Chest ACCP Career Connection
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Guest Access | Sign In via User Name/Password
This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pagani, J.
Right arrow Articles by Ronchetti, R.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pagani, J.
Right arrow Articles by Ronchetti, R.
(Chest. 2003;124:1487-1493.)
© 2003 American College of Chest Physicians

Pulse Transit Time as a Measure of Inspiratory Effort in Children*

Jacopo Pagani, MD, PhD; Maria Pia Villa, MD; Giovanni Calcagnini, PhD; Arianna Alterio, MD; Rosa Ambrosio, MD; Federica Censi, PhD and Roberto Ronchetti, MD

* From the Department of Pediatrics (Drs. Pagani, Villa, Alterio, Ambrosio, and Ronchetti), II Faculty S. Andrea University of Rome "La Sapienza"; and Biomedical Engineering Laboratory (Drs. Calcagnini and Censi), Istituto Superiore Sanità, Rome, Italy.

Correspondence to: Jacopo Pagani, MD, PhD, Department of Pediatrics, University of Rome ‘La Sapienza,’ Ospedale "S. Andrea," Via Colle Sangiovese 36, 00043 Ciampino, Rome, Italy; e-mail: jacopo.pagani{at}uniroma1.it


   Abstract
TOP
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 References
 
Study objectives: The current criterion standard for measuring inspiratory effort, esophageal manometry, is an invasive procedure that young patients find intolerable. Inspiratory effort can also be assessed noninvasively by measuring the pulse transit time (PTT). PTT is the time the pulse wave (PW) takes to travel between two arterial sites (normally heart to finger). The speed at which the PW travels is directly proportional to arterial BP. When BP rises, PTT shortens. Conversely, when BP falls, PTT lengthens. In this study, we investigated PTT as a measure for evaluating inspiratory effort in children.

Participants: We studied 15 healthy children (age range, 5 to 12 years; mean age [± SD], 8.3 ± 2.74; 9 male children) selected from patients referred to our pediatric center for routine assessment.

Measurements and results: We assessed changes in the PTT during breathing against known resistances in awake children. Resistance was applied to the nose and mouth with a modified, two-way, nonrebreathing facemask. Our data show a good correlation between the induced inspiratory effort and the amplitude of PTT variations.

Conclusions: PTT should be a useful method for quantifying changes in inspiratory effort due to augmented upper airway resistance in awake children.

Key Words: children • inspiratory effort • obstructive sleep apnea • pulse transit time


   Introduction
TOP
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 References
 
Current knowledge suggests that polysomnographic studies should include monitoring of respiratory effort during sleep.1 In particular, Guilleminault et al2 3 emphasized the importance of increased upper airway resistance in causing sleep fragmentation and daytime symptoms. These obstructive nonapneic events are difficult to detect without sensitive measures of respiratory effort.4 The criterion standard for assessing respiratory effort consists of measuring changes in endoesophageal pressure through an endoesophageal balloon catheter.5 In children, this technique causes some discomfort and can lead to fragmentary sleep.6 7 Another disadvantage is that the presence of the esophageal monitor can modify airway collapsibility,8 thereby altering the normal respiratory pattern in children during sleep. Common noninvasive techniques currently used for measuring respiratory effort have various limitations, including high costs, complex measurement procedures, and poor sensitivity in detecting changes in airflow and inspiratory effort.9

Studies10 11 12 seeking an alternative to esophageal monitoring in adults have validated a noninvasive method that measures respiratory effort from the ECG and pulse oximetry signals in standard polysomnographic recordings. This technique, pulse transit time (PTT), takes its name from the time needed for the pulse wave (PW) to travel from the aortic valve to the periphery, estimated as the delay between the R wave in the ECG and the arrival of the PW at the finger as determined by pulse oximetry.9

PTT discloses acute changes in arterial pressure13 generated by increased oscillations in pleural pressure due to inspiratory effort induced by obstructive events.14 Changes in PTT yield a valid measure of inspiratory effort. Studies4 10 14 conducted in adult patients with obstructive sleep apnea syndrome have found a significant correlation of variations in endoesophageal pressure (measured by esophageal balloon) induced by an episode of augmented airways resistance, and PTT variations between inspiration and expiration. These observations support PTT as an alternative to esophageal pressure measurement for quantitatively assessing inspiratory efforts in adults.10 What is now lacking are data on the use of PTT in children. Our aim in this study was to assess the usefulness of PTT as a measure for evaluating inspiratory effort in children.


