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Comparison of single-breath and plethysmographic measurements of resistance in infancy
I Dundas1, C A Dezateux, M E Fletcher
1Portex Anaesthesia, Intensive Therapy and Respiratory Medicine Unit, Institute of Child Health, London, United Kingdom.
Insights
The single-breath technique (SBT) for measuring total respiratory resistance (Rrs) in infants showed higher failure rates and variability than plethysmography. While simple for studies, its clinical use in individual infants is limited.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
- Infant Health
Background:
- Assessing infant respiratory resistance is crucial for diagnosing and managing lung conditions.
- Plethysmography is a standard method, but alternative techniques are explored for ease of use.
- Understanding respiratory mechanics in infants requires accurate resistance measurements.
Purpose of the Study:
- To compare the single-breath technique (SBT) for measuring total respiratory resistance (Rrs) with standard plethysmography for airway resistance (Raw) in infants.
- To evaluate the technical success rate and agreement between SBT and plethysmography across different infant age groups and with prior wheeze.
- To determine the applicability of SBT in clinical and epidemiological settings for infant respiratory assessment.
Main Methods:
- Comparison of Rrs measurements from SBT against Raw measurements from plethysmography.
- Inclusion of three infant groups: healthy infants <= 13 weeks, healthy infants > 13 weeks, and infants > 13 weeks with prior wheeze.
- Analysis of technical success rates, failure reasons (e.g., flow-volume curve nonlinearity), and differences in resistance values between techniques and groups.
Main Results:
- SBT had a significantly higher technical failure rate (19%) compared to plethysmography (2%), primarily due to flow-volume curve nonlinearity.
- Both Rrs and Raw were significantly higher in infants with prior wheeze.
- Rrs was consistently higher than initial expiratory Raw across all groups, with varying differences for end-expiratory Raw.
Conclusions:
- The single-breath technique is simple to use and may be suitable for infant respiratory resistance studies, particularly in epidemiology.
- High between-subject variability and a notable failure rate limit the clinical application of SBT for individual infant assessments.
- Plethysmography remains more reliable for detecting dynamic changes in infant airway resistance, crucial for clinical decision-making.
Abstract:
Single-breath technique (SBT) measurements of total respiratory resistance (Rrs) were compared with plethysmographic measurements of airway resistance (Raw) in healthy infants < or = 13 wk of age (Group 1; n = 49) and > 13 wk of age (Group 2; n = 37) and in infants > 13 wk of age with prior wheeze (Group 3; n = 49). A significantly higher percentage of Rrs (19%) than of Raw (2%) measurements were technically unsatisfactory, alinearity of the flow-volume curve accounting for 54% of Rrs failures. Although both Rrs and Raw were significantly higher in Group 3 infants, between-subject variability was wide in all groups. Rrs was significantly higher than initial expiratory (IE) Raw in all groups. Mean difference Rrs-IE Raw (95% CI) values were 1.98 (1.51, 2.48), 1.29 (0.96, 1.62), and 1.97 (1.56, 2.38) kPa.L-1.s for Groups 1, 2, and 3, respectively. Significant but smaller differences were seen for end-expiratory (EE) Raw in Groups 1 and 2 but not in Group 3. Mean difference Rrs-EE Raw (95% CI) values were 0.68 (0.11, 1.26), 0.55 (0.19, 0.92), and 0.31 (-0.06, 0.69) kPa.L-1.s for Groups 1, 2, and 3, respectively. Despite wide between-subject variability in Rrs and a relatively high failure rate, the SBT is simple to use, and it may be applicable to epidemiologic studies. However, clinical applications in individual infants may be limited by failure to detect the dynamic changes in resistance throughout the breath evident from plethysmographic studies.