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Biomedical subjects

A L Coates

Publications and source records attributed to A L Coates.

At least 55 records · Page 3Linked to original sources
PubMed1994

Pulmonary impedance as an index of severity and mechanisms of neonatal lung disease.

The measurement of resistive and elastic components of the respiratory system in neonates has been used to define disease severity and the response to therapy. The lung resistance (RL) and dynamic lung compliance (CLdyn) partition the impediment to gas flow into two components, each of which may be altered independently. The concept of lung impedance (ZLdyn) is the combined effect of the elastic and resistive loads presented to the respiratory muscles, which determines the gas flow that will result from the pressures generated by the respiratory muscles. In a first order system where RL and CLdyn are single values (independent of volume or respiratory rate), ZLdyn is the vector sum of the reactive [1/2 pi fb x CLdyn)] and resistive (RL) components at the infant's breathing rate (fb), if the transpulmonary pressure (Ptp) generated by the respiratory muscles during spontaneous respiration can be modeled mathematically by a sinusoidal function. Furthermore, the phase angle (theta) between the impedance and the resistive component will represent the relative magnitude of the resistive and reactive components. The validity of this model can be establishing by comparing the calculated theta to the observed temporal difference (measured theta) between the Ptp and flow derived from the polygraph tracing. This hypothesis was tested in 10 spontaneously breathing neonates with lung disease of differing etiology and severity. No significant difference was found between the measured and calculated theta values (mean difference, 1.2 +/- 3.9 degrees).(ABSTRACT TRUNCATED AT 250 WORDS)

Bronchopulmonary Dysplasia↗
PubMed1994

Effect of caffeine on the ventilatory response to inhaled carbon dioxide.

We investigated the effect of caffeine on the hypercapnic ventilatory response (HCVR) using steady state (SS) and rebreathing (RB) methods in 6 subjects. They received caffeine (5 mg/kg) or saline intravenously in a randomized, double-blind, crossover manner, with measurement of serum caffeine levels. PETCO2 and (VE), normalized for vital capacity (VC), were measured continually during RB and during the last 5 min of SS runs. The slope of the VE-PETCO2 response increased from 0.21 +/- 0.14 to 0.38 +/- 0.14 and from 0.23 +/- 0.12 to 0.59 +/- 0.45 VC.min-1.mmHg-1, measured by RB and SS respectively (P < 0.05). Plotting VT vs PETCO2 revealed a parallel shift (additive effect) in the response measured by RB after caffeine; but an increased slope (multiplicative effect) in the VT-PETCO2 relation measured in SS. We conclude that caffeine acts as a respiratory stimulant and increases the HCVR, but that assessment of the caffeine-CO2 interaction is dependent on the methodology employed.

Administration, Inhalation↗
PubMed1994

Sources of variation in FEV1.

The American Thoracic Society (ATS) recommendations to establish reproducibility of the forced expiratory volume in one second (FEV1) are that the value come from "at least 3 acceptable forced expiratory curves" where "the largest forced vital capacity maneuver (FVC) and the second largest FVC should not vary by more than 5%." It has been suggested that there is a "negative effort dependence" of the FEV1 and, alternatively, that the magnitude of the FVC influences the FEV1. We examined the relationship between FEV1 and a direct measurement of effort, or work, defined as the area under the alveolar pressure-volume curve in 1 s. Thirteen normal individuals and 17 patients with cystic fibrosis or asthma were instructed to make a series of maximal efforts, as in routine testing. Comparing the maneuver that resulted in the greatest work to that with the lowest work, all with FVCs within 5% of one another, there was no correlation between change in work and change in FEV1 (delta FEV1). There was a significant relationship between delta FEV1 and changes in FVC (r = 0.49, p < 0.01). The delta FEV1 did not correlate with the degree of hyperinflation (the FRC) or degree of airflow limitation (the initial FEV1). The magnitude of changes in FEV1 was small and almost always within acceptable limits for reproducibility. Because a larger FVC is due either to an increased inspiration, which could affect the FEV1, or to an increased expiratory reserve volume, which occurs only after the first second, these results emphasize the importance of a maximal inspiration at the start of the test.

Adolescent↗
PubMed1994

Effect of salbutamol on gas compression in cystic fibrosis and asthma.

