| Autonomic dysfunction in Parkinson’s disease and its correlates to medication and dopamine transporter binding. | ||
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The author examined all the PD patients with special attention being paid to neurological deficits caused by PD, and to symptoms and signs referring to autonomic dysfunction. The clinical examination was performed before starting the PD medication, after six months on medication and after a 6-week washout period. The clinical disability caused by PD was graded using the Hoehn and Yahr stages (Hoehn & Yahr 1967) and the UPDRS (Fahn et al. 1987).
The clinical severity of the autonomic failure was presented as the sum of scores obtained on 3-point rating scales used to assess 11 different modalities of ANS measures (postural dizziness, disturbances of sweating, urinary function, bowel function, sexual function, HR regulation, salivation, breathing, signs of peripheral circulation disturbances, sluggish pupillary reactions and seborrhoea), the dysfunction being graded from 0 to 2 (0 = absent, 1 = mild, 2 = moderate to severe) (Turkka 1987). Orthostatic hypotension was evaluated in a test where patients stood up after a 30-minute rest taken in a supine position and stood still in an upright position for 10 minutes. The BP was recorded just before and immediately after standing up, as well as at 1-minute intervals during the standing. Orthostatic hypotension was defined as a reduction of systolic BP of at least 20 mmHg or of diastolic BP of at least 10 mmHg within 3 minutes of standing (Consensus statement 1996).
Cardiovascular autonomic function tests, based on HR and BP responses at rest and after various stimuli, were performed on all patients included in the study and on 28 control subjects under standardised environmental conditions between 8 and 9 a.m. before breakfast. The patients were allowed to take their regular drugs before the test. The tests were performed before PD medication, six months after starting the medication and after a 6-week washout period. First, with the patient in a supine position on the tilt table, the maximum contraction power (handgrip) of the patient’s dominant hand was measured three times with a dynamometer for the isometric work test. At the end of a 30-minute resting period, the baseline BP was measured three times using an automatic arm sphygmomanometer. Thereafter, the following five tests were performed: normal breathing, paced breathing at six breaths per minute, the Valsalva manoeuvre, upright tilting and isometric work. The interval between these tests was standardised so that the next test was not begun until HR and BP had returned to the rest level.
In the analyses of the deep breathing test the thermistor signal ascertained that the paced deep but not maximum breathing was evenly performed. In the Valsalva manoeuvre the blowing pressure was monitored and only steadily maintained blowings were accepted. In the isometric work test the contraction power on the dynamometer was monitored graphically and thereby maintained at the optimal level.
The ECG and nasal thermistor signals were conveyed through a 12-bit A/D converter with a sampling frequency of 320 Hz to a PC and were analysed after visual off-line checking of the raw ECG and breathing signal. Test performances in deep breathing, the Valsalva manoeuvre and the isometric work tests were checked on-line and off-line and only adequately accomplished test performances were accepted for analysis (Turkka et al. 1987b, Havanka-Kanniainen et al. 1988, Suominen 1997).
In the normal breathing test, the consecutive RR intervals for a period of 10 minutes were measured from the ECG, and the standard deviation (SD) of the RR intervals was used as a variable. Successive RR intervals were measured and the square root of the mean squares of the differences between successive intervals (rMSSD) was calculated, so reflecting the true beat-to-beat variation.
In the deep breathing test, the ratios of the longest (expiration) to the shortest (inspiration) RR interval of five consecutive breathing cycles was calculated. The test was performed twice, and the higher median RR interval ratio of the tests was used as the ”maximum-minimum (max-min) ratio”.
In the Valsalva manoeuvre, the ratio on the longest RR interval after blowing (at 40 mm Hg or at least 50% of the subject’s maximum blowing power for 15 seconds) to the shortest one during blowing was calculated. The highest ratio of three manoeuvres was used as the ”Valsalva ratio”.
In the tilting test, the ratio of the longest RR interval at approximately beat 30 (between beats 20 to 40) to the shortest RR interval at approximately beat 15 (between beats 10 to 20) after quick passive upright tilting (2 seconds, 80˚) was used as the ”30:15 ratio”. The systolic and diastolic BP responses to passive upright tilt were measured immediately and at 2 and 5 minutes after tilting. The largest drop (or lowest increase) in systolic and diastolic BP was also quantified. The largest increase in systolic and diastolic BP during a 5-minute period of sustained handgrip with a dynamometer at 30% of the maximum voluntary force was also noted (the isometric work test).
All the subjects were monitored for 24 hours with an ambulatory two-channel ECG recorder (Electrocardiocorder, Del Mar Avionics, California). The PD patients were encouraged to continue their daily activities during the recording in a hospital ward.
