Rotatory Chair Testing -- Effects of age

Timothy C. Hain, MD • Page last modified: March 30, 2021 Norms for rotatory chair testingReturn to testing index

There have been many studies of the VOR in aging, largely concluding that there are modest reductions in the VOR gain, time constant (Tc) and phase over age. Phase at a particular frequency and time constant are proxies for one another, and one can use a formula convert the phase at a particular frequency (usually a low one, such as .05 or .02) to a time constant.

Baloh and associates (1993) reported the gains and time constants of the VOR in a study of 75 “elderly” normal people, averaging 79.6 years old, who were compared to 25 normal younger people, averaging 26.2 years old (Baloh et al., 1993). The gain, Tc respectively for young was 0.63, 15.1, and 0.58, 11.7 for "Elderly". The responses were from 100 deg/sec step responses.

age (mean) 26.2 79.6
gain 0.63 0.58
Tc 15.1 11.7

This documents a small decline with age in both gain and Tc over 50+ years.

 

Paige et al (1992) reported on 3 age groups, rotated at 0.025 hz, at 50 deg/sec peak velocity.

age (mean) 31 57 79.5
gain 50 0.53 0.49 0.46
phase 50 14.3 17.2 24.6
Tc 24.98 20.57 13.90

Again over 50 years, gain gradually declines with age, phase increases, and the time constant is reduced. The time constant is computed by the formula of T=tan(90-phase)/(2piF).

 

Furman and Redfern (2001) reported the gain and time constant for 3 age groups, with a total of 90 subjects. They computed a "model gain and model Tc", from sinusoids.

age (mean) 24.3 65.2 75.35
model gain 0.54 0.51 .54
model Tc 17.8 15.3 12

 

So all three of these studies documented a slight decline in gain, and a much larger decline in time constant, over roughly 50 years.

Somewhat different than this, according to Maes and associates (2014), children's rotatory chair testing show no effect of age (between 4-12 years of age). In their data, for older persons, there is also surprisingly little effect on rotatory chair testing results, although one would expect a downward trend in gain/phase based on pathological studies showing loss of vestibular hair cells and neurons in the ganglia. There is an effect, but it isn't very large. We are puzzled why this study did not reveal similar results to the other three.

Gain-TC

Considering the rather high variability in gain/TC values reported in the literature for normal subjects, as is documented in the plot above from the "norms" page, it is not surprising to find variability by age, as there is high scatter.

Gain-TC product, as a way to summarize gain and Tc together.

The gain-TC product, which provides a single number to express VOR total response (Hain et al, 2018). Thee numbers in the studies above as well as others can be used to compute the gain-TC product as a function of age.

Baloh and associates, in the study referenced above, results in a GainTc product of 9.5 for the younger subjects, and 6.8 for the older subjects, from which it can be calculated that the slope of the GainTc/year is -0.051/year. (Hain et al, 2018)

Paige (Paige, 1992) in the study refereced above, was also used to compute the GainTc products for the 0.025Hz -- 50 deg/sec stimulus. These were computed to be 13.23 and 10.07 for young and middle-aged, respectively, resulting in a slope of -0.12 deg/year. The GainTc product in the 79 year old group was only 6.4. This analysis suggests that the GainTc product declines slowly with age. (Hain et al, 2018)

Furman and Redfern, in the study referenced above, reported the effect of age on rotatory chair responses as well, providing gain and time constant. One can compute the gain-TC from this as follows:

age (mean) 24.3 65.2 75.35
model gain 0.54 0.51 .54
model Tc 17.8 15.3 12
Gain-TC product 9.6 7.8 6.48

 

Gain-TC product in normals by age

This composite from 3 studies suggest that the Gain-TC product, on average, declines slowly with age, going from roughly 10 to about 6.5. (i.e. a decline of 35%)

Gain TC product by Decade

Not quite the same, but still generally reflective of this situation is data from our clinical practice (Chicago Dizziness and Hearing). The gain-TC product was calculated from rotatory chair data collected over many years in nearly 6000 unique patients with dizziness. Some of these patients had vestibular damage, which reduces the gain-TC product. Nevertheless, the means are remarkably stable through the 5th decade (11.21 to 11.88), thereafter undergoing a modest decline to 8.86 and 8.88 at the 8th and 9th decade respectively (a decline of 23%). While there are other possible explanations related to distribution of illness in the groups being tested by decade, still it seems reasonable to infer that the effect of age on the gain-TC product is not very large. The R code that generated the above plot is found here:

This reduction in gain_TC product is much more than the reduction in age in the VHIT gain, suggesting that VHIT gain is a poor measure of vestibular output. Perhaps this is due to the efforts of the central nervous system to maintain VOR gain using plasticity, while there is less of an imperative to maintain the time constant.

References: