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(Chest. 2002;122:464-472.)
© 2002 American College of Chest Physicians

Effects of Training With Heliox and Noninvasive Positive Pressure Ventilation on Exercise Ability in Patients With Severe COPD*

James E. Johnson, MD; Daniel J. Gavin, MD, MAJ USAR, MC and Stacy Adams-Dramiga, MA

* From Cardiopulmonary Rehabilitation (Dr. Johnson), University of Alabama at Birmingham, Birmingham, AL; and the Departments of Pulmonary and Critical Care Medicine (Dr. Gavin) and Cardiopulmonary Rehabilitation (Ms. Adams-Dramiga), Brooke Army Medical Center, Fort Sam Houston, TX.

Correspondence to: James E. Johnson, MD, Pulmonary and Critical Care Division, UAB Hospital, THT 215, 1500 Third Ave S, Birmingham, AL 35294-0006; e-mail: jjohnson{at}pulm.dom uab.edu


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
Study objectives: We sought to determine whether breathing heliox or using nasal noninvasive positive pressure ventilation (NIPPV) would produce immediate improvements in exercise capability in patients with COPD, and whether training for 6 weeks with one of these modalities would result in greater exercise improvement than with training unassisted.

Setting: US military medical center.

Methods: Thirty-nine patients with severe COPD (mean FEV1 of 33.5% predicted) underwent three incremental treadmill tests to exhaustion unassisted, breathing heliox, or breathing with NIPPV. They were then randomized to undergo 6 weeks of twice-weekly rehabilitation with unassisted exercise training (UT group), training while breathing heliox (HT group), or training while breathing with NIPPV (NT group). The three exercise tests were then repeated.

Results: Heliox treatment did not produce any immediate benefit in exercise time or maximum workload in the 39 patients initially tested, the 32 patients who completed the protocol, or the HT group. Furthermore, no training advantage was evident in the HT group (n = 10) compared to the UT group (n = 11). NIPPV did not produce an immediate benefit in the initial tests, but produced a small increase in exercise time in the 32 patients completing the protocol in the final tests. This effect was primarily because of the NT group, who exercised significantly longer (mean ± SD, 16.8 ± 4.9 min vs 14.2 ± 5.6 min, p = 0.0045) and to a higher workload (4.46 ± 1.55 metabolic equivalents [METs] vs 4.09 ± 1.75 METs, respectively; p = 0.038) when tested using the ventilator. Compared to the UT group, the NT group started out with a lower exercise time (7.9 ± 3.5 min vs 12.3 ± 5.2 min, p = 0.031) in preliminary testing, but the statistical difference was eliminated in the final tests (14.2 ± 5.6 min vs 16.0 ± 5.8 min, respectively; p = 0.451). The NT group actually slightly exceeded the UT group when they used the ventilator in final testing, although this was not statistically significant (16.8 ± 4.9 min vs 16.0 ± 5.8 min, respectively).

Conclusion: Heliox treatment does not appear to offer an immediate or training advantage with exercise in patients with COPD. For patients who have undergone regular exercise conditioning with NIPPV, use of the ventilator produces an immediate improvement in both exercise time and maximum workload attained, and it may confer a training advantage.

Key Words: bilevel positive airway pressure • COPD • exercise • heliox • helium • noninvasive positive pressure ventilation • pulmonary rehabilitation


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Conclusion
 References
 
COPD is a major cause of disability and is the fifth-leading cause of death in the United States. It ranks second only to coronary artery disease in terms of overall morbidity among Social Security disability recipients.1 2 Multiple randomized studies1 3 4 5 6 have shown that rehabilitation programs incorporating regular exercise lead to improvements in exercise tolerance in these patients.

The mechanism for the improvement in functional ability appears to be cardiovascular reconditioning rather than improvement in lung function. Casaburi et al7 demonstrated a true aerobic training effect in patients with COPD undergoing exercise rehabilitation, with greater gains seen in a high-intensity exercise group. Other studies8 9 have demonstrated improved aerobic capacity without significant changes in pulmonary function test results.

