Objective: To compare the changes in heart rate variability (HRV) and blood pressure (BP) between standard head-up tilt test (HUT) and nitroglycerin administration.
Methods: Eighteen healthy men and women aged 23-58 years participated. HRV was assessed using standard methods at rest and during both tests. Heart rate and BP data were collected during a standard HUT (maximal tilt = 70 degrees for 10 minutes) and following administration of 0.4 mg of nitroglycerin during supine rest. Test order was randomized. Repeated measure ANOVA was used to determine if changes in HRV and BP were significantly different between treatments. Paired t tests were used to examine the change from baseline to treatment for each variable.
Results: As compared to HUT, the change in diastolic blood pressure and HRV measures was significantly (P < 0.05) less after nitroglycerin administration. However, no significant differences (P > 0.05) in HRV variables were found between nitroglycerin administration and HUT during the 5th and 6th minutes of each test.
Interpretation: Nitroglycerin administration and HUT caused significantly different changes in HRV over a ten-minute average. However nitroglycerin produced its maximal effect on HRV during the 5th and 6th minutes, which was similar to the effect caused by HUT at the same time. When using nitroglycerin administration to assess changes in HRV indices, the fifth and sixth minutes of testing will provide information similar to that of a HUT protocol.