A case–control study conducted at the neurophysiology Unit, Baghdad Teaching Hospital and Al-Imammain Al-Kadhimiyain Medical City for the periods from May 2019 to November 2020. Ethical approval was obtained from the Iraqi Council of Medical Specialization (Decision No. 931: date: 1/3/2020). Written informed consent was also granted by all participants.
A total of 57 PwE diagnosed based on clinical neurological examination, EEG findings, and 3-Tesla brain magnetic resonance imaging (MRI) were studied. The duration of their illness ranged from 2 to 15 years. They were classified according to the ILAE 2007 to have either TLE or IGE. Five patients with brain structural abnormality on MRI, one pregnant female, one patient with status epilepticus of < 15 min, and two patients with recent convulsions within 48 h before the study were excluded.
The remaining 48 PwE were with uncontrolled seizure frequency ranged from 1 attack/month to 1–3 attacks/week and the EEG records show interictal temporal spikes/sharp, spike/sharp waves discharges, and generalized spike wave or poly spike wave with the normal background. They were on two or more appropriately chosen and used antiepileptic drugs (AEDs) including carbamazepine, sodium valproate, levetiracetam, lamotrigine, and ethosuximide. None of them was refractory to treatment. All were free from any disease that may affect the ANS and cerebral blood flow, including polyneuropathies, multiple sclerosis, diabetes mellitus, Parkinson’s disease, heart disease, hypertension, and central NS infection or head trauma). Another 51 age- and sex-matched subjects serve as controls were studied.
Study participants were told to abstain from food, alcohol, coffee, cola, energy drinks, tea, and tobacco, and ANS-altering drugs at least for 4 h on the scheduled test day [11] and to avoid activities that would affect BP (like running and jumping) for 2 h before the tests [12]. The patients are advised to wear comfortable clothes and to shower the night before testing without using anybody lotions, powders, or creams below the neck, also to drink water and stay hydrated.
Before the autonomic function tests were conducted, each subject’s medical history, demographic data, and physical examination findings were recorded.
To evaluate ANS functions, SSR, HRV (R–R interval variation), and BP changes were measured using Micromed (Italy) and Medtronic Keypoint (Denmark) 4-channel electromyography equipment. The tests were conducted in a quiet room at room temperature of 22 ± 2 °C. A surface recording disk electrode fixed to the left anterior chest area at the fourth and fifth intercostal space and a reference electrode is fixed at the left anterior axillary line over the fifth or sixth rib. The ground electrode was placed on the midline of the sternum. The sensitivity and sweep speed are adjusted to display the QRS complexes on the screen. HRV analyses are based on the measurement of the time intervals between successive QRS complexes, which reflect the regulation of the HR by the ANS via its sympathetic and parasympathetic control mechanisms [13]. This means that HRV analyses can be used to provide indirect clues about NS activity.
The test battery included recording of HR responses at rest (normal breathing), deep breathing, Valsalva maneuver, and standing as well as measurements of BP changes during isometric handgrip, after 3-min standing, and mental stress test.
The HR response to deep breathing was expressed as deep breathing difference, which was the difference between the maximum HR (shortest RR interval during inspiration) and the minimum HR (longest RR interval during expiration), in a patient breathing at six cycles per minute. The exhalation:inspiration (E:I) ratio was obtained using the following formula: the RR-IV% = (the longest RR − the shortest RR) × 100/mean of RR values [14].
The HR response to Valsalva maneuver expressed as Valsalva ratio was tested while the patient in supine position and the head slightly elevated to about 30°. The patient was asked to strain against 40 mmHg for 15 s by blowing into a mouthpiece attached to a sphygmomanometer. The ratio of the longest RR interval 30–45 s following the release of strain to the shortest RR interval during strain was calculated. The minimal HR occurs at 15–20 s after releasing the strain [15].
HR response to standing was obtained after the patient has been resting at least for 20 min. It is expressed as the 30:15, which is the ratio of the longest RR interval (slowest HR) at 30 s to the shortest RR interval (fastest HR) at 15 s, following an abrupt change in position from supine for 3 min to standing. The 30/15 ratio should be at least 1.04 [16].
Changes in systolic BP following change of position from supine to standing after 3 min were also calculated. The postural decrease in BP after 3 min was taken as the difference between BP (systolic and diastolic BP) lying and the BP (systolic and diastolic BP) standing. A decline in systolic BP by more than 20 mmHg and by more than 10 mmHg for diastolic BP is considered abnormal [15].
The isometric handgrip test involved periodic BP recordings (1-min interval), whereas subjects contracted a hand dynamometer at 30% of maximum voluntary contraction for 4 min. The difference between the highest diastolic BP just before the contraction was released, and the handgrip started was taken as a measure of the response. It should normally be more than 15 mmHg [15].
The systolic BP response to mental stress test was calculated when the patient performs mental arithmetic calculations by removing the number 7 successively from 100. The increase in systolic BP should exceed 10 mmHg in normal individuals [15].
When measuring SSR, an active Ag/AgCl disk electrode was placed on the palm of the hands, while reference electrode was placed on the dorsum of the hand, and the ground electrode on the wrist. A single electrical stimulus ranged from 12 to 20 mA with a pulse width of 0.1 ms was given unexpectedly to the median nerve opposite the recorded side. To avoid any habituation, the inter-stimulus interval was between 20 and 30 s. Five responses were recorded to document the reproducibility and the response with minimum latency (the time required to reach the initiation of the first deflection of the wave) was used for further analysis [17].
Interictal EEG was recorded before the autonomic function testing, using a video-EEG monitoring system (NicoletTM Viking Quest, Italy); the electrodes were arranged according to the International 10–20 system. The duration of video-EEG is at least 3 h. All patients were partially sleep deprived; and the usual dose of their AEDs was regularly taken.
Statistical analysis was performed using IBM-SPSS (statistical package for Social Sciences) version 25 (IBM Corporation, USA). Quantitative variables were presented as mean ± standard deviation (SD) and analyzed with independent Student’s t-test. Categorical variables were expressed as counts and percentages and analyzed with Chi-square test. Correlations between different quantitative variables were performed with two-tailed Pearson’s correlation analysis. For all the tests, a significant level of statistics was considered when p < 0.05.