Since ventilatory limitation is the key factor that leads to inactivity and subsequent cardiovascular deconditioning in these patients, measures aimed at reducing the ventilatory limitation should allow these patients to exercise to higher intensities and achieve greater cardiovascular reconditioning. We undertook this study to explore ways to maximize the gains from pulmonary exercise rehabilitation by reducing mechanical ventilatory limitation.

Heliox, a mixture of helium (79%) and oxygen (21%), is known to increase the forced expiratory flow in both normal subjects and patients with obstructive airway diseases because of its effects on turbulent flow resistance.10 Heliox has had only variable results in increasing exercise tolerance in normal volunteers.11 12 13 14 15 This is not surprising given that maximal exertion is not usually limited by ventilation in the absence of lung disease.16 The use of heliox in the treatment of acute exacerbations of obstructive airway disease has received more attention in recent years, and it may provide modest benefits.17 18 19 Little has been written about the use of heliox during exercise in patients with COPD. Bradley et al20 showed no statistically significant difference in endurance, oxygen uptake, heart rate, or ventilatory parameters when patients with COPD were acutely subjected to incremental exercise while breathing heliox; however, his study included only seven patients.

Noninvasive positive pressure ventilation (NIPPV) has been found to be an effective ventilatory supplement for patients with acute and/or chronic ventilatory failure due to obstructive lung disease or neuromuscular deficits.21 Furthermore, NIPPV has been demonstrated to increase minute ventilation, tidal volume, and reduce inspiratory effort and the sensation of dyspnea22 as well as a reducing respiratory acidosis23 during exercise testing in patients with severe COPD. Four studies23 24 25 26 have shown immediate increases in exercise endurance time at constant workload with NIPPV in patients with COPD.

To our knowledge, the regular use of heliox or NIPPV during an exercise program for patients with severe COPD has not been previously evaluated. Our hypotheses were as follows: (1) patients with COPD would immediately increase their exercise capability when receiving either heliox or NIPPV compared to unassisted exercise; and (2) patients with COPD receiving either heliox or NIPPV during training in a 6-week rehabilitation program would have greater gains in exercise capability than would subjects training without assistance.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Conclusion
 References
 
Study Population
All patients referred to the comprehensive pulmonary rehabilitation program during the period from March 1, 1996, to January 31, 1997, were considered for the study. Patients were referred from their pulmonologist or primary health-care provider from the population of military beneficiaries in the San Antonio, TX metropolitan area. The inclusion criteria were a diagnosis of COPD, an FEV1 < 50% of predicted, and the ability to walk on a treadmill. Patients were excluded if they had exertional angina, congestive heart failure, valvular heart disease, uncontrolled cardiac dysrhythmias, or other conditions limiting their ability to exercise or use a nasal mask. The study was approved by the institutional review committee, and informed consent was obtained from all subjects.

Rehabilitation Program
The program consisted of education by means of lectures and group discussions on topics including disease pathophysiology, medication use, nutrition, breathing techniques, and lifestyle modifications to reduce dyspnea. Smoking cessation was included for those who had not stopped using tobacco products. The program also stressed activity and exercise, and included supervised treadmill exercise training. Approximately six to nine patients were enrolled at a time, with each session meeting twice per week for 6 weeks.

Entry Evaluation
All patients underwent a history and physical examination, serum electrolytes, CBC count, room air arterial blood gas, ECG, spirometry, lung volumes, and diffusing capacity of the lung for carbon monoxide. Each patient also underwent a maximal graded exercise treadmill test with ECG and pulse oximetry monitoring to evaluate for evidence of coronary artery disease and to determine the possible need for oxygen with exercise.

Study Protocol
Patients accepted for the study spent 8 weeks in the program. The first and last weeks were used for exercise testing, and the middle 6 weeks were used for exercise training and education as described above (Fig 1 ). During the first and last weeks, each patient underwent three separate maximal graded exercise treadmill tests, one with each of these three different modalities: (1) humidified air, 10 L/min via nonrebreather mask, supplied by a compressor; (2) humidified heliox (79% helium, 21% oxygen), 10 L/min via nonrebreather mask, supplied from a tank; and (3) NIPPV with room air.



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  		Figure 1. Study sequence.

