TITLE: Physical therapy for airway clearance improves cardiac autonomic
modulation in children with acute bronchiolitis

  ABSTRACT.BACKGROUND:
The effects of physical therapy on heart rate variability (HRV), especially
in children, are still inconclusive. 

ABSTRACT.OBJECTIVE:
We investigated the effects of conventional physical therapy (CPT) for airway
clearance and nasotracheal suction on the HRV of pediatric patients with
acute bronchiolitis. 

ABSTRACT.METHOD:
24 children were divided into two groups: control group (CG, n=12) without
respiratory diseases and acute bronchiolitis group (BG, n=12). The heart
rate was recorded in the BG at four different moments: basal recording (30
minutes), 5 minutes after the CPT (10 minutes), 5 minutes after nasotracheal
suction (10 minutes), and 40 minutes after nasotracheal suction (30
minutes). The CG was subjected to the same protocol, except for nasotracheal
suction. To assess the HRV, we used spectrum analysis, which decomposes the
heart rate oscillations into frequency bands: low frequency
(LF=0.04-0.15Hz), which corresponds mainly to sympathetic modulation; and
high frequency (HF=0.15-1.2Hz), corresponding to vagal modulation. 

ABSTRACT.RESULTS:
Under baseline conditions, the BG showed higher values in LF oscillations,
lower values in HF oscillations, and increased LF/HF ratio when compared to
the CG. After CPT, the values for HRV in the BG were similar to those
observed in the CG during basal recording. Five minutes after nasotracheal
suction, the BG showed a decrease in LF and HF oscillations; however, after
40 minutes, the values were similar to those observed after application of
CPT. 

ABSTRACT.CONCLUSIONS:
The CPT and nasotracheal suction, both used for airway clearance, promote
improvement in autonomic modulation of HRV in children with acute
bronchiolitis.

BODY.INTRODUCTION:
Respiratory affections are the main factors of morbidity and mortality in children
given that newborns have peculiar aspects involving the respiratory system that can
easily lead to respiratory failure1 and acute viral bronchiolitis is a respiratory infection
frequently seen in children younger than 2 years old. The objective of the use of
respiratory physical therapy in these children is to assist in the removal of
secretions and, consequently, improve oxygenation. Because these pediatric patients
may not cooperate, we can use passive techniques, such as percussion, vibration, and
postural drainage also known as conventional physical therapy (CPT), prolonged slow
expiration (PSE), and expiratory flow increase technique followed (or not) by
nasotracheal suction. However, the results for efficacy and side effects are
controversial2-4.  In fact, the objective of respiratory physical therapy is a decrease in the length of
hospital stay, thus decreasing hospital-related physical, psychological, and social
stress5. Pediatric
inpatients may present significant alterations in cardiovascular autonomic control,
since constant oscillations in the cardiac and hemodynamic parameters are observed.
However, there are very few studies correlating heart rate variability (HRV) and
respiratory pathological conditions in pediatric inpatients either before or after
respiratory physical therapy procedures, such as application of CPT.  The study of HRV is a method allowing non-invasive and selective evaluation of the
changes in cardiac autonomic modulation. HRV oscillations in the low frequency band
(LF: 0.04â€"0.15Hz) in awake humans have been associated with sympathetic and
parasympathetic modulation, whereas oscillations in the high frequency band (HF:
0.15â€"0.5Hz) have been associated only with parasympathetic (vagal)
modulation6.  The use of HRV analysis in several clinical situations has provided important
information and serves as an evaluation instrument for a better understanding of the
influence of the autonomic nervous system in various physiopathological
conditions6. With regard
to the applicability of HRV analysis in pediatric populations, it is known that the
maturity progression of the sympathetic and vagal divisions is accompanied by a
growing increase in autonomic modulation over the pre- and post-natal
periods7. In turn, a few
studies have addressed the association between pathological pediatric conditions and
changes in the cardiac autonomic modulation, consequently, HRV.  In light of these facts, our hypothesis is that pediatric inpatients with acute
bronchiolitis may have impairments in HRV, and respiratory physical therapy can play
a positive role in improving the cardiac autonomic parameters. In this sense, it is
possible that HRV analysis, a relatively simple and non-invasive instrument, can
reflect the effects of respiratory physical therapy on autonomic modulation.
Therefore, the objective of the present study was to assess the effects of
respiratory conventional physical therapy (CPT) and nasotracheal suction on
autonomic modulation in pediatric inpatients with acute viral bronchiolitis.

