Evaluation of carotid wave intensity in firefighters following firefighting.

Sudden cardiac events are the leading cause of line-of-duty firefighter deaths, but little information exists elucidating the physiologic responses. Wave intensity (WI) is a new hemodynamic index that provides information about the dynamic behavior of the heart and the vascular system and their interaction. The larger first peak wave (W1) occurs during early systole and is associated with cardiac contractility. The second smaller peak (W2) follows a period of relatively little net wave (NA) production and may be caused by reflected waves from the brain. This study aimed at determining arterial WI changes in response to live firefighting activities. We examined the WI of 39 firefighters (2 females) with a mean age of 28 ± 1 years and BMI of 26.6 ± 0.7 kg m(-2) at rest, and immediately after 3 h of live firefighting drills. WI was assessed on the right common carotid artery using an Aloka high-resolution ultrasound. The magnitude of the W1 decreased significantly from 15,925 ± 1,341 to 11,540 ± 886 mmHg m s(-3), p < 0.05. The magnitude of W2 remained unchanged (W2: from 2,080 ± 200 to 2,144 ± 358 mmHg m s(-3)). Net NA decreased from 53 ± 5 to 40 ± 4 mmHg m s(-2). In conclusions, our data suggest that left ventricular function and arterial-ventricular coupling decreased following live firefighting, and this may be related to the documented increase in risk of clinical events during and after firefighting activities.

Acute effects of firefighting on arterial stiffness and blood flow.

Sudden cardiac events are responsible for 40-50% of line-of-duty firefighter fatalities, yet the exact cause of these events is unknown. Likely, combinations of thermal, physical, and mental factors impair cardiovascular function and trigger such events. Therefore, the purpose of this study was to examine the impact of firefighting activities on vascular function. Sixty-nine young (28 ± 1 years) male firefighters underwent 3 hours of firefighting activities. Carotid, aortic, and brachial blood pressures (BP), heart rate (HR), augmentation index (AIx), wave reflection timing (TR), aortic pulse wave velocity (PWV), forearm blood flow (FBF), and forearm reactive hyperemia (RH) were measured before and after firefighting activities. Paired samples t-tests revealed significant (p < 0.05) increases in aortic diastolic BP, HR, AIx, PWV, RH, and FBF, and significant decreases in brachial and aortic pulse pressure and TR following firefighting activities. In conclusion, these results suggest that 3 hours of firefighting activities increase both arterial stiffness and vasodilation.

Energetic optimization during over-ground walking in people with and without Down syndrome.

Individuals with Down syndrome (DS) show reduced gait stability that may increase the metabolic rate (MR) during over-ground walking and alter their energetic cost per unit distance (EC(transport)) to speed relationship. If so, the preferred walking speed (PWS) of people with DS may coincide with their speed at minimal EC(transport), reflecting energetic optimization. This study therefore examined whether MR and EC(transport) during over-ground walking differ between individuals with and without DS and whether PWS minimizes their EC(transport). Expired gases were collected from 18 individuals with DS and 18 without during six over-ground walking trials, each lasting 6 min, at PWS and at 0.51, 0.76, 1.01, 1.26, and 1.51 m/s. Gross- and net-MR, and gross- and net-EC(transport) were expressed in dimensionless form. Energetically optimal walking speeds and minimal gross- and net-EC(transport) were determined from the gross- and net-EC(transport) to speed curves for each participant. Individuals with DS showed higher gross-MR, net-MR, gross-EC(transport), and net-EC(transport). PWS minimized gross-EC(transport) in participants with DS, but not in those without. PWS did not minimize net-EC(transport) in either group. Therefore, gross-EC(transport) minimization during over-ground walking may determine PWS when impairments alter the gross-EC(transport) to speed relationship.

Metabolic rate and accelerometer output during walking in people with Down syndrome.

UNLABELLED: People with Down syndrome (DS) have reduced gait stability and aerobic fitness that increase the metabolic rate during walking, potentially altering the relationship between metabolic rate and accelerometer output and lowering predictability of energy expenditure from accelerometry. PURPOSE: This study examined whether the relationship between metabolic rate and activity count rate differs between individuals with and without DS and whether predictability of metabolic rate is different between groups. METHODS: Metabolic rate was measured in METs with portable spirometry in 18 subjects with DS (24.7±6.7 yr; 10 women) and 18 subjects without DS (26.3±5.2 yr; 10 women) during five overground walking trials, each lasting 6 min, at 0.5, 0.75, 1.0, 1.25, and 1.5 m·s. A uniaxial accelerometer secured at the right side of the hip allowed for the determination of activity count rate. RESULTS: The relationship between METs and activity count rate in the two groups was analyzed with multilevel modeling with random intercepts and slopes, demonstrating a significant interaction between group and activity count rate (P<0.001). Separate models for each group showed that the activity count rate and its squared significantly predicted METs (P≤0.001). Actual and predicted METs did not differ in each group. Bland-Altman plots showed greater variability in the difference between actual and predicted METs for participants with DS. Mean absolute error of prediction was 19.92% and 14.55% for participants with and without DS, respectively. CONCLUSIONS: Individuals with DS show altered METs to activity count rate relationship during overground walking and have lower predictability of metabolic rate from uniaxial accelerometer output than individuals without DS.