In cystic fibrosis (CF), it has been suggested that increases in FEV1 postbronchodilator (BD) can be accompanied by paradoxical decreases in isovolume maximal flow at 25% of vital capacity (V25iso) measured from maximum expiratory flow-volume curves (MEFVC), raising concerns about determining the benefits of BD in CF. MEFVC measured using expired volume has been shown to be subject to errors due to gas compression. In the present study, BD response was assessed in 91 patients with asthma and 78 with CF using the percentage of change in FEV1 and V25iso determined using MEFVC from both mouth (m) and plethysmograph (p) volumes. From the two curves, volume of compression (Vcomp) was measured. Baseline measurements were similar for both groups, except that the residual volume to total lung capacity ratio (RV/TLC) was higher and Vmax25 and FVC were lower in CF. Both groups showed significant (p < 0.05) increases in FVC, FEV1, and V25iso after BD. The percentage of change in FEV1 correlated with the percentage of change in V25iso (r = 0.53 for CF and 0.66 for asthma, p < 0.001). Baseline Vcomp25 was higher in asthma than in CF. The percentage of change in V25iso was not related to the change in Vcomp25iso for either group. Only four patients with CF showed a paradoxical decrease in V25iso, and the differences in flow were small. Two had an increase in Vcomp and two had a decrease. We conclude that paradoxical decreases in V25iso are rare, are associated with small changes in flow, and are not related to changes in Vcomp.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1993

Lung recoil and the determination of airflow limitation in cystic fibrosis and asthma.

A reduction of lung recoil pressure could aggravate any airflow limitation that might be present in patients with cystic fibrosis (CF) or asthma. In a group of 22 children and young adults (8 with cystic fibrosis, 8 with asymptomatic asthma, and 6 healthy controls) aged 8-24 years, lung recoil pressure (Pst) at 100%, 90%, and 60% of TLC and static lung compliance (Cst) were measured using an esophageal balloon. The indices of airflow limitation, including maximal expiratory flow at 25% VC (Vmax25), forced expiratory volume in 1 second (FEV1), and specific airway conductance (sGaw), were also measured. In all patients, Vmax25 was reduced, the airway obstruction being more pronounced in patients with CF. Pst was reduced in CF and asthma, again more in the patients with CF. Cst was normal in both groups because the pressure volume curve was shifted up and to the left. There were significant correlations between Pst at 60%, 90%, and 100% of TLC and both Vmax25 and FEV1 (P < 0.01). sGaw correlated with Pst90 and Pst60 (r = 0.47 and 0.53, respectively; P < 0.05 for both). No correlation was found between Cst and Pst at any lung volume. No correlations were observed between Cst and Vmax25, FEV1, or sGaw. These results suggest that loss of elastic lung recoil pressure is a factor in airflow limitation of children and young adults with CF or asthma.

Adolescent↗
PubMed1993

Spirometry in the asthmatic child: is FEF25-75 a more sensitive test than FEV1/FVC?

The use of spirometry in the assessment of children with asthma is taking on new importance with the realization that considerable airway obstruction may exist in the absence of clinically detectable abnormalities. There has been controversy over the value and relative sensitivity of various spirometry indices. This study evaluated the forced expiratory flow between 25% and 75% of vital capacity (FEF25-75), forced expired volume in 1 second (FEV1), and the ratio between the FEV1 and the forced vital capacity (FVC) in 100 asthmatic children aged 6-17 years, 29 of whom were wheezing at the time of the evaluation. All children with clinical wheezing had a FEV25-75 < 2 standard deviations (SD) below the mean (-2 SD), whereas 8 had a normal FEV1. The majority of the wheezing children had abnormalities of all 3 indices, whether expressed as < or = -2 SD or, in the case of the FEV1/FVC, arbitrarily taken as < 80%. Sixty-seven children of the entire study group had at least 1 abnormal spirometric index, but 38 of these had no clinical abnormalities. Twelve children had a reduced FEF25-75 as the only abnormality. These results suggest that FEF25-75 is a sensitive index of airway obstruction.

Adolescent↗
PubMed1993

A simplified method for determining the frequency response of pneumotachographs used in infants.