   Materials and Methods
TOP
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 References
 
Study Subjects
The 15 children (age range, 5 to 12 years; mean age [± SD], 8.3 ± 2.74; 9 male children) were selected among patients attending our pediatric service for routine assessment. The criteria for inclusion included the absence of active nocturnal and diurnal respiratory symptoms and chronic cardiorespiratory disease. None of the children selected had received medications during the 2 weeks before the study.

Study Protocol
Participants were tested in the supine position. Each child was fitted with a custom-designed, nasal and mouth, two-way, nonrebreathing facemask (series 7910; Hans Rudolph; Kansas City, MO) modified to simulate an inspiratory effort. The inhalation valve port of the mask was adapted to lodge three small plastic cylinders (inner diameters, 3 mm, 5 mm, and 8 mm). The openings were gauged to obtain moderate and severe airway resistances (11.3-13.3 cm H2O/L/s and 85.1 cm H2O/L/s, respectively) for inspiratory flows ranging from 0.05 to 0.3 L/s.

No extra respiratory resistance was applied to the expiratory port. The mask was also equipped with a transducer for measuring negative pressure generated by inspiratory efforts (Fig 1 ). After a 3-min trial to stabilize breathing at zero resistance (baseline), the three progressive resistance levels were applied to the inspiratory port, allowing 3 min for each trial and a 2-min recovery period with zero resistance between each trial.



View larger version (70K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 1.. Left, panel A: Custom-designed nasal and mouth two-way, nonrebreathing facemask modified to simulate an inspiratory effort. Right, panel B: Facemask (A). The inhalation valve port (B) was adapted to lodge small plastic cylinders (b1). No extra respiratory resistance was applied to the expiratory port (C). The mask was also equipped with a transducer for measuring negative pressure generated by inspiratory efforts (D).

 
Subjects were asked to breathe normally through the nose, to relax, and to remain still during measurement. Before starting the protocol, all of the children received a short training session. To make sure that sequence had no effect on measurements, resistances were applied in random order. The physiologic variables were recorded with a Grass multichannel instrument (Model Heritage Grass Instruments; Quincy, MA) and sampled at 250 Hz. Polygraphic data included ECG (II lead), arterial blood oxyhemoglobin saturation, and PW recorded with a pulse oximeter (Nellcor NPB290; Nellcor; Pleasanton, CA) at the finger,15 mask pressure, and abdominal and chest movements (by inductive plethysmography).

PTT Measurement Technique
Data were digitally acquired and transferred to a personal computer. PTT was calculated with software custom designed in our laboratory. R waves were detected according to the methods of Pan and Tompkins.16 Parabolic interpolation of QRS was used to refine the R-wave detection. After the R wave had been detected, the relative minimum and maximum PWs were identified in the same beat. PTT was calculated as the interval between the ECG R wave and the point at which the PW reached 90% amplitude (PW maximum - PW minimum) [Fig 2 , top, A]. PTT values obtained were automatically converted by the software into a beat-to-beat PTT trace (Fig 2 , bottom, B).



View larger version (27K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 2.. Top, panel A: Fiducial points for PTT estimation. PTT is calculated as the time interval between each R wave of the ECG and 90% of the PW rise, for each beat. Bottom, panel B: Example of a 45-s section from traces for beat-to-beat (PTT) [top] and intramask pressure (bottom) traces. The {Delta}PTT were calculated as the difference between the peak and trough for each breath. Vertical lines indicate the selected breath. max = maximum; min = minimum.

 
Because individual PTT values correlate poorly with absolute intrathoracic pressure values,9 to evaluate inspiratory efforts more accurately we also calculated amplitude of PTT variations ({Delta}PTT), as suggested by Pitson et al.17 {Delta}PTT was calculated as the difference between the maximum and minimum PTT values within the same respiratory cycle (Fig 2 , bottom, B).

The maximum and minimum PTTs were detected for every respiratory cycle. For each breathing cycle, we also measured the maximal intramask pressure drop (Pdrop). For each subject, we analyzed 16 consecutive breaths from the second and third minute of each 3-min breathing trial at baseline and against resistance. We calculated the average {Delta}PTT and Pdrop over 16 consecutive breaths, for each resistance. The local ethics committee approved the study protocol, and all of the children’s parents gave their informed consent to the procedures.

