Use of protective equipment by in-line skaters: an observational study.

OBJECTIVE: To determine the extent of protective equipment use (that is, helmets, wrist guards, elbow pads, knee pads) in a representative sample of in-line skaters. SETTING: Fifteen municipalities throughout the province of British Columbia. METHOD: A province-wide observational survey was conducted in the summer of 1999. Skaters were observed at four types of sites (commuter, recreational, neighbourhood, general community) in 15 municipalities to provide a representative sample of in-line skaters. RESULTS: The observed use of protective equipment by the 877 in-line skaters was relatively low: wrist guards 25%, helmets 13%, elbow pads 14%, and knee pads 10%. CONCLUSION: Despite the availability of relatively inexpensive protective equipment, few in-line skaters take advantage of the opportunity to protect themselves from injury. Policies and programs that serve to increase the use of protective equipment by in-line skaters are needed to help reduce the frequency of skating related injuries.

Redefining end of test (EOT) criteria for pulmonary function testing in children.

In order for an individual FVC maneuver to be considered acceptable according to the 1994 American Thoracic Society (ATS) standards it must meet end of test (EOT) criteria of a minimum expiration time of 6 s with minimal volume change (0.03 L) over 1 s. We have found that while these criteria are often not met in children, most of the tests do meet the ATS criteria for reproducibility with repeated efforts. We, therefore, sought to develop new EOT criteria that would be more appropriate for children and in keeping with the findings for reproducibility. Using an exponential curve fitting of the volume time tracing, we determined a theoretical curve that closely approximated the actual curve (mean difference between actual and derived FEV1 0.01 +/- 0.04 L). The theoretical FVC (FVCFULL) at the point where the curve reached its asymptote was then determined using the fitted curve. Since this point could be difficult to reach for some patients, 95% of FVCFULL (FVC95) was proposed as the new EOT in children. Data from 382 patients were reviewed. Their ages ranged from 5 to 18 yr and their FEV1s from 21 to 120% of predicted. Only 19% of the patients met current ATS EOT requirements despite the fact that 91% met the reproducibility criteria for both FEV1 and FVC. However, 90% of them reached their FVC95. When this was broken down by age, 37% of those < or = 7 yr failed to reach FVC95 whereas only 4% of the older children failed to do so. It is proposed that patients be coached to obtain maximal effort and that the curves be individually fitted to an exponential equation to determine whether the patient has achieved EOT as defined by FVC95.

The simplified version of Boyle's Law leads to errors in the measurement of thoracic gas volume.

When using Boyle's Law for thoracic gas volume (Vtg) measurement, it is generally assumed that the alveolar pressure (Palv) does not differ from barometric pressure (Pbar) at the start of rarefaction and compression and that the product of the change in volume and pressure (delta P x delta V) is negligibly small. In a gentle panting maneuver in which the difference between Palv and Pbar is small, errors introduced by these assumptions are likely to be small; however, this is not the case when Vtg is measured using a single vigorous inspiratory effort. Discrepancies in the Vtg between the "complex" version of Boyle's Law, which does not ignore delta P x delta V and accounts for large swings in Palv, and the "simplified" version, during both a panting maneuver and a single inspiratory effort were calculated for normal control subjects and patients with cystic fibrosis or asthma. Defining the Vtg from the complete version as "correct," the errors introduced by the simplified version ranged from -3 to +3% for the panting maneuver whereas they ranged from 2 to 9% for the inspiratory maneuver. Using the simplified equation, the Vtg for the inspiratory maneuver was 0.135 +/- 0.237 L greater (p < 0.02) than for the panting maneuver. This discrepancy disappeared when the complete equation was used. While the errors introduced by the use of the simplified version of Boyle's Law are small, they are systematic and unnecessary.

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)

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.

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.

The effects of nutritional status and hyperinflation on respiratory muscle strength in children and young adults.

Malnutrition and hyperinflation may both lead to respiratory muscle weakness. To assess separately the effects of chronic hyperinflation and malnutrition on respiratory muscle strength (RMS), 22 subjects with cystic fibrosis (CF) with both hyperinflation and malnutrition were compared to 10 asthmatic patients, a group with hyperinflation without malnutrition, 9 subjects with anorexia nervosa (AN), a group with malnutrition without lung disease, and 14(6 males and 8 females) control subjects with neither compromise. Nutritional status was assessed by body mass percentile (BMP) and percentage ideal weight (PIWT). RMS was diminished in the AN and CF groups (PImax 90 +/- 27, 88 +/- 31 versus 124 +/- 40 cm H2O, p less than 0.05; PEmax 87 +/- 12, 93 +/- 39 versus 121 +/- 32 cm H2O, p less than 0.05), but no difference was found when the AN group was compared with only the female controls. The decrease in PImax in the CF group was primarily due to the mechanical disadvantage placed on the diaphragm by their marked hyperinflation, a mean RV/TLC ratio of 50 +/- 23%. As older CF subjects had previously been shown to have decreased RMS when malnourished, a CF subgroup in the same age range as the controls was evaluated. RMS in this group did not differ from controls despite the presence of malnutrition and hyperinflation. RMS is mildly influenced by nutritional status as assessed by BMP and PIWT but not to any degree of clinical significance.

