Scaling submaximal exercise cardiac output and stroke volume: the HERITAGE Family Study.

This study investigated different methods of scaling submaximal cardiac output (Q) and stroke volume (SV) to best normalize for body size (body surface area [BSA], height [Ht], weight [Wt], and fat-free mass [FFM]). Q and SV were measured at both an absolute (50 W) and a relative power output (60 % of VO2max) in 337 men and 422 women, 17 to 65 years of age. Traditional ratio scaling was examined in addition to allometric scaling, where scaling exponents ( B) were determined for each body size variable (x) that best normalized the physiological outcome variables (y) for body size (y = ax(b)). With ratio scaling, regardless of the body size variable (x = BSA, Ht, Wt, FFM), there was no evidence of a linear relationship between x and y (y = Q or SV). A linear relationship is a necessary condition for appropriate normalization. Further, when ratio-scaled variables (e.g., Q/BSA) were correlated to the body size variable (e.g., BSA) by which they were scaled, significant (p

The chemoreflex in young boys and girls.

In order to determine the influence of the chemoreflex on the cardiovascular system of young children, 35 boys and 35 girls (all 7 - 9 years old) performed three minutes of 30 % maximal voluntary contraction (MVC) static handgrip (SHG) exercise followed by four minutes of blood flow occlusion in the previously exercised arm, and then six minutes of passive recovery. Heart rate (HR) and blood pressure (BP) were measured each minute. Twenty girls performed a second occlusion trial to determine reliability. Reliability coefficients for HR (R = 0.51 - 0.78), diastolic (R = 0.46 - 0.81) and systolic (R = 0.57 - 0.78) BP throughout the occlusion trial were moderately high. There was a similar increase in HR (19 +/- 8 vs. 16 +/- 10 %), diastolic (34 +/- 12 vs. 34 +/- 16 %) and systolic (18 +/- 9 vs. 15 +/- 7 %) BP in boys and girls, respectively, during three minutes 30 % MVC exercise. During the occlusion period, diastolic (43 +/- 31 vs. 47 +/- 26 %) and systolic (51 +/- 25 vs. 54 +/- 32 %) BP dropped similarly during minute one but remained elevated significantly above baseline in both boys and girls the entire four-minute period. During the recovery period, minute one SBP and DBP dropped similarly in boys (23 +/- 37, 20 +/- 37 %) and girls (20 +/- 38, 12 +/- 38 %), respectively. In boys and girls DBP remained significantly above baseline the entire recovery period. HR in boys and girls returned to baseline immediately following SHG exercise and remained there through recovery. In conclusion, as reported in adults, the drop in HR to baseline during post-exercise ischemia with a concomitant maintenance of BP significantly above baseline indicates that at least two separate mechanisms, with varying influence, are responsible for HR and BP control in young children. Further, the chemoreflex operates similarly in young boys and girls.

Reproducibility of cardiovascular, respiratory, and metabolic responses to submaximal exercise: the HERITAGE Family Study.

This study determined the reproducibility of cardiovascular, respiratory, and metabolic responses to submaximal cycle ergometer exercise at two power outputs (50 W and 60% VO2max) on each of two separate days in a sample of 390 subjects (198 men and 192 women) participating in the HERITAGE Family Study. The same protocol was conducted across 3 d in an intracenter quality control substudy which included an additional 55 subjects. Reproducibility estimates included technical error, coefficient of variation, and intraclass correlation for each of the selected variables for both subject populations. Further, since the data were collected across four clinical centers, intraclass correlations were also computed separately by clinical center. Most variables were highly reproducible, with coefficients of variation below 9% and intraclass correlations over 0.80. These results were consistent for both subject populations and across all four clinical centers. Reproducibility indicators were generally better at the higher power output. It is concluded that within-subject day-to-day variation and measurement unreliabilities are generally small compared with the between-subject variance in the response to submaximal exercise at each of the clinical centers of the HERITAGE Family Study.

Cardiovascular responses to exercise in children.

The cardiovascular system of children responds to exercise differently than does that of an adult, although the mechanisms behind the differences are unclear. During dynamic exercise, it has been reported that heart rate (HR) response to the initiation of exercise is both faster and slower in children than adults. Furthermore, HR recovery has been reported to be faster in children. During submaximal steady state exercise, HR and total peripheral resistance are higher, while stroke volume [SV (ml)] and cardiac output [Q (L/min)] are lower in children at a given rate of work. At maximal exercise intensities HR is higher while SV and Q are lower in children than adults. Differences in cardiovascular responses to dynamic exercise between young boys and girls have also been reported. The majority of studies report that HR is lower and SV is higher in boys than girls at a given rate of work, although data to the contrary have been reported. These differences seem to be related to larger hearts in the boys. Further, the majority of the studies report that Q is similar in young boys and girls at a given rate of work. Few studies have reported differences between boys and girls at maximal intensities of exercise, and the results of those studies are inconsistent. Less is known about cardiovascular responses of children to static exercise compared with adults. A number of studies have reported that HR response to handgrip exercise is greater in children than adults, while others have reported no difference in this response. Even fewer studies have compared boys and girls in their cardiovascular response to static exercise and the results of these studies are also inconsistent. During prolonged exercise both children and adults exhibit cardiovascular drift (gradual increase in HR and decrease in SV). The direction and degree to which these changes differ between children and adults is unclear, with both greater and lesser responses being reported in children. Few studies have investigated differences in cardiovascular response to prolonged exercise between boys and girls. Those that have, report no difference between young boys and girls.

