The Influence of Cardiorespiratory Fitness on Firefighter Cardiovascular Health Under Exercise Conditions

Subjects were attached to an Oscar2 automatic noninvasive ABP monitor (Suntech Medical Instruments Inc., Raleigh, North Carolina, USA) on the nondominant arm to be worn until the next morning. The ABP monitor was programmed to record BP at regular intervals three times per waking hour and two times per sleeping hour.

Resting BP was measured according to the American Heart Association (AHA) standards using an automated BPTRU monitor (BPTRU Medical Devices, Coquilam, British Columbia, Canada). Subjects were seated for 5 minutes and then BP was measured three times, 1 minute apart in each arm. If the readings obtained were within 5 mmHg, these values were averaged and recorded as resting BP. If these readings did not agree within 5 mmHg, up to three additional readings were taken. If there were three readings obtained that agreed within 5 mmHg, these values were averaged and recorded as resting BP. If after the additional readings were taken and there were not three readings obtained that agree within 5 mmHg, the three closest values were averaged and recorded as resting BP.

The fasting blood sampling occurred prior to and immediately after the GEST and was performed to obtain lipid-lipoprotein profiles and baseline biomarkers associated with cardiovascular disease. A trained phlebotomist collected five tubes of venous blood (52 cc or 3.5 tablespoons) from the antecubital vein of each subject. Serum total cholesterol (mg/dL), triglycerides (mg/dL), high-density lipoprotein cholesterol (HDL-C) (mg/dL), and low-density lipoprotein cholesterol (LDL-C) (mg/dL) were determined by colorimetric enzymatic assays. Serum glucose (mg/dL) was determined by enzymatic/spectrophotometric methods.

The fasting blood sampling occurred prior to and immediately after the GEST and was performed to obtain lipid-lipoprotein profiles and baseline biomarkers associated with cardiovascular disease. A trained phlebotomist collected five tubes of venous blood (52 cc or 3.5 tablespoons) from the antecubital vein of each subject. Serum insulin (uIU/mL) was determined by radioimmunoassay.

The fasting blood sampling occurred prior to and immediately after the GEST and was performed to obtain lipid-lipoprotein profiles and baseline biomarkers associated with cardiovascular disease. A trained phlebotomist collected five tubes of venous blood (52 cc or 3.5 tablespoons) from the antecubital vein of each subject. High sensitivity-C-reactive protein (mg/L) was determined by immunoturbidimetry.

Usual dietary and alcohol intake were measured using the National Health and Nutrition Examination Survey (NHANES) semi-quantitative Food-Frequency Questionnaire. The NHANES Food Frequency Questionnaire is a validated tool for measuring dietary intake of both macro- and micro-nutrients based on 127 food items. Subjects were asked to self-report their average daily consumption of 124 food items. The data derived from the Food Frequency Questionnaire were coded and analyzed by members of the National Cancer Institute utilizing Diet*Calc software v1.4.3 (Bethesda, MD) in order to produce daily food frequency estimates of the 127 nutrient and dietary constituents. The Diet*Calc software analyzed Diet History Questionnaire data and generated nutrient and food group intake estimates from the Diet History Questionnaire.

VO2peak was measured by the maximal graded exercise stress test (GEST). The VO2peak test is the gold standard measure of cardiorespiratory fitness.

Subjects performed four health-related fitness assessments. The first assessment was the Flexibility test. All tests were performed with a one-minute rest between tests.

Subjects performed four health-related fitness assessments. The second assessment was the Handgrip Strength test. All tests were performed with a one-minute rest between tests.

Subjects performed four health-related fitness assessments. The third assessment was the Sit-Up test. All tests were performed with a one-minute rest between tests.

Subjects performed four health-related fitness assessments. The fourth assessment was the Push-Up test. All tests were performed with a one-minute rest between tests.

Height and weight were measured with a calibrated balance beam scale to calculate body mass index (BMI) (kg·m2).

Waist circumference (cm) was measured at the iliac crest using a non-distensible Guilick tape measure.

Subjects rested in the supine position for 5 minutes. CIMT was measured using doppler ultrasound on the carotid arteries at three sites (common, bulb, and internal bilateral). The artery will be imaged using a 5- to 12-MHz multifrequency linear-array transducer attached to a high-resolution ultrasound machine (Terason t3000; Burlington, MA). The image will be digitized and edge detection software (Carotid Analyzer; Medical Imaging Applications, Inc.) will then be used to trace the lumen-intima and intima-medial boundaries of the artery over a 1 minute clip to calculate the average intima-medial thickness at three sites. Mean and maximal distances will be compared to established norms by age, sex/gender, and race/ethnicity.

The CPV system (SphygmoCor® CPV Central Blood Pressure/Pulse Wave Velocity System) measured pulse wave velocity (PWV). PWV gives an indication of central arterial parameters. Briefly, the subjects rested in the supine position for 10 minutes. After this rest period, central PWV measures (carotid-femoral), and PWA (radial) were made.

The resting HRV assessment was performed in a quiet, low-light and temperature-controlled room in the supine position after a 5 min rest period using the GE Case Exercise Testing System (GE Healthcare, Wauwaposa, WI). Following the resting period, electrocardiogram (ECG) RR intervals will be measured in the supine position for 5 min. During these measurements, the subject's breathing frequency was paced at 12 breaths•min-1 with the aid of a metronome.

Subjects were fitted for a Polar® V800™ HR monitor for the ambulatory HRV assessment for 24 hr. An elastic HR belt was placed below the chest muscles with conductive gel and applied as described by the manufacturer. RR intervals were recorded with a resolution of 1ms and captured by the receptor belt and stored by a wrist watch receiver under free living conditions without controlling for respiratory rate or tidal volume.