Do night and around-the-clock firefighters' shift schedules induce deviation in tau from 24 hours of systolic and diastolic blood pressure circadian rhythms?

Shift work and cardiovascular strain on working and non-working days

BACKGROUND

Shift work is often associated with adverse effects on cardiovascular health of employees. Only a few studies address the strain of shift and day workers on non-working days compared to working days.

AIMS

This study aims to determine how the cardiovascular strain of hotel and catering industry (HCI) employees who work alternating shifts differs from those working normal day shifts-on both a working day (WD) and a non-working day (ND).

METHODS

The sample consisted of 60 alternating shift (morning and afternoon, mean age: 31.5 ± 8.5 years) and 88 day workers (mean age: 35.3 ± 9.4 years). A 24-h ambulatory measurement of blood pressure (BP) and heart rate (HR) on WD and ND with the time phases DAY, SLEEP, and 24-h TOTAL was used to analyse cardiovascular strain. BP status was assessed by self-measurement (36% hypertensives).

RESULTS

The total strain over 24 h was slightly higher on WD than ND (mean BP: 134/79 versus 127/75 mmHg, P = 0.002-0.020; mean HR: 78 versus 75 bpm, P = 0.055). In trend, shift workers had higher systolic BP than day workers during the individual time phases of DAY, SLEEP, and 24-h TOTAL on WD. Known cardiovascular risk factors emerged as critical determinants of cardiovascular strain: older age, male gender, and hypertensive blood pressure status.

CONCLUSIONS

The results revealed no clear association between the alternating shift system in HCI and increased cardiovascular strain. The 24-h ambulatory measurement is considered ideal for determining cardiovascular strain in everyday life and under working conditions.

Relationship Between Various Coronary Artery Disease Risk Factors in Firefighters

OBJECTIVE

To determine the correlation between the various coronary artery disease risk factors in firefighters.

METHODS

The study used a quantitative, cross-sectional, and correlational study design. A total of 124 full-time firefighters were conveniently recruited to participate. Research procedures were based on the ACSM guidelines.

RESULTS

Significances were found between age and body mass index (BMI) (r = 0.42, P < 0.001), age and waist circumference (WC) (r = 0.52, P < 0.001), BMI and WC (r = 0.88, P < 0.001), BMI and diastolic blood pressure (DBP) (r = 0.48, P < 0.001), between WC and DBP (r = 0.48, P < 0.001) and between gender and cigarette smoking (χ2[1] = 5.66, P = 0.017).

CONCLUSION

There were significant strong relationships between BMI, SBP, DBP, dyslipidemia, and increasing age, especially in male firefighters. Reducing key risk factors should be emphasized.

Prevalence of coronary artery disease risk factors in firefighters in the city of Cape Town fire and rescue service - A descriptive study

Background: Over 45% of firefighter deaths are attributable to sudden cardiac death related to coronary artery disease (CAD), with many of these deaths attributed to comorbidities. The purpose of the study is to determine the prevalence of coronary artery disease (CAD) risk factors in firefighters in the City of Cape Town (CoCT). Design and Methods: The study used a quantitative, cross-sectional and descriptive design. A total of 124 full-time firefighters were conveniently recruited between September and November 2019 from the City of Cape Town Fire and Rescue Service. Results: The most prevalent CAD risk factors among firefighters were hypertension (33.1%), obesity (37.1%), cigarette smoking (39.5%) and dyslipidaemia (40.3%). A total of 41.9% of firefighters were categorized as low-risk, 54.8% as moderate-risk, and 3.2% as high-risk for CAD. Conclusion: The majority of firefighters had at least one CAD risk factor, with older males having the highest prevalence of multiple CAD risk factors. Compared to other regions of the world, the (CoCT) firefighters have higher prevalence of dyslipidaemia and cigarette smoking. Preventative behavioural strategies and education on CAD should be promoted to mitigate the development of CAD.

Timing of Food Intake Drives the Circadian Rhythm of Blood Pressure

Timing of food intake has become a critical factor in determining overall cardiometabolic health. We hypothesized that timing of food intake entrains circadian rhythms of blood pressure (BP) and renal excretion in mice. Male C57BL/6J mice were fed ad libitum or reverse feeding (RF) where food was available at all times of day or only available during the 12-h lights-on period, respectively. Mice eating ad libitum had a significantly higher mean arterial pressure (MAP) during lights-off compared to lights-on (113 ± 2 mmHg vs 100 ± 2 mmHg, respectively; P < 0.0001); however, RF for 6 days inverted the diurnal rhythm of MAP (99 ± 3 vs 110 ± 3 mmHg, respectively; P < 0.0001). In contrast to MAP, diurnal rhythms of urine volume and sodium excretion remained intact after RF. Male Bmal1 knockout mice (Bmal1KO) underwent the same feeding protocol. As previously reported, Bmal1KO mice did not exhibit a diurnal MAP rhythm during ad libitum feeding (95 ± 1 mmHg vs 92 ± 3 mmHg, lights-off vs lights-on; P > 0.05); however, RF induced a diurnal rhythm of MAP (79 ± 3 mmHg vs 95 ± 2 mmHg, lights-off vs lights-on phase; P < 0.01). Transgenic PERIOD2::LUCIFERASE knock-in mice were used to assess the rhythm of the clock protein PERIOD2 in ex vivo tissue cultures. The timing of the PER2::LUC rhythm in the renal cortex and suprachiasmatic nucleus was not affected by RF; however, RF induced significant phase shifts in the liver, renal inner medulla, and adrenal gland. In conclusion, the timing of food intake controls BP rhythms in mice independent of Bmal1, urine volume, or sodium excretion.

