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Figure 1.
Cry Volume and Vocal-Fold Mobility
Cry Volume and Vocal-Fold Mobility
Figure 2.
Cry Volume vs Vocal-Fold Motion Impairment Receiver Operating Characteristic (ROC) Curve
Cry Volume vs Vocal-Fold Motion Impairment Receiver Operating Characteristic (ROC) Curve
Figure 3.
Cry Volume vs Aspiration Receiver Operating Characteristic (ROC) Curve
Cry Volume vs Aspiration Receiver Operating Characteristic (ROC) Curve
Table.  
Cry Volume vs Vocal-Fold Movement and Aspiration
Cry Volume vs Vocal-Fold Movement and Aspiration
1.
Richardson  BE, Bastian  RW.  Clinical evaluation of vocal fold paralysis.  Otolaryngol Clin North Am. 2004;37(1):45-58.PubMedGoogle ScholarCrossref
2.
Rizzardini  G, Restelli  U, Bonfanti  P,  et al.  Cost of human immunodeficiency virus infection in Italy, 2007-2009: effective and expensive, are the new drugs worthwhile?  Clinicoecon Outcomes Res. 2012;4:245-252.PubMedGoogle ScholarCrossref
3.
Pereira  KD, Webb  BD, Blakely  ML, Cox  CS  Jr, Lally  KP.  Sequelae of recurrent laryngeal nerve injury after patent ductus arteriosus ligation.  Int J Pediatr Otorhinolaryngol. 2006;70(9):1609-1612.PubMedGoogle ScholarCrossref
4.
Benjamin  JR, Smith  PB, Cotten  CM, Jaggers  J, Goldstein  RF, Malcolm  WF.  Long-term morbidities associated with vocal cord paralysis after surgical closure of a patent ductus arteriosus in extremely low birth weight infants.  J Perinatol. 2010;30(6):408-413.PubMedGoogle ScholarCrossref
5.
Zbar  RI, Chen  AH, Behrendt  DM, Bell  EF, Smith  RJ.  Incidence of vocal fold paralysis in infants undergoing ligation of patent ductus arteriosus.  Ann Thorac Surg. 1996;61(3):814-816.PubMedGoogle ScholarCrossref
6.
Clement  WA, El-Hakim  H, Phillipos  EZ, Coté  JJ.  Unilateral vocal cord paralysis following patent ductus arteriosus ligation in extremely low-birth-weight infants.  Arch Otolaryngol Head Neck Surg. 2008;134(1):28-33.PubMedGoogle ScholarCrossref
7.
Dewan  K, Cephus  C, Owczarzak  V, Ocampo  E.  Incidence and implication of vocal fold paresis following neonatal cardiac surgery.  Laryngoscope. 2012;122(12):2781-2785.PubMedGoogle ScholarCrossref
8.
Skinner  ML, Halstead  LA, Rubinstein  CS, Atz  AM, Andrews  D, Bradley  SM.  Laryngopharyngeal dysfunction after the Norwood procedure.  J Thorac Cardiovasc Surg. 2005;130(5):1293-1301.PubMedGoogle ScholarCrossref
9.
Averin  K, Uzark  K, Beekman  RH  III, Willging  JP, Pratt  J, Manning  PB.  Postoperative assessment of laryngopharyngeal dysfunction in neonates after Norwood operation.  Ann Thorac Surg. 2012;94(4):1257-1261.PubMedGoogle ScholarCrossref
10.
Pacheco-Lopez  PC, Berkow  LC, Hillel  AT, Akst  LM.  Complications of airway management.  Respir Care. 2014;59(6):1006-1019.PubMedGoogle ScholarCrossref
11.
Rosenthal  LH, Benninger  MS, Deeb  RH.  Vocal fold immobility: a longitudinal analysis of etiology over 20 years.  Laryngoscope. 2007;117(10):1864-1870.PubMedGoogle ScholarCrossref
12.
Sachdeva  R, Hussain  E, Moss  MM,  et al.  Vocal cord dysfunction and feeding difficulties after pediatric cardiovascular surgery.  J Pediatr.2007;151(30):312-315, e311-312.Google ScholarCrossref
13.
Truong  MT, Messner  AH, Kerschner  JE,  et al.  Pediatric vocal fold paralysis after cardiac surgery: rate of recovery and sequelae.  Otolaryngol Head Neck Surg. 2007;137(5):780-784.PubMedGoogle ScholarCrossref
14.
Carpes  LF, Kozak  FK, Leblanc  JG,  et al.  Assessment of vocal fold mobility before and after cardiothoracic surgery in children.  Arch Otolaryngol Head Neck Surg. 2011;137(6):571-575.PubMedGoogle ScholarCrossref
15.
Grundfast  KM, Harley  E.  Vocal cord paralysis.  Otolaryngol Clin North Am. 1989;22(3):569-597.PubMedGoogle Scholar
16.
Fan  LL, Flynn  JW.  Laryngoscopy in neonates and infants: experience with the flexible fiberoptic bronchoscope.  Laryngoscope. 1981;91(3):451-456.PubMedGoogle ScholarCrossref
17.
Ongkasuwan  J, Yung  KC, Courey  MS.  The physiologic impact of transnasal flexible endoscopy.  Laryngoscope. 2012;122(6):1331-1334.PubMedGoogle ScholarCrossref
18.
Smith  MM, Kuhl  G, Carvalho  PR, Marostica  PJ.  Flexible fiber-optic laryngoscopy in the first hours after extubation for the evaluation of laryngeal lesions due to intubation in the pediatric intensive care unit.  Int J Pediatr Otorhinolaryngol. 2007;71(9):1423-1428.PubMedGoogle ScholarCrossref
19.
De Oliveira  NC, Ashburn  DA, Khalid  F,  et al.  Prevention of early sudden circulatory collapse after the Norwood operation.  Circulation. 2004;110(11)(suppl 1):II133-II138.PubMedGoogle Scholar
20.
Berger  RM, Beghetti  M, Humpl  T,  et al.  Clinical features of paediatric pulmonary hypertension: a registry study.  Lancet. 2012;379(9815):537-546.PubMedGoogle ScholarCrossref
21.
LaGasse  LL, Neal  AR, Lester  BM.  Assessment of infant cry: acoustic cry analysis and parental perception.  Ment Retard Dev Disabil Res Rev. 2005;11(1):83-93.PubMedGoogle ScholarCrossref
22.
Goberman  AM, Robb  MP.  Acoustic characteristics of crying in infantile laryngomalacia.  Logoped Phoniatr Vocol. 2005;30(2):79-84.PubMedGoogle ScholarCrossref
23.
Gerber  SE, Lynch  CJ, Gibson  WS  Jr.  The acoustic characteristics of the cry of an infant with unilateral vocal fold paralysis.  Int J Pediatr Otorhinolaryngol. 1987;13(1):1-9.PubMedGoogle ScholarCrossref
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Citations 0
Original Investigation
September 2017

