Effect of changes in tidal volume on multiple breath washout outcomes

Abstract

The lung clearance index (LCI), measured by multiple breath washout (MBW), reflects global ventilation inhomogeneity and is a sensitive marker of early obstructive airway disease. For the MBW test to accurately reflect a subject’s gas mixing within the lungs, the breathing pattern should represent physiologically appropriate tidal volumes (V T ) and respiratory rate (RR). We aimed to assess whether changes in V T impact MBW outcome measures with a series of prospective and retrospective studies. MBW testing was performed using the Exhalyzer ® D (EcoMedics AG, Switzerland). Healthy adult subjects performed MBW with uninstructed tidal breathing and a series of instructed tidal breathing tests, designed to isolate specific features of the breathing pattern. In addition, we retrospectively analyzed MBW data from two pediatric multi-centre interventional studies of cystic fibrosis (CF) subjects to determine the range of V T observed during uninstructed breathing, and whether breathing outside this range impacted results. The LCI was lower, but not significantly different between deep breathing at 20 ml/kg body weight and uninstructed tidal breathing; whereas LCI was significantly higher during shallow breathing compared with normal tidal breathing. For the majority of subjects with CF (80%), V T ranged from 9-15mL/kg. Within the observed V T range, LCI was similar in trials with mean V T / kg below this range compared to trials with V T /kg within the range. If subjects breathe naturally and are not instructed to use specific targets, the range of V T is within physiologically appropriate limits and normal variations observed do not impact MBW outcomes.

Controlledversusfree breathing for multiple breath nitrogen washout in healthy adults

“…Indeed, the foundational studies on ventilation distribution clearly demonstrated an effect of breathing pattern (including V T ) on MBNW indices [ 4 ]. Recently, R atjen and colleagues [ 24 ] investigated the effects of altered V T on MBNW indices and found that shallow breathing (compared to “unrestricted” breathing) significantly increased LCI. The authors speculated that this was due to the effects of increased dead space to V T ratio on the determinants of LCI (both CEV and FRC).…”

“…Second, 4 out of 27 participants required coaching before or after free breathing testing due to insufficient expired volume for S III estimation. Thus, there is a chance our results may actually underestimate the true discrepancy between the two protocols, particularly in shallow breathers [ 24 ] or in lung disease where increased dead space further complicates S III estimation [ 33 ]. Third, our results only apply to a healthy population tested on a single MBNW device.…”

An Analysis on the Performance of a Mobile Platform with Gas Sensors for Real Time Victim Localization

“…The volume of the average breath (tidal volume) of an adult or elderly person is estimated between 390 (women) and 500 mL (men) [ 16 ]. Infants’ and children’s tidal volume is between 0.1 and 0.2 l ( Table 2 ).…”

“…However, in absolute terms, the amount of air a person needs is determined by the mass of the person. On average a person requires 7 mL or air per kg of body weight [ 16 ]. So an average male adult weighing 75 kg would have a tidal volume of 0.525 L, and as such, an exhaled air flow rate of .…”

“…Children have a faster breathing frequency reaching up to 25-40 breaths per minute for infants [15], as shown in Table 2. The volume of the average breath (tidal volume) of an adult or elderly person is estimated between 390 (women) and 500 mL (men) [16]. Infants' and children's tidal volume is between 0.1 and 0.2 l (Table 2).…”