The rise in carboxyhemoglobin from repeated pulmonary diffusing capacity tests☆
Highlights
► Repeated 5-s single breath-hold diffusing capacity tests were performed. ► 55 ppm NO and 0.28% CO, 19.5% O2, 9.5% He, Bal N2, was inhaled per test. ► Carboxyhemoglobin percentage increased by 0.44% per test between the second and 22nd test. ► Pulmonary diffusing capacity for CO was significantly reduced when carboxyhemoglobin percentage was 6% (the 10th test). ► Pulmonary diffusing capacity for NO was not altered after 22 tests while methemoglobin percentage only changed minimally.
Introduction
The repeated measurement of pulmonary diffusing capacity for carbon monoxide (DLCO) raises the carboxyhemoglobin percentage in the blood, COHb. An increase in COHb affects the DLCO in two ways. First, the rise in COHb reduces carbon monoxide (CO) driving pressure across the alveolar membrane due to the CO back pressure in capillary blood. Second, the increase in COHb reduces the available hemoglobin binding sites, which results in an anemia-like effect. For every 10 s breath-hold maneuver during a diffusing capacity test, the rise in COHb is about 0.7–0.8% per test (Forster et al., 1954, Frey et al., 1987), which results in a 1% decrease in DLCO for every 1% rise in COHb (Frey et al., 1990, Mohsenifar and Tashkin, 1979, Suri et al., 1987).
However, few data exist on the rate of increase in COHb or methemoglobin percentage (METHb) from the modified Roughton and Forster one-step technique in which 0.28% CO and 55 ppm nitric oxide (NO) is inhaled simultaneously for 5 s (The one-step DLCO–DLNO method). The combination of CO and NO inhaled together allows for determination of pulmonary capillary blood volume in a single breath-hold maneuver (Guenard et al., 1987). However, multiple inhalations of NO may produce METHb due to its reaction with oxyhemoglobin, and reacts with deoxyhemoglobin to produce iron nitrosyl hemoglobin (HbNO) (Zavorsky et al., 2010). Thus, oxygen carrying capacity in the blood can be impaired since neither METHb nor HbNO can bind oxygen (Zavorsky et al., 2010). As such, the purpose of this study was to determine the rate of increase in COHb and METHb from repeated 5 s single breath-hold maneuvers using the modified one-step DLCO–DLNO technique. This would be compared to the traditional 10 s single breath-hold method of measuring pulmonary diffusing capacity. The hypothesis was that the rise in COHb from the modified one-step technique would be about 0.5% per test (based on preliminary data conducted on the investigator), while METHb would increase by an undetermined amount. Furthermore, the drop in DLCO per test would be similar to the rise in COHb.
Section snippets
Methods
Nine healthy nonsmokers (5 males) were studied on two different days due to the convenience of accessible volunteers from a concurrent study (Zavorsky et al., 2012) and not as a deliberate part of the protocol. They were asked to participate in two separate sessions separated by at least 24 h between sessions. Subjects were asked not to consume any alcohol or caffeine 6 h prior to testing, and no food 2 h prior to testing. All subjects, students from Marywood University, signed an informed consent
Results
The nine subjects, as a whole, had normal pulmonary function (Table 1). It took 22 diffusing capacity tests using the 5 s modified one-step DLCO–DLNO technique to raise COHb to 11.1 (SD 1.4)% (Table 2) compared to 14 tests using the traditional 10 s breath hold maneuver (Table 3). The individual responses are presented in Fig. 1. The mean rate of increase in COHb was 0.44% per diffusing capacity test using the 5 s modified one-step DLCO–DLNO technique compared to 0.64% using the traditional 10 s
Discussion
Nine healthy nonsmokers were studied on two different days due to the convenience of accessible volunteers from a concurrent study being performed in the Human Physiology Laboratory at Marywood University (Zavorsky et al., 2012). No study, to my knowledge, has examined the rate of increase in COHb or METHb from repeated 5 s breath hold maneuvers using the modified one-step DLCO–DLNO technique. As such, this was a novel research question to address. It was found that after 22 trials using the
Funding
No funding was received for this work.
Conflict of interest
The author of the present study has no conflicts of interest.
Acknowledgments
The author would like to thank Kaleen M. Lavin, Allison M. Straub, Christopher R. Cadman and Kathleen A. Uhranowsky for help with data collection and the creation of the figures. The author would also like to acknowledge Dr. Brian L. Graham for helping out with some of the calculations for the CO backpressure effects on pulmonary diffusing capacity.
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This study was presented in a thematic poster session at the 2012 European Respiratory Society Conference in Vienna, Austria.