Association between circadian disruption and diseases: A narrative review

Circadian rhythms play an important role in a wide range of human physiology and pathology. Individuals increasingly experience situations such as night-shift work schedules, likely leading to circadian disruption. Recent studies have also demonstrated that patients with other diseases often show symptoms of circadian disruption as manifested by the sleep-wake cycle and other biological rhythms. Circadian disruption often results in changes to the phase, period, and amplitude of the sleep-wake cycle, melatonin rhythm, and core body temperature. Several cardiometabolic, psychiatric, and neurodegenerative diseases are closely related to circadian disruption. Several interventions are also available, including phototherapy, exogenous melatonin, and exercise. The cumulative findings suggest that circadian disruption can increase risk for some cardiometabolic diseases. Circadian disruption also acts as a concomitant symptom of several psychiatric and neurodegenerative diseases. More attention should be paid to evaluating the impact of circadian disruption on these related diseases, as well as the benefits of the mitigation interventions for both circadian disruption and related diseases.

Circadian Regulation of Blood Pressure: of Mice and Men

PURPOSE OF REVIEW

Blood pressure (BP) exhibits strong diurnal variations that have been shown to be important for normal physiology and health. In this review, we highlight recent advances in both basic and clinic research on how the circadian clock affects these BP rhythms.

RECENT FINDINGS

Tissue-specific and inducible knockout rodent models have provided novel ways to dissect how circadian clocks regulate BP rhythms and demonstrated that loss of these rhythms is associated with the development of disease. The use of circadian-specific research protocols has translated findings from rodent models to humans, providing insight into circadian control of BP, as well as how sleep, activity, and other factors influence diurnal BP rhythms. Circadian mechanisms play an important role in the regulation of diurnal BP rhythms. Future research needs to extend these findings to clinical populations and determine the extent to which circadian factors may play a role in the development of novel treatment approaches to the management of hypertension.

Twenty-four-hour pattern of operations-related injury occurrence and severity of off-site/on-call volunteer French firefighters

We assessed the 24-h pattern of operations-related injuries (ORI) experienced by scheduled off-site/on-call French volunteer firefighters (VFF) through analysis of an archival database. Occurrence and severity - evaluated by number of lost work days (LWD) and total medical costs (TMC) - of ORI were explored in terms of risk ratios, respectively, number of ORI/number of service operations (RR_ORI), number of LWD/number of ORI (RS_LWD,) and TMC/number of ORI (RS_TMC). Additionally, the collective work performance of all involved VFF was measured in terms of the lag time (LT) between emergency call-center firefighter-answered communication for service of observer-presumed out-of-hospital cardiac arrest (OHCA) and departure of vehicle from fire station to render aid, designated LT_OHCA. Cosinor and cross-correlation statistical methods were applied. A total of 252 ORI occurred while performing 146,479 service operations. High-amplitude 24 h variation was detected in RR_ORI (p < .003), SR_LWD (p < .001), SR_TMC (p < .012), and LT_OHCA (p < .001), all with nocturnal peak time. Coherence was found between the day/night variation of LT_OHCA and RR_ORI (r = 0.7, p < .0002), SR_LWD (r = 0.5, p < .02), and SR_TMC (r = 0.4, p < .05). This investigation verifies the occurrence and severity of ORI of scheduled off-site/on-call VFF exhibit high-amplitude 24 h patterning with nocturnal excess that closely coincides with their day/night work performance measured by LT_OHCA. These findings, which are essentially identical to ones of a previous study entailing on-site/on-call career firefighters, indicate the need for fatigue management and ORI prevention programs not yet available to VFF, who compose the majority of the field service workforce of French fire departments. Abbreviations:FF: firefighters; CFF: career firefighters; VFF: volunteer firefighters; FD: fire department; LT_OHCA: lag time (LT) response in min:sec between fire department call-center-answered communication for service of presumed out-of-hospital cardiac arrest (OHCA) and departure from fire station of vehicle to render aid; LWD: lost work days; ORI: operations-related injuries; SR_LWD: severity ratio of operations-related injuries in terms of number of lost work days, calculated as number of lost work days/number of operations-related injuries; RR_ORI: risk ratio of operations-related injuries calculated as number of operations-related injuries/number of operations; SR_TMC: severity ratio of operations-related injuries in terms of total medical costs, calculated as total medical costs/number of operations-related injuries; TMC: total medical costs.