Prediction of oxygen uptake during over-ground walking in people with and without Down syndrome.

The reduced gait stability and aerobic fitness of people with Down syndrome (DS) may increase their rate of gross oxygen uptake (gross-VO(2)) during over-ground walking. If so, the ACSM equation predicting gross-VO(2) from speed may not be appropriate and an equation specifically for these individuals may be needed. This study therefore examined whether the relationship between gross-VO(2) and speed differs between individuals with and without DS during over-ground walking and attempted to develop a gross-VO(2) prediction equation for people with DS. Gross-VO(2) was measured in 18 persons with DS (24.7 ± 6.8 years; 8 men) and 22 persons without DS (25.9 ± 4.8 years; 9 men) at rest and during five over-ground walking trials, each lasting 6 min, at 0.5, 0.75, 1.0, 1.25, and 1.5 m/s. Multi-level modeling with random intercepts and slopes demonstrated significant effects of speed, group, group-by-speed interaction, and speed squared (P < 0.001). In each group, actual gross-VO(2) did not differ from gross-VO(2) predicted by the regression equation across speeds. Bland-Altman plots showed somewhat greater variability in the difference between actual and predicted gross-VO(2) for participants with DS. Mean absolute error of prediction was 10.75 and 10.67% for participants with and without DS, respectively. In participants with DS, the ACSM formula under-estimated gross-VO(2) across speeds, whereas, in participants without DS, only at 1.5 m/s (P < 0.001). Therefore, individuals with DS show altered curvilinear gross-VO(2) to speed relationship during over-ground walking. The present regression equation appears to offer accurate prediction in people with DS and could be used for prescribing over-ground walking intensities.

Autonomic response to upright tilt in people with and without Down syndrome.

This study examined whether the autonomic response to passive upright tilt as evidenced by changes in measures of heart rate and blood pressure variability differs between individuals with DS and without DS. Beat-to-beat blood pressure was measured in 26 individuals with Down syndrome (DS) and 11 individuals without DS during 5 min of rest and 5 min of upright tilt. Dependent variables included heart rate, blood pressure, frequency component measures of heart rate and blood pressure variability, and baroreflex sensitivity. The normalized high frequency (HF) power, normalized low frequency (LF) power, and LF/HF of heart rate variability, as well as the LF of blood pressure variability were reduced in persons with DS in response to upright tilt (p<0.05). This was accompanied by smaller change in baroreflex sensitivity (p<0.05) in individuals with DS. Blood pressure responses to upright tilt were also reduced in individuals with DS (p<0.05), but the heart rate response did not differ between groups. Individuals with DS show less vagal withdrawal and sympatho-excitation in response to passive upright tilt. These effects may be partially mediated by smaller change in baroreflex sensitivity in individuals with DS. The results support the hypothesis of altered autonomic modulation in people with DS.

Impact of excess body weight on arterial structure, function, and blood pressure in firefighters.

Cardiovascular disease is the leading cause of death among firefighters. The purpose of the present study was to examine the effect of excess body weight on arterial structure and function and blood pressure (BP) in relatively young, apparently healthy, firefighters. The body mass index, brachial BP, carotid BP, aortic BP, radial augmentation index, central pulse wave velocity, forearm blood flow, forearm vasodilatory capacity, carotid arterial compliance, carotid intima-media thickness, and brachial flow-mediated dilation were assessed in 110 firefighters (aged 29.7 +/- 8.0 years). The group was divided into equal tertiles according to the body mass index (<25.9, 25.9 to 29.4, and >or=29.5 kg/m(2)). Group differences in hemodynamics, anthropometrics, microvascular function, and macrovascular structure and function were tested using multivariate analysis of variance. The obese group was older, heavier, and had a larger waist circumference compared to the lean and overweight groups (p <0.05). The overweight group was also older, heavier, and had a larger waist circumference than the lean group (p <0.05). Compared to the lean group, the overweight and obese groups had a greater systolic BP (p <0.05). The obese group also had a significantly greater mean arterial BP and carotid systolic BP than the lean group (p <0.05). The obese group had greater beta stiffness and elastic modulus compared to the lean and overweight groups (p <0.05), but no group differences were found in endothelial function. In conclusion, in a population of relatively young firefighters, an increased body mass index was associated with elevated peripheral BP and arterial stiffness, with no apparent decrements in endothelial function.