BODY.METHOD:
This is an interventional controlled study that included 24 term-born children into
two groups: control group (CG), consisting of children with normal respiratory
condition (N=12; 7 females and 5 males), and bronchiolitis group (BG), consisting of
hospitalized children with acute viral bronchiolitis (N=12; 7 females and 5 males)
and mean hospital stay length of 13±2 days. The age ranged from 2 to 11
months (with a mean age of 6±2 months).  Both groups were submitted to a physical therapy treatment protocol and measurements,
and the multidisciplinary medical team was instructed on the collection procedures.
The children's caregivers were also informed about the procedures and the objective
of this study, with all of them signing an informed consent approved by the Research
Ethics Committee of the Clinical Hospital of the School of Medicine of
Ribeirão Preto, Universidade de São Paulo (USP), Ribeirão
Preto, SP, Brazil (No.13464/2006).  Personal and clinical data were obtained from medical records. Heart rate (HR),
respiratory rate (RR), and oxygen saturation (SpO2) were measured by one
of the investigators (Cynthia Pelegrino Jacinto, CJP). The following exclusion
criteria were adopted in the present study: age above 12 months, presence of
cardiovascular disease or chronic respiratory disease, prescription of vasoactive
drugs or sedatives, invasive mechanical ventilation, and children on contact
isolation.

BODY.EXPERIMENTAL PROTOCOL:
Physical therapy techniques: Respiratory physical therapy using CPT
was applied by the same physical therapist and conducted according to auscultation,
patient tolerance, and clinical evaluation. The CPT protocol included thoracic
percussion, manual vibration, postural drainage, and cough stimulation. In the BG,
CPT was followed by nasotracheal suction, if necessary. The CG received the same
physical therapy treatment, except nasotracheal suction, which was not performed due
to ethical reasons.  Heart Rate Recording: The collection procedure from the CG and BG
was performed using a heart rate monitor (Polar® - model S810i)
that received the heart rate (HR) signals on a beat-by-beat basis by means of a
transmission belt made of elastic material (3 cm width) containing embedded
electrodes connected to a frequency transmitter. The transmission belt was
positioned around the child's chest next to the xiphoid process without causing pain
or discomfort. HR was recorded with the children in dorsal decubitus at 30-degree
elevation at four different moments in sequence: basal recording for 30 minutes
before performing the respiratory CPT; 5 minutes after CPT (10 minutes); 5 minutes
after nasotracheal suction (10 minutes); and 40 minutes after nasotracheal suction
(30 minutes).  Analysis of the Heart Rate Variability. The HRV analysis was
performed using interval time series on a beat-by-beat basis obtained from the
frequency records, transferred to computer through an interface (Polar IR
InterfaceTM) using specific software (Polar Precision Performance
SW®). The resulting time series were divided into continuous
segments of 200 beats per minute, with 50% superposition between the adjacent
segments. After calculating means and variance for each segment, these values were
submitted to spectral analysis through the autoregressive method as described in the
literature8,6. The oscillatory components
existing in the stationary segments of the beat-by-beat interval time series were
modeled by using the Levinson-Durbin recursion, and the method was chosen according
to Akaike's criteria8. This
procedure allows the frequency axis and power of each relevant oscillatory component
in the time series to be automatically quantified. The oscillatory components were
classified as follows: very-low frequency (VLF: 0.001 to 0.04 Hz), low frequency
(LF: 0.04 to 0.15 Hz), and high frequency (HF: 0.15 to 1.2 Hz). LF and HF
oscillation power was also expressed in normalized units, which was obtained by
calculating the ratio between band power (LF or HF) and total power after
subtracting the VLF component. The normalization procedure was performed in order to
minimize the total power variations in the absolute values of LF and HF
components8,6. In addition, the LF/HF ratio was
calculated to establish an index for assessment of cardiac autonomic modulation.

