Manuscript
To the Editor,
The current documented global prevalence of asthma is 300 million and is
continuously rising due to rapid changes in gene-environment
interactions1. Documentation of expiratory airflow
obstruction at diagnosis and resolution in follow-up is necessary for
its appropriate management. Pulmonary function monitoring is also
desired in restrictive lung diseases, including COVID-19 pneumonia, at
start and during subsequent visits. Spirometry, the widely used
technique for measuring lung functions, has been questioned in recent
times due to potential risk of outspreading COVID-19 apart from its
restricted diagnostic utility for smaller airways and restrictive lung
diseases. Another important drawback is requirement of patient’s
understanding and optimal performance during the procedure which makes
this procedure a nightmare for pediatric population. With the pandemic
progressing at current pace, we are far away from trivialization of the
situation. With the limited utility of aerosol generating and strenuous
procedures like spirometry, there is an immediate need for more safer
alternatives to monitor lung functions in the indigent.
Procedures involving vigorous expiratory efforts like coughing, sneezing
and spirometry can impose an enhanced transmission risk of respiratory
infections among the healthcare workers and fellow pulmonology patients,
due to increased aerosol generation2. Several studies
have reported that forceful deep exhalation increased the particle
concentrations as well as duration of suspension in the surrounding
environment (Table 1). The phenomenon of increased aerosol generation
during forceful breathing maneuvers can be explained by ‘airway
reopening hypothesis’3. During physiological
conditions, apical portion of lungs is more ventilated than basal
segments, the condition is further aggravated and mismatched during
disease. A tidal breath, at low volume, will not disturb the dependent
airways configuration whereas a forceful breathing effort will reopen
the collapsed segments causing more turbulence and hence increased
production of aerosols3. Any procedure involving
forceful inspiration and/or expiration is highly likely to cause more
airflow disruption and further aerosol generation.
As the procedure of spirometry requires cooperation and forceful
respiratory efforts, it is cumbersome in children, elderly, patients
with neuromuscular weakness and in those with learning difficulties.
Moreover, its use has been restricted to minimum during current pandemic
situation2. Using negative pressure rooms, HEPA
filters, adequate ventilation, hand hygiene, complete personal
protective equipments and social distancing will only reduce the spread
and contamination but will not eliminate the aerosol
generation2. The current COVID-19 pandemic has
re-emphasized the unmet need of a more child friendly breathing
operation with lesser aerosol production for monitoring pulmonary
functions.
Impulse oscillometry (IOS), being tidal breath-based technique,
satisfies most of the shortcomings of spirometry. IOS is simple,
reliable and rapid method where requirement of patient cooperation is
minimal. It detects airway characteristics (resistance, reactance and
resonant frequency) by superimposing ultrasound waves (5-20 Hz) over
tidal breath4. Different waveform frequencies define
discrete segment of airways. Pressure and flow, measured at individual
frequency, defines respiratory characteristics by using fast fourier
transform technique4. Its potential, in detecting lung
functions in children, ventilated patients and during sleep, has been
tested previously. It requires minimal patient cooperation and can be
used in preschool age group, overcoming a major limitation of
spirometry. Gupta et al have recently demonstrated its utility for
monitoring bronchodilator reversibility of asthmatic airways in children
as young as 2 years of age5. As no forceful breathing
effort is involved, the expected aerosol generation is much less than
spirometry (Table 1), when used during active viral infections like
Corona and Influenza viruses. IOS is more sensitive to detect peripheral
airway obstruction and lung parenchymal diseases with its unique sonic
detection technique. This distinctive feature may be more useful in
serial monitoring of patients suffering from COVID-19 pneumonia.
Pulmonary function measurements (either by spirometry or IOS) can vary
with ethnicity and regional reference values should be referred for
comparison. In the absence of available benchmark values for specific
height, age or ethnicity, bronchodilator responsiveness can be compared
with the baseline measurements5.
Monitoring of periodic lung functions in both obstructive and
restrictive disease is necessary for optimal disease control and
improved quality of life. IOS seems to have a good potential in the
current pandemic and afterwards to reliably monitor pulmonary functions
with reduced risk of disease transmission, as compared to spirometry.
Apart from universal inhaler (with mask and holding chamber) and
individual filter use, when combined with other protective strategies
like adequate room ventilation, air exchanges, equipment disinfection,
self-isolation and staff protection, this technique can prove to be a
real boon to pulmonologists and their patients.