 
NIPPV was provided as bilevel positive airway pressure via a tight-fitting nasal mask with an inspiratory positive airway pressure (IPAP) of 8 to 12 cm H2O (as high as possible based on patient tolerance) and an expiratory positive airway pressure (EPAP) of 2 cm H2O. The ventilator used was a Respironics BiPAP S/T-D with a plateau exhalation valve (Respironics; Murrysville, PA). During both testing and training with the machine, patients were encouraged to inhale through the nose with the mouth closed and exhale through the mouth with pursed lips. Pursed-lips breathing was taught and encouraged for all patients during exercise whether receiving mechanical ventilation or not.

The treadmill tests were performed on 3 consecutive days, with the order randomized for each patient. The air and heliox tests were double blinded. Treadmill speeds at the beginning (1.0 to 2.0 miles per hour [mph]) and at the maximal level (2.0 to 3.0 mph) were individualized for each patient based on their stride length and comfort, as determined during the baseline treadmill testing described above. Starting inclines were set to zero. Each treadmill test progressed in 4-min intervals, by speed increments of 0.5 mph up to the predetermined maximum speed. Once maximum speed was obtained, the incline was increased at 3% grade per additional 4-min interval that the patient exercised. All treadmill tests were performed to exhaustion. The speed and incline protocol used for each individual patient was the same for all three tests during the first week and all 3 weeks during the last week. Oxygen was supplied and adjusted, as needed, via nasal cannula or in-line with the bilevel positive airway pressure nasal mask, to maintain oxygen saturation by pulse oximetry at least 90% throughout the entire testing and training periods.

During treadmill testing, heart rate, oxygen saturation, and oxygen flow rates were monitored continuously and recorded every minute. A Borg score27 obtained from a visual analog scale, was recorded every minute to evaluate the patient’s sensation of dyspnea. BP was recorded every 2 min. The workload achieved during each stage of treadmill testing was estimated from standardized tables based on speed and incline of the treadmill, and expressed as metabolic equivalents (METs). Total exercise time and maximum workload achieved for at least 30 s were recorded for each test.

During the middle 6 weeks, the subjects completed the standard pulmonary rehabilitation program as described above. Patients were randomized to the exercise training for this entire period into one of three groups: unassisted exercise training (UT group), training while breathing heliox (HT group), or training while breathing with by NIPPV (NT group). The HT group did their exercise sessions with a nonrebreather mask powered with 10 L/min of humidified heliox. The NT group exercised wearing the nasal mask with an EPAP of 2 cm H2O and an IPAP of 8 to 12 cm H2O (as high as patient comfort would allow). UT group patients did not wear ventilatory masks of any type. (No attempt was made to blind HT group and UT group patients to their training modality.) Patients were treated in the same manner with respect to all other aspects of the rehabilitation program.

Exercise training consisted of twice-weekly exercise treadmill work to maximal patient tolerance. The patients were generally started at an MET level of approximately 50 to 60% of their maximum based on their initial tests, and exercised for a total of 20 min even if they had to stop to rest. Once the patient could exercise for 20 min continuously at this level and at each subsequent exercise level, the treadmill intensity was increased. Walking speed was increased first up to the maximum comfortable stride length, and then the grade was increased. Patients also exercised at least once per week at home, and this was accomplished without NIPPV or heliox.

Outcomes and Statistical Analysis
The study goals were: first, to evaluate for an immediate effect of breathing heliox or using NIPPV on exercise performance; and second, to look for the training effect of the two modalities. The immediate effect was sought in all study enrollees who finished the first set of treadmill tests, and the primary outcome variable was total exercise time. Maximum workload attained for at least 30 s was a secondary outcome variable. Assuming day-to-day variation in treadmill results of approximately ± 20% (SD of differences of approximately 20%), a true increase in performance of 11.5% can be detected with 39 patients assuming {alpha} and ß errors of 5% each. The actual SD for the differences in the heliox and air initial exercise times for the 39 patients was 22%, so this estimate was accurate. A paired two-tailed t test was used to compare the heliox test to the unassisted test, and the NIPPV test to the unassisted test.