Sources of error in flow-volume curves. Effect of expired volume measured at the mouth vs that measured in a body plethysmograph.

The popularity of the maximum expiratory flow-volume curve (FVC) is in part due to the effort independence of expiratory flow. Of interest are expiratory flow rates at specific lung volumes, usually 50 and 25 percent of vital capacity (VC); Vmax50 and Vmax25, which make accurate assessment of lung volumes essential. Changes in lung volume during the test are due to both the volume of gas expired and the volume change due to gas compression (Vcomp). In normal subjects, Vcomp is small but may be considerable in those with airflow obstruction. When the FVC is measured in a plethysmograph (FVCp), both expired volume and Vcomp are measured. When the volume of the FVC is derived from gas expired at the mouth (FVCm), Vcomp is not considered and differences in Vmax25 or Vmax50 may occur. The magnitude of these errors was assessed in 30 children and young adults: nine normal subjects, ten with cystic fibrosis (CF) and 11 with asthma. For Vmax50, use of FVCm instead of FVCp resulted in an error of 8 +/- 7 percent (mean +/- 1 SD) in the normal subjects compared to 32 +/- 23 in those with CF (p less than 0.01) and 24 +/- 18 for those with asthma (p less than 0.05). For Vmax25, the errors were similar. These errors were not predictable from FEV1 or RV/TLC but were related to a combination of expiratory effort, the shape of the FVCp, and the absolute volume of gas that was being compressed (p less than 0.0001). These findings suggest that expiratory flows in the FVCm are not effort-independent in the face of significant airflow obstruction and that comparisons of values derived from an FVCp with those from an FVCm may not be valid.

An alternate method for the determination of functional residual capacity in a plethysmograph.

The validity of measuring thoracic gas volume using a single inspiratory effort against an occlusion (Vtginsp) was determined in children and young adults (8 normal control subjects and 17 patients with cystic fibrosis [CF] or asthma). In addition, the validity of the measurement of Vtg at FRC in children at a low panting frequency (Vtgpant) was also determined. During both the panting (encouraged to be about 1 Hz) and inspiratory maneuvers, mouth pressure (Pm) and esophageal pressure (Pes) were measured simultaneously. Hence, Vtgpant and Vtginsp were determined using both delta Pm and delta Pes. Vtginsp using delta Pm was found to be similar to Vtginsp using delta Pes. Values for Vtgpant using either delta Pm or delta Pes were also found to be similar. The percent difference between Vtginsp (using delta Pm) and the average of Vtgpant and Vtginsp (using delta Pes for both) was calculated as an indication of the error of the inspiratory method. The error ranged from -13 to +13% and did not correlate with indices of air-flow limitation or hyperinflation. We have found that Vtginsp can be used to determine FRC in normal children and young adults as well as in those with CF or asthma. In addition, we have also validated the use of Vtgpant at a low panting frequency in these subjects.

The mechanical effects of expiratory airflow limitation on cardiac performance in cystic fibrosis.

The influence of altered lung mechanics on cardiac performance in cystic fibrosis (CF) was examined in an analysis of cardiorespiratory performance during exercise. The stroke volume (SV) response to exercise, derived from an indirect Fick (CO2) determination of cardiac output during submaximal steady-state exercise served as the index of cardiac performance. The relationship between exercising SV and forced expiratory volume in one second (FEV1), inspiratory duty cycle during exercise (Tl/Ttot) and exercising systemic arterial oxygen tension (PaO2) was examined in 15 studies involving 11 individuals with CF. The subjects were 12 to 25 yr of age and the FEV1 ranged from 15 to 72% predicted. Although a relationship existed between the SV expressed as a percentage of the mean predicted from height and gender (SV%) and PaO2 (r = 0.61, p less than 0.02), a more striking relationship was noted between SV% and either FEV1 or Tl/Ttot (r = 0.79 and 0.73, p less than 0.002). A multiple regression analysis of SV% identified an element of the relationship between FEV1 or Tl/Ttot and cardiac performance which was distinct from the influence of the coexisting hypoxia (p less than or equal to 0.05). The limitation in the SV response to exercise was noted to be in part reversible, coincident with an improvement in ventilatory mechanics that had occurred in 2 of the 4 persons in whom repeated studies were available. These observations suggest that in individuals with CF and a moderately severe degree of expiratory airflow limitation, there is a mechanical element of cardiopulmonary interdependence.

Measuring the oxygen cost of breathing in normal adults and patients with cystic fibrosis.

It has been suggested that the oxygen consumption of the respiratory muscles (VO2 resp) may play a role in limiting exercise performance in both healthy subjects and those with chronic airflow limitation (CAL). In order to measure VO2 resp reproducibly at both rest and on exercise, ventilation (VE) and total oxygen consumption (VO2) in 3 normal subjects and in 3 patients with cystic fibrosis were measured while breathing air and again when VE was stimulated by the addition of CO2 to the inspired gas. Since external work was the same it was assumed that any changes in VO2 would be due to the increase in VO2 resp during stimulated breathing allowing for the calculation of VO2 resp. The oxygen cost of breathing was higher in the patients with the increasing ventilation of exercise. These values were reproducible on repetitive measurements. It is concluded that the method employed is applicable in normal subjects and in patients with CAL, and that the O2 cost of breathing is higher in patients with CAL. The O2 cost of breathing increases as VE increases but even during exercise the VO2 resp is only a small fraction of the total VO2 and is unlikely to be a determining factor limiting exercise performance in either normal subjects or those with CAL.