Statistical Methods
All data are expressed as mean ± SD. A nonparametric, repeated-measures analysis of variance with the Friedman test was used to compare changes in PTT at various inspiratory resistances. A logarithmic correlation was determined between Pdrop and {Delta}PTT; p <= 0.05 was considered statistically significant. Data were analyzed with a statistical software program (Version 10.1; SPSS; Chicago, IL).


   Results
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 References
 
All subjects had normal height and weight for age. Of the 15 participants selected, 13 children completed the trial and 2 children did not because of poor compliance with the procedure.

No significant difference was found for mean PTT values in boys and girls. The various airway resistances applied left the mean, maximum, and minimum PTT values unchanged (Table 1 ).


View this table:
[in this window]
[in a new window]

  		Table 1.. Mean, Maximum, and Minimum PTT Values in the 13 Subjects*

 
As the applied inspiratory resistance increased, the mean {Delta}PTT increased significantly (from 11.13 ± 1.41 ms at zero resistance to 21.02 ± 3.00 ms at maximum; analysis of variance, Friedman, p < 0.05) [Table 2 ; Fig 3 , top, A]. No significant differences were found between {Delta}PTT values according to sex (Table 2) . A positive logarithmic correlation was found between Pdrop values and {Delta}PTT values (R2 = 0.544) [Fig 3 , bottom, B].


View this table:
[in this window]
[in a new window]

  		Table 2.. Mean {Delta}PTT Values and Mean Pdrop*

 


View larger version (20K):
[in this window]
[in a new window]
[Download PPT slide]
  		Figure 3.. Top, panel A: {Delta}PTT (difference between the maximum and minimum PTT values within the same respiratory cycle) at the various airway resistances applied. Bottom, panel B: Positive logarithmic correlation (R2 = 0.544) between Pdrop values (maximal intramask pressure drop) and {Delta}PTT values. Each child is represented by a different symbol.

 

   Discussion
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
References
 
These results, to our knowledge among the first obtained in healthy awake children and under standardized conditions, indicate that PTT is a sensitive descriptor of inspiratory effort also in children. Our data show a good correlation between the induced inspiratory effort and {Delta}PTT values. Conversely, the mean, maximum, and minimum PTT values seem unable to evaluate inspiratory effort, as others have reported in adults.9

In our study, pressure falls in the mask (- 8.31 ± 3.35 cm H2O) induced important changes in mean {Delta}PTT values from baseline (11.13 ± 1.41 ms vs 21.02 ± 3.00 ms, p < 0.001). {Delta}PTT also increased significantly already at a Pdrop of approximately - 1 cm H2O (Pdrop from - 1.10 ± 0.31 to - 2.42 ± 0.75 cm H2O, p < 0.001; {Delta}PTT from 11.13 ± 1.41 to 15.82 ± 2.90 ms, p < 0.001) [Table 2 ]. This finding shows that {Delta}PTT is a sensitive indicator capable of describing even small changes in inspiratory effort.

In some of the children we studied, we found no correspondence between Pdrop values in the mask and {Delta}PTT. For example, at maximum resistance, child 1 and child 3 had distinctly different Pdrop values (- 4.63 ± 0.10 cm H2O vs - 9.35 ± 0.26 cm H2O) but similar {Delta}PTT (21.55 ± 2.83 ms vs 21.05 ± 1.72 ms, respectively) [Table 2 ]. This finding could have several explanations. One is that emotional factors induced variations in arterial pressure and heart rate.18 Nonetheless, this hypothesis receives no support from the mean heart rate data in our patients, insofar as heart rates remained appreciably unchanged throughout the test. An alternative, more likely explanation is that our subjects differed in vascular compliance.

Interestingly, as the pressure exerted on the respiratory airways increased, {Delta}PTT increased not linearly but in a logarithmic manner, thus tending to saturate. Again, this behavior may have arisen from cardiovascular factors such as elasticity and compliance of the arterial vascular tree that prevented the PTT velocity from increasing or slowing down beyond a certain limit. Nevertheless, because we compared inspiratory effort evaluated by PTT with Pdrop at the mouth, mouth pressure was not linearly related to intrapleural pressure. This finding may also explain the nonlinear relationship between Pdrop and {Delta}PTT.

