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Determinants of tidal flow volume loop indices in neonates and children with and without asthma
K C Lødrup Carlsen1, A Stenzler, K H Carlsen
1Department of Paediatrics, Ullevål Hospital, Oslo, Norway.
Insights
Tidal flow volume (TFV) loop ratios change with age and obstructive airways disease (OAD). In neonates, changes are due to respiratory rate, while in asthmatic children, they reflect airway obstruction.
Area of Science:
- Pediatric Pulmonology
- Respiratory Physiology
Background:
- Tidal flow volume (TFV) loop ratios, including time to peak flow (tPTEF) to total expiratory time (tE) [tPTEF/tE] and volume to peak flow (VPTEF) to expired volume (VE) [VPTEF/VE], are known to decrease with age and in obstructive airways disease (OAD).
- The underlying mechanisms for these observed changes in TFV loop ratios are not fully understood.
Purpose of the Study:
- To reanalyze TFV loop data from neonates and young children to determine the mechanisms responsible for changes in tPTEF/tE and VPTEF/VE ratios.
- To differentiate between age-related changes and those indicative of obstructive airways disease in TFV loop parameters.
Main Methods:
- TFV loops were measured in healthy neonates at 1 hour and 1 day of life.
- Lung function was assessed in asymptomatic asthmatic children and controls before and after bronchodilator administration.
- Data from 24 neonates, 26 asthmatic children, and 26 controls were reanalyzed.
Main Results:
- In neonates, decreases in tPTEF/tE and VPTEF/VE from 1 hour to 1 day of life were attributed to increased expiratory time (tE) and expired volume (VE) due to a decreased respiratory rate.
- In asthmatic children, reduced baseline tPTEF/tE and VPTEF/VE were associated with lower tPTEF and VPTEF, with no significant differences in tE and VE compared to controls.
- Bronchodilator administration improved TFV loop ratios in asthmatic children, primarily through increases in tPTEF and VPTEF.
Conclusions:
- Age-related changes in TFV loop ratios in neonates are primarily driven by alterations in respiratory rate and expiratory duration/volume.
- In young children, diminished TFV loop ratios, particularly in asthmatics, are linked to airflow limitation (lower tPTEF and VPTEF).
- Evaluating both tPTEF and the ratios (tPTEF/tE or VPTEF/VE) is crucial for distinguishing age-related physiological changes from obstructive airway disease.
Abstract:
The tidal flow volume (TFV) loop ratios of (1) time to peak flow (tPTEF) to total expiratory time (tE) [tPTEF/tE] and (2) volume to peak flow (VPTEF) to expired volume (VE) [VPTEF/VE] are reported to decrease with age in early life, and to decrease in subjects with obstructive airways disease (OAD). However, the mechanisms behind these changes are not well known. Thus, we reanalyzed data from 24 healthy neonates (mean birthweight: 3.49 kg +/- 0.42 kg (SD)), 26 presently asymptomatic asthmatic children (age: 33 +/- 21 months), and 26 controls (age: 34 +/- 19 months) to elucidate what is responsible for the changes in these ratios in health and disease. Lung function was measured by TFV loops (SensorMedics 2600) at 1 hour of life and on the following day in the neonates, and before and after inhaled nebulized salbutamol (0.05 mg/kg) in the asthmatics and their controls. The observed decreases in mean tPTEF/tE and VPTEF/VE from 1 hour to 1 day of life (neonates) were entirely due to increased tE and VE, respectively secondary to a decrease in respiratory rate (P = 0.03). In asthmatics (young children), the decreased baseline tPTEF/tE and VPTEF/VE were due to lower tPTEF and VPTEF, with no significant differences in tE and VE in asthmatics and controls. The improved ratios in asthmatic children following inhalation of a bronchodilator were mainly due to increased tPTEF and VPTEF. Our observations point out the importance of evaluating both tPTEF and either tPTEF/tE or VPTEF/VE when attempting to differentiate between changes in ratios that are related to age versus changes that reflect underlying obstructive airways disease.