Trapped gas and airflow limitation in children with cystic fibrosis and asthma.

Trapped gas (TG) has been shown to be present in cystic fibrosis (CF) and asthma, but its relationship with airflow limitation (AL) has not been explored. TG was defined as the difference between the functional residual capacity measured by body plethysmography [FRC(BP)] and that measured by helium dilution [FRC(He)] expressed as a percentage of total lung capacity (TLC). We studied 21 children with CF and 15 with asthma who had a similar degree of AL and hyperinflation, however the children with CF had greater amounts of TG compared with asthma [15% +/- 2 (mean +/- 1 SE) vs 8 +/- 2, P less than 0.05]. Mixing efficiency (ME), an index of the distribution of ventilation, was found to be lower in the CF children than in those with asthma (34 +/- 4 vs 54 +/- 4). In CF, TG correlated with forced expiratory flow between 25 and 75% of vital capacity (FEF25-75), ME, RV/TLC, and maximal expiratory flow rates at 25 and 50% of vital capacity (Vmax25 and 50, respectively; r = -0.66, -0.61, 0.72, -0.71, -0.74). ME also correlated with the above measures. In asthma, TG did not correlate with the FEF25-75, ME, RV/TLC, Vmax25, or Vmax50. Furthermore, TG was frequently found in patients with asthma with moderate AL while it was often absent in patients with severe AL. For both CF and asthma, neither the severity of AL nor the magnitude of the TG could be predicted from the increase in Vmax50 with helium (delta V50).(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship between the partial pressure of arterial oxygen and airflow limitation in children with cystic fibrosis.

To assess whether it would be possible to avoid repeated arterial blood sampling in children with cystic fibrosis, the relation between the forced expiratory flow at 25% to 75% of the vital capacity (FEF25%-75%) and the partial pressure of arterial oxygen (PaO2) was examined. The PaO2 and the logarithm of the FEF25%-75% (expressed as a percentage of that predicted) showed the strongest correlation (r = 0.89, p less than 0.001). Although this relation cannot be used when an accurate value for the PaO2 is required, it can sometimes be useful for determining the need for an arterial puncture.

Immediate and long-term effects of chest physiotherapy in patients with cystic fibrosis.

Both the immediate and long-term effects of chest physical therapy administered by a parent were evaluated in eight children with cystic fibrosis. Spirometric and plethysmographic evaluations were performed pre-CPT and at 5 and 30 minutes post-CPT. The pre-CPT measurements after a three-week period with no CPT were compared with the values while receiving CPT on a regular twice daily basis. There was a significant decrease after three weeks without CPT for FVC (P less than 0.025), FEV1 (P less than 0.005), FEF25-75 (P less than 0.005), and Vmax60TLC (P less than 0.025). When the patients had been receiving CPT on a regular basis, the only immediate effect was an increase in PEFR after 30 minutes post-CPT (P less than 0.05). After three weeks without CPT, there were increases at 30 minutes post-CPI for FVC (P less than 0.005) and Vmax60TLC (P less than 0.05). These findings indicate that although there may be little immediate functional improvement when CPT is received on a regular basis, a three-week period without CPT leads to a worsening of the functional status, which is reversed with renewal of regular CPT.

Ventilation, respiratory center output, and contribution of the rib cage and abdominal components to ventilation during CO2 rebreathing in children with cystic fibrosis.

Although there has been extensive research into the control of breathing in adults with chronic obstructive lung diseases, there is little information in this area in children with cystic fibrosis (CF). The purpose of this study was to investigate the respiratory response of children with CF to CO2 under hyperoxic conditions. Using a standard CO2 rebreathing technique, we studied 14 children with CF. We evaluated their response to CO2 in terms of ventilation (VE), mean inspiratory flow rate (VT/TI), and the pressure generated at the mouth after 0.1 s of an inspiratory effort against an occlusion (P0.1). In order to understand the contributions of the rib cage and abdominal components to ventilation, we assessed the volume change in each compartment by attaching magnetometers to the chest and abdomen. Overall changes in lung volume were assessed in a volume displacement plethysmograph. We found that, when corrected for the height of the child, the slope of VE versus end tidal CO2 (PETCO2), as well as the slope of VT/TI versus PETCO2 correlated significantly with the degree of airway obstruction as expressed by the forced expiratory flow between 25 and 75% of vital capacity. The values for P0.1 were all within the normal range and showed no correlation with the degree of airway obstruction. The contribution of the rib cage and abdomen to ventilation during rebreathing was similar to that previously reported for adults. No changes were observed in functional residual capacity during rebreathing. We showed that tests involving a mechanical response to CO2 correlated with the degree of airway obstruction, but there was no evidence that the neuromuscular drive was abnormal.