The training effect of each modality was sought by comparing the three groups of patients who completed the entire study. The primary outcome variable was the percentage change in exercise time when tested unassisted during week 8 compared to testing unassisted in week 1. Specifically, for an individual patient in each group, the following quantity was calculated and compared:

where UET = unassisted exercise time.

At the beginning of the study, the SD for the percentage improvement in exercise time was uncertain so that sample size for this portion of the study could not be determined. Given the final SD of 37% for the improvement in the UT group and a group size of about 10, the study had the power to detect an approximate 60% actual difference in improvement between an intervention group compared to the UT group given {alpha} and ß error levels of 5% each (ie, an improvement of approximately 97% compared with 37%).

Average values are presented as mean ± SD. Various other comparisons were made using paired and unpaired t tests as appropriate. A p value < 0.05 was considered statistically significant.

Patient Satisfaction
Patients completed a questionnaire on the last day of the study. They were asked about the change in their overall condition, exercise capability, and their breathing ability in three separate questions with possible responses as follows: greatly improved, somewhat improved, not either better or worse, somewhat worse, substantially worse. Also, if they were trained on heliox or NIPPV, they were asked whether it helped them exercise, with possible responses as follows: helped a great deal, helped somewhat, did not help, made it somewhat harder, made it substantially harder to exercise.


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Conclusion
 References
 
Forty-one patients were enrolled in the pulmonary rehabilitation program during the study period. Two patients were excluded because of a primary diagnosis of interstitial lung disease. Thirty-nine patients entered the study, and 32 patients completed the entire program. Seven patients dropped out, one each for exertional angina, congestive heart failure, a flare of chronic liver disease, a COPD exacerbation, a tibial fracture, a scheduling conflict, and noncompliance. Of these, four patients were from the NT group, two patients were from the UT group, and one patient was from the HT group.

Of the 39 patients initially enrolled, 24 were men and 14 were women. The average FEV1 was 33.5% of predicted, and the mean age was 69 years. Table 1 lists the baseline data for the patients who completed the study in each group. No significant differences were detected between the groups for demographic, pulmonary function, or blood gas parameters.


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  		Table 1. Patient Demographics*

 
Immediate Effects of Heliox and NIPPV
For the 39 patients enrolled who completed the first week of testing, there were no statistically significant differences in total exercise time or maximum workload when comparing exercising on the different modalities (Table 2 ). An immediate effect was also sought among the 32 patients completing the study during testing in the final week, with the idea that greater familiarity with treadmill exercise might allow identification of an effect not initially seen (Table 2) . Heliox produced no immediate effect on exercise time or maximum workload in this group. Furthermore, the HT group had no improvement with breathing heliox during final testing in either exercise time (16.2 ± 4.0 min vs 16.6 ± 4.0 min, p = 0.674) or maximum workload (4.47 ± 1.37 METs vs 4.59 ± 1.36 METs, respectively; p = 0.499).


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  		Table 2. Immediate Effects of Heliox and NIPPV for Entire Group*

 
NIPPV did produce a small increase in exercise time (16.7 min vs 15.6 min; Table 2 ) but not workload for the entire group of 32 patients completing the study. This small increase appeared to be related to the subgroup of 11 patients who trained on NIPPV (NT group). Table 3 shows the immediate effect of NIPPV in this subgroup during final testing. All but one of these patients exercised longer with NIPPV, so that they went an average of 2.6 min longer (p = 0.0045) to a workload that was 0.37 METs higher (p = 0.038). At maximum exercise, this subgroup achieved a higher heart rate when assisted by NIPPV, but there was no significant difference in systolic BP, Borg score, oxygen saturation, or oxygen flow rate. At the isotime during the NIPPV test when the test had to be stopped due to exhaustion during the unassisted test, these patients had a significantly lower average Borg score (5.3 ± 3.0 vs 7.3 ± 1.7, p = 0.026) and higher oxygen saturation level (95.0 ± 2.2% vs 92.7 ± 1.8%, p = 0.026) on a similar oxygen flow rate (2.4 ± 1.8 L/min vs 2.8 ± 1.8 L/min), respectively.


