اضطراب و انعطاف پذیری اتونوم: یک رویکرد قلبی عروقی

Abstract Autonomic characteristics of panickers, blood phobics, and nonanxious controls were compared with a variety of cardiovascular measures, including spectral analysis of the cardiac inter-beat interval time series (derived from the electrocardiogram). Responses to laboratory stressors (shock avoidance and cold face stress) of 16 participants who reported recent occurrences of frequent severe panic attacks, 15 participants who reported strong somatic reactions and fainting to the sight of blood, and 15 controls, were recorded. Results suggested distinct autonomic patterns among the three groups. Across conditions, panickers displayed the highest heart rates (HR) coupled with the least HR variability, which indicates low levels of cardiac vagal tone. Blood phobics showed more vagally mediated HR variability than panickers, with a significant association between cardiac rate and mean arterial pressure. Controls generally showed the most HR variability and `spectral reserve' (a quality that indicates flexible responsivity). Results are discussed in the context of traditional models of anxiety and autonomic activity in contrast to contemporary notions of stability and change in biological systems.

. Results Contrast and correlational analyses were performed with CSS software (Statsoft, 1987); nonparametric tests were conducted on the slope measure using Minitab (Minitab, 1987). 4.1. A priori contrasts In line with directional predictions based on data from Friedman et al. (1993b), as well as with the underlying conceptual model of the present study, one-tailed t-tests were performed on contrasts between blood phobics and panickers for all dependent measures except for slope. Two-tailed tests were used in contrasts involving the control group. Data were aggregated across experimental periods. Significant contrasts are shown in Table 1; no significant differences were found for LF or MAP. Table 1. Significant contrasts among panickers, blood phobics, and controls Variable Panic (mean, S.D.) Blood phobic (mean, S.D.) Control (mean, S.D.) T ratio, df, p value IBI (ms) 761.8 (141.0) 837.1 (92.4) 905.2 (132.5) P<B 4.59 (215) p<0.001 P<C 7.65 (214) p<0.001 B<C 4.30 (207) p<0.001 VAR (ms2) 3942 (4009) 4334 (2663) 6112 (4563) P<C 3.70 (214) p<0.001 B<C 3.44 (207) p<0.001 P=B N.S. MSD (ms) 44.4 (31.2) 55.6 (22.7) 71.4 (32.1) P<B 3.05 (215) p<0.001 P<C 6.34 (214) p<0.001 B<C 4.11 (207) p<0.001 HF power (ms2 Hz−1) 991 (1225) 1385 (1073) 2239 (1911) P<B 2.49 (212) p<0.01 P<C 5.67 (212) p<0.001 B<C 3.90 (203) p<0.001 LF/HF 2.1(2.5) 1.3 (1.8) 1.0 (1.5) P<B 2.41 (209) p<0.005 P<C 3.64 (203) p<0.001 B=C N.S. P, panic; B, blood phobic; C, control. Table options To summarize, the panickers had shorter IBIs, less MSD and HF spectral power, and higher LF/HF than blood phobics. The controls had longer IBIs, greater VAR and MSD, and more HF power than both panickers and blood phobics, and lower LF/HF ratios than the panickers. The trend across groups (from panic to control) is therefore towards increasing levels of vagally mediated HR variability. 4.2. Correlations Pearson correlations among all dependent measures were calculated to assess the coupling parameters between CV indices, and are displayed in Table 2. Correlation coefficients were calculated within subjects and across conditions, in accord with within-person correlational and pooled cross-sectional time series designs that have been advocated to capture the dynamic functioning of a system across diverse situations (Dielman, 1983Michela, 1990). Data were standardized within subjects across tasks to avoid confounding between- and within-subject sources of variance. Table 2. Correlations among CV variables for panickers, blood phobics, and controls IBI VAR MSD LF HF LF/HF Panickers VAR 0.32*** MSD 0.52*** 0.75*** LF 0.25** 0.48*** 0.32*** HF 0.51*** 0.53*** 0.76*** 0.20* LF/HF −0.25** −0.04 −0.29** 0.58*** −0.50c MAP −0.03 0.37*** 0.27** 0.19* −0.26b −0.07 Blood phobics VAR 0.13 MSD 0.60*** 0.56*** LF 0.09 0.59*** 0.31** HF 0.57*** 0.41*** 0.89*** 0.12 LF/HF −0.26* 0.26** −0.20* 0.65*** −0.42*** MAP −0.21* 0.10 −0.05 −0.01 −0.01 0.03 Controls VAR 0.16 MSD 0.50*** 0.63*** LF 0.18 0.48*** 0.35** HF 0.36*** 0.34*** 0.71*** 0.05 LF/HF −0.13 0.15 −0.12 0.70*** −0.46*** MAP −0.05 0.16 0.11 0.22* 0.04 0.21* *p<0.05; **p<0.01; ***p<0.001 (df=203). Table options Several patterns of association observed by Friedman et al. (1993a)were replicated in the present study. A significant correlation between LF power and IBI was found in the panickers in the present study; this relationship was nonsignificant in the control group and in the blood phobic groups in both studies. The panickers also showed a significant relationship between LF and HF power in both studies, which was absent in the other experimental groups. Alternatively, the blood phobics were the only group in either study to display a significant association between MAP and IBI. 4.3. Spectral reserve slopes As the distribution of spectral reserve slopes is not likely to be normal (Lipsitz et al., 1990), a nonparametric procedure (Wilcoxon Signed Rank Test) was used to compare groups on this measure. The panickers had significantly steeper slopes (median slope=−0.4736) than either the blood phobics (median slope=−0.4265; W statistic=1698, n=105, p<0.001) or controls (median slope=−0.4035; W statistic=1432.5, n=105, p<0.001). The difference in slope between blood phobics and controls was not significant. In order to use the slope in conjunction with overall variance, multivariate planned comparisons (from MANOVA) were conducted between the three groups, with slope and VAR as dependent measures. The use of these two indices in a multivariate manner allows for concomitant assessment of the totality of the HR variability (with VAR) and the sources of that variability (with slope). This approach represents a conceptual replication of the finding of Lipsitz et al. (1990), in which it was found that these two measures in combination were able to distinguish the cardiovascular dynamics of their experimental groups. All three groups could be distinguished using this combination of variables. Blood phobics were significantly different from panickers (Wilk's Lambda=0.969 (2,204), p<0.04) and controls (Wilk's Lambda=0.960 (2,189), p<0.02). Controls and panickers were also significantly different (Wilk's Lambda=0.934 (2,190), p<0.002).