BackgroundNight shift work is a well established risk factor for cardiovascular disease. Endothelial dysfunction represents an early stage in the development of atherosclerosis. We investigated whether medical residents and fellows have reduced endothelial function immediately after two consecutive night shifts and whether this dysfunction is prolonged. MethodWe evaluated endothelial function in 12 doctors at three different timings, after two consecutive night shifts, 3-5 days after the last night shifts and on a regular work day with no night shifts the previous 7 days. To assess the endothelial function we assessed the degree of reactive hyperemia by peripheral arterial tonometry (RH-PAT). RH-PAT is a non-invasive method which measures the reactive hyperemia response in a finger after 5 minutes of forearm ischemia. The research subjects also filled out a questionnaire regarding other factors which might affect their endothelial function.
ResultsThe median RH-PAT ratio at baseline (PAT1) was 2.08 (25-percentile 1.60, 75-percentile 2.98), the morning after two consecutive night shifts (PAT2) 1.64 (1.39, 2.19), and 3-5 days later (PAT3) 1.77 (1.60, 2.71). The PAT2 was significantly reduced compared to the baseline ratio (p=0.041). There was no significant difference between PAT2 and PAT3 or between PAT1 and PAT3. However, the PAT3 values appeared to be intermediate between values at baseline and immediately following the night shift. Weight and systolic blood pressure were inversely correlated to PAT2 (r=-0,606 and r=-0,621). There was no significant correlation between PAT2 and other variables.
ConclusionEndothelial function as measured by RH-PAT is significantly reduced immediately after two consecutive night shifts. Although not significant, the RH-PAT ratio 3-5 days after the night shifts tended to be lower than values at baseline. Further studies in larger populations of night shift workers are required to confirm these findings.