ASSESSMENT OF BARORECEPTOR-CARDIAC REFLEX SENSITIVITY USING TIME-DOMAIN ANALYSIS IN PATIENTS WITH IDDM AND THE RELATION TO LEFT-VENTRICULARMASS INDEX

Autonomic dysfunction in insulin-dependent diabetic (IDDM) patients ha s been associated with abnormalities of left ventricular function and an increased risk of sudden death. A group of 30 patients with IDDM an d 30 age, sex and blood pressure matched control subjects underwent tr aditional tests of autonomic function. In addition, baroreceptor-cardi ac reflex sensitivity (BRS) was assessed using time domain (sequence) analysis of systolic blood pressure and pulse interval data recorded n on-invasively using the Finapres beat-to-beat blood pressure recording system. 'Up BRS' sequences-increases in systolic blood pressure assoc iated with lengthening of R-R interval, and 'down BRS' sequences-decre ases in systolic blood pressure associated with shortening of RR inter val were identified and BRS calculated from the regression of systolic blood pressure on R-R interval for all sequences. We also assessed he art rate variability using power spectral analysis and, after expressi ng components of the spectrum in normalised units, assessed sympathova gal balance from the ratio of low to high frequency powers. IDDM subje cts underwent 2-D echocardiography to assess left ventricular mass ind ex. Standard tests of autonomic function revealed no differences betwe en IDDM patients and control subjects, but dramatic reductions in baro receptor-cardiac reflex sensitivity were detected in IDDM patients. 'U p BRS' when supine was 11.2 +/- 1.5 ms/mmHg (mean +/- SEM) compared wi th 20.4 +/- 1.95 in control subjects (p < 0.003) and when standing was 4.1 +/- 1.9 vs 7.6 +/- 2.7 ms/mmHg (p < 0.001). Down BRS when supine was 11.5 +/- 1.2 vs 22 +/- 2.6 (p < 0.001) and standing was 4.4 +/- 1. 9 vs 7.3 +/- 2.5 ms/mmHg (p < 0.003). There were significant relations between impairment of the baroreflex and duration of diabetes (p < 0. 001) and poor glycaemic control (p < 0.001). From a fast Fourier trans formation of supine heart rate data and using a band width of 0.05-0.1 5 Hz as low-frequency and 0.2-0.35 Hz as high frequency total spectral power of R-R interval variability was significantly reduced in the ID DM group for both low-frequency (473 +/- 62.8 vs 746.6 +/- 77.6 ms(2) p = 0.002) and high frequency bands 125.2 +/- 12.9 vs 459.3 +/- 89.8 m s(2) p < 0.0001. When the absolute powers were expressed in normalised units the ratio of low frequency to high frequency power (a measure o f sympathovagal balance) was significantly increased in the IDDM group (2.9 +/- 0.53 vs 4.6 +/- 0.55, p < 0.002 supine: 3.8 +/- 0.49 vs 6.6 +/- 0.55, p < 0.001 standing). Thus, time domain analysis of barorecep tor-cardiac reflex sensitivity detects autonomic dysfunction more freq uently in IDDM patients than conventional tests. Impaired BRS is assoc iated with an increased left ventricular mass index and this abnormali ty may have a role in the increased incidence of sudden death seen in young IDDM patients.