(Chest. 2003;124:1658-1662.)
© 2003
American College of Chest Physicians
Advantages of the Intrabreath Technique as a Measure of Lung Function Before and After Heart Transplantation*
Mackenzie Quantz, MD;
Steven Wilson, BSc;
Charles Smith, BSc;
Larry Stitt, MSc;
Richard Novick, MD, MSc and
Dildar Ahmad, MD, FCCP
* From the Divisions of Cardiac Surgery (Drs. Quantz and Novick, and Mr. Smith) and Respirology (Mr. Wilson and Dr. Ahmad), and the Department of Clinical Epidemiology and Biostatistics (Mr. Stitt), London Health Sciences Center, London, ON, Canada.
Correspondence to: Mackenzie A. Quantz, MD, London Health Sciences Center, University Campus, PO Box 5339, 339 Windermere Rd, London, ON, Canada N6A 5A5; e-mail: maquantz{at}uwo.ca
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Abstract
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Background: Pulmonary function testing is an integral part of evaluating patients who are being considered for cardiac transplantation. The accurate measurement of diffusing capacity (DLCO) and alveolar volume (VA) is dependent on a 10-s breath-holding maneuver that may be difficult for patients with congestive heart failure to perform. The intrabreath (IB) technique is not dependent on a breath-holding maneuver and may provide more accurate pulmonary function testing results in chronically debilitated patients.
Methods: Seventy-five patients performed maneuvers with IB and single-breath (SB) techniques during evaluation for heart transplantation and at 3 and 12 months following transplantation. The DLCO, VA, and total lung capacity (TLC) were compared using Pearson correlation coefficients, a Student t test, and intercorrelation coefficients.
Results: The DLCO and VA, when determined with the IB technique, had excellent correlations to the SB technique over all ranges of DLCO values. VA values that were determined by the IB technique were greater than those determined by the SB technique and more closely approximated the TLC values. The satisfactory correlation between the two techniques was maintained when DLCO was corrected for VA. However, due to the lower values for VA as determined by the SB method, the corrected measurements were consistently higher for the SB technique.
Conclusion: Pulmonary function can be measured accurately in a population of patients with long-standing congestive heart failure, both before and after cardiac transplantation, using the IB technique. Furthermore, the IB technique may provide a more accurate measurement of VA.
Key Words: cardiac transplantation • diffusing capacity • intrabreath method • pulmonary function testing • single-breath method
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Introduction
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Pulmonary function testing is an essential part of the evaluation process of patients being considered for cardiac transplantation. Patients with severe congestive heart failure may have a restrictive or obstructive ventilatory defect with a decreased diffusing capacity of the lung for carbon monoxide (DLCO) that remains depressed following transplantation.1
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However, accurate measurements of DLCO and alveolar volume (VA) using the single-breath (SB) technique are dependent on the performance of a breath-holding maneuver lasting 10 s. This is quite difficult for patients with long-standing congestive heart failure and may lead to erroneous measurements or an inability to complete pulmonary testing to American Thoracic Society (ATS) standards. Conversely, the intrabreath (IB) technique of determining DLCO does not require a breath-holding maneuver, and may be easier for dyspneic and debilitated patients to perform.3
However, its accuracy has never been validated in a patient population with severe congestive heart failure or following heart transplantation. This study examines the correlation between the IB and SB techniques in patients with severe congestive heart failure, both before and after undergoing cardiac transplantation.
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Patients and Methods
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Patient Population
Our patient cohort consisted of a total of 75 patients who were referred to the London Health Sciences Centre, University Campus, from February 1993 to January 1998. These patients were being assessed for cardiac transplantation secondary to end-stage heart failure that was refractory to medical management. Patient demographics are shown in Table 1
. Age and spirometry values are presented as the mean ± SD. Forty-four patients were evaluated as a part of their pretransplant evaluation. Fifty-four patients were evaluated at 3 months posttransplant, and 39 were evaluated at 1 year posttransplant.
