Effects of Menstrual Cycles on VOR Gain Functions

Introduction

The menstrual cycle is the regular natural change in the uterus and ovaries that make pregnancy possible in females.¹ During the menstrual cycle, levels of hormones in healthy females differ during different phases of the cycle. The level of estrogen and progesterone in the body has a dynamic regulation during the ovarian cycle. Estrogen may directly affect steroid receptors in the cochlea, which have been identified both in animals and humans.^2-4Sampio⁵ reported changes in calcium, magnesium, vitamin D, iron metabolism in the body, emotional hypersensitivity, generalized pain, and dietary habits changes during the luteal phase. The concentration of Na⁺/K+ ions in the cochlea fluid also changes during the menstruation cycle.⁵

It has also been reported that estrogen and progesterone modulate the cochlear blood supply and the cochlear fluids electrolyte balance.^6,7 These changes in the inner ear function result in changes in various auditory processes, such as pure tone thresholds, spontaneous otoacoustic emissions, auditory brainstem responses, speech evoked auditory brainstem response, and auditory event-related potentials.^8-13 During the luteal phase, the amplitude of N1-P2 peak in auditory late latency responses significantly reduces compared with the menstrual and follicular phase of females menstrual cycle.⁹ It has also been reported that the latency of wave V of auditory brainstem responses increases during the follicular phase and latency of wave V of auditory brainstem responses decreases during the luteal phase of the menstrual cycle¹¹ There are also reports suggesting an increase in amplitude and decrease in latency of frequency following responses during the menstrual cycle's mid-phase.¹³ Females perform better on dichotic listening tasks during the menstrual cycle's follicular phase, indicating the influence of estrogen level on dichotic listening in women.¹⁴

As the inner ear's cochlea and vestibular compartments are interconnected with ductus reunions, the inner ear chemical composition changes can affect both the cochlea and the vestibular system during the menstrual cycle in young healthy women. Various reports suggest changes in some of the ocular motor functions in females during the menstrual cycle. Ishii et al¹⁵ reported an alteration in the frequency of spontaneous saccades, spontaneous nystagmus, positional nystagmus different from benign paroxysmal positional vertigo typical nystagmus, and abnormal caloric test findings during the menstrual cycle. Abdel Nabi et al¹⁶ reported spontaneous nystagmus and positional nystagmus in females premenstrual period. It has also been reported that Meniere's disease symptoms exacerbate during the late luteal phase in females.¹⁷ Shahin et al¹⁸ reported better postural stability during the menstrual cycle's mid-phase.

However, some other reports suggest that the latency and the amplitude of the vestibular evoked myogenic potentials (VEMP) do not change during the various phases of the menstrual cycle in young healthy demales.^19,20 There is a dearth of information on how the vestibuloocular reflex (VOR) gain function changes during the various phases of the menstrual cycle in young healthy females. Recording the VOR reflex in females is crucial as it might affect the video head impulse test (vHIT) interpretations during the various phases of the menstrual cycle. This will help the clinician rule out the possibility of misdiagnosing a case and creating different standard norms for females.

vHIT is a recent test in vestibular test battery that assesses the VOR function in individuals with different vestibular pathologies. The test-retest reliability of the vHIT in individuals with normal hearing is excellent.²¹ vHIT is helpful in the diagnosis of various vestibular disorders such as vestibular neuritis, Meniere's disease, benign paroxysmal positional vertigo, vestibular migraine, and posttraumatic vertigo.^22-24

Aims and Objectives

The current study aimed to see the variations in VOR gain and VOR gain asymmetry ratios of the three semicircular canal planes during the various phases of the menstrual cycle in young healthy females. The aim was also to look for the presence or absence of any saccades during the menstrual cycle three phases.

Method

Results

VOR gain and VOR gain asymmetry were calculated for all the participants in three phases of the menstrual cycle. VOR gain for one of the participants for three phases of the menstrual cycle is given in ►Figs. 1 to 3, respectively.

Close

Fig. 1

Waveforms of video head impulse test results of all six semicircular canals from three different planes for the first phase of menstruation cycle

Export to PPT

Close

Fig. 2

Waveforms of video head impulse test results of all six semicircular canals from three different planes for the second phase of the menstruation cycle

Export to PPT

Close

Fig. 3

Waveforms of video head impulse test results of all six semicircular canals from three different planes for the third phase of menstruation cycle

Export to PPT

The mean and standard deviation for the VOR gain and asymmetry values for all the three phases are given in ►Tables 1 and 2, respectively.

