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* From the Department of Speech and Hearing Sciences and National Center for Neurogenic Communication Disorders (Drs. Hoit, Dr. Hixon, and Ms. Lohmeier), University of Arizona, Tucson, AZ; Physiology Program (Dr. Banzett), Harvard School of Public Health, Boston, MA; and Pulmonary Section (Dr. Brown), Veterans Administration Boston Healthcare System, Boston, MA.
Correspondence to: Jeannette D. Hoit, PhD, Department of Speech and Hearing Sciences, PO Box 210071, University of Arizona, Tucson, AZ 85721; e-mail: hoit{at}email.arizona.edu
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Abstract |
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Subjects: We studied 15 adults with spinal cord injuries or neuromuscular diseases receiving long-term ventilation.
Interventions: The ventilator was adjusted using lengthened inspiratory time (TI), positive end-expiratory pressure (PEEP), and combinations thereof.
Results: When TI was lengthened (by 8 to 35% of the ventilator cycle), speaking time increased by 19% and pause time decreased by 12%. When PEEP was added (5 to 10 cm H2O), speaking time was 25% longer and obligatory pauses were 21% shorter. When lengthened TI and PEEP were combined (with or without reduced tidal volume), their effects were additive, increasing speaking time by 55% and decreasing pause time by 36%. The combined intervention improved speech timing, loudness, voice quality, and articulation. Individual differences in subject response to the interventions were substantial in some cases. We also tested high PEEP (15 cm H2O) in three subjects and found speech to be essentially identical to that produced with a one-way valve.
Conclusions: These simple interventions markedly improve ventilator-supported speech and are safe, at least when used on a short-term basis. High PEEP is a safer alternative than a one-way valve.
Key Words: neurogenic communication disorders • quadriplegia • respiration • tracheostomy • ventilation, mechanical
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Introduction |
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The settings on positive-pressure ventilators are adjusted to accommodate cardiopulmonary requirements, but they are not optimal for speech. Speech produced with typical ventilator adjustments is often characterized by short phrases, long pauses between phrases, abnormal loudness, and poor voice quality.5
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These speech problems can be attributed, in large part, to the nature of the tracheal pressure (Pt) waveform. To produce speech, Pt must be at least 2 cm H2O to vibrate the vocal folds,7
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and it should be relatively constant to maintain steady loudness and normal voice quality.9
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When speech is produced in able-bodied individuals, Pt is nearly constant at 5 to 10 cm H2O throughout expiration.11
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In sharp contrast, the Pt during volume-controlled, positive-pressure ventilation rises rapidly to 
20 cm H2O during inspiration, then falls rapidly to zero during expiration and remains there until the next inspiration. Thus, Pt is too low to vibrate the vocal folds for much of the ventilator cycle, and when it is high enough, it changes so rapidly that it is impossible to maintain constant loudness and normal voice quality.
One remedy would be to cycle the ventilator so as to optimize Pt for speech production while simultaneously accommodating cardiopulmonary requirements and comfort. This approach involves straightforward adjustments that are within the capabilities of most clinical positive-pressure ventilators. Such adjustments are designed to improve speech by modifying the Pt waveform to: (1) maintain Pt above the minimum required for voicing for a longer period so that more speech can be produced per breath and less time need be spent in mandatory silence, and (2) reduce the rate of change of Pt to allow loudness and voice quality to be more even. We and others have demonstrated the feasibility of this general approach.6 13 The present study extends previous work by examining two single-adjustment interventions and a combined-adjustment intervention, and by including an increased range of ventilator adjustments.
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Materials and Methods |
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Lengthened TI can improve speech produced during the inspiratory phase of the ventilator cycle (Fig 1 , top left, a). With lengthened TI, air flows through the larynx longer so that Pt remains above the voicing threshold longer during inspiration. Also, the flow is lower so that the rate of rise of Pt is reduced.
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The specific levels of TI and PEEP were determined individually for each subject by briefly testing a range of levels. The level that was most comfortable for the subject was used for the study. It was not possible to test all subjects on all interventions due to time limitations imposed by nursing staff schedules, subject fatigue, subject preferences (eg, rejection of lengthened TI), and the fact that several subjects also participated in additional interventions not reported here.
With each condition, we recorded several breaths with nose and mouth closed (except in the four subjects whose usual condition included use of a one-way valve). The subject read a paragraph19 aloud, and then was asked "How does your speech sound?" and "How does your breathing feel?" The subject responded by using a rating scale (- 2 = much worse than usual; - 1 = slightly worse than usual; 0 = usual; + 1 = slightly better than usual; + 2 = much better than usual).