Use of Audiometric Measurement for Assessment of Vocal-Fold Function in Postextubation Infants

Author Affiliations
  • 1Department of Otolaryngology–Head and Neck Surgery, Baylor College of Medicine/Texas Children’s Hospital, Houston
JAMA Otolaryngol Head Neck Surg. 2017;143(9):908-911. doi:10.1001/jamaoto.2017.0848
Key Points

Question  Is there a statically significant difference in the cry volume between normal vocal-fold function and vocal-fold movement impairment?

Findings  A cry volume of 90 dB or greater has a 90.47% sensitivity of identifying normal vocal-fold mobility, whereas a cry volume of 75 dB or less has a 90.5% specificity of identifying infants with vocal function movement impairment.

Meaning  Patients with a cry volume of 90 dB or greater should be observed, and those with a cry volume less than 90 dB should undergo flexible nasolaryngoscopy.

Abstract

Importance  Infants with vocal-fold motion impairment (VFMI) have an increased risk of aspiration and pulmonary complications. Flexible nasolaryngoscopy (FNL) is the gold standard for evaluation of vocal-fold mobility. Although safe, FNL causes measurable physiologic changes. Noxious stimuli, especially in neonates in the cardiovascular intensive care unit, may cause imbalance between the pulmonary and systemic circulations and potentially circulatory collapse.

Objective  To examine whether bedside measurement of infant cry volume using a smartphone application can be a screening tool for vocal-fold movement in FNL.

Design, Study, and Participants  This case-control study performed from December 1, 2013, through January 31, 2015, included 42 infants in the intensive care unit at Texas Children's Hospital, Houston.

Main Outcomes and Measures  Patient cry volume in decibels was recorded using a smartphone application placed 12 in from their mouth.

