Investigating Markers of Cardiovascular Disease Risk in Female Hospital Employees

Abstract

Shift work is an increasingly popular work pattern and there is evidence that it is associated with an increased risk of cardiovascular disease (CVD). The causal pathways linking shift work and CVD risk are unclear, however, there is evidence that endothelial dysfunction and high reactivity to mental stress may play a role in disease progression. No studies in women have investigated the impact of a history of shift on 1) endothelial function assessed using two distinct tests (RH-FMD and HGEX-FMD) and 2) cardiovascular and cortisol reactivity to an acute stressor. The purpose of this thesis was to compare 1) RH-FMD and HGEX-FMD and 2) cardiovascular and cortisol stress reactivity in a group of female shift workers (SW) and non-shift workers (NSW). 20 healthy SW (41.1 ± 11.4 years) and 19 NSW (41.6 ± 11.4 years) participated. Each participant preformed two RH-FMD and two HGEX-FMD tests. Brachial artery diameter and blood velocity were assessed using Echo and Doppler ultrasound, respectively. For stress reactivity, serum cortisol, heart rate (HR), systolic blood pressure (SBP), and diastolic blood pressure (DBP) were measured before, during, and after a speech and mental arithmetic stress task. All values are means ± SD. There was no difference between SW and NSW in terms of RH-FMD (SW: 7.34 ± 2.78%, NSW: 7.86 ± 3.47, p=0.610) or HGEX-FMD (SW: 5.46 ± 3.24%, NSW: 4.14 ± 2.10, p=0.15). HR, SBP, and DBP stress reactivity were not significantly different between groups (HR: SW: 22.35 ± 15.68 beats•min-1, NSW: 20.42 ± 10.53 beats•min-1, p=0.66; SBP: SW: 20.93 ± 10.72 mmHg, NSW: 19.57 ± 11.92 mmHg, p=0.72; DBP: SW: 14.27 ± 6.58 mmHg, NSW: 11.20 ± 6.28 mmHg, p=0.16), however the magnitude of difference in DBP reactivity between groups (3.07 mmHg) had a moderate effect size (d = 0.5). Cortisol stress reactivity was significantly higher in SW than NSW (8.53 ± 6.04 µg/dL vs. 1.41 ± 2.92 µg/dL). These preliminary data suggest that shift work experience did not have a negative impact on endothelial function, but did result in elevated HPA-axis reactivity and modest increases in cardiovascular reactivity to acute mental stress.