Thesis (MSc)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: Chapter 1 presents a general literature review on the acute isocapnic hypoxic ventilatory
response (HVR).
The main findings from Chapter 2 indicate that our modified breathing circuit effectively
measured the HVR while maintaining isocapnia. The measured ventilatory variables
changed significantly with repeated short-term exposure to hypoxia over a 30-minute
period, and the within- and between-day variability did not differ significantly.
Furthermore, the variability in the HVR response (as measured by the coefficient of
variation, (CV» amounted to approximately 27% between tests in both parameters.
Repeated measures are recommended in future determinations of the HVR.
In Chapter 3 the main findings were that hypoxic sensitivity does not differ between
Caucasian and Xhosa sea-level populations in South Africa, and that ventilatory
components in both normoxia and hypoxia differed between these two populations. Two
distinct patterns of breathing were evident: shallow, rapid breathing among Xhosa
subjects, and deeper, slower breathing among Caucasians. Moreover, lower arterial
oxygen saturation levels during hypoxia among Xhosa subjects suggest that these two
patterns of breathing differ in the effectiveness with which they oxygenate the blood.
Inter-individual variation in HVR within each population is of the same high magnitude
as that reported in the literature (Beall et al., 1997), further supporting the use of repeated
measures in future studies.
As previously reported (Sahn et al., 1977, Reeves et al., 1993), in Chapter 3 I document a
significant correlation between HVR and partial pressure of end-tidal CO2 (PETCO).
Future studies of HVR should consider PETCO2 as a covariate, despite the fact that my
analyses of covariance (ANCOV A) showed no inter-population differences in HVR.
In Chapter 4 I report that regression analysis shows that the HVR of parents is not a
predictor of that of their offspring. No significant heritability was evident for any of the
additional key variables of hypoxic VE ,hypoxic Sa02, and the CV for HVR, but a priori
analyses showed that I tested too few subjects to be able to demonstrate heritability (or
the lack thereof) conclusively by means of regression analyses. Importantly, repeatability
estimates within populations (86 %) revealed that despite its high variability, the HVR is
highly repeatable, and therefore remains a useful comparative research tool for studies of
human adaptation to hypoxia. / AFRIKAANSE OPSOMMING: Hoofstuk 1 gee 'n algemene literatuuroorsig van die akute isokapniese hipoksiese
ventilatoriese reaksie (HVR).
Die hoofbevindