Left coronary blood flow (LCBF), left ventricular oxygen, extraction [(a-v)O₂ ], and myocardial oxygen consumption (MVO₂) were monitored in 10 dogs. HR was paced at 120 bpm and then increased to 180 bpm to elicit a hyperemic response (ΔLCBF). During the hyperemia, the vaso-dilatory response to exogenous adenosine (F_AD) was tested. Twenty min. after injection of aminophylline (100 mg/i.v.), HR was again increased. F_AD was again tested. The pacing-induced increase in MVO₂ (ΔMVO₂) was not affected by aminophylline (P>0.05). However, the slope ΔLCBF/ΔMVO₂ was decreased, and the slope (a-v)O₂ /ΔMVO₂ was increased. F_AD was also decreased and the magnitude of the reduction was correlated with the decrease in ΔLCBF/ΔMVO₂ (r=0.82). These results suggest that adenosine may play an role in coronary functional hyperemia induced by increases in heart rate.

Bibliography: leaves 306-353. / xiii, 353 leaves : ill. ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Utilizing a paired transcoronary sampling technique, serial determination of myocardial drug content was determined following intravenous bolus injection in patients undergoing diagnostic cardiac catheterization for the investigation of chest pain. There was significant modulation of haemodynamic effects of all three drugs according to changes in systolic interval. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, Queen Elizabeth Hospital, Cardiology Unit

The first chapter of this thesis consists in a critical review of the literature on cardiac and cardiac-related autonomic activity, and infant development. Empirical findings are presented on mechanisms of interaction between heart rate and the autonomic nervous system; their relationship with infant development; their genetic and environmental influences; their gender effects; and related quantification issues. / This is followed by a study of 322 5-month-old twin pairs that investigated the genetic and environmental influences on sleeping heart rate and cardiac-related autonomic activity, as indexed by spectral analysis of heart rate variability and response to postural change. The postural change elicited only minor changes in cardiovascular activity, perhaps due to immaturity of the baroreflex. As a result, analyses focused on supine cardiovascular activity. Multivariate genetic modeling indicated that individual differences in sleeping HR and high frequency HR variability were determined by unique environmental and distinct additive genetic factors. These variables, along with low frequency HR variability, were also affected by overlapping familial environmental influences. Familial influences on individual differences in high frequency HR variability were more pronounced for baby girls than boys. Estimates of relative low and high frequency HR variability were determined by common (familial) and unique environmental factors; familial influences on these estimates of HR variability did not overlap with familial influences on sleeping HR. / A second study using the same twin sample is then presented. Its objectives were to investigate the indices of genetic and environmental etiology of individual differences in five month-old twins' HR reactivity and to evaluate the possible overlap, if any, between the familial influences on HR in states of sleep and reactivity. Multivariate genetic modeling showed that the total variance of individual differences was decomposed in the following manner: Sleeping and awake HR were under the influence of shared additive genetic factors; sleeping HR also shared common environmental influences with the absolute power spectrum values; and absolute high frequency power additionally had phenotype-specific additive genetic factors influencing its expression. Relative power spectrum values were under the influence of phenotype-specific common environmental factors. / Overall, these results suggest the presence of important familial (genetic and environmental) influences on heart rate and cardiac-related autonomic activity at five months of age: There is an absence of overlap of these (familial) additive genetic influences but the presence of a partial overlap of the (familial) environmental influences.