The speech signal was sensed by a head-mounted microphone (C451EB; AKG Acoustics; E Wein, Austria). Pt was sampled using a polyethylene catheter inserted through the sealed port of a swivel adapter (Portex 0803; Concord/Portex; Keene, NH) and advanced through the tracheostomy tube to a point just within its proximal end. The catheter was connected to a transducer (Validyne MP45 with ± 50 cm H2O diaphragm; Validyne Engineering; Northridge, CA) and amplifier (Validyne MC 1–3). Tidal PCO2 was sampled from the common ventilator line and measured with a clinical monitor (Cardiocap II; Datex Engstrom; Helsinki, Finland). Noninvasive measure of arterial oxygen saturation (SpO2), heart rate, and noninvasive BP were monitored continually. A digital audiotape recorder (PC208A; Sony; Tokyo, Japan) was used to record the speech signal, Pt, end-tidal PCO2, and ventilator flow.
Ten objective measures were computed (Macintosh Quadra 950, LabVIEW Software; National Instruments; Austin, TX) [Table 2 ]. Auditory perceptual analysis was conducted by five listeners, all of whom were certified speech-language pathologists. Each listener was presented pairs of speech samples, one with the subject’s usual ventilator settings and one with an intervention. Listeners were asked to mark on a visual analog scale whether the second sample was better, worse, or the same as the first (usual) sample, and provide descriptors. The scale was centered around zero (same as usual), and ranged from - 2 (much worse than usual) to + 2 (much better than usual).
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level of 0.05 was used. |
Results |
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Lengthened TI
Six subjects (subjects 1, 3, 5, 7, 14, and 15) were tested with lengthened TI (lengthened by 8 to 35% of the cycle) compared to their usual TI (Table 3
). Expiratory time (TE) decreased by the same amount in subjects who did not actively trigger the ventilator (subjects 3, 7, and 14). For those who did trigger, TE did not necessarily decrease because they triggered less often than usual.
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Thus, objective measures of speech improved with lengthened TI. The primary improvement was an increase in speech produced during inspiration.
PEEP
Eight subjects (subjects 1, 3, 6, 8, 9, 11, 12, and 14) who did not use one-way valves were tested with low levels of PEEP (5 to 10 cm H2O) compared to no PEEP (Table 4
). Minimum Pt equaled the PEEP setting when the nose and mouth were occluded, and it usually fell near (or to) zero during speaking trials.
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Thus, objective measures revealed that speech improved with PEEP. Improvement was primarily in the form of shorter pauses and more speech produced during expiration.
Lengthened TI Plus PEEP (Plus Reduced Tidal Volume)
Six subjects (subjects 3, 6, 11, 12, 14, and 15) were tested with the combination of lengthened TI (lengthened by 17 to 25% of the cycle) and low PEEP (5 to 10 cm H2O) [Table 5
]. For subjects 11 and 15, tidal volume (VT) was also reduced slightly (by 0.1 to 0.2 L) because they commented that the pressure felt too high.
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Speech improvements were in the form of both objective and subjective measures. Specific improvements were shorter pauses, more speech produced during inspiration and expiration, and listener ratings reflecting improvements in several perceptual dimensions.
High PEEP vs One-Way Valve
High PEEP (15 cm H2O) was tested in three subjects (subjects 5, 7, and 13) who used one-way valves with positive-pressure ventilation (Table 6
). Objective measures obtained with high PEEP were nearly identical to those for the one-way valve in all subjects. Listeners tended to rate speech with high PEEP as better than with the one-way valve, though this was not statistically significant. The subjects rated their speech and breathing as the same as usual with high PEEP. Pt waveforms generated with high PEEP were highly similar to those generated with one-way valves (Fig 2
).
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Subject 4 had advanced amyotrophic lateral sclerosis and concomitant laryngeal neuromotor and upper airway control problems. Because she could not speak, we tested her while she sustained a vowel. Interventions were attempted with the hope of increasing loudness and duration of voicing to improve her ability to alert caregivers when she wanted to communicate (she used a foot-operated computer to type messages); however, the interventions were not effective.
Subject 2, unlike other subjects in this study, spent most of his waking time with his cuff inflated. His cuff was deflated only occasionally to allow him to speak (with a one-way valve). When we deflated his cuff and adjusted his ventilator, his larynx remained open during inspiration so that only a small portion of the ventilator-delivered volume reached his lungs. His SpO2 dropped below 90%, and we immediately stopped the test and reinflated his cuff.