Results  Forty-two infants were identified at the intensive care unit (median age, 33 days; 20 [48%] female and 22 [52%] male), 21 with VFMI and 21 without, based on FNL findings. A statistically significant difference was found in the mean cry volume of infants with (76.60 dB) and without (85.72 dB) VFMI. The absolute difference in the mean cry volume was 9.12 dB (95% CI, 2.74-15.50 dB). A cry volume of 90 dB or greater had a sensitivity of 90.4% (95% CI, 71%-97%) for identification of normal vocal-fold mobility. A cry volume of 75 dB or less had a specificity of 90.5% (95% CI, 71%-97%) for the identification of VFMI. The mean (SE) area under the receiver operating characteristic curve was 0.721 (0.080) (95% CI, 0.565-0.877). The cry volume, however, was not a good screen for aspiration.

Conclusions and Relevance  Bedside measurement of the cry volume with a smartphone application can be used by untrained health care professionals to screen patients for further evaluation of vocal-fold mobility using FNL.

Introduction

Vocal-fold movement impairment (VFMI) can arise from injury to the recurrent laryngeal nerve or mechanical fixation of the cricoarytenoid joint. Neurologic impairment can result from various causes, including iatrogenic injury, trauma, infections, or neoplastic process, or can be idiopathic.1,2 In the neonatal and pediatric cardiovascular intensive care units, iatrogenic injury related to surgery or intubation is the most common cause of VFMI. The incidence of recurrent laryngeal nerve injury during manipulation of the aortic arch is 8.8% to 58.7%.3-9 In neonates and infants, endotracheal intubation can result in granulation, stenosis, and VFMI.10 Intubation is estimated to cause 4% to 7.5% of unilateral VFMI and 9% to 25% of bilateral VFMI.11 Infants with VFMI may have stridor, a weak cry, and aspiration or feeding problems resulting in prolonged length of stays.3,6-9,12-14

Currently, the criterion standard for the evaluation of vocal-fold movement is flexible nasolaryngoscopy (FNL). Although commonly performed, FNL has physiologic effects, including laryngospasm, desaturation, tachycardia, bradycardia, and epistaxis.15-18 These physiologic effects do not appear to be clinically significant in the adult population but can be particularly worrisome in children with congenital heart disease or pulmonary hypertension, for whom there is a fine balance between the systemic and pulmonary circulations.17,19,20 A catastrophic circulatory event has been reported secondary to airway manipulation, such as suctioning the airway in children in this population. This finding prompted the search for a screening tool to narrow the population of patients who undergo FNL to evaluate vocal-fold mobility.19,20 Experienced listeners are often able to determine vocal-fold closure (and by extension infer vocal-fold mobility) based on the volume and quality of an infant’s cry, which may then inform the pre-FNL probability of finding VFMI. This skill is often honed over years and is not always available to bedside nurses and intensivists unfamiliar with voice disorders.

Cry characteristics, such as extremely high pitched or variable cries, have been correlated with poor neural control and neurologic disorders, the prototypical example being crit-du-chat syndrome.21 Expiratory and inspiratory cry segments, as well as the long-time spectral characteristics, differ between infants with laryngomalacia and healthy children.22 Gerber et al23 performed analysis of cry data from a single child with vocal-fold paralysis, which revealed relatively flat intensity amplitude compared with healthy children. Although objective measurements for voice quality are available, such as the noise-harmonic ratio, that correlate with glottic incompetence, it is not typically feasible to perform these measurements in the intensive care unit.23 In addition, infants are not able to participate in phonatory tasks, such as maximum phonation time. The purpose of this study was to use a decibel meter application on a smartphone to measure voice volume during crying and determine whether it could be used as a screening tool for VFMI.

Methods

This case-control study, performed from December 1, 2013, through January 31, 2015, included 42 infants in the intensive care unit at Texas Children's Hospital, Houston. Audiometric measurements are routinely obtained during FNL and are available as part of the procedure note. The data were obtained during the retrospective medical record review and deidentified. Institutional review board approval was received from the Baylor College of Medicine Institutional Review Board.

The cry volume was recorded using a smartphone (HTC Desire 610) with an audiometric measurement application (Sound Meter, version 1.6, Smart Tools Co) placed 12 in from either side of patient’s mouth while the patient was in the supine position. Three subjective peak measurements (in decibels) were recorded while the patient was crying during FNL. Intensive care unit background noise was not recorded to account for background noise. Additional information recorded included age, sex, duration of intubation, associated operations, and swallow evaluation. Data analysis was performed from December 1, 2013, through January 31, 2015, using the unpaired, 2-tailed t test, Pearson correlation, and receiver operating characteristic (ROC) curves with SPSS statistical software, version 24 (IBM Inc).