The repeated measure analysis of variance (ANOVA) revealed no significant main effect for the VOR gain values during the three phases of the menstruation cycle in the lateral plane for the left lateral canal [F(2, 56) = 1.54, p = 0.22], the right lateral canal[F(2, 56) = 1.89, p = 0.16]; and in LARP plane for left anterior canal [F(2, 56) = 1.04, p = 0.36], right posterior canal [F(2, 56) = 1.12, p = 0.33]. However, there was a significant main effect for the VOR gain values between the phases for the RALP plane in the right anterior canal [F(2, 56) = 3.34, p = 0.04] and left posterior canal [F(2, 56) = 3.63, p = 0.03]. Bonferroni pairwise comparison revealed significant differences between phase I and phase II of the menstrual cycle in both the right anterior and left posterior canal VOR gain function (p < 0.05).

Further, repeated measure ANOVA revealed no significant main effect for the VOR gain asymmetry ratio for the lateral plane [F(2, 56) = 0.08, p = 0.93], LARP [F(2, 56) = 0.92, p = 0.41], and RALP planes [F(2, 56) = 0.1, p = 0.91], during the three phases of the menstrual cycle. Also, there was an absence of saccades in all the participants during the menstrual cycle's three phases.

Discussion

Understanding the results in the context of hormonal fluctuations during the menstrual cycle and their effect on the VOR gain function is essential for differential diagnosis of vestibular disorders. Despite the well-known effects of hormonal changes in inner ear physiology, the present study indicates no VOR gain differences in the menstrual cycle's three phases.

Previous studies have found the presence of several hormones in the inner ear. As these hormones are present in the inner ear, patients with hormonal deficiency, hormonal replacement therapy, and hormonal hypersecretion may cause an abnormal auditory function.^11,26 Several studies have found alterations in the auditory function during the different phases of the menstrual cycle.^27,28 These alterations in the auditory functions could be due to the changes in the concentration of hormones, affecting the inner ear homeostasis in the different phases of the menstrual cycle in females.^29,30

Since the inner ear consists of the cochlea and the vestibular system, the hormone's concentration could also affect the peripheral vestibular system. However, there are equivocal findings on the hormonal influences on vestibular system functions. Sinha et al¹⁹ recorded cervical (cVEMP) during the three phases of the menstrual cycle in 20 healthy female participants to see the effect of hormonal changes on cVEMP. They also noted no significant impact of hormonal changes during the different phases of the menstrual cycle on the latency or amplitude parameters of cVEMP. Similarly, Sinha and Sahu²⁰ reported no significant effect of hormonal changes during the menstrual cycle on latency or amplitude parameters of ocular VEMP.

However, several other studies have reported a significant change in various vestibular functions such as saccadic eye movements, directional preponderance, and caloric test results.¹⁶ These authors have hypothesized that in cases with peripheral nystagmus, dizziness and vertigo may be due to salt and water retention occurring in the premenstrual period; this condition is caused by estrogen rise, progesterone, and aldosterone. However, such hormonal changes may not be affecting all the women equally or may not be affecting all the vestibular functions equally in all the females during the menstrual cycle.

Ishii et al¹⁵ reported various vestibular symptoms such as giddiness, vomiting, headache, and nausea occur only in 5 to 20% of the female participants. Darlington et al.³⁰ also observed that hormonal changes during the menstrual cycle affect the lateral sway in female participants and not the anterior-posterior sway. Additionally, they reported that central vestibular functions such as the optokinetic system are not affected by the hormonal changes during the different phases of the menstrual cycle. The authors concluded that the lateral sway variation is not directly related to the vestibular system but could arise from multiple sources. Hence, we hypothesize that hormonal changes occurring during the menstrual cycle may not influence the VOR gain and VOR gain asymmetry in female participants during different phases menstrual cycle.

However, there was a significant difference in the VOR gain values between the first and the second phase of the menstrual cycle for the RALP plane in the right anterior canal and left posterior canal. Such isolated differences in VOR gain values between the two phases of the menstrual cycle may not be significant. Also, the absence of any saccades in all the participants indicates the absence of any peripheral pathology in all the participants.

Conclusions

The results of the study indicate no significant change in VOR gain function and VOR gain asymmetry during the three phases of the menstrual cycle in healthy females. It can be concluded that there is no need to consider the menstrual cycle as one of the criteria while administering and interpreting the vHIT test.