Introduction Heart rate variability (HRV) is regarded as a useful, non-invasive method for investigating the autonomic nervous system (ANS). Over the past decade there has been an increase in the number of HRV investigations in the disciplines of medical, sport and exercise science. Despite the extensive use of HRV in investigations of ANS functioning, there are questions relating to the reliability of the technique. Therefore, HRV reliability studies for different population groups have been advocated. Furthermore, research on gender differences in HRV is contradictory. This has resulted in the need to investigate gender characteristics in HRV. Objectives The objective of this study was to evaluate the reliability of short-term (5min) recordings of HRV, and to determine the association between HRV and gender. Methods Forty four physically active students (n= 21, age= 21.17 (1.55) males and n=23, age= 19.75 (1.76) females) participated in the study. Heart rate variability parameters were determined from five minute recording of interbeat intervals (IBI) using a Suunto t6 heart rate monitor (HRM). Testing was repeated over 4 consecutive days under the same conditions. The following HRV time and frequency domain measures were calculated using Kubios HRV Software Version 2.0: mean heart rate (HR), standard deviation of normal to normal intervals (SDNN), root mean square of successive differences (RMSSD), percentage of beats that changed more than 50 ms from the previous beat (pNN50), low frequency in normalized units (LFnu), high frequency in normalized units (HFnu) and low frequency to high frequency ratio in normalized units (LF/HFnu ratio). The data was summarized using routine descriptive statistics. Relative reliability was calculated using interclass correlation coefficients (ICC) (ICC of >0.80 indicated good to excellent reliability) and absolute reliability using typical error of measurement (TEM) and TEM as a percentage of the mean score (TEM%). This statistical measures were computed for days 2 vs 3 (REL 1), 3 vs 4 (REL 2). Day 1 was used as a familiarization day. An unpaired T-test was used to determine whether there were any differences between males and females for the above HRV parameters. Significance was set at p .0.05. Results The ICCs for both REL 1 and REL 2 indicated good to excellent (ICC >0.8) reliability for IBIs and pNN50 for the time domain results. In general, the time domain results had a higher relative reliability than the frequency domain results. Males had an overall lower relative reliability than females for frequency domain parameters. Absolute reliability for REL 2 showed a slightly lower TEM value as compared to REL 1.The largest gender differences in TEM were seen in the frequency domain parameters. Specifically, for males, the TEM was higher than females for the LF/HFnu ratio (REL 2: 116%), the HFnu (REL 1: 90%) and the LFnu (REL 1: 68%). Overall the TEM% was relatively high in most HRV parameters specifically for LF/HFnu (REL 1: 31.4% females and 48.1% males; REL 2: 29.7% females and 40.4% males). These findings indicate that males have decreased absolute reliability compared to females and that random error is greater in men for the frequency domain parameters. Gender differences illustrated significant differences for resting HR (16% higher in females (p < 0.0001)), IBIs (21% higher in females (p <0.0001)) and LF/HFnu ratio (41% higher in males (p = 0.003)). The findings indicate that females have higher total HRV. Conclusions Short term recordings of HRV over consecutive days using the Suunto t6 HRM and Kubios custom HRV software are reliable depending on the HRV parameter being analysed. Overall, the relative reliability results suggest that HRV using the Suunto t6 and Kubios is good. However, the absolute reliability results suggest low reliability. In particular, males demonstrated a poorer absolute reliability (high TEM and TEM%) than females, suggesting a larger day to day random error in males. Furthermore, specific HRV measures differed between males and females demonstrating that females have higher parasympathetic modulation compared to men. The overall higher HRV in females could explain the possible cardio-protective mechanism observed in premenopausal women. Key words: Heart rate variability, Parasympathetic, Reliability, Interbeat Intervals / Thesis (M.Sc.)-University of KwaZulu-Natal, Westville, 2011.

This study investigated the heart rates of children in the first, third, and fifth grades of two schools during physical education class and recess time. One hundred and nine children (56 females, 53 males) participated in the eight-week study. Each participant wore a Polar Vantage XL receptor strap and watch receiver during physical education class and recess time on the same day. The average heart rates and percentage of time in and above the target heart zone of 150 to 200 beats per minute were recorded. A MANOVA analysis revealed no significant difference between heart rates during physical education and recess over the eight-week period. Gender differences, however, were significant as boys average heart rates were higher than girls and boys were in or above the target heart zone a higher percentage of the time than girls. This difference was especially evident at recess. / Fisher Institute for Wellness

Access to abstract permanently restricted to Ball State community only / Access to thesis permanently restricted to Ball State community only / School of Physical Education, Sport, and Exercise Science

Thesis (M.S.)--University of Wisconsin -- La Crosse, 1987. / Includes bibliographical references (leaves 43-45).

Thesis (M.A.)--Texas State University--San Marcos, 2009. / Vita. Includes bibliographical references (leaves 45-50). Also available on microfilm.

Thesis (M. App. Sc.)--Carleton University, 2004. / Includes bibliographical references (p. 114-117). Also available in electronic format on the Internet.

Thesis (Ph. D.)--Auburn University. / Abstract. Includes bibliographical references.