Cardiovagal Baroreflex Sensitivity is Reduced in Middle‐Age and Older Men with Low Testosterone

Abstract

BACKGROUNDMale aging is associated with a general decline in serum testosterone (T) concentrations. Endogenous low T is associated with increased cardiovascular disease risk. Following orchiectomy or androgen suppression, rats have reduced cardiovagal baroreflex sensitivity (BRS), a key antecedent to the development of hypertension and other cardiovascular diseases. BRS is determined by mechanical (i.e. arterial stiffness) and neural factors, and heart rate variability (HRV) may provide insight into the contribution of these mechanical and neural factors. However, the effects of low T on BRS in middle‐age and older men is unknown.PURPOSEDetermine whether BRS and HRV are reduced in middle‐age and older men with low T.METHODSEight healthy older men between the ages of 50–75 years (BMI: 28.7±6.3 kg/m2, systolic blood pressure: 130±9 mmHg, diastolic blood pressure: 78±7 mmHg; mean±SD) with either low (<300 ng/dL; n=4) or normal (≥400 ng/dL; n=4) T underwent simultaneous recordings of blood pressure (finger photoplethysmography) and R‐R interval (electrocardiogram) during supine rest. Spontaneous cardiovagal BRS was assessed in sequences of ≥4 cardiac cycles in which R‐R interval and systolic blood pressure changed in the same direction. Time (standard deviation of R‐R intervals of normal sinus beats; SDNN, and root‐mean‐square of successive differences in R‐R interval differences; RMSSD) and frequency (low frequency and high frequency power) domain indices of HRV were determined during six minutes of paced breathing at 0.2 Hz. Serum T was measured in the morning under fasting conditions.RESULTST concentrations were significantly lower in the low T group compared to the normal T (269.3±40.5 vs. 561.0±109.8 ng/dL; p=0.002). Age (56±3 vs. 57±5 years; p=0.836) and mean arterial pressure (96±9 vs. 98±8 mmHg; p=0.794) were similar between groups. Cardiovagal BRS was significantly lower in the low T compared to normal T group ( 8.2±3.1 vs. 16.2±4.2 ms/mmHg; p=0.021). Cardiovagal BRS was strongly correlated with T concentrations when considered as a continuous variable (R=0.71, p=0.049), but cardiovagal BRS was not correlated to age (R=0.06, p=0.891). No indices of HRV were significantly different between groups (p≥0.20 for all).CONCLUSIONSThese preliminary data indicate that spontaneous cardiovagal BRS is reduced in men with low T. The absence of differences in HRV suggest that differences in BRS may be influenced by mechanical (i.e. arterial stiffness), rather than neural mechanisms.Support or Funding InformationSupported by NIH Grants R01AG049762 and T32AG000279‐16A1