Cardiovascular drift can occur during prolonged exercise and is characterized by a gradual decrease in stroke volume (SV) and a corresponding increase in heart rate (HR) over time, despite the maintenance of a constant level of work; cardiac output (CO) usually is unchanged. A number of factors may cause cardiovascular drift to occur, including increases in peripheral blood flow, decreases in plasma volume, increases in circulating catecholamines, and metabolic acidosis. These physiological events may be influenced by the relationship of the exercise intensity to ventilatory threshold (VT). Therefore, the purpose of this study was to examine the cardiovascular responses during prolonged exercise in boys and men at an intensity set relative to VT. Eight boys (10-13 yrs.) and 10 men (18-25 yrs.) completed an orientation trial, a graded maximal exercise test, and a 40 minute submaximal exercise bout at an intensity equal to the V02 at VT. During the 40 minute exercise bout, V02 increased significantly over time (P_<0.05),although the magnitude of change was similar in boys and men (P>0.05). Heart rate was higher and SV was lower in the boys compared to the men (P<_0.05), and the changes in HR and SV were significant over time. Although there was a trend for the HR increase and SV decrease to be greater in the men, the group-by-time interaction was not significant. Cardiac output and arteriovenous oxygen difference were higher in the men compared to the boys (P<0.05), but remained constant over time. Mean arterial blood pressure (MABP) was higher in the men than the boys (P<_0.05). In the men, MABP decreased significantly from 10 to 40 minutes, while in the boys, MABP decreased (P<_0.05) from 10 to 30 minutes and then increased to a value similar to that at 10 minutes. This differential response in MABP over time resulted in a significant groupby-time interaction. Total peripheral resistance was significantly higher in the boys than the men, but remained constant over time (P>0.05). Men exhibited a greater decrease in plasma volume from 0 to 40 minutes. There was no group difference in perceived exertion (RPE) between the boys and the men, although the boys exhibited a greater increase in RPE over time than the men (P<0.05). In conclusion, the cardiovascular responses during prolonged exercise are similar in boys and men, although there is a tendency for the magnitude of cardiovascular drift to be greater in the men. In addition, due to the fact that these results are similar to previous studies not accounting for individual differences in VT, it would seem that these differences in VT should not be of concern when studying the cardiovascular responses during prolonged exercise. / School of Physical Education

The purpose of this study was to examine VT and LT in boys and men. Eight boys (10-11 years) and nine men (18-30 years) completed a graded exercise test on a cycle ergometer. A two-way (group x threshold) ANOVA compared physiological responses (V02 1/min and ml/kg/min, percentage of V02max, and HR) at VT and LT. Statistical significance was set at P < 0.05. No significant interaction was observed. Significant main effects for group included a higher V02 (1/min) in the men, and a higher percentage of VO2max in the boys. Significant main effects for threshold showed all variables were greater at VT than LT. Within each group, all variables were significantly higher at VT than LT. For the boys and all subjects together, significant correlations between thresholds were observed for V02 (1/min and ml/kg/min) and HR, but not percentage of VO2max. For the men alone, no significant correlations were found. Together, these results suggest that physiological changes associated with LT may contribute to the onset of VT, and the occurrence of the thresholds (expressed as a percentage of VO2max) declines with maturation. / School of Physical Education

[Truncated abstract] Respiratory system impedance (Zrs) is commonly measured at low to medium frequencies (0.5 - 40 Hz) to infer structural and physiological information about the respiratory system. Coupled with the use of mathematical models of the lungs, Zrs has been used to partition the behaviour of the conductive airways and the respiratory tissues. High-frequency (HF) Zrs beyond 100 Hz has been comparatively less studied and understood. Past work has revealed spectral features at high frequencies termed antiresonances, marked by peaks in the real part of Zrs, often coinciding with zero-crossings in the imaginary part. It has been shown that the first occurrence of antiresonance in humans primarily reflects the contribution of the airways, and is a property of sound wave propagation in the airways. Also, the first antiresonance is altered in diseases such as chronic airflow obstruction, and wheeze in infants. The main aim of this project is to shed further understanding about the first antiresonance, via the behaviour of two parameters characterising this feature of the HF spectrum: the frequency at which the first antiresonance occurs, far,1, and the magnitude of the real part of Zrs at this frequency, Rrs(far,1). In our studies, Zrs is measured as an input impedance using the forced oscillation technique with a loudspeaker-in-box and wavetube setup, and employing pseudorandom frequency signals. We studied the effects of altered lung conditions, first in an animal model, then progressed on to humans. v vi In the rat, we found that both far,1 and Rrs(far,1) tended to decrease together with increasing lung volume. With methacholine(MCh)-induced bronchoconstriction, rats showed increases in far,1 and Rrs(far,1) with increasing MCh dose, but these occurred at higher doses compared to increases in airway resistance. The changes in these HF parameters were independent of the changes in tissue properties. ... It was found that in a group of patients with emphysema, VDRrs(far,1) was significantly more negative, potentially due to alterations to airway dimensions and wall properties. Furthermore, VDRrs(far,1) was correlated with extent of obstruction and hyperinflation, suggesting a relationship with severity of emphysema. These results show that the first antiresonance reflect changes in the airways, and its measurement shows promise as a clinical tool, in its potential as an easy-to-perform assessor of conditions in which the airways are altered. Keywords: antiresonance, respiratory input impedance, high frequencies, emphysema

<div> <div> <div> <p>People with epilepsy have an increased risk of mortality when compared to the general population. These increased mortality risks include deaths related to status epilepticus and sudden unexpected death in epilepsy (SUDEP). Physiological data describing cardiac, respiratory, and brain function prior to sudden death in epilepsy is crucial to the studying the underlying mechanisms behind these deaths. Because it is unknown when sudden deaths in epilepsy may occur, continuous monitoring is necessary to guarantee the capture of physiological data prior to death. </p> <p>I have used custom designed implantable devices to continuously measure cardiac, respiratory, and neurological signals in freely behaving rats with chronically induced epilepsy. Due to the continuous respiration measurements, the resultant dataset is the first of its kind. This dataset indicates that respiratory abnormalities (reduced respiration and short apneas) occur during and after seizures. These abnormalities may indicate SUDEP onset because obstructive apneas due to laryngospasm have been indicated as possible causes of SUDEP in other studies. </p> <p>Laryngospasms can be caused by gastric acid coming into contact with the larynx. During a laryngospasm, intrinsic laryngeal muscles contract, resulting in the closure of the airway. Recently published research has indicated that acid reflux may be responsible for triggering fatal laryngospasms in rats with induced seizures. I have found that the larynx can be opened during a laryngospasm by electrically stimulating the recurrent laryngeal nerves. I have also found that performing gastric vagotomies leads to a statistically significant reduction in mortality due to fatal apneas in rats with induced seizures. </p> </div> </div> </div>