In all rapidly changing systems, an appropriate response time of all sensing devices is essential for the accurate conversion of a physiological parameters to a proportional electrical signal. The frequency response of equipment is the ability to accurately reflect both the magnitude and temporal relationship of dynamic events over a defined frequency range. The phase lag expresses the temporal delay between the physical event being measured and the output signal. The attenuation expresses diminution of the amplitude ratio of the output signal in relation to the input signal over a range of frequencies. We have developed a method that specifically addresses the measurement of frequency response and attenuation of pneumotachographs and low pressure transducers. The system consists of a 81 liter rectangular box separated in the middle by a 30.5 cm acoustic loudspeaker, the cone sealed by latex, and driven by a signal generator coupled to a low frequency amplifier. This system can produce an undistorted sinusoidal signal between 0 and 20 Hz, and the peak flow through the pneumotachograph is only minimally affected by changes in frequency. Rapid analysis is possible using an oscilloscope to produce Lissajou loops. There is no measurable attenuation between the electrical signal and the pressure generated over frequencies from 1 to 20 Hz. The system is accurate at low frequencies and can generate appropriate signals over the frequency range of interest for respiratory applications, and it can be inexpensively constructed.

Humans↗
PubMed1993

Pulmonary function abnormalities in childhood sickle cell disease.

Pulmonary function tests in adults with sickle cell disease have shown a restrictive pattern that has been attributed to the sequelae of acute chest syndrome (ACS). We compared pulmonary function test results in 37 children with sickle cell anemia (20 with SS hemoglobin (HbSS), 14 with SC hemoglobin, and 3 with S beta hemoglobin) with those in 22 control subjects matched for sex, race, and height and compared pulmonary function in patients with and without a history of ACS. Of the 10 patients with a history of ACS, all but one had HbSS. Pulmonary function tests measured forced vital capacity (FVC), the diffusion capacity of carbon monoxide, and the plethysmographic determination of lung volumes. The FVC and forced expiratory volume in 1 second (FEV1), expressed as the percentage of the predicted value, were significantly less for those with HbSS with or without a history of ACS than for control subjects (p < 0.05), but the FEV1/FVC ratio, an index of airway obstruction, was normal in all groups. Total lung capacity was also significantly lower in patients with HbSS with or without a history of ACS than in control subjects (p < 0.05), but the ratio of residual volume to total lung capacity, another index of airway obstruction, was normal. We conclude that children with sickle cell disease, particularly those with HbSS, may have abnormally small lungs that function normally relative to their size; clustering of ACS episodes is not specifically associated with the observed abnormality.

Adolescent↗
PubMed1993

Pulse oximetry in sickle cell disease.

Patients with sickle cell disease usually have mild hypoxaemia and their oxyhaemoglobin dissociation curve is shifted to the right. It follows that oxygen saturation in sickle cell disease should be lower than normal. Most subjects in this clinic had normal oxygen saturation by pulse oximetry, however. To improve the understanding of this paradox, arterialised capillary oxygen tension (PO2) and oxygen saturation were compared with simultaneously measured pulse oximeter saturation in 20 children with sickle cell disease. In addition, the PO2 at 50% haemoglobin saturation (P50) was compared with saturation measured by pulse oximetry in all 20 patients. It was found that saturation measured by pulse oximetry was, on the whole, similar to that calculated from the sampled blood. Individual deviations were not random, however, and were partly explained by differences in P50 values. It is concluded that pulse oximetry gives variable results in patients with sickle cell disease and should be used with caution to predict arterial saturation in this patient group.

Anemia, Sickle Cell↗
PubMed1993

Flow limitation while breathing HeO2.

Flow limitation during a maximum expiratory flow-volume curve (MEFVC) while breathing air occurs at lung volumes below 70% vital capacity (VC). To evaluate small airways function, use has been made of the volume of isoflow (VisoV), comparing an MEFVC done in air to one done in 80% helium, 20% O2 (HeO2). The VisoV has high intra-subject variability. This study investigated whether this variability was due to an inability to flow limit while breathing HeO2. This would occur if the velocity of expiratory muscle contraction did not result in sufficient intrathoracic pressures to cause dynamic airway compression in the face of increased expiratory flows while breathing HeO2. Seven healthy adult male subjects performed repeated VC expirations of varying effort with an esophageal balloon in place in a body plethysmograph while breathing air and HeO2. The flow-volume curves were matched at residual volume and transpulmonary pressure-flow plots were constructed at volume isopleths of 70, 50, and 25% VC. In air, flow limitation was demonstrated in 3, 6, and 7 subjects at 70, 50, and 25% VC, respectively. In HeO2, flow limitation was achieved in 1 and 4 subjects at 70 and 50% VC. Although one subject demonstrated intermittent glottic closure, the remaining 6 demonstrated flow limitation at 25% VC. We concluded that dynamic airways compression occurs even with the increased flows in HeO2.