Pulmonary Function Testing
The IB and SB techniques for determining DLCO were performed sequentially (model 2200; SensorMedics; Yorba Linda, CA). Methane was used as an inert tracer to simultaneously measure VA. The total lung capacity (TLC) was determined by N2 gas dilution. The equipment was calibrated daily according to ATS recommendations using a 3-L syringe.4
The software used the Jones and Meade5
method for the measurement of breath-holding time. The SB technique was performed in accordance with the guidelines of the ATS including a 10-s breath-hold at TLC.4
The IB technique is performed in the same way until the point of breath-holding. However, instead of a 10-s breath-hold, the patient immediately begins to exhale slowly at a constant rate to residual volume.3
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The exhaled IB target flow rate was 500 mL/s (acceptable range, 300 to 600 mL/s). No ATS standards exist for the IB technique. Therefore, the ATS criteria for inspired vital capacity and inspiratory time were used. No patients who could perform testing to meet the ATS standards were excluded from the analysis. Exclusion criteria included the following: extreme illness preoperatively precluding pulmonary function testing; inability to meet ATS standards during pulmonary function testing; and inability to perform follow-up testing in the postoperative period.
Data Analysis
As both the IB and SB techniques were performed for each patient with each set of pulmonary function tests, these were directly compared. The correlation between the IB and SB methods was determined using Pearson correlation coefficients. These were calculated for the DLCO, VA and DLCO/VA ratio at each time point (ie, pretransplant, and 3 and 12 months postoperatively). A Student t test determined whether there was a difference among the values of DLCO, VA, and DLCO/VA ratio at each time point. A p value of < 0.05 was considered to be significant for both tests. An intracorrelation coefficient (ICC) with a 95% confidence interval was calculated as a measure of agreement between the values obtained with the IB and SB techniques.
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Results
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There was an excellent correlation between DLCO values determined by the IB and SB techniques when performed both pretransplant and at 3 and 12 months following transplantation by both Pearson correlation coefficients and ICC (Table 2
). This correlation was true for all values of DLCO (Fig 1
). The mean values at 3 and 12 months posttransplantation were not significantly different (Table 2)
. VA values measured by both techniques had an excellent correlation (Table 2)
. However, the VA values were significantly higher when measured using the IB method compared to the values derived for the SB technique (p < 0.0001 for all time periods). Overall, however, ICCs demonstrated a good-to-excellent agreement between the two sets of volumes. When the VA values were compared to the TLC, once again there was an excellent correlation between the values obtained using the IB and SB methods (Table 2)
. The VA values determined by the IB method, however, more closely approximated the TLC than those determined by the SB method (Fig 2
). This is demonstrated with the overall excellent agreement between the TLC and VA values with the IB technique compared to a good agreement with the SB technique (Table 2)
. The good-to-excellent correlation between values using the two methods was maintained when the DLCO values were corrected for VA (Table 2)
. Once again, due to the lower VA values measured with the SB technique, the corrected DLCO values were consistently lower for the IB technique (p < 0.0001 for all time periods).
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Table 2.. Comparison of Values Using IB and SB Techniques in Patients With Severe Heart Failure Before and After Transplantation
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Discussion
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The objective of this study was to compare the IB technique with the traditional SB method for measuring DLCO and VA in patients with severe congestive heart failure before and after cardiac transplantation. The data indicated that DLCO, when determined by the IB method, had a good correlation with the SB method. This was also true for VA. However, the correlation between VA and TLC was better with the IB technique than for the SB method.
Pulmonary function is frequently impaired in patients with congestive heart failure.2
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A restrictive ventilatory pattern may be secondary to the presence of cardiomegaly, pleural effusions, pulmonary venous congestion, impaired alveolar perfusion, and interstitial edema. Pulmonary function testing, including the determination of DLCO, is a standard component of determining a patient’s candidacy for heart transplantation. DLCO has traditionally been determined using the SB technique. This includes a standardized 10-s breath-hold of an inspired vital capacity of at least 90% of the best previously measured vital capacity.4
This maneuver may prove to be difficult to perform for patients with chronic disease states, such as congestive heart failure, and may result in an inability to complete the testing or in errors in measurements. The IB technique, by comparison, is not dependent on a breath-holding maneuver and is easier for debilitated or dyspneic patients to perform.
The determination of DLCO with the IB method demonstrated an excellent correlation with the SB technique over all ranges of DLCO. These findings are similar to those of Kiss et al6
and Wilson et al,3
who examined subjects with normal and obstructive ventilatory function.