BODY.STATISTICAL ANALYSIS:
The sample size calculation was performed using the "GraphPad StatMate 1.01",
confidence level of 95%, Power 80% using the LF variable in normalized units. A
sample of 12 children was suggested. All statistical tests were performed with
SigmaStat 3.5 software (Systat Software Inc., San Jose, CA, USA). The Shapiro-Wilk
normality test was used, and the data are expressed as mean ± standard
deviation of the mean (SD). A one-way ANOVA followed by the Student-Newman-Keuls
multiple comparison test was performed to evaluate the effects of respiratory CPT
and nasotracheal suction on the HRV of the CG vs. BG. Student's t test was used for
the comparisons between groups before respiratory ACT. The differences were
considered significant at P<0.05.

BODY.RESULTS:
Table 1 shows mean values for HR, RR, and
SpO2 at baseline and after respiratory CPT application. The results
showed that the BG had higher HR and lower SpO2 than the CG before
respiratory CPT. However, after the respiratory CPT the values were similar.   Table 1 Values for heart rate (HR), respiratory rate (RR), and oxygen saturation
(SpO2) obtained from the control group (CG) and the bronchiolitis group (BG)
before (pre) and after (post) respiratory conventional physical therapy
(CPT). 
  Control Group  Bronchiolitis Group 
  Pre-CPT  Post-CPT  Pre-CPT  Post-CPT HR 143±9 142±8 153±14 * + 149±10 RR 42±5 38±6 44±6 39±7 SpO 2 98±2 97±2 95±3 * 96±2 All values expressed as mean±SD.  * P<0.05 vs. CG before conventional physical therapy (pre-CPT); + P<0.05 vs. CG after conventional physical therapy (post-CPT).   Table 2 shows the baseline values of the HRV
in the frequency domain evaluated by spectral analysis before and after the
respiratory CPT. The BG showed lower RRi values before the respiratory CPT, greater
sympathetic autonomic influence, and lower vagal influence characterized by major
oscillations in the LF band and minor oscillations in the HF band in absolute and
normalized units when compared to the CG. Consequently, the BG showed a higher LF/HF
ratio compared to the CG indicating an exaggerated predominance of cardiac
sympathetic modulation in relation to the CG. However, after respiratory CPT, the BG
had values similar to the CG suggesting an improvement in cardiac autonomic
modulation.  Table 2 Spectral parameters of R-R intervals (RRi) calculated using spectral analysis
(autoregressive method) before (pre) and after (post) conventional physical
therapy (CPT) for the control group (CG) and the bronchiolitis group
(BG). 
  Control Group (CG)  Bronchiolitis Group (BG) 
  Pre-CPT  Post-CPT  Pre-CPT  Post-CPT 
 Baseline values 
 