Cardiovascular responses to treadmill and cycle ergometer exercise in children and adults.

This study was conducted to determine whether submaximal cardiovascular responses at a given rate of work are different in children and adults, and, if different, what mechanisms are involved and whether the differences are exercise-modality dependent. A total of 24 children, 7 to 9 yr old, and 24 adults, 18 to 26 yr old (12 males and 12 females in each group), participated in both submaximal and maximal exercise tests on both the treadmill and cycle ergometer. With the use of regression analysis, it was determined that cardiac output (Q) was significantly lower (P

Cardiovascular responses to submaximal exercise in 7- to 9-yr-old boys and girls.

The purpose of this study was to investigate whether differences exist between boys and girls in submaximal cardiovascular responses to exercise on both the treadmill and cycle ergometer. Twenty-four (12 boys and 12 girls) 7- to 9-yr-old children participated in two maximal (one treadmill and one cycle) and four submaximal tests (two treadmill and two cycle). There were no significant differences between the boys and girls in maximal oxygen consumption (L.min-1 or mL.kg-1.min-1) or physical characteristics except for a significantly larger left ventricular mass in the boys versus the girls (78.8 vs 66.0 g, respectively). Submaximal cardiovascular variables were measured at three different work rates on both exercise modalities. Oxygen consumption at the different work rates was not different between boys and girls on either exercise modality. The trend was for heart rate to be lower and stroke volume higher in boys versus girls, but this difference was only significant for heart rate at 4 miles.h-1 (142.9 vs 155.5 beats.min-1, respectively). It is concluded that in this sample of 7- to 9-yr-old boys and girls there are few significant differences in submaximal cardiovascular responses to exercise on either exercise modality.

Comparison of maximal oxygen consumption with oral and nasal breathing.

The major cause of exercise-induced asthma (EIA) is thought to be the drying and cooling of the airways during the 'conditioning' of the inspired air. Nasal breathing increases the respiratory system's ability to warm and humidity the inspired air compared to oral breathing and reduces the drying and cooling effects of the increased ventilation during exercise. This will reduce the severity of EIA provoked by a given intensity and duration of exercise. The purpose of the study was to determine the exercise intensity (%VO2 max) at which healthy subjects, free from respiratory disease, could perform while breathing through the nose-only and to compare this with mouth-only and mouth plus nose breathing. Twenty subjects (11 males and 9 females) ranging from 18-55 years acted as subjects in this study. They were all non-smokers and non-asthmatic. At the time of the study, all subjects were involved in regular physical activity and were classified, by a physician, as free from nasal polyps or other nasal obstruction. The percentage decrease in maximal ventilation with nose-only breathing compare to mouth and mouth plus nose breathing was three times the percentage decrease in maximal oxygen consumption. The pattern of nose-only breathing at maximal work showed a small reduction in tidal volume and large reduction in breathing frequency. Nasal breathing resulted in a reduction in FEO2 and an increase in FECO2. While breathing through the nose-only, all subjects could attain a work intensity great enough to produce an aerobic training effect (based on heart rate and percentage of VO2 max).

Resting metabolic rate measured after subjects spent the night at home vs at a clinic.

This study determined the effect on resting metabolic rate (RMR) of subjects spending the night before measurement at home vs at a clinic. Ten subjects participated in six randomized RMR measurements; three measurements were made after subjects slept the evening before the measurements in their home (H1, H2, and H3) and three after they slept in a clinical setting (C1, C2, and C3). There were no significant differences (P < 0.05) in oxygen consumption (VO2, mL/min), RMR (kJ/min, kJ.kg body wt-1.h-1, or kJ.kg fat-free mass-1.h-1), or respiratory exchange ratio (RER) between any of the six RMR measurements, or between mean values for the three home trials (VO2 = 216 +/- 41 mL/min, RER = 0.80 +/- 0.04, heart rate = 51 +/- 3 beats/min, ventilation = 7.1 +/- 1.1 L/min) vs the three clinical trials (VO2 = 216 +/- 45 mL/min, RER = 0.80 +/- 0.04, heart rate = 52 +/- 5 beats/min, ventilation = 7.0 +/- 1.1 L/min). We conclude that under most circumstances it is not important that subjects spend the night before RMR assessment at the measurement facility. However, when basal metabolic rate is to be assessed, an overnight stay at the clinical facility would generally be necessary.