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  		Table 3. Immediate Effect of NIPPV in the NT Group During Final Week of Testing*

 
Exercise Improvement for the Entire Group
The 32 patients completing the study had substantial improvement in exercise ability. When their final and initial unassisted tests were compared, they exercised longer (15.6 ± 5.2 min vs 11.1 ± 5.2 min, p < 0.000001) and to a higher workload (4.60 ± 1.63 METs vs 3.43 ± 1.42 METs, respectively; p < 0.000001).

Training Effects for the HT Group vs the UT Group, and the NT Group vs the UT Group
Tables 4 , 5 show the average initial and final unassisted exercise times and maximum workloads for the three groups. The HT group had a similar average exercise time and workload as the UT group in both initial and final testing. The NT group had a shorter initial exercise duration and lower initial workload than the UT group, but the differences were no longer statistically significant after 6 weeks of training.


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  		Table 4. Initial and Final Unassisted Exercise Times for the Three Groups*

 

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  		Table 5. Initial and Final Unassisted Maximum Workloads for the Three Groups*

 
When considered from the standpoint of the primary study variable of percentage increase in exercise time with training (Table 6 ), the HT group demonstrated no clear benefit when compared to the UT group. The NT group when compared to the UT group did show a greater improvement in the primary study variable (exercise time increase 89.6 ± 57.7% vs 37 ± 33%, respectively; p = 0.016). The difference in workload improvement was not statistically significant.


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  		Table 6. Percentage Improvement in Unassisted Testing for the Three Groups, Final vs Initial Week*

 
Exercise Intensity During Training
Figure 2 shows the exercise intensity during training for the three groups in METs times total minutes of treadmill time averaged for each group for 10 of the training sessions. Nearly all of the patients were present for 10 sessions, but enough had absences to render comparisons for the 11th and 12th sessions less reliable. There was a trend toward the UT group exercising more vigorously than the other two groups, which was statistically significant only in the initial sessions.



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  		Figure 2. Exercise intensity during training. *p < 0.05.

 
Patient Satisfaction
Thirty of the patients completed questionnaires, and all indicated that they were either somewhat or greatly improved in terms of their overall condition (6 patients and 24 patients), exercise capability (5 patients and 25 patients), and breathing ability (4 patients and 26 patients, respectively). There were no meaningful differences in these responses based on the group they trained with. All of the patients in the NT group indicated that NIPPV helped a great deal with exercise. Five of the nine patients in the HT group completing the form said that heliox helped a great deal, three patients said it helped a little, and one patient said that it made no difference.


   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Conclusion
 References
 
This study answered some questions but not others. The two primary questions were whether heliox or NIPPV treatment produces an immediate improvement in exercise capability in patients with COPD, and whether exercising with the assistance of these modalities produces a greater training effect than exercising unassisted. We chose to use individualized treadmill tests to produce our end points. Considerable variability has been documented in how exercise testing is performed between pulmonary rehabilitation programs.28 Timed walks are used most commonly, but these only allow patients to demonstrate improvement by increasing speed. Many elderly patients have relative limitation in stride length due to musculoskeletal problems such as degenerative joint disease, but can show improved work capability with walking the same speed up a grade on a treadmill. A single standardized protocol does not optimally allow for the considerable differences in these patients, so we used individualized protocols. After creating an individualized protocol for a given patient, it was used for all six tests in order to produce comparable data.

Immediate Effects of Heliox and NIPPV
The lack of an effect of heliox was disappointing, particularly given the ease with which it could be used as a rehabilitation adjunct. Heliox is known to increase forced expiratory flow,10 and in our laboratory, nine patients with COPD (mean FEV1 of 1.11 L) breathing for 5 min from a bag containing heliox via a one-way valve demonstrated a mean increase in FEV1 of 17.2%. At rest, 10 L/min of heliox via nonrebreather mask would be expected to approximate this degree of improvement. However, at maximum exertion with minute ventilations of 25 to 50 L/min, the patient’s helium concentration in expired gas would be expected to drop substantially. Nevertheless, it was hoped that there would be enough of an effect on expiratory flow and dynamic hyperinflation to produce an effect on exercise performance. There was no measurable immediate effect in the initial tests with 39 subjects, the final tests with 32 subjects, or the final tests within the group of 10 patients who trained on it, consistent with the findings of Bradley et al.20

The effect of NIPPV was more complicated, and this modality holds more promise as a useful adjunct to training. NIPPV applied via nasal mask with bilevel positive airway pressure at the settings mentioned above in patients with COPD unfamiliar with bilevel positive airway pressure does not immediately improve exercise performance when compared with exercising unassisted. The initial group of 39 patients actually did somewhat worse with NIPPV, exercising on average about 1 min less when using the machine.

