HEART RATE VARIABILITY DURING COLD PRESSOR TEST IN DOWN SYNDROME

Abstract

Cardiovascular responses are attenuated in individuals with Down syndrome (DS). Analysis of heart rate variability (HRV) allows the assessment of cardiac autonomic control through the measurement of beat-to-beat variations in R-R intervals. PURPOSE To investigate HRV in response to cold pressor test (CPT) in individuals with DS. METHODS Thirteen individuals with DS (age = 28.2±6.9 yr) and 13 healthy controls (age = 26.5±7.3 yr) were exposed to a cold pressor test (CPT) by immersing a hand in cold water (−9°C) for 2 min while arterial blood pressure (Portapres) and heart rate (ECG) were continuously recorded. HRV parameters in the time and frequency domains were obtained through an autoregressive model. Two min of rest and 2 min of recovery were recorded before and after CPT. RESULTS CPT resulted in a similar significant increase in systolic and diastolic blood pressure in both groups. At baseline, the R-R interval was lower in individuals with DS. R-R interval did not change from rest to CPT to recovery in individuals with DS (796, 797, 802 ms) whereas controls showed the expected response (961, 902, 981 ms, p = .08). Parasympathetic indicators of HRV, number of interval differences of successive R-R > 50 ms (NN50) and the root of mean squared differences of successive R-R [RMSSD-log transformed (LN)], changed (p < .05) in the opposite direction in controls (NN50: 34, 24, 31; RMSSD-LN: 7.9, 7.4, 7.8 a.u.) and individuals with DS (NN50: 15, 19, 15; RMSSD-LN: 7.0, 7.2, 7.0 a.u.). There was a trend for a reduction in high frequency-LN (p = .07) and total power-LN (p = .1) in controls compared to individuals with DS. CONCLUSION These HRV data suggest that individuals with DS exhibit an abnormal increase in parasympathetic activation during CPT, which could explain the lack of change in R-R interval. Our data are consistent with autonomic dysfunction in individuals with DS.