  RRi, ms 421±28 424±25 395±35 * + 405±29 
 Spectral parameters 
 
  Variance, ms 2 293±28 319±26 361±21 * + 316±35 # 
  LF, ms 2 189±20 206±16 228±33 * 187±18 # 
  LF, nu 81±4 79±5 88±3 * + 79±4 # 
  HF, ms 2 46±9 53±14 30±7 * + 49±10 # 
  HF, nu 19±4 21±5 12±3 * + 22±4 # 
  LF/HF 4.3±1.2 4.2±1.3 8.1±2.4 * + 4.0±1.1 # 
 All values expressed as mean±SD. RRi: R-R interval; LF: low
frequency; HF: high frequency; and nu, normalized units. * P<0.05 vs. CG before conventional physical therapy (pre-CPT) + P<0.05 vs. CG after conventional physical therapy (post-CPT) # P<0.05 vs. BG before conventional physical therapy (pre-CPT)   Table 3 shows the behavior of HRV at four
different sequential moments: basal recording (30 minutes pre-CPT); 5 minutes after
CPT application (10-minute record post-CPT); 5 minutes after nasotracheal suction
(10-minute record); and 40 minutes after nasotracheal suction (30-minute record).
Following the application of respiratory CPT, there was a decrease in LF
oscillations and an increase in HF oscillations compared to baseline values in
absolute and normalized units as shown previously (Table 2). In turn, 5 minutes after nasotracheal suction, there were
reductions in overall variance and in LF and HF oscillations (compared to those
values after CPT) in absolute and normalized units resulting in a significant
increase in the LF/HF ratio. On the other hand, 40 minutes after nasotracheal
suction (final record), variability patterns similar to those observed after
respiratory CPT (post-CPT) application were observed.  Table 3 Spectral parameters of RR intervals (RRi) for the bronchiolitis group (BG) at
four different sequential moments: before conventional physical therapy
(pre-CPT), after CPT (post-CPT), 5 minutes after nasotracheal suction
(5'post-NS), and 40 minutes after nasotracheal suction (40' post-NS). 
  Bronchiolitis Group 
  pre-CPT  post-CPT  5'post-NS  40'post-NS 
 Baseline values 
 
  RRi, sec 395±35 405±29 389±20 393±30 
 Spectral Parameters 
 
  Variance, ms 2 361±21 316±35 * 132±34 * + 280±51 * # 
  LF, ms 2 228±33 187±18 * 96±28 * + 169±38 * # 
  LF, nu 88±3 79±4 * 89±4 + 74±10 * # 
  HF, ms 2 30±7 49±10 * 12±4 * + 56±19 * # 
  HF, nu 12±3 21±4 * 11±4 + 26±12 * # 
  LF/HF 8.1±2.4 4.0±1.1 * 9.3±4.4 + 3.5±1.3 * # All values expressed as mean±SD. RRi: R-R interval; LF: low
frequency; HF: high frequency; and nu, normalized units. * P<0.05 vs. before conventional physical therapy (pre-CPT) + P<0.05 vs. after conventional physical therapy (post-CPT) # P<0.05 vs. 5 minutes after nasotracheal suction (5' post-NS) 

