Tongue-palate pressure is a parameter of considerable interest in the field of dysphagia. Maximum isometric tongue-palate pressures (MIPs) decline in healthy aging and in dysphagia. Functional reserve (FR) is the difference between MIPs and swallowing pressures. Reduced FR is thought to constitute a risk for developing functional swallowing impairments. We compare different approaches for calculating FR and recommend an optimal approach. Tongue-palate pressure data were collected from 78 healthy adults (
The ability to generate tongue-palate pressure has emerged as a measure of considerable clinical and research interest in the field of dysphagia over the past two decades. Key to this interest is that tongue strength, measured during maximum isometric tongue-palate pressure tasks (MIPs), appears to decline in healthy aging [
Functional reserve is the term coined to describe the difference in pressures generated in maximum isometric pressure (MIP) tasks compared to swallowing tasks. Robbins and colleagues were the first to point out that swallowing pressures appear to be preserved in healthy older adults, even in the presence of reduced MIPs. Reductions in functional reserve, due to reductions in MIPs, were argued to have important clinical implications and to place a person at greater risk of developing functional swallowing impairments, particularly in the case of decompensation [
Functional reserve describes a tongue-palate pressure range that is bounded at the top by a maximum pressure task and at the bottom by a swallowing task. The swallowing task used to define the bottom of the functional reserve range has varied across studies, leading to some confusion regarding the measure. Furthermore, different instruments have been used across studies, without clear demonstration that measures can be generalized across instruments. We are conducting a program of research exploring the relationship between tongue pressure capacity and swallowing behaviors. We are specifically interested in confirming whether or not limited tongue pressure capacity contributes to constrained variability in swallowing behaviors and whether such constraints are seen as a function of healthy aging. We have recently reported that functional reserve, which we defined as the difference between MIPs and regular effort saliva swallow (RESS) pressures, does not necessarily decline with age [
Of particular note is the study of Youmans et al. [
These observations led us to question whether functional reserve is indeed a parameter that changes in healthy aging and to explore which elements need to be included in a robust and psychometrically valid measure of functional tongue pressure reserve. We propose that such a parameter should display three characteristics. A measure of functional reserve should be sensitive to, and positively correlated with, changes in maximum strength measures (MIPs). A measure of functional reserve should be sensitive to changes that occur across the age span, but in order for these to support a hypothesis that functional reserve declines with age, the trend should be visible in a parameter where swallowing pressures are expressed as a percentage of a person’s maximum tongue strength, in order to control for individual variations in strength. A measure of functional reserve should be one that can be collected easily, without posing a risk of aspiration for the patient.
In this paper, we explore 6 different candidate measures of functional reserve to determine an optimum method for capturing functional reserve in future research and clinical situations.
Tongue pressures at the anterior, medial, and posterior palate were collected from 78 healthy consenting adults in two sex-balanced age groups. The younger participant group ranged in age from 18 to 39 years, with a mean age of 27 years. The older participant group ranged in age from 60 to 87, with a mean age of 70 years. The protocol was approved by the local institutional research ethics board. Exclusion criteria included participant-reported history of type I diabetes, chronic sinusitis, taste disturbance, or any swallowing, motor speech, gastroesophageal, or neurological difficulties. During intake, a brief oral mechanism examination and a water swallow screening were performed by a licensed speech-language pathologist to confirm eligibility to participate.
We used the 3-bulb tongue array of the KayPentax Swallowing Signals Lab to collect tongue pressures, with the bulbs spaced 8 mm apart and adhered to the palate in midline using Stomahesive (Convatec, St-Laurent, Quebec, Canada). The anterior bulb was positioned on the alveolar ridge, immediately behind the upper incisors. Pressure signals were sampled at 250 Hz with the range calibrated to record an upper amplitude limit of 750 mmHg. Five different pressure tasks were included, with each performed in a block of 4 task repetitions. The protocol commenced with the maximum anterior isometric pressure task (AMAX) and then proceeded to one of four randomly assigned sequences for the collection of regular effort saliva swallows (RESS), effortful saliva swallows (ESS), maximum posterior isometric pressures (PMAX), and discrete water swallows (i.e., single sips of ~8–10 mL taken from a cup). The PMAX data have been reported elsewhere and are not used for the calculations reported in this paper.
Anterior, medial, and posterior palate pressure waveforms were displayed on a computer monitor. The onset, peak, and offset of each pressure event were indexed by a trained research assistant and pressure amplitudes at each of these timepoints were recorded. Pressure amplitude (in mm Hg) was calculated as the amplitude difference (in mm Hg) between the highest peak pressure amplitude and the lowest baseline pressure amplitude (usually zero mm Hg) seen across all three pressure waveforms (anterior, medial, and posterior) for a given task repetition. Figure
Illustration of tongue-palate pressure waveforms on the KayPentax Digital Swallow Workstation. The highest peak pressure (in mm Hg) across the anterior, medial, and posterior sensors was used as the value of peak pressure for each task.