The ECG data from the recordings were sampled digitally and transferred from the Oxford Medilog scanner to a microcomputer for analysis of HRV. All the RR interval time series were first edited automatically, after which careful manual editing was performed by visual inspection of the RR intervals. Each RR interval time series was passed through a filter that eliminates premature beats and artefacts and deletes the filling gaps (Korpelainen et al. 1999). In the final analysis of the linear and non-linear components of HRV, 24-hour measurements were divided into segments of 8000 RR intervals, and only segments with >85% sinus beats were included.
The mean duration of all RR intervals and the standard deviation of the RR intervals (SDNN) in the whole epoch were computed as time domain measures. An autoregressive model was used to estimate the power spectrum densities of the HRV (Kay & Marple 1981). The size of 20 was used as the model order in the analysis of the RR interval data. The power spectra were quantified by measuring the area in three frequency bands: 0.005 to 0.04 Hz (VLF), 0.04 to 0.15 Hz (LF) and 0.15 to 0.4 Hz (HF).
For quantitative two-dimensional vector analysis, the standard deviation of the continuous long-term RR interval variability (SD2) and the instantaneous beat to beat RR interval variability (SD1) were analysed, and visually presented as Poincaré plot scatter grams in which each RR interval is plotted as a function of the previous one (Tulppo et al. 1996, Korpelainen et al. 1999). In the computerised analysis, the Poincaré plot was first turned 45° clockwise, and the standard deviation of the plot data was then computed around the horizontal axis, passing through the data centre (SD1). The standard deviation of the continuous long-term RR intervals was quantified by turning the plot 45° counterclockwise (SD2) and by computing the data points around the horizontal axis, passing through the centre of the data.
The power-law relationship of the RR interval variability, a spectral measure reflecting the distribution of the spectral characteristics of the RR interval oscillations, was calculated from the frequency range of 10−4 to 10−2 by a previously described method (Bigger et al. 1992). The point power spectrum was logarithmically smoothed in the frequency domain, and the power was integrated into bins spaced 0.0167 log(Hz) apart. A robust line-fitting algorithm of log(power) on log(frequency) was then applied to the power spectrum between 10-4 to 10−2, and the slope of this line was calculated. This frequency band was chosen on the basis of previous observations regarding the linear relationship between log(power) and log(frequency) in the frequency band (Saul et al. 1991, Bigger et al. 1996).
SSRs to various stimuli were used to assess the sympathetic sudomotor activity in 51 untreated PD patients and 20 age-matched controls. The SSR recordings of the PD patients were performed before PD medication, six months after starting the medication and after a 6-week washout period. The experiment was performed under standard conditions in an illuminated and silent room with ambient temperature at 22°C to 24°C. The subject was awake and relaxed in a lying position.
Recordings were carried out using an electromyograph (Counterpoint®, Dantec, Skovlunde, Denmark) with an amplifier gain of 0.1–2 mV per division and filter settings at 0.2–50 Hz. The SSRs were provoked by using two types of stimulation separately: an auditory click (0.1 ms, 120 dB) delivered to both ears, and an electric single square pulse (0.5 ms, intensity adjusted to 20% to 30% above the motor threshold) for stimulating the median nerve at the wrist. Both types of stimulation were performed two times and given at irregular rates after intervals of at least 60 seconds. The electrodes (discs) connected to the negative input of the amplifier were attached to the palms of the hands and soles of the feet, and the electrodes connected to the positive input of the amplifier were attached to the dorsum of the hands and feet. Skin temperatures on the recording areas were measured in all the recording sessions. There were no skin temperature differences between the PD patients and the controls and between the recording sessions, and there was no difference between the left and right body sides of the subjects.
The data were sampled digitally with a sampling frequency of 34 Hz, and transferred to a computer for the off-line analysis of the SSR. SSR signals were recorded simultaneously on both hands and feet and the recording continued for two minutes after each stimulus, and the mean peak-to-peak amplitudes and latencies of the right and the left side of the recording that showed greater responses were included in the analysis. The number of SSRs after a single stimulus was analysed. Only the SSR waves showing the same morphology and having a minimum of 25 % of the amplitude of the primary response were considered. The response adaptation (an amplitude decrease of 30% in a repeated procedure) from the two successive stimuli was calculated.
Striatal dopamine transporters (DATs) were evaluated in 29 and serotonin transporters (SERTs) in 27 of the PD patients included in the study and compared to 21 and 16 healthy control subjects, respectively. SPECT studies were performed using a dual head gamma camera (ADAC Vertex) equipped with high-resolution fan beam collimators. SPECT scans were done 4 and 24 hours after the slow (30 s) intravenous injection of 120–185 Mbq high specific activity [123I];β -CIT (MAP, Medical Technologies Inc., Tikkakoski, Finland). The ligand was synthesized according to a method described previously (Hiltunen et al. 1998). Thyroid uptake was blocked with 400 mg potassium perchlorate taken orally 30 min before tracer injection.