BODY.DISCUSSION:
HRV analysis has been studied by several researchers in the last decades. This
interest has increased because HRV analysis allows non-invasive and selective
evaluation of the influence of the autonomic nervous system on the cardiovascular
system. The results of this growing research on HRV, mainly the clinical studies,
have demonstrated that such an assessment can be used as a hemodynamic and metabolic
marker, as well as a predictive index for cardiovascular events6.  In pediatric patients, the clinical use of HRV was first described in the 1960s when
a study demonstrated that fetal distress was preceded by alterations in the
inter-beat intervals long before any heart rate change9, but not until the 1980s did the advent of computer
techniques allow the concept of HRV analysis to be employed for evaluation of
cardiovascular autonomic control10.  Several linear and non-linear methods have been applied to HRV analysis. However,
spectral analysis is the most common linear method used in the frequency domain,
decomposing the crucial oscillatory components into their occurrence frequencies,
which allows investigation of the influence of autonomic, sympathetic (LF), and
parasympathetic (HF) components on the HR modulation. Therefore, this method can be
applied to individuals of all ages11.  With regard to the influence of cardiac autonomic components on cardiovascular
control during fetal development and in newborns, it is know that the maturation of
neuro-cardiac control increases cardio-regulatory influence on HR variability,
mainly through the baroreflex system12. This neural cardiac maturation, which occurs between the
31st and the 38th week of gestation, is accompanied by a
reduction in fetal HR. In this sense, the reduction in HR and HRV is due to a
decrease in the randomized oscillatory components and to variability patterns
coherent with the cardiac autonomic drive12,13. The importance
of this maturation process on the cardiac autonomic regulation became evident in a
study showing the correlation between deficient cardio-vagal development and sudden
infant death syndrome14.  In contrast, the homeostasis of cardiac autonomic regulation, maintained by defined
autonomic modulation patterns, can be affected by different pathological
situations6. In this
sense, the hypothesis raised by the present study was based on the fact that
respiratory affections (acute viral bronchiolitis) in pediatric patients could
provoke HRV changes resulting from the impairment of cardiac autonomic modulation
and that respiratory physical therapy might promote beneficial systemic effects by
restoring a more coherent autonomic influence in relation to the normality
patterns.  In fact, respiratory physical therapy is mainly aimed at acting on physical and
social factors affecting a given acute or chronic respiratory pathological
condition. In the daily routine, the integration of a physical therapist into the
multidisciplinary team speeds recovery, thus reducing the length of hospital stay.
However, although respiratory physical therapy is crucial for improving the
ventilatory pattern, the lack of instruments does not allow a more precise
assessment of the therapy-induced systemic effects on both the cardiovascular
autonomic system and homeostasis, and there are very few studies correlating
pediatric respiratory pathological conditions with HRV behavior. In general, these
studies were based on short-term records in which the HRV was associated with
inducing tests only (respiratory procedures, postural tests, etc.)15.  Accordingly, our results have shown that at baseline, that is, prior to respiratory
CPT, the pediatric inpatients typically presented with increased LF and decreased HF
oscillations. Despite the lack of similar studies on the pediatric population with
acute viral bronchiolitis, these findings are corroborated by results obtained from
adults, such as patients with COPD who showed changes in sympathetic cardiac
autonomic modulation16,17. Additionally, our results have
also shown that CPT intervention restored the autonomic modulation patterns of HRV
in these hospitalized children by improving the cardiac autonomic balance, which was
confirmed by the reduction in the LF/HF ratio. This fact was observed after
application of CPT and 40 minutes after nasotracheal suction. The improvement in
autonomic modulation in both situations was supposedly due to the movement of
secretions and improved respiratory function despite no significant changes in any
respiratory parameter, such as respiratory rate and oxygen saturation. In the first
case, the combination of CPT and cough stimulation may have improved respiratory
function and, consequently, influenced the pattern of cardiac autonomic modulation.
In turn, immediately after nasotracheal suction, there was a reduction in LF and HF
oscillations in absolute and normalized units, possibly due to the intense stress
caused by the procedure. Interestingly, this reduction in LF oscillations soon after
the nasotracheal suction seems to be a paradox because of the aggressive nature of
this procedure, which could increase the influence of sympathetic modulation and
consequently the LF oscillations as well. However, the decrease in LF oscillations
may be due to the sympathetic over-activity resulting from this extremely stressing
intervention. This has also been observed in other situations, such as intense
physical exercise18or severe heart
failure19. In these
situations, when the physiological mechanisms are at maximum capacity in order to
maintain homeostasis, the cardiovascular system may not keep its variability. In
fact, the cause for reduction in LF and HF oscillations 5 minutes after nasotracheal
suction is unknown, but sympathetic over-activity may be involved.  Indeed, other studies support this idea by demonstrating that hospitalized patients
can exhibit symptoms such as agitation, dyspnea, cyanosis, and tachycardia, but
despite the risks inherent to this procedure, the hypersecretive patients benefit
from this technique20. As
described above, the pattern of cardiac autonomic modulation was restored 40 minutes
after nasotracheal suction, which was characterized by values of LF and HF
oscillations similar to those observed following CPT application in experimental and
control groups. In fact, several studies have demonstrated that the changes in HRV
quickly return to baseline values following transitory perturbations induced by
maneuvers such as mild exercise, administration of rapid action vasoconstrictors,
and transitory coronary occlusion, whereas only more intense stimuli such as heavy
exercise and administration of long-term action drugs result in a longer interval
prior to the return to baseline values6. Therefore, our results showed that respiratory CPT followed (or
not) by nasotracheal suction significantly improves the pattern of cardiac autonomic
modulation, thus restoring values similar to those of control children with no
respiratory affection.  Moreover, although our findings point to an improvement in autonomic parameters
evaluated in pediatric patients with viral bronchiolitis, the application of
respiratory CPT in this situation has been widely questioned and is the subject of
discussion in the literature. In fact, the purpose of the use of respiratory
physical therapy in infants with acute viral bronchiolitis is helping to remove
secretions and improve oxygenation indices. However, there are arguments against
respiratory physical therapy as part of routine care of these patients according to
the level of bronchiolitis caused by respiratory distress, the absence of
substantial proven benefits, and possible adverse effects21.  Accordingly, two review studies 2,3 that aimed to examine the efficacy of respiratory
physical therapy in children under 24 months old, with acute bronchiolitis,
concluded that there is not sufficiently evidence who show the benefits of physical
therapy in reducing the length of hospital stay, but also concludes that the studies
were insufficient to define the indication and contraindication of respiratory
physical therapy. Meanwhile, a recent review of Postiaux et al.4 showed better results with
conventional and new therapy techniques, especially prolonged slow expiration (PSE).
However, this study concludes that further research is required to better define the
indications and contraindications to CPT in patients with bronchiolitis.  A previous study22 that compared a
control group with two groups submitted to CPT and expiratory flow increase
technique showed lower HR values in both treatment groups, with no adverse effects
attributed to CPT. Additionally, other studies have evaluated the effect of the
expiratory flow increase technique in infants with bronchiolitis, two of which were
multicenter studies23,24 that did not find differences in
length of hospital stay. In the first23, there was a higher frequency of discomfort in the intervention
group and, in the second25, there
was a better clinical score in the intervention group with expiratory flow increase
technique and PSE.  The PSE technique has also been used by other authors26-28. In one
study, there was a lower clinical score, respiratory rate and HR for the group
treated with CPT and prolonged slow expiration technique, as well as a shorter
hospital stay (although not statistically significant) for the group submitted to
PSE26. Another study
showed shorter time evolution and reduction in hours on oxygen support in the group
using vibration with PSE compared to controls27. Additionally, the results of other authors also
demonstrated a better clinical score and a reduction in chest retractions in the
groups treated with CPT and PSE, with improvement in oxygen saturation and
bronchospasm in the group submitted only to PSE.  Finally, the results of these studies clearly show the need for other evaluation
parameters more sensitive to changes promoted by respiratory physical therapy. As
far as we know, this is the first study that used HRV analysis in these conditions.
Accordingly, our results showed an improvement in the autonomic parameters evaluated
by spectral analysis of the HRV. These findings may be related to the primary
objective of the treatment of these children, which is to reduce the discomfort
caused by airway secretions and reduce stress related to ventilation.  In sum, the respiratory physical therapy by means of CPT and nasotracheal suction,
both used for airway clearance, promote improvement in autonomic modulation of HRV
in children with acute viral bronchiolitis, suggesting that HRV analysis can be used
as an indirect marker of the clinical status of patients undergoing such an
intervention.