Although esophageal balloon measurement would probably have yielded a better correlation of the data for inspiratory force and changes in {Delta}PTT, unfortunately this study protocol failed to receive ethics committee approval; however, the Pdrop values at which {Delta}PTT tended to saturate in our study exceeded - 8 cm H2O. In children during sleep, even these subatmospheric mouth pressures are probably sufficient to cause complete upper airway occlusion.19 This observation implies that the mouth Pdrop values at which {Delta}PTT values tend to saturate are at the limits of the maximal respiratory effort induced by transient upper airway obstructive events, such as sleep apneas.20 21

Hence, because the {Delta}PTT reached a plateau at high subatmospheric mouth pressures, our patients were presumably already at their maximum tolerable resistance. Augmenting resistance would therefore have left esophageal pressure unchanged.

Two findings are of importance in judging the clinical value of the method we propose. First, the significant increase in absolute values began at relatively low applied resistances (and hence Pdrop) [resistance, < 14 cm H2O/L/s; Pdrop, < 3 cm H2O]. Second, the nonlinear relationship is a problem if {Delta}PTT is to be used as a quantitative measure of changes in respiratory effort when children are close to the maximum resistance they can tolerate. {Delta}PTT could nonetheless be useful as a qualitative measure for identifying obstructive events associated with increased respiratory effort. Last, for clinical application, the normalized values we obtained from baseline suggest that the method needs to be calibrated for each patient.

Our results imply that {Delta}PTT will detect even moderate inspiratory efforts in children. {Delta}PTT measurement could provide a valid noninvasive alternative to the endoesophageal balloon technique for measuring inspiratory effort during sleep study. Only few published data are available on the use of PTT in children during sleep.22 These data indicate that, as happens in the adult,4 9 10 the minor changes in pulmonary dynamics during sleep are unlikely to alter the ability of PTT to detect inspiratory effort. For these reasons, PTT could have a clinical application in polysomnographic studies for the diagnosis of upper airways resistance syndrome and obstructive sleep apnea syndrome in children. Software based on {Delta}PTT measurement might also help to simplify portable polysomnographic systems.

In conclusion, techniques based on the detection of {Delta}PTT values may be useful for evaluating increased inspiratory resistance in children. The PTT technique we propose for measuring changes in inspiratory effort in children merits further validation in a sleep laboratory.


   Acknowledgements
 
We thank Professor Carole L. Marcus for her suggestions in reviewing this manuscript.


   Footnotes
 
Abbreviations: Pdrop = maximal intramask pressure drop; PTT = pulse transit time; {Delta}PTT = amplitude of pulse transit time variations; PW = pulse wave

Received for publication July 8, 2002. Accepted for publication March 25, 2003.


