MPT and DSI: A Clinical Implementation Guide

MPT is sometimes described as a measure of respiratory function, sometimes as a measure of vocal fold efficiency. Both descriptions are partly correct and partly misleading.

A short MPT can reflect any of three underlying problems—or some combination of them:

• Glottal incompetence. Air leaks through an incompletely closed glottis (vocal fold paresis, presbyphonia, sulcus vocalis), so the patient burns through their breath faster than the vocal folds convert it into sound.
• Reduced respiratory support. The patient simply has less air available to begin with (pulmonary disease, deconditioning, neuromuscular weakness).
• Hyperfunction. Pressed phonation with high subglottal pressure can also shorten MPT, even when glottal closure is otherwise efficient.

Because MPT cannot distinguish among these mechanisms on its own, it is best interpreted alongside other measures—the S/Z ratio, perceptual evaluation, vital capacity if available, and laryngoscopic findings. As an isolated number it is suggestive; in a profile it becomes diagnostic.

MPT looks simple, but small protocol differences produce surprisingly large variations in measured values. Standardizing the procedure within and across sessions matters more than the exact protocol chosen.

MPT varies substantially with sex, age, body size, and physical conditioning, so a single "normal value" is not very useful. The ranges below come from healthy adult reference samples in the published literature and are reasonable clinical anchors, not strict thresholds.

Two patterns from the literature deserve clinical attention:

• MPT below ~10 seconds in an adult is clinically significant regardless of sex or age. Such values reliably indicate either glottal incompetence, severely reduced respiratory support, or both, and warrant fuller workup.
• Healthy older adults preserve MPT better than expected. When normative samples exclude pulmonary disease, neurological conditions, and voice complaints, mean MPT in the seventh-to-ninth decade does not differ much from younger adults. A short MPT in an older patient is not "just aging"—it suggests a process worth investigating.

MPT alone captures only one dimension of voice function. Wuyts and colleagues, working at the University of Antwerp, asked a more ambitious question: could a small set of objective measurements be combined into a single score that reliably predicts perceptual dysphonia severity?

Their 2000 study on 387 subjects identified four measurements—each capturing a different aspect of vocal function—that together explained perceptual severity better than any one measure alone. The result was the Dysphonia Severity Index, defined by the formula:

The DSI scale was designed so that +5 corresponds to a perceptually normal voice (GRBAS Grade 0) and –5 to severe dysphonia (Grade 3), with intermediate values reflecting graded severity. The more negative the DSI, the worse the perceived voice quality. However, the +5 anchor represents the theoretical ceiling, not the population average: a 2020 meta-analysis of 14 studies and 1,330 healthy subjects found a mean DSI of 3.05 for perceptually normal voices, with a 95% confidence interval of 2.13–3.98 (Sobol & Sielska-Badurek, 2022). This means many healthy voices produce DSI values well below +5, and clinical interpretation bands should be anchored to the empirical distribution rather than the theoretical maximum.

The DSI is not arbitrary—each of its four components was selected because it indexes a different physiological aspect of voice production. Understanding what each measures helps interpret why a patient's DSI is what it is, beyond just the global score.

The DSI is most useful in two clinical scenarios.

1. Establishing baseline severity. The DSI value at first evaluation, contextualized against the +5/–5 scale, gives a reproducible numerical anchor for the perceptual impression. A DSI of +3.5 quantifies "mildly impaired" in a way that two clinicians can compare across sessions and across cases.

2. Documenting therapy progress. This is what the DSI was specifically designed for. Because it integrates four parameters, it is more sensitive to incremental change than any single measure—improvement on one component (longer MPT) will show up in the DSI even if jitter and intensity remain stable. Wuyts and colleagues explicitly framed the DSI as a tool for tracking "therapeutic evolution," and subsequent studies have validated this use.

The DSI is widely used, but it has well-documented limitations that affect how its values should be interpreted.

For clinicians integrating MPT and DSI into routine voice assessment, a simple, reproducible workflow tends to work best: