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Chapter 3
The following outcomes are recorded and registered per consistency separately: total duration (time between substance touching lips until the end of the last swallow), grams swallowed (for thin and thick liquid measured with a measuring cup and for solid estimated as a percentage of leftover outside the mouth of 3.125 g), number of swallows (based on facial and laryngeal movement) , number of chews (based on mandibular movement), and whether the participant coughed at any time during or directly after ingestion of the consistency. The following outcomes are calculated: speed of ingestion per consistency (g/s) and average swallow volume (g/swallow). The primary outcome of the SPEAD-test is the SPEAD-rate (g/s), which is the mean ingestion speed of the three consistencies.
SPEAD-rate (g/s) = (speed thin liquid + speed thick liquid + speed solid) / 3
A higher SPEAD-rate thus represents better swallowing capacity. In case a participant is not able or not allowed (based on earlier videofluoroscopy studies) to ingest one or more of the consistencies, a speed of 0 g/s is used for that consistency. An instruction form for clinical use is presented in Appendix 1. Other outcomes, including number of swallows and chews and coughing, can be monitored when compared after repeating the SPEAD-test.
Safety, feasibility, and costs
To assess safety, we recorded whether any unsafe situations (e.g., noticeable aspiration or choking) occurred. To evaluate feasibility, after completion of one trial of the test, the participants were asked whether the test was uncomfortable in any way, and if this was the case to elaborate what was uncomfortable and how this could be avoided. Also, they were asked whether they had any other comments or suggestions after taking the test. Also, the time needed to perform the entire SPEAD-test, including preparation and cleaning time was assessed, and the costs for the products used for the test were calculated.
Reliability
Reliability of the assessment of duration, number of swallows and number of chews was assessed. To assess test-retest reliability, the SPEAD-test was performed three times by each participant, with at least fifteen minutes in between trials, timed by the observer. In order to determine intra-rater reliability, one observer evaluated the videotaped records of each test undertaken by all participants in random order three times. The interval between the evaluations was at least two weeks, to avoid the influence of recall. In order to assess inter-rater reliability, three different observers evaluated the videos of the first trial of all participants.
Validity
In order to assess validity of the SPEAD-test, several subjective as well as objective swallowing related outcomes were collected in all participants, except for VFS to avoid unacceptable radiation of the healthy participants. SPEAD-test and validity measures were collected on the same day, except for VFS. Median time between VFS and the other assessments was 9 days (range 0-41 days).