 (n = 28) had significantly smaller within-pair differences in plasma apolipoprotein A-II levels (2.2 vs 5.8 mg/dl, P < 0.02; Mann-Whitney) than those with other genotypes (n = 14). The M2 allele may be in linkage disequilibrium with a functional mutation that restricts the variability of plasma apolipoprotein A-II in response to environmental conditions. This provides a new example of a 'variability' gene, one of an important group of loci which may alter responses to hypolipidaemic therapy and cardiovascular risk.

Adult↗
PubMed1993

Assessment of passive respiratory compliance in healthy preterm infants: a critical evaluation.

The airway occlusion techniques for assessing passive respiratory mechanics have become well established methods in fullterm neonates and older infants. The single breath technique (SBT) is frequently used for assessing lung function in intubated infants on neonatal intensive care units. However, less is known about the reliability of these quick and noninvasive techniques in healthy preterm infants. The aim of this study was to evaluate these methods in healthy unintubated preterm infants to facilitate both establishment of reference values and more meaningful interpretation of lung function assessments in the neonatal unit. Forty-seven studies were attempted in 31 healthy preterm infants (gestational age 29-36 weeks; body weight 1.88 +/- 0.28 kg; mean +/- SD) during the first 2 weeks of life, using both the multiple occlusion technique (MOT) and the SBT. Whereas technically acceptable respiratory system compliance (Crs) data from either the MOT or the SBT were obtained on 37 occasions in 25 infants, satisfactory results from both techniques were achieved only on 22 occasions. In these infants mean +/- SD Crs was 28.1 +/- 5.2 mL kPa-1 when assessed by MOT and 29.1 +/- 6.0 mL kPa-1 when using the SBT. The mean difference between technically satisfactory paired Crs values obtained with MOT and SBT was less than 5% (range, +28 to -18%). By contrast, in infants in whom data were invalidated as a result of expiratory airflow braking, failure to relax or instability of the end-expiratory level, gross discrepancies occurred between the techniques.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1993

Comparison of nitrogen washout and plethysmographic measurements of lung volume in healthy infants.

Functional residual capacity (FRC), the only lung volume to be assessed routinely in infants, can be measured using plethysmography or gas dilution. Although it is well recognized that both methods yield similar FRC values in healthy adults, gas dilution techniques have consistently produced lower values in healthy infants when compared with plethysmography. However, interpretation of this difference is difficult since data comparing the different techniques within the same infants have rarely been reported. We performed paired measurements of FRC using an automated open-circuit nitrogen washout technique (FRCN2) and whole-body plethysmography (FRCpleth) in 11 healthy infants with a median age of 12 months (range, 2 to 18 months). The mean (SD) FRC was 21.7 (4.0) ml/kg for the N2 washout and 25.6 (4.9) ml/kg for plethysmography. The mean within-subject difference between FRCN2 and FRCpleth was 3.9 (range, -0.3 to 7.2) ml/kg (p = 0.001). Both N2 washout and plethysmography yielded reproducible results, with the mean of the coefficients of variation (CV) being 3.6 and 3.9%, respectively. The results from these paired measurements support previously reported data from separate populations of infants which suggest that gas dilution techniques consistently yield smaller values for FRC than do those measured by plethysmography.

Female↗
PubMed1992

Respiratory compliance in infants--a preliminary evaluation of the multiple interrupter technique.

Measurements of total respiratory system compliance (Crs) using the multiple occlusion technique (MOT) in spontaneously breathing infants can be difficult to interpret in the presence of an unstable end-expiratory level. Similarly, measurements using the passive flow volume technique (PFV) are invalidated if there is alinearity of the expiratory time constant (Trs), irrespective of respiratory effort. For possibly overcoming these problems, we assessed the feasibility of a technique using multiple interruptions of of a single expiration (MIT), obtaining several pairs of volume-pressure data, from one expiration, which relate to a single end-expiratory level. Crs was measured in 16 infants aged 0.5 to 20 months using the MOT, MIT, and PFV technique. The MOT and the MIT each failed in one (different) infant, both succeeding where the other failed. The PFV technique failed in five infants in whom no acceptable plateau of airway pressure during occlusion and no Trs could be obtained from a single breath. Failure to obtain a linear Trs was accompanied by failure of the MIT in only one infant. Individual differences between the MIT and the MOT were less than 9%. However, the PFV measurements varied from -16.3% and +25.7% of the values from MIT or MOT. The greatest differences between Crs values coincided with the greatest differences between volume intercepts of the extrapolated volume-pressure (MOT, MIT) and flow-volume (PFV) data. From this preliminary study, the MIT proved as successful as the MOT, requiring fewer occluded breaths to measure Crs. In infants with a rapid respiratory rate, the data from several expirations can be merged and analyzed as for the MOT.

Humans↗
PubMed1992

Polymorphisms at the GLUT1 (HepG2) and GLUT4 (muscle/adipocyte) glucose transporter genes and non-insulin-dependent diabetes mellitus (NIDDM).

In order to determine the possible contribution of the GLUT1 (HepG2) glucose transporter gene to the inheritance of non-insulin-dependent diabetes mellitus (NIDDM), two restriction fragment length polymorphisms (RFLPs) and the related haplotypes at this locus were studied in 48 Italian diabetic patients and 58 normal subjects. Genotype frequencies for the XbaI polymorphism were significantly different between patients and controls (XbaI: chi 2 = 9.80, df = 2, P less than 0.0079). A significant difference was also found in the allele frequencies between NIDDM patients and controls (chi 2 = 9.39, df = 1, P less than 0.0022), whereas no differences were found for the StuI RFLP. No linkage disequilibrium was detected between the XbaI and StuI RFLPs in this sample. The analysis of the four haplotype frequencies (X1S1, X1S2, X2S1, X2S2) revealed a significant difference between diabetic patients and controls (chi 2 = 14.26, df = 3, P less than 0.002). By comparing single haplotype frequencies, a significant difference between the two groups was found for the X1S1 and X2S2 haplotypes. A two-allele RFLP at the GLUT4 (muscle/adipocyte) glucose transporter gene, detected with the restriction enzyme KpnI, was also examined; no differences were found between patients and controls for this RFLP. The finding of an association between polymorphic markers at the GLUT1 transporter and NIDDM suggests that this locus may contribute to the inherited susceptibility to the disease in this Italian population.

Adipose Tissue↗
PubMed1992

Sib-pair analysis of adenosine deaminase locus in NIDDM.

Recently, linkage between the ADA gene locus and MODY, a subtype of NIDDM, has been reported. The possibility that the region of chromosome 20q containing the ADA locus also may play a role in susceptibility to NIDDM needs to be investigated. Therefore, we examined the linkage between the ADA locus and NIDDM in affected siblings of 50 European white diabetic pedigrees--21 Italian and 29 British. Departure from independent segregation of the disease and an Alu VpA polymorphism within the 5' flanking region of the ADA locus was tested in the affected sib-pairs with the APM statistical method. After DNA amplification by the PCR and PAGE, five alleles were identified in the ALU VpA tract at the ADA locus in the two populations. Allele frequencies did not differ significantly between the two populations (chi 2 = 2.426, P > 0.05 [NS]). Analysis of the 50 diabetic sib sets, and independently of the Italian and British groups of affected sib pairs, revealed no segregation distortion between the marker locus and NIDDM. We conclude that mutations within or around the ADA locus are unlikely to play a major role in the etiology of NIDDM.

Adenosine Deaminase↗