Results

Forty-two infants were identified at the intensive care unit (median age, 33 days; 20 [48%] female and 22 [52%] male), 21 with VFMI and 21 without, based on FNL findings. There was no difference in sex, age at nasolaryngoscopy examination, or duration of intubation between the VFMI and normal mobility groups. Sex, age, and duration of intubation did not correlate with any difference in cry volume. The age of the patient at the time of FNL did not correlate with the presence of VFMI. A statistically significant difference was found in the mean (SD) cry volume for infants with normal vocal-fold mobility (85.72 [8.467] dB) vs infants with VFMI (76.60 [11.58] dB) (Figure 1). The absolute difference of the mean cry volume was 9.12 dB (95% CI, 2.74-15.50 dB). Three patients (14%) with normal vocal fold mobility and 14 (67%) with VFMI had aspiration on swallow evaluation.

A cry volume of 90 dB or greater had a sensitivity of 90.4% for identification of normal vocal-fold mobility. A cry volume of 75 dB or less had a specificity of 90.5% for the identification of VFMI (Table). The mean (SE) area under the ROC was 0.721 (0.080) (95% CI, 0.565-0.877) (Figure 2). An area of 0.90 to 1 represents an excellent test result, 0.80 to 0.90 represents a good test result, 0.70 to 0.80 represents a fair test result, 0.60 to 0.70 represents a poor test result, 0.50 to 0.60 represents a failed test, and an area less than 0.50 is not statistically significant.

As a screening tool for aspiration, a cry volume of greater than 90 dB had a sensitivity of 82.4% for normal vocal-fold mobility. A volume of 70 dB had a specificity of 83.3% for VFMI (Table). The mean (SE) area under the ROC curve was 0.583 (0.096) (95% CI, 0.395-0.771) (Figure 3).

The number needed to treat (NNT) was also calculated using 75 and 90 dB as the cutoffs. Normal vocal-fold movement was considered to be the control, whereas VFMI was the event. The first group of patients was divided into those with a cry volume of 90 dB or greater and a cry volume less than 90 dB. Among patients with a cry volume of 90 dB or greater, 7 had normal mobility and 2 had VFMI. In patients with a cry volume of less than 90 dB, 14 had normal mobility and 19 had VFMI. The experimental event rate was 0.905 (19/[19 + 2]), and the control event rate was 0.667 (14/[14 + 7]). The NNT was 4.2 for the patients using 90 dB as the cutoff. The second group of patients was divided into those with a cry volume of 75 dB or greater and a cry volume less than 75 dB. Among patients with a cry volume of 75 dB or greater, 19 had normal mobility and 11 had VFMI. Among patients with a cry volume of less than 75 dB, 2 had normal mobility and 10 had VFMI. The experimental event rate was 0.476 (10/[10 + 11]), and the control event rate was 0.095 (2/[2 + 19]). The NNT was 2.62 for the patients using 75 dB as the cutoff.

Discussion

Glottic incompetence related to VFMI places individuals at increased risk for aspiration and pulmonary complications. Although FNL is the criterion standard for the evaluation of VFMI, it can have significant physiologic effects and potentially adverse effects on infants with cardiopulmonary disease. In addition, the view of the infant larynx on FNL may be limited by secretions, movement, or floppy supraglottic structures. Clinicians may use other information, such as the quality of the cry and the clinical history, to aid in the assessment of vocal-fold mobility. Although formal objective audiometric measurements correlate with VFMI, these measurements are difficult to bring to the bedside in the intensive care unit. Loudness, of course, is not the only vocal parameter affected by VFMI; however, it is the most accessible to untrained listeners using a decibel meter smartphone application as a screening tool.

Our data indicate that if a patient’s peak cry decibel is 75 dB or less, the likelihood of the patient having VFMI is significant, with a specificity of 90.5%. Furthermore, if a patient’s peak cry decibel is 90 dB or greater, it is unlikely the patient has VFMI and FNL can be avoided with the high sensitivity of 90.5%. Our data are not able to stratify patients with a peak cry decibel of 75 to 90 dB. Therefore, we recommend observation for patients with a cry volume of 90 dB or greater, whereas those with a cry volume of less than 90 dB should undergo FNL after extubation to confirm or rule out VFMI.