The group of 32 patients completing the study did a little better with NIPPV than with unassisted exercise, but this was primarily due to the substantial improvement it provided to the subgroup of 11 patients who trained with it for 6 weeks (NT group). With NIPPV, this subgroup exercised > 2.5 min longer and achieved a significantly higher workload. This is the first study, to our knowledge, to show an immediate effect of NIPPV on maximum workload, since all others23 24 25 26 have looked only at exercise duration at constant workload.

Keilty et al24 found that application of IPAP of 12 to 15 cm H2O and EPAP of 6 cm H2O with a full facemask increased submaximal median treadmill walking distance by 62% in eight men with COPD (mean FEV1 0.73 L) compared with using a sham circuit. Dolmage and Goldstein25 found an increase in cycling endurance time with NIPPV administered as proportional-assist ventilation (PAV) combined with an EPAP of 5 cm H2O administered by mouthpiece in 10 patients with COPD with a mean FEV1 of 29% of predicted. They were not able to document an effect with either PAV or continuous positive airway pressure (CPAP) alone. Bianchi et al26 demonstrated that cycling endurance time was increased by PAV, pressure support with an IPAP of 12 to 16 cm H2O and an EPAP of 1 cm H2O, and CPAP of 6 cm H2O compared to sham ventilation via a nasal mask in 15 patients with COPD with stable hypercapnia. The greatest effect was with PAV followed by pressure support and then by CPAP. Likewise, Hernandez et al23 demonstrated an increase in cycling endurance time with PAV without EPAP in eight patients (mean FEV1 of 0.70 L).

While the response of the NT group is consistent with the studies mentioned above, the lack of benefit of NIPPV in our original 39 untrained patients was surprising. There are a number of possible explanations for this. One is lack of familiarity with the equipment. The patients were asked to exercise with it after being fitted with a mask and being given 5 to 10 min to breathe with it at rest. Some patients related that they had difficulty due to the mask itself, with a dyspneic feeling from the tight fit and the sensation of air being pushed in. This may have prompted them to breathe primarily through the mouth, reducing the potential benefit of the pressure assistance from the nasal mask. Keilty et al24 and Bianchi et al26 both mention having more than one preliminary session to familiarize the patients with the equipment, Dolmage and Goldstein25 mention having one such session, and Hernandez et al23 had none.

Another related explanation is that the previous studies compare NIPPV against sham ventilation with the same mask or mouthpiece, such that active ventilation may just be overcoming an apparatus-related decrement in performance. This seems unlikely to be the entire explanation since both Keilty et al24 and Bianchi et al26 measured exercise performance without the ventilator equipment and found no significant difference in endurance time between that and sham ventilation.

Another possibility is that our patients may have been rebreathing carbon dioxide within the circuit, reducing ventilatory efficiency. Carbon dioxide rebreathing has been documented to be a problem with this system,29 since there is only one hose attaching the machine to the mask and exhaled gas can enter it. Increasing the expiratory flow of gas from the machine by increasing the EPAP level has been shown to reduce the amount exhaled gas resident in the circuit during exhalation.29 30 Of the available valves, the commonly used Whisper-Swivel (Respironics) valve has the greatest rebreathing problem, and even EPAP levels of 5 cm H2O do not completely eliminate it.30 The plateau valve that we used allows less carbon dioxide into the ventilator hose; and with standard use of the machine, no carbon dioxide rebreathing occurs even at an EPAP of zero.29 However, use with exercise places greater demands on the machine with higher minute ventilations and larger tidal volumes, which may allow for less complete clearance of exhaled gas within the circuit. The patients who trained with the machine (NT group), mastered inhaling through the nose and exhaling through the mouth, a technique that would be expected to eliminate entry of exhaled gas into the circuit with subsequent rebreathing. If rebreathing was part of the problem, this technique may be one reason why the NT group did so much better than the rest of the group with NIPPV during final testing.