Six different equations were calculated as possible measures of functional reserve as follows. Maximum peak pressure on the AMAX task minus maximum peak pressure on the water swallowing task. Maximum peak pressure on the AMAX task minus mean peak pressure on the water swallowing task. Maximum peak pressure on the AMAX task minus maximum peak pressure on the RESS task. Maximum peak pressure on the AMAX task minus mean peak pressure on the RESS task. Maximum peak pressure on the ESS task minus maximum peak pressure on the RESS task. Maximum peak pressure on the ESS task minus mean peak pressure on the RESS task.
Scatter plots were prepared in IBM SPSS 19.0, plotting each measure of functional reserve, first as a function of maximum isometric pressure (maximum peak pressure on the AMAX task) and second as a function of age. An
Table
Pearson’s correlations between different measures of functional reserve: maximum isometric pressure and age.
Functional reserve measure | Unit of measurement | Maximum isometric pressure (MIP) | Age | ||
---|---|---|---|---|---|
Pearson’s correlation | Significance (2-tailed) | Pearson’s correlation | Significance (2-tailed) | ||
MIP minus maximum water swallow pressures | mm Hg |
|
.000 | −.304 | .007 |
% MIP | .314 | .005 | −.104 | .368 | |
MIP minus mean water swallow pressures | mm Hg |
|
.000 | −.359 | .001 |
% MIP | .320 | .005 | −.107 | .354 | |
MIP minus maximum regular effort saliva swallow pressures | mm Hg |
|
.000 | −.250 | .031 |
% MIP |
|
.000 | −.042 | .716 | |
MIP minus mean regular effort saliva swallow pressures | mm Hg |
|
.000 | −.312 | .006 |
% MIP |
|
.000 | −.078 | .500 | |
Maximum effortful minus maximum regular effort saliva swallow pressures | mm Hg | .285 | .013 | n/a | n/a |
Maximum effortful minus mean regular effort saliva swallow pressures | mm Hg | .325 | .004 | n/a | n/a |
Correlations with
As shown in Figure
(a) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to water swallowing pressures and tongue strength, as measured by MIP. (b) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to regular effort saliva swallowing pressures and tongue strength, as measured by MIP. (c) Scatter plot showing the relationship between functional reserve measures comparing maximum effortful saliva swallowing pressures to regular effort saliva swallowing pressures and tongue strength, as measured by MIP.
With respect to the relationship between functional reserve measures and age, Figure
(a) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to water swallowing pressures and age. (b) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to regular effort saliva swallowing pressures and age.
Finally, we explored what happened to the previously observed correlations when we transformed our measures of swallowing pressure into values normalized to a percentage of each participant’s maximum strength measure. As shown in Figure
(a) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to water swallowing pressures and tongue strength, as measured by MIP, with swallow pressures expressed as a percentage of MIP. (b) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to regular effort saliva swallowing pressures and tongue strength, as measured by MIP, with swallow pressures expressed as a percentage of MIP.
(a) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to water swallowing pressures and age, with swallow pressures expressed as a percentage of MIP. (b) Scatter plot showing the relationship between functional reserve measures comparing maximum isometric pressure (MIP) to regular effort saliva swallowing pressures and age, with swallow pressures expressed as a percentage of MIP.
We conclude that optimally robust measures of functional reserve are those comparing maximum tongue strength (MIPs) to mean water or saliva swallowing pressures. Of these two options, saliva swallows involve less risk of aspiration during data collection. The results of the analysis in this study suggest that it would be reasonably straight forward for clinicians to routinely incorporate the measurement of tongue pressure functional reserve into swallowing assessment, using a short series of MIPs and saliva swallows.
We recommend that functional reserve measures should use a data transformation to account for individual differences in maximum tongue strength measures, by expressing swallowing pressures as a percent of a person’s MIP. Using this transformation, functional reserve measures comparing MIP to either mean or maximum saliva swallow pressure retain statistically significant strong correlations with strength. However, this transformation has the effect of negating apparent age-related differences in functional reserve.
When normalized to control individual variations in strength, our data concur with those of Youmans and colleagues [
This work was supported by the National Institutes of Health (Grant no. 5R01DC011020 to C. M. Steele); and from the Toronto Rehabilitation Institute, which receives funding under the Provincial Rehabilitation Research Program from the Ontario Ministry of Health and Long-Term Care (MOHLTC). The views expressed do not necessarily reflect those of the ministry. The author would like to thank Drs. Mark Bayley, Cathy Pelletier, and Julie Cichero for their contributions to the study design and interpretation. Assistance from Rebecca Cliffe Polacco, Sarah Hori, Sonja Molfenter, Melanie Peladeau-Pigeon, and Clemence Tsang during data collection and processing is gratefully acknowledged.
There is no conflict of interests to disclose.