VA values were significantly higher when determined by the IB technique. Jansons et al11
have demonstrated that the SB method increasingly underestimates residual volume with increasing amounts of unequal ventilation when compared to the rebreathing method. Therefore, the SB technique may be consistently underestimating the VA in this patient population. To determine which was more accurate at measuring VA, the methods were compared to the TLC, which was calculated by gas dilution. The VA values, as determined by the IB technique, were in closer agreement to the TLC than were the SB values. This relationship was consistent for the three different follow-up periods. Kiss et al6
found that VA is a closer approximation of the TLC when it is determined using the IB technique vs the SB technique in obstructed patients. The reason for this improved correlation is not clear but may be due to the less demanding nature of the IB testing, making this method easier for debilitated or dyspneic patients to perform. Similarly DLCO/VA ratio tended to be lower for the IB technique than for the SB method. This would be expected with the smaller VA values that were determined with the SB method. However, there was still a good correlation between the two. Furthermore, these good-to-excellent correlations exist for the posttransplant period, as well as for the pretransplant period, and are consistent for all ranges of DLCO or VA.
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Conclusion
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The determination of the DLCO and the VA using the IB technique is accurate in patients with both severe end-stage heart failure and following cardiac transplantation. The VA as measured by the IB technique correlates better with the TLC than when it is determined by the SB technique. Therefore, the IB method may be a more accurate technique of measuring VA in this patient population. Furthermore, the IB technique is a less demanding test for ill patients to perform, and has greater patient acceptance and compliance.
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Figure 2.. VA determined by the IB and SB techniques compared to the TLC pretransplant and at 3 and 12 months after cardiac transplantation. ICCs are shown for VA IB vs TLC and for VA SB vs TLC.
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Acknowledgements
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We thank Janice Motloch and Jennifer Doroshenko for the preparation of the manuscript.
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Footnotes
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Abbreviations: ATS = American Thoracic Society; DLCO = diffusing capacity of the lung for carbon monoxide; IB = intrabreath; ICC = intracorrelation coefficient; SB = single breath; TLC = total lung capacity; VA = alveolar volume
Received for publication November 25, 2002.
Accepted for publication March 18, 2003.
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References
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- Ewert, R, Wensel, R, Bettmann, M, et al (1999) Ventilatory and diffusion abnormalities in long-term survivors after orthotopic heart transplantation. Chest 115,1305-1311[Abstract/Free Full Text]
- Ulrik, CS, Carlsen, J, Arendrup, H, et al Pulmonary function in chronic heart failure. Scand Cardiovasc J 1999;33,131-136[CrossRef][ISI][Medline]
- Wilson, AF, Hearne, J, Brenner, M, et al Measurement of transfer factor during constant exhalation. Thorax 1994;49,1121-1126[Abstract]
- American Thoracic Society. Single-breath carbon monoxide diffusing capacity (transfer factor): recommendations for a standard technique; 1995 update. Am J Respir Crit Care Med 1995;152,2185-2198[ISI][Medline]
- Jones, RS, Meade, F A theoretical and experimental analysis of anomalies in the estimation of pulmonary diffusing capacity by the single breath method. Q J Exp Physiol 1961;46,131-143
- Kiss, D, Popp, W, Wagner, C, et al Comparison of the single breath with the intrabreath method for the measurement of the carbon monoxide transfer factor in subjects with and without airways obstruction. Thorax 1995;50,902-905[Abstract]
- Hosenpud, JD, Stibolt, TA, Atwal, K, et al Abnormal pulmonary function specifically related to congestive heart failure: comparison of patients before and after cardiac transplantation. Am J Med 1990;88,493-496[CrossRef][ISI][Medline]
- Puri, S, Baker, BL, Dutka, DP, et al Reduced alveolar-capillary membrane diffusing capacity in chronic heart failure. Circulation 1995;91,2769-2774[Abstract/Free Full Text]
- Puri, S, Baker, BL, Oakley, CM, et al Increased alveolar/capillary membrane resistance to gas transfer in patients with chronic heart failure. Br Heart J 1994;72,140-144[Abstract/Free Full Text]
- Mettauer, B, Lampert, E, Charloux, A, et al Lung membrane diffusing capacity, heart failure, and heart transplantation. Am J Cardiol 1999;83,62-67[CrossRef][ISI][Medline]
- Jansons, H, Fokkens, JK, van der Tweel, I, et al Rebreathing TLCO versus single breath TLCO at different degrees of unequal ventilation. Respiration 1994;61,32-36[ISI][Medline]
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Abstract
Introduction