Adult↗
PubMed1992

Cardiopulmonary response to exercise in anorexia nervosa.

Malnutrition is associated with a number of systemic diseases that are often accompanied by severe exercise limitation. Anorexia nervosa (AN) is a disease characterized by malnutrition due to psychological factors rather than systemic disease. Diminished exercise capacity in AN has been attributed to a loss of muscle mass, dysfunction of remaining muscle, and impaired cardiovascular responses. In order to evaluate the role of malnutrition in the cardiopulmonary response to exercise, nine adolescent girls with AN were evaluated during progressive and steady-state exercise testing using a cycle ergometer. Nutritional status was assessed by body mass percentile (BMP) and percent ideal weight (PIWT). Cardiac output was measured by the indirect (CO2 rebreathing) Fick method. Maximum work capacity (Wmax) was expressed as a percent of predicted for sex and height, and cardiac output as a percent of predicted for oxygen consumption. To ensure that the laboratory values were comparable to the predicted values, a control group consisting of ten adolescents was studied concurrently. Wmax was below the 95% confidence interval in six of nine of the AN group (mean +/- SD: 70 +/- 22% predicted), whereas two of ten controls were below and one above this interval (112 +/- 37%). Wmax correlated with nutritional status (BMP: r = 0.75; P less than 0.001; PIWT: r = 0.8, P less than 0.001). Ventilatory responses for CO2 production at steady state and for Wmax were appropriate in both groups. Cardiac output was appropriate in both the controls (103 +/- 12%) and the AN group (104 +/- 14%).(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1991

Pulse oximetry versus measured arterial oxygen saturation: a comparison of the Nellcor N100 and the Biox III.

Pulse oximetry is noninvasive, fast, and simple, making it a very popular way of assessing oxygenation in pediatric patients. However, there are few studies that establish the accuracy of this technology over a wide range of oxygen saturations in children. This study, done in 47 children aged from 1 day to 16 years with congenital heart disease and undergoing cardiac catheterization, compared the direct measurement of arterial oxygen saturation to values from pulse oximetry. Oxygen saturation was measured by an IL-282 Co-oximeter, which also measured carboxyhemoglobin and methemoglobin, and was compared to values obtained from both a Biox III and Nellcor N100. Both pusle oximeters gave values that closely correlated with the actual saturation (r = 0.91 and 0.93, respectively) with standard errors of the estimate of 4.1 and 3.2%, respectively. For both devices, the error increased with decreasing saturations, being progressively larger below a saturation of 80%. The difference between the actual saturation and that measured by pulse oximetry bore no relationship to the presence of carboxyhemoglobin, methemoglobin, fetal hemoglobin, bilirubin, cardiac index, or age of the patient. In conclusion, pulse oximetry, while a very useful technology in pediatrics, must be interpreted with some caution in children with severe cyanosis.

Adolescent↗
PubMed1991

The effects of diuresis and transfusion on pulmonary function in children with thalassemia major.

