Biomedical Physiology and Kinesiology, Department of

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Heart Rate Variability and Short Duration Spaceflight: Relationship to Post-Flight Orthostatic Intolerance

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2004
Abstract: 

Background

Upon return from space many astronauts experience symptoms of orthostatic intolerance. Research has implicated altered autonomic cardiovascular regulation due to spaceflight with further evidence to suggest that there might be pre-flight autonomic indicators of post-flight orthostatic intolerance. We used heart rate variability (HRV) to determine whether autonomic regulation of the heart in astronauts who did or did not experience post-flight orthostatic intolerance was different pre-flight and/or was differentially affected by short duration (8 – 16 days) spaceflight. HRV data from ten-minute stand tests collected from the 29 astronauts 10 days pre-flight, on landing day and three days post-flight were analysed using coarse graining spectral analysis. From the total power (PTOT), the harmonic component was extracted and divided into high (PHI: >0.15 Hz) and low (PLO: = 0.15 Hz) frequency power regions. Given the distribution of autonomic nervous system activity with frequency at the sinus node, PHI/PTOT was used as an indicator of parasympathetic activity; PLO/PTOT as an indicator of sympathetic activity; and, PLO/PHI as an estimate of sympathovagal balance.

Results

Twenty-one astronauts were classified as finishers, and eight as non-finishers, based on their ability to remain standing for 10 minutes on landing day. Pre-flight, non-finishers had a higher supine PHI/PTOT than finishers. Supine PHI/PTOT was the same pre-flight and on landing day in the finishers; whereas, in the non-finishers it was reduced. The ratio PLO/PHI was lower in non-finishers compared to finishers and was unaffected by spaceflight. Pre-flight, both finishers and non-finishers had similar supine values of PLO/PTOT, which increased from supine to stand. Following spaceflight, only the finishers had an increase in PLO/PTOT from supine to stand.

Conclusions

Both finishers and non-finishers had an increase in sympathetic activity with stand on pre-flight, yet only finishers retained this response on landing day. Non-finishers also had lower sympathovagal balance and higher pre-flight supine parasympathetic activity than finishers. These results suggest pre-flight autonomic status and post-flight impairment in autonomic control of the heart may contribute to orthostatic intolerance. The mechanism by which higher pre-flight parasympathetic activity might contribute to post-flight orthostatic intolerance is not understood and requires further investigation.

Document type: 
Article

The Prognostic Effect of Ethnicity for Gastric and Esophageal Cancer: The Population-Based Experience in British Columbia, Canada

Peer reviewed: 
Yes, item is peer reviewed.
Date created: 
2011
Abstract: 

Background: Gastric and esophageal cancers are among the most lethal human malignancies. Their epidemiologyis geographically diverse. This study compares the survival of gastric and esophageal cancer patients amongseveral ethnic groups including Chinese, South Asians, Iranians and Others in British Columbia (BC), Canada.Methods: Data were obtained from the population-based BC Cancer Registry for patients diagnosed with invasiveesophageal and gastric cancer between 1984 and 2006. The ethnicity of patients was estimated according to theirnames and categorized as Chinese, South Asian, Iranian or Other. Cox proportional hazards regression analysis wasused to estimate the effect of ethnicity adjusted for patient sex and age, disease histology, tumor location, diseasestage and treatment.Results: The survival of gastric cancer patients was significantly different among ethnic groups. Chinese patientsshowed better survival compared to others in univariate and multivariate analysis. The survival of esophagealcancer patients was significantly different among ethnic groups when the data was analyzed by a univariate test(p = 0.029), but not in the Cox multivariate model adjusted for other patient and prognostic factors.Conclusions: Ethnicity may represent underlying genetic factors. Such factors could influence host-tumorinteractions by altering the tumor’s etiology and therefore its chance of spreading. Alternatively, genetic factorsmay determine response to treatments. Finally, ethnicity may represent non-genetic factors that affect survival.Differences in survival by ethnicity support the importance of ethnicity as a prognostic factor, and may provideclues for the future identification of genetic or lifestyle factors that underlie these observations.

Document type: 
Article