Figure 2.

Abnormal HRV responses after postural change in pSS patients. All analyses were performed by repeated measures analysis of variance. (a) Brachial systolic blood pressure (SBP). The initial SBP response to standing was normal in patients who have primary Sjögren's syndrome (pSS). However, between 2 and 5 minutes after standing, there was a relative decline in SBP in pSS patients and a relative increase in control individuals (P = 0.015). (b) RR intervals. There was a relative tachycardia in pSS patients. This was most pronounced during standing (P = 0.039). (c) The proportion of successive RR intervals differing by more than 50 ms (pNN50) was lower in pSS patients than in control individuals over both postural positions (P = 0.025). (d) SBP power. The normal response to standing is an increase in SBP power, most evident in the low frequency (0.04 to 0.15 Hz) domain. This was significantly attenuated in pSS patients (P = 0.01). (e) RR power. Parasympathetic withdrawal upon standing results in a decrease in heart rate variability (HRV). In the low frequency (LF) domain, this is counterbalanced by an increase associated with increased LF blood pressure variability (see panel c). The net result of a normal response to standing is very little change in LF HRV and a substantial decrease in high frequency HRV. In control individuals, there was minimal change in LF HRV in response to standing, consistent with a normal response. However, in pSS there was a substantial decrease in LF HRV upon standing, and therefore standing LF HRV was significantly lower in pSS patients (P = 0.024).