Training Effect
Like many previous studies, this one showed substantial increases in the patients’ subjective impression and the objective measurement of exercise capability in the group as a whole. The improvement is likely to represent both increased efficiency and a modest increase in maximal oxygen uptake based on previous studies.3 4 5 6 7 8 9 Review of the patients’ exercise logs showed that they uniformly exercised more than the supervised sessions, with an average total of approximately four times per week. Hence, our comparison of training modalities represented assistance during only a portion the patient’s exercise sessions since the others were done at home.

Breathing heliox did not appear to confer an advantage during training. A trend toward a greater percentage improvement in exercise time in the HT group compared to the UT group was noted, but this did not reach statistical significance. Since the study was only powered to find a difference in average improvement of 60%, it is possible that a smaller improvement was missed. However, the lack of any immediate effect of heliox on exercise tolerance in any group or subgroup argues against this. Exercising with higher heliox flow rates to maintain greater exhaled helium concentrations may confer an advantage, but this is unproven and would be less practical.

NIPPV may confer a training advantage. The NT group was similar to the UT group in demographic measures and standard pulmonary function test results, but had lower initial exercise capability parameters. This can happen since standard pulmonary function tests such as FEV1 have only limited correlation with maximum exercise.31 By the fifth training session, the statistical difference in exercise intensity had been eliminated although the average exercise intensity for the NT group remained below the UT group in all the sessions. During final testing, there was no statistical difference in unassisted testing between the NT and UT groups (14.2 min vs 16.0 min, respectively; Table 4 ). In fact, when the NT group was allowed to use bilevel positive airway pressure, they actually exercised slightly longer than the UT group (16.8 min vs 16.0 min; Tables 3 , 4 ). While this added exercise time represents an immediate effect of the NIPPV, it may also represent a cardiovascular training effect acquired during rehabilitation that can be demonstrated only with relief of the respiratory limitation with ventilatory assistance.

In terms of the primary study variable of percentage increase in exercise time unassisted, the NT group had a significantly greater increase than the UT group. However, since the NT group had lower initial exercise times, this difference may be a mathematical artifact due to the lower denominators and hence cannot be regarded as definitive substantiation that NIPPV produces greater gains in exercise tolerance.


   Conclusion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
References
 
Heliox administered in the fashion described offers no immediate or training benefits for patients with COPD. NIPPV administered as an IPAP of 8 to 12 cm H2O does confer an immediate benefit in terms of both exercise duration and maximum workload for patients trained on it. Whether NIPPV enhances exercise reconditioning enough to have a demonstrable effect that carries over to unassisted exercise is still uncertain. It seems intuitive that the increased exercise capability with NIPPV should translate into some degree of reconditioning benefit with training even if it is only demonstrable while testing with ventilatory assistance. Although performing strenuous activities of daily living with ventilatory assistance is impractical at this point, advances in technology may change this. For example, the development of a portable jet ventilator that could be used with transtracheal catheters already in use for oxygen delivery could allow ventilatory assistance without a cumbersome tight fitting nasal mask. In the meantime, further research on the relief of exercise limitation via mechanical ventilation for patients with COPD is warranted.


   Footnotes
 
Abbreviations: CPAP = continuous positive airway pressure; EPAP = expiratory positive airway pressure; HT group = training while breathing heliox; IPAP = inspiratory positive airway pressure; MET = metabolic equivalent; mph = miles per hour; NIPPV = noninvasive positive pressure ventilation; NT group = training while breathing with noninvasive positive pressure ventilation; PAV = proportional-assist ventilation; UT group = unassisted exercise training

The opinions or assertions contained herein are the private views of the authors and should not be construed as reflecting the views of the Department of the Army or the Department of Defense.

Funded completely through Brooke Army Medical Center local research funds.

Received for publication May 13, 1999. Accepted for publication March 18, 2002.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Conclusion
 References
 

  1. Redline, S (1991) The epidemiology of COPD. Cherniak, NS eds. Chronic obstructive pulmonary disease WB Saunders Philadelphia, PA.
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