The investigator performing the region-of-interest (ROI) analyses was unaware of the subject demographics. Transaxial slices oriented along the orbitomeatal line were reconstructed and the two slices corresponding to the highest striatal uptake were summed, yielding a final slice of thickness of 9.2 mm (Laine et al. 1999). The ROIs were drawn over the right and left striata using a colour scale with about 60% isocontour cutoff boundaries for delineation. The size of the average striatal ROI was about 20 pixels. Occipital white matter (OWM) ROIs were drawn as a reference (nondisplaceable activity) because postmortem studies have shown a very low density of DAT and SERT in cerebral cortices and the cerebellum (Laruelle et al. 1988, Palacios et al. 1988, De Keyser et al. 1989). The cerebellar region was not taken as a reference for nondisplaceable activity since this region is situated close to the bed surface and could cause interference for raw SPECT data. In addition to the whole striatal areas the putamen and caudate ROIs were determined. Average templates for the putamen and caudate nuclei in 6 controls were determined using magnetic resonance imaging. These average templates were placed individually into the putamen and caudate areas. The average ROI areas for the putamen and caudate were 10 and 9 pixels, respectively. In addition to the striatal dopamine areas ROIs for monoamine transporters, mainly reflecting SERT (Laruelle et al. 1988), were visually positioned on the summed transversal slices of the hypothalamus/midbrain (including the raphe nuclei, substantia nigra and colliculi; average size 9 pixels), the thalamus (average size 11 pixels) and the medial prefrontal area at the striatal level (average size 15 pixels). The hypothalamus/midbrain activity was consistently detected on the midline about 12 mm below the level of the striatal transversal slice. These areas were identified by reference to the Talairach and Tournoux stereotactic atlas (1988) and magnetic resonance imaging scans were performed in 6 controls.
Specific striatal DAT binding was calculated as the ratio of the total binding in the striatum minus the nondisplaceable binding in the OWM divided by the OWM, i.e. (STRIATUM-OWM)/ OWM, reflecting the specific-to-nondisplaceable binding. As it has been shown that a state of equilibrium in the striatal and occipital areas exists at 20–24 hours after the injection, the ratio at this time point was used as an estimate of the Binding Potential (Abi-Dargham et al. 1996). This estimate, the binding potential index (BPI), reflects the equilibrium partition coefficient described by Salmon et al. (1990). A caudate to putamen uptake ratio was calculated as the ratio of the BPI of the caudate to the BPI of the putamen.
The demographic data between the PD patients and controls, and between the medication groups were analysed with the Mann-Whitney U two-sample test (continuous data) and the χ2 test (rate and proportional data). The results of the clinical evaluation of the disease severity and autonomic dysfunction were correlated with Spearman’s correlation coefficients, as were the results of the autonomic disability grading and the β -CIT SPECT measurements. The values of the HR responses (after logarithmic transformation) of the PD patients and the control subjects in Study I were compared with each other using covariance analysis with age and baseline HR as covariants, since cardiovascular autonomic responses have been shown to be dependent on both age and HR (Wieling & Karemaker 1999). Covariance analysis was also used to compare the BP responses in the PD patients and the control subjects with age as covariant. The BP responses were normalised to the baseline BP by expressing BP change as a percentage of the baseline BP. For the isometric work the genders were analysed separately as the BP responses are greater in males than females (Piha 1993, Khurana & Setty 1996), while other parameters were analysed without separation of the genders (Matthews 1988, Braune et al. 1996). Within the patient groups the comparisons between the cardiovascular responses at different time points were performed using the general linear model with repeated measures analysis. Friedman’s test was used to evaluate the prevalence of orthostatic hypotension at different time points.
The Mann-Whitney U two-sample test was used for comparing the HRV values (II) and the SSR amplitudes and latencies (III) of the PD patients with those of the control subjects. The correlation between the clinical parameters of PD and the various measures of HRV was analysed with Spearman’s correlation coefficient (II). The Wilcoxon matched pairs test was used to compare the SSR amplitudes and latencies at different time points and to compare the responses of the affected limbs with those of the contralateral limbs in patients with hemiparkinsonian syndrome (III). The number of PD patients and control subjects showing repetitive responses and adaptation was compared with the χ2 test.
Comparisons of the regional SPECT data of the PD patients and controls were made utilizing unpaired two-tailed t tests since the results of the measurements were normally distributed (IV). ANOVA with age as covariant was used to factor out age in the comparisons between the groups. Relationships between variables were calculated with Pearson’s correlation coefficient. The equality of age was tested with the Mann-Whitney U-test. Bonferroni correction was not used since it is highly conservative for large numbers of comparisons (Altman 1991). All analyses were made on observed cases and calculated using the SPSS Windows version 7.0.