Subject 10 had a significant air leak because her tracheostoma was larger than the largest tube her trachea could accommodate. Thus, expiratory Pt fell to zero and speech improvement was minimal. The leak was reduced substantially by securing a donut-shaped foam seal around the shaft of the tube. As a result, her potential speaking time increased markedly (by 3.5 s); however, her actual speaking time increased only slightly (by 0.5 s). Also, pause time increased (by 0.7 s) because she ceased triggering extra breaths, thereby causing cycle periods to increase (by 31%). Thus, her speech became worse because of her behavioral response to the intervention.
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Discussion |
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What Improvements Result From These Interventions?
All three interventions—lengthened TI, PEEP, and lengthened TI plus PEEP (plus reduced VT)—reduced the duration of the obligatory pause and increased the amount of speech produced per breath. This was because they maintained Pt above the voicing threshold for a greater portion of the ventilator cycle (not because subjects altered articulation rate or breathing frequency). The combined-adjustment intervention was the most successful of the three. It elicited especially high ratings from listeners who noted improvements not only in temporal features of the speech, but also in loudness, voice quality, and articulation precision. These latter features reflect changes in laryngeal and upper airway behavior, which appear to have been facilitated by modifications to the Pt waveform.
Speech improved immediately after the ventilator was adjusted. Speech might have improved even more with practice and behavioral therapy. For example, subjects used only a portion of their potential speaking time (range, 49 to 93%). With practice and therapy, subjects might have learned to take greater advantage of the entire time available to speak.
We observed speech improvement during a reading task. Improvement may have been even more impressive if speech had been assessed while subjects engaged in conversation. Conversation requires continual cognitive-linguistic formulation and carries more rigorous timing demands than reading (eg, to follow turn-taking conventions). Because these interventions allow greater flexibility in speech timing, they are likely to be especially potent in enhancing conversational interchange.
A side benefit of these interventions was that breathing felt better. Why this occurred is not clear, but we can speculate. First, tidal stretch of pulmonary afferents is known to relieve air hunger,20 and it may be that the increase in mean lung volume caused by PEEP has a similar effect. Second, certain subjects may have experienced a reduction in perceived breathing effort because they did not need to trigger as many breaths as they usually did when speaking.
Which Intervention Is Most Effective for Improving Speech?
Lengthened TI and PEEP each improved speech. When combined, their effects on speaking time were additive because they worked on opposite phases of the ventilator cycle. Specifically, lengthened TI caused Pt to stay above the voicing threshold longer during the inspiratory phase, and PEEP caused Pt to stay above the threshold longer during the expiratory phase.
The relative benefits of the interventions can be appreciated by examining the amount of speech (eg, number of syllables) produced over an extended period (eg, a minute). Syllables per minute is a global measure that reflects interactions among several speech variables (speaking time, articulation rate, pause time, and breathing frequency) across a series of consecutive breaths. Using this measure to compare interventions, we determined that subjects produced an average of nearly 20 syllables per minute more than usual with lengthened TI, an average of 23 syllables per minute more than usual with PEEP, and an average improvement of > 50 syllables per minute (50.3% increase) with combined lengthened TI and PEEP (with or without reduced VT) [Fig 3 , top]. A similar additive effect was evident in a single subject who received all interventions (Fig 3 , bottom; the combined intervention appears more than additive in this subject because PEEP was slightly higher for the combined intervention than for the PEEP-alone intervention).
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Responses to interventions were more predictable within a given subject than across different subjects. For example, data from one subject (subject 6) show a nearly linear relation of syllables per minute to the magnitude of PEEP (Fig 4 ).
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During this study, we noted that sometimes the "acceptance" of an intervention was influenced by the sequence with which the components were introduced. For example, an individual may have rejected lengthened TI alone. However, if PEEP was added first, the same individual may have been more likely to accept, or even prefer, the lengthened TI. The same was true for reduced VT.
Who Are Candidates for These Interventions?
The conclusions drawn from our work apply to individuals with spinal cord injuries and neuromuscular diseases (eg, muscular dystrophy, Guillain-Barré syndrome, postpoliomyelitis syndrome, arteriovenous malformation) who are without significant airway disease and who are receiving long-term ventilation. Clinical experience of one of the authors (R. Brown) indicates that the interventions described here can also be applied successfully to those who have received ventilation for only a short time or who may be in an acute stage of recovery.
Although our findings suggest that most individuals with neuromotor disorders can benefit from these ventilator-adjustment interventions, those with significant laryngeal dysfunction or significant stoma leaks may not. When the problem is maladaptive behavioral control of the larynx (eg, subject 2), behavioral therapy from a speech-language pathologist may be beneficial. When the problem is poor neuromotor control of the larynx (eg, subject 4), there may be little that can be done to improve speech. When there is a significant stoma leak that cannot be repaired, adding PEEP may not improve speech (although improvement may still be possible with lengthened TI).