The NNT for the 90-dB cutoff groups indicated that 4.2 patients with VFMI are needed to undergo FNL to identify 1 patient who does not need the procedure. The NNT for the 75-dB cutoff group indicated that 2.62 patients with VFMI are needed to undergo FNL to identify 1 patient who does not need the procedure. The NNT data are not significant compared with the data of sensitivity, specificity, and the area under ROC because of the small patient sample in our study.

To date, no publications in the literature have used the strength of a patient's voice measured in decibels to determine the likelihood of VFMI. The criterion standard for evaluation of VFMI is FNL, which although low risk, still necessitates a procedure and its associated risks. By using a noninvasive smartphone application as a screening tool, a number of patients with normal mobility may be able to avoid undergoing this intervention.

Unfortunately, cry volume was not a good determinant of aspiration on swallow evaluation. The 3 children with normal vocal-fold mobility and aspiration also had cry volumes greater than 80 dB. Swallowing is more complex than vocal-fold closure; thus, it is not surprising that cry volume alone cannot determine dysphagia.

Limitations

The limitations of our study include a small sample size and the use of only 1 audiometric measurement application (Sound Meter). The data obtained using the Sound Meter application were not validated against other audiometric measurement applications to determine whether there are interapplication consistencies. The future goals of the study include increasing the number of patients to further refine the decibel range of patients who will need to undergo FNL for vocal-fold mobility evaluation. In addition, various applications will be tested to study the consistency of the decibel value reported.

Conclusions

Bedside measurement of the cry volume using a smartphone application is a new measure that can be used by untrained health care professionals to screen patients for further evaluation of vocal-fold movement using FNL. This technique could decrease the number of FNLs performed in infants in intensive care units and help allocate resources in facilities with limited access to otolaryngologists.

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Article Information

Corresponding Author: Julina Ongkasuwan, MD, Department of Otolaryngology–Head and Neck Surgery, Baylor College of Medicine/Texas Children’s Hospital, 6701 Fannin, Ste 640, Houston, TX 77030 (julinao@bcm.edu).

Accepted for Publication: April 17, 2017.

Published Online: June 29, 2017. doi:10.1001/jamaoto.2017.0848

Author Contributions: Drs Liu and Ongkasuwan had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.

Study concept and design: Ongkasuwan.

Acquisition, analysis, or interpretation of data: All authors.

Drafting of the manuscript: Liu.

Critical revision of the manuscript for important intellectual content: All authors.

Statistical analysis: Liu, Varier.

Administrative, technical, or material support: Liu.

Study supervision: Ongkasuwan.

Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.