Previous pulmonary function studies in subjects with thalassemia major (TM) who were on regular transfusion programs have demonstrated results ranging from small airway obstruction to a restrictive pattern. Ten subjects with TM were studied pre- and postdiuresis, and again 24 hr after transfusion, in order to evaluate the role of possible fluid overload in altering pulmonary function. Subjects underwent spirometry and had lung volume and flow volume curves (MEFVC) measured in a volume displacement plethysmograph while breathing air and a mixture of 80% helium and 20% oxygen (HeO2). Six patients had pulmonary mechanics measured with esophageal balloons in place. Baseline function was normal and no change occurred following diuresis. Following transfusion, the volume of isoflow (VisoV) decreased, but other parameters did not change. Subsequent analysis revealed 5 subjects with an initial VisoV greater than 20 (% FVC) but, paradoxically, less evidence of flow limitation in the small airways than those with a VisoV less than 20 (% FVC). Posttransfusion, in those subjects with an initially high VisoV, the Vmax25(air) tended to fall without a change of MEFVC in HeO2, resulting in a decreased VisoV. This was interpreted as evidence of subtle abnormalities in the small airways caused by volume expansion, raising doubts about the value of the VisoV as a measure of small airway disease. As a group, our subjects did not demonstrate any abnormalities in baseline function. Some subjects had mild flow limitation in small airway while other developed comparable levels of flow limitation following the volume expansion associated with transfusion.

Blood Transfusion↗
PubMed1991

Ventilation and gas exchange during exercise in sickle cell anemia.

Adults with sickle cell anemia (SCA) have restrictive lung impairment, increased alveolar dead space, and hypoxemia. These factors, together with increased anaerobic metabolism, are thought to cause exercise hyperventilation. To assess the role of each of these in children, 34 patients with SCA and 16 control subjects performed pulmonary function and exercise tests. Twenty-eight patients with SCA had spirometric values and lung volumes, and all but two patients with SCA had arterial saturation greater than 91% during exercise. Despite a low VO2max (30.07 +/- 6.55 ml/min/kg), the ventilatory anaerobic threshold (VAT) in the patients occurred at a similar %VO2max as in the control subjects (69 +/- 9% versus 63 +/- 12%). The slope of the delta VE/delta VCO2 relationship for sub-VAT work was steeper in the patients (29.4 +/- 6.5 versus 24.7 +/- 5.2, p = 0.01), and the ventilatory equivalent for CO2 (VE/VCO2) in steady-state exercise was greater in the patients than in the control subjects (33.2 +/- 3.5 versus 30.8 +/- 3.5, p = 0.03). End-tidal PCO2 did not differ (38.3 +/- 3.0 versus 39.2 +/- 3.1), indicating equivalent alveolar ventilation. The patients had a higher dead space:tidal volume ratio (VD/VT) than did the control subjects (0.204 +/- 0.033 versus 0.173 +/- 0.024, p = 0.0005). The PaCO2 was significantly lower in those with lower Hb, but there was no difference in pH. In conclusion, children with SCA have an increased exercise ventilatory response caused in part by increased physiologic dead space, and in part by their low Hb. The greater dead space may be the result of sickle cells impairing capillary perfusion to ventilated alveoli.

Adolescent↗
PubMed1991

Cardiac output and oxygen delivery during exercise in sickle cell anemia.

Desaturation in patients with sickle cell anemia (SCA) can lead to intravascular sickling and vascular occlusion. The increased metabolic demands of exercise tend to increase oxygen extraction, giving rise to a fall in saturation in the capillary bed that may predispose to sickling. This could be minimized with an increase in cardiac output. The aims of this study were to assess the role of increased stroke volume (SV) in augmenting cardiac output (Q) and to estimate the role of enlarged arteriovenous O2 content difference in maintaining O2 transport in children with SCA. A group of 30 children with SCA (Hb 65 to 133 g/L) and 16 healthy controls of the same racial group and of similar height and weight performed incremental and steady-state exercise at 50% Wmax. Cardiac output (Q) was measured by the indirect (CO2) Fick method during steady state. The slope of delta HR/delta VO2 during incremental exercise was higher in SCA subjects compared with controls (4.01 +/- 1.73 versus 2.80 +/- 0.61 bpm per ml/min/kg VO2, p = 0.001). Q for VO2 was abnormally high in patients, particularly older ones with lower Hb levels. HR (% predicted) was higher in patients than in controls (106 +/- 11 versus 92 +/- 8% predicted, p less than 0.0001), as was SV (113 +/- 16 versus 98 +/- 14% predicted, p = 0.002). Multiple linear regression of Q % predicted and SV % predicted on Hb and age showed a positive correlation with age and a negative correlation with Hb (r = 0.84 for Q and r = 0.76 for SV).(ABSTRACT TRUNCATED AT 250 WORDS)

Anemia, Sickle Cell↗