Arterial stiffness and wave reflection following exercise in resistance-trained men.

PURPOSE: Resistance training increases arterial stiffness and pressure wave reflection. We tested the hypothesis that potentially greater tonic arterial stiffness in resistance-trained (RT) men may alter the vascular response to an acute exercise stressor. METHODS: Thirty participants (age 22 +/- 0.5 yr; 15 highly RT men and 15 sedentary non-RT men) underwent measures of central (carotid femoral) and peripheral (femoral dorsalis pedis) pulse wave velocity (PWV) and augmentation index (AIx; index of central pressure wave reflection derived from radial artery applanation tonometry and pulse wave analysis) before and 10, 20, and 30 min after maximal aerobic exercise. RESULTS: RT men were significantly stronger (bench press 143 +/- 7 vs 85 +/- 2 kg, P < 0.05) and heavier (93 +/- 3 vs 82 +/- 3 kg, P < 0.05) than sedentary men. Groups did not differ in resting central/peripheral PWV or in AIx. AIx was not changed at 10 min after maximal aerobic exercise in both groups and was reduced similarly in both groups at 20 and 30 min after maximal aerobic exercise (P < 0.05). Peripheral PWV decreased similarly at all time points after maximal aerobic exercise in both groups and was not recovered by 30 min (P < 0.05). There was no change in central PWV after maximal aerobic exercise. CONCLUSIONS: The arterial response to maximal aerobic exercise was similar in highly RT and non-RT men. There was no change in intensity of central pressure wave reflection 10 min after exercise, despite significant reductions in peripheral muscular artery stiffness. Arterial reactivity to an acute exercise stressor is not impaired in young, highly RT men.

Tissue Doppler assessment of ventricular function during cycling in 7- to 12-yr-old boys.

PURPOSE: Studies utilizing submaximal supine exercise have indicated that tissue Doppler imaging (TDI) may be useful for assessing ventricular systolic and diastolic function during exercise and might offer a means of detecting patients with early myocardial dysfunction. This investigation of 14 healthy boys ages 7-12 yr was designed to assess measures of inotropic and lusitropic function during maximal upright cycle exercise. METHODS: Color tissue Doppler imaging (S and E' waves, indicative of systolic and diastolic function, respectively), stroke volume, and mitral peak inflow velocity (E wave) were recorded at rest and during a progressive upright cycle test to exhaustion. RESULTS: Values of TDI-S and TDI-E' were obtained at exhaustive exercise in all but one subject. Mean value of S rose 163% (3.8+/-1.2 to 10.0+/-2.5 cm.s), and average E' increased by 92% (-6.3+/-2.2 to -12.1+/-3.2 cm.s). No significant changes were observed in the ratio of E' to mitral peak flow velocity (E), suggesting that left ventricular end-diastolic pressure remained stable. CONCLUSIONS: These data indicate that measurement of TDI is feasible during maximal upright exercise, and velocities obtained may provide insights into ventricular systolic and diastolic functional capacity.

Cardiovascular responses to static exercise in boys: insights from tissue Doppler imaging.

Ventricular functional changes and mechanisms of the cardiovascular responses during static exercise have not been well delineated in children. In this study, Doppler echocardiographic techniques were utilized to assess cardiovascular adaptations to bilateral isometric leg extension at 30% maximal voluntary contraction for three minutes in a group of 14 healthy boys (mean age 10.2 +/- 1.5 years). Mean heart rate rose from 77 +/- 9 to 106 +/- 11 bpm, stroke volume fell from 59 +/- 9 to 52 +/- 7 ml, and cardiac output increased from 4.58 +/- 0.58 to 5.62 +/- 0.81 l min(-1) (P < 0.05). Mean arterial pressure rose from 86 +/- 7 to 109 +/- 9 mm Hg, with no significant change in peripheral vascular resistance. By tissue Doppler imaging markers, inotropic function improved by 59%, while lusitropic function increased 38%. These findings suggest that (1) cardiovascular responses to static leg extension in boys are similar to those in adult men, and (2) isometric leg extension triggers modest increases in both systolic and diastolic function.