References
1.
Richardson  BE, Bastian  RW.  Clinical evaluation of vocal fold paralysis.  Otolaryngol Clin North Am. 2004;37(1):45-58.PubMedGoogle ScholarCrossref
2.
Rizzardini  G, Restelli  U, Bonfanti  P,  et al.  Cost of human immunodeficiency virus infection in Italy, 2007-2009: effective and expensive, are the new drugs worthwhile?  Clinicoecon Outcomes Res. 2012;4:245-252.PubMedGoogle ScholarCrossref
3.
Pereira  KD, Webb  BD, Blakely  ML, Cox  CS  Jr, Lally  KP.  Sequelae of recurrent laryngeal nerve injury after patent ductus arteriosus ligation.  Int J Pediatr Otorhinolaryngol. 2006;70(9):1609-1612.PubMedGoogle ScholarCrossref
4.
Benjamin  JR, Smith  PB, Cotten  CM, Jaggers  J, Goldstein  RF, Malcolm  WF.  Long-term morbidities associated with vocal cord paralysis after surgical closure of a patent ductus arteriosus in extremely low birth weight infants.  J Perinatol. 2010;30(6):408-413.PubMedGoogle ScholarCrossref
5.
Zbar  RI, Chen  AH, Behrendt  DM, Bell  EF, Smith  RJ.  Incidence of vocal fold paralysis in infants undergoing ligation of patent ductus arteriosus.  Ann Thorac Surg. 1996;61(3):814-816.PubMedGoogle ScholarCrossref
6.
Clement  WA, El-Hakim  H, Phillipos  EZ, Coté  JJ.  Unilateral vocal cord paralysis following patent ductus arteriosus ligation in extremely low-birth-weight infants.  Arch Otolaryngol Head Neck Surg. 2008;134(1):28-33.PubMedGoogle ScholarCrossref
7.
Dewan  K, Cephus  C, Owczarzak  V, Ocampo  E.  Incidence and implication of vocal fold paresis following neonatal cardiac surgery.  Laryngoscope. 2012;122(12):2781-2785.PubMedGoogle ScholarCrossref
8.
Skinner  ML, Halstead  LA, Rubinstein  CS, Atz  AM, Andrews  D, Bradley  SM.  Laryngopharyngeal dysfunction after the Norwood procedure.  J Thorac Cardiovasc Surg. 2005;130(5):1293-1301.PubMedGoogle ScholarCrossref
9.
Averin  K, Uzark  K, Beekman  RH  III, Willging  JP, Pratt  J, Manning  PB.  Postoperative assessment of laryngopharyngeal dysfunction in neonates after Norwood operation.  Ann Thorac Surg. 2012;94(4):1257-1261.PubMedGoogle ScholarCrossref
10.
Pacheco-Lopez  PC, Berkow  LC, Hillel  AT, Akst  LM.  Complications of airway management.  Respir Care. 2014;59(6):1006-1019.PubMedGoogle ScholarCrossref
11.
Rosenthal  LH, Benninger  MS, Deeb  RH.  Vocal fold immobility: a longitudinal analysis of etiology over 20 years.  Laryngoscope. 2007;117(10):1864-1870.PubMedGoogle ScholarCrossref
12.
Sachdeva  R, Hussain  E, Moss  MM,  et al.  Vocal cord dysfunction and feeding difficulties after pediatric cardiovascular surgery.  J Pediatr.2007;151(30):312-315, e311-312.Google ScholarCrossref
13.
Truong  MT, Messner  AH, Kerschner  JE,  et al.  Pediatric vocal fold paralysis after cardiac surgery: rate of recovery and sequelae.  Otolaryngol Head Neck Surg. 2007;137(5):780-784.PubMedGoogle ScholarCrossref
14.
Carpes  LF, Kozak  FK, Leblanc  JG,  et al.  Assessment of vocal fold mobility before and after cardiothoracic surgery in children.  Arch Otolaryngol Head Neck Surg. 2011;137(6):571-575.PubMedGoogle ScholarCrossref
15.
Grundfast  KM, Harley  E.  Vocal cord paralysis.  Otolaryngol Clin North Am. 1989;22(3):569-597.PubMedGoogle Scholar
16.
Fan  LL, Flynn  JW.  Laryngoscopy in neonates and infants: experience with the flexible fiberoptic bronchoscope.  Laryngoscope. 1981;91(3):451-456.PubMedGoogle ScholarCrossref
17.
Ongkasuwan  J, Yung  KC, Courey  MS.  The physiologic impact of transnasal flexible endoscopy.  Laryngoscope. 2012;122(6):1331-1334.PubMedGoogle ScholarCrossref
18.
Smith  MM, Kuhl  G, Carvalho  PR, Marostica  PJ.  Flexible fiber-optic laryngoscopy in the first hours after extubation for the evaluation of laryngeal lesions due to intubation in the pediatric intensive care unit.  Int J Pediatr Otorhinolaryngol. 2007;71(9):1423-1428.PubMedGoogle ScholarCrossref
19.
De Oliveira  NC, Ashburn  DA, Khalid  F,  et al.  Prevention of early sudden circulatory collapse after the Norwood operation.  Circulation. 2004;110(11)(suppl 1):II133-II138.PubMedGoogle Scholar
20.
Berger  RM, Beghetti  M, Humpl  T,  et al.  Clinical features of paediatric pulmonary hypertension: a registry study.  Lancet. 2012;379(9815):537-546.PubMedGoogle ScholarCrossref
21.
LaGasse  LL, Neal  AR, Lester  BM.  Assessment of infant cry: acoustic cry analysis and parental perception.  Ment Retard Dev Disabil Res Rev. 2005;11(1):83-93.PubMedGoogle ScholarCrossref
22.
Goberman  AM, Robb  MP.  Acoustic characteristics of crying in infantile laryngomalacia.  Logoped Phoniatr Vocol. 2005;30(2):79-84.PubMedGoogle ScholarCrossref
23.
Gerber  SE, Lynch  CJ, Gibson  WS  Jr.  The acoustic characteristics of the cry of an infant with unilateral vocal fold paralysis.  Int J Pediatr Otorhinolaryngol. 1987;13(1):1-9.PubMedGoogle ScholarCrossref
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