BODY.STUDY LIMITATIONS:
Some limitations regarding this study should be considered, such as long-term
evaluation of the patient undergoing respiratory physical therapy and application of
other interventions aimed at better interpreting the results obtained from HRV
analysis (e.g.: serum dosages of catecholamine and cortisol). The choice of
experimental design in which the respiratory physical therapy procedures were
stratified to involve CPT and nasotracheal suction is justified by the fact that
both interventions demonstrate different hemodynamic and cardiovascular parameters.
Within this context, the analysis of cardiac autonomic modulation during different
moments of the respiratory physical therapy has allowed us to score the HRV behavior
in different procedures, thus providing another useful instrument for quantifying
the risk-benefit of techniques applied to hospitalized children.

BODY.CLINICAL IMPLICATIONS:
The search for and use of new tools and evaluation parameters that do not promote
adverse effects or compromise the patient's condition should be encouraged. In this
sense, the analysis of HRV, a noninvasive and painless method, can provide valuable
information about the patient's clinical status and systemic effects on the
cardiovascular system, both before and after physical therapy intervention.

Question: Compared to control group (CG); conventional physical therapy (CPT) for airway clearance what was the result of acute bronchiolitis group (BG); conventional physical therapy (CPT) for airway clearance and nasotracheal suction on higher LF/HF ratio in HRV?
Evidence: Five minutes after nasotracheal
suction, the BG showed a decrease in LF and HF oscillations
Answer: significantly increased