Are These Interventions Safe?
Certain of these interventions can reduce alveolar ventilation. Lengthened TI can reduce ventilation because there is more time to speak during inspiration. Speech produced during inspiration diverts air away from the lungs (through the larynx) so that it is not available for ventilation (whereas air used for speech during expiration has already ventilated the lungs). Because individuals with respiratory paralysis can usually perceive air hunger,15
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this can serve as a signal to simply close the larynx and stop speaking. This increases ventilation because the full VT is delivered to the lungs. By contrast, reduced VT decreases alveolar ventilation whether or not the subject is speaking. Although acute increases in arterial PCO2 can produce discomfort (air hunger),15
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this did not occur in our subjects, probably because the PCO2 changes were small (within 2 to 5 mm Hg). Even if they had experienced acute air hunger, subjects receiving mechanical ventilation are known to adapt within 3 days to an increased level of arterial PCO2.16
In certain cases, a reduction in ventilation may actually be beneficial. This is because many individuals who receive long-term positive-pressure ventilation because of neuromotor impairments are overventilated (eg, end-tidal PCO2 was < 30 mm Hg in nearly all of our subjects). In such cases, speech adjustments could have the advantage of moving alveolar ventilation toward normal. Whether a given adjustment actually does alter alveolar ventilation depends on how the individual manipulates the ventilator-delivered inspiration.
Decreasing TE (by increasing TI) reduces the time available for the lungs to empty. This did not pose problems for the present subjects, as they were all able to expire completely even when TE occupied as little as 33% of the ventilator cycle. Nevertheless, such a short TE could pose problems for individuals with significant obstructive airway disease.
PEEP has theoretical safety risks that include barotrauma and reduced cardiac output due to reduced venous return. These risks are associated with high intrathoracic pressure, but usually are of concern only at levels of PEEP higher than those used in this study. PEEP did not increase peak Pt during speech production because diversion of air through the larynx allowed Pt to return to zero during speech breaths. PEEP did not produce adverse effects in the present study, in our previous work,6 or in a recent study13 of speech with pressure-support ventilation and PEEP. Nevertheless, caution should always be used when applying PEEP to individuals with compromised cardiac function (eg, congestive heart failure) or those with autonomic nervous system dysfunction (eg, spinal cord injury, Guillain-Barré syndrome, and syringomyelia).
Is High PEEP Better Than a One-Way Valve?
If PEEP is set at or above the peak Pt, it has the same functional effect as occlusion of the expiratory line (as achieved with a one-way valve in the common ventilator line or a cork in the ventilator expiratory line). We found that speech produced with 15 cm H2O of PEEP was as good as speech produced with a one-way valve. The advantage of PEEP is that it is safer and less expensive than a one-way valve.23
With a one-way valve, inflation of the tracheostomy tube cuff or occlusion of the upper airway could be harmful or fatal. Severe hypoventilation will ensue if the pressure-limit safety device of the ventilator works properly. Severe barotrauma and reduced cardiac output (and reduced venous return) will ensue if the pressure-limit safety device fails to work properly. Substitution of PEEP substantially reduces these risks.
Summary and Conclusions
All of our interventions improved speech, but the most successful was the combination of lengthened TI and PEEP (and, in some cases, reduced VT). Speech improved immediately and substantially. Further improvement could probably be achieved with practice and with behavioral therapy provided by a speech-language pathologist.
These ventilator adjustment interventions were safe and comfortable. Such interventions are simple and inexpensive (or free) and can be implemented easily with any clinical ventilator. Speech produced with high PEEP was as good as speech produced with a one-way valve. For individuals who use one-way valves, we recommend that PEEP be substituted (using an adjustment internal to the ventilator or by coupling an external valve to the expiratory line) because PEEP is safer.
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Acknowledgements |
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Footnotes |
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Drs. Banzett and Brown are currently affiliated with the Pulmonary and Critical Care Unit, Massachusetts General Hospital, Boston, MA.
Support was provided by National Institute on Deafness and Other Communication Disorders grants DC-03425 and DC-01409.
Received for publication September 30, 2002. Accepted for publication March 12, 2003.
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References |
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  H. Prigent, D. Orlikowski, M. B. Blumen, K. Leroux, L. Legrand, M. Lejaille, L. Falaize, M. Ruquet, J-C. Raphael, and F. Lofaso Characteristics of tracheostomy phonation valves. Eur. Respir. J., May 1, 2006; 27(5): 992 - 996. [Abstract] [Full Text] [PDF]
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