   References
TOP
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 References
 

  1. Guilleminault, C, Pelayo, R, Leger, D, et al (1999) Validation of the sleep-EVAL system against clinical assessments of sleep disorders and polysomnographic data. Sleep 22,925-930[ISI][Medline]
  2. Guilleminault, C, Stoohs, R, Clerk, A, et al From obstructive sleep apnea syndrome to upper airway resistance syndrome: consistency of daytime sleepiness. Sleep 1992;15(6 Suppl),S13-S16[ISI][Medline]
  3. Guilleminault, C, Stoohs, R, Clerk, A, et al A cause of excessive daytime sleepiness: the upper airway resistance syndrome. Chest 1993;104,781-787[Abstract/Free Full Text]
  4. Argod, J, Pepin, JL, Smith, RP, et al Comparison of esophageal pressure with pulse transit time as a measure of respiratory effort for scoring obstructive non apneic respiratory events. Am J Respir Crit Care Med 2000;162,87-93[Abstract/Free Full Text]
  5. Baydur, A, Behrakis, PK, Zin, WA, et al A simple method for assessing the validity of the esophageal balloon technique. Am Rev Respir Dis 1982;126,788-791[ISI][Medline]
  6. Hoffstein, V Snoring. Chest 1996;109,201-222[Free Full Text]
  7. Chediak, AD, Demirozu, MC, Nay, KN Alpha EEG sleep produced by balloon catheterization of the esophagus. Sleep 1990;13,369-370[Medline]
  8. Woodson, BT, Wooten, MR A multisensor solid-state pressure manometer to identify the level of collapse in obstructive sleep apnea. Otolaryngol Head Neck Surg 1992;107,651-656[ISI][Medline]
  9. Smith, RP, Argod, J, Pepin, JL, et al Pulse transit time: an appraisal of potential clinical applications. Thorax 1999;54,452-457[Free Full Text]
  10. Pitson, DJ, Sandell, A, van den Hout, R, et al Use of pulse transit time as a measure of inspiratory effort in patients with obstructive sleep apnoea. Eur Respir J 1995;8,1669-1674[Abstract]
  11. Pitson, DJ, Stradling, JR Value of beat-to-beat blood pressure changes, detected by pulse transit time, in the management of the obstructive sleep apnoea/hypopnoea syndrome. Eur Respir J 1998;12,685-692[Abstract]
  12. Standards and indications for cardiopulmonary sleep studies in children. American Thoracic Society. Am J Respir Crit Care Med 1996;153,866-878[ISI][Medline]
  13. Leas, S, Ali, NJ, Goldman, M Systolic blood pressure swings reflect inspiratory effort during simulated obstructive apnea. Horne, J eds. Sleep 90 1990,178-181 Prateganel Press. Bochum, Germany:
  14. Brock, J, Pitson, J, Stradling, J Use of pulse transit time as a measure of change in inspiratory effort. J Ambul Monit 1993;6,295-302
  15. Allen, J, Murray, A Similarity in bilateral photoplethysmographic peripheral pulse wave characteristics at the ears, thumbs and toes. Physiol Meas 2000;21,369-377[CrossRef][Medline]
  16. Pan, J, Tompkins, WJ A real-time QRS detection algorithm. IEEE Trans Biomed Eng 1985;32,230-236[ISI][Medline]
  17. Pitson, DJ, Chhina, N, Knijn, S, et al Changes in pulse transit time and pulse rate as a marker of arousal from sleep in normal subjects. Clin Sci 1994;87,269-273[Medline]
  18. Drinnan, MJ, Allen, J, Murray, A Relation between heart rate and pulse transit time during paced respiration. Physiol Meas 2001;22,425-432[CrossRef][Medline]
  19. King, ED, O’Donnell, CP, Smith, PL, et al A model of obstructive sleep apnea in normal humans: role of the upper airway. Am J Respir Crit Care Med 2000;161,1979-1984[Abstract/Free Full Text]
  20. Malhotra, A, Pillar, G, Fogel, R, et al Upper-airway collapsibility: measurements and sleep effects. Chest 2001;120,156-161[Abstract/Free Full Text]
  21. Marcus, CL, Moreira, GA, Bamford, O, et al Response to inspiratory resistive loading during sleep in normal children and children with obstructive apnea J Appl Physiol 1999;87,1448-1454[Abstract/Free Full Text]
  22. Poyares, D, Guilleminault, C, Rosa, A, et al Arousal, EEG spectral power and pulse transit time in UARS and mild OSAS subjects. Clin Neurophysiol 2002;113,1598-1606[CrossRef][ISI][Medline]



This article has been cited by other articles:


Home page
 ChestHome page
J. Y. A. Foo, S. J. Wilson, A. P. Bradley, G. R. Williams, M.-A. Harris, and D. M. Cooper
Use of Pulse Transit Time To Distinguish Respiratory Events From Tidal Breathing in Sleeping Children
Chest, October 1, 2005; 128(4): 3013 - 3019.
[Abstract] [Full Text] [PDF]

Home page
 ChestHome page
J.-L. Pepin, N. Delavie, I. Pin, C. Deschaux, J. Argod, M. Bost, and P. Levy
Pulse Transit Time Improves Detection of Sleep Respiratory Events and Microarousals in Children
Chest, March 1, 2005; 127(3): 722 - 730.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF) Free
Right arrow Submit a response
Right arrow Alert me when this article is cited
Right arrow Alert me when eLetters are posted
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Article Archive
Right arrow Download to citation manager
Right arrow reprints & permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via ISI Web of Science (5)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Pagani, J.
Right arrow Articles by Ronchetti, R.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Pagani, J.
Right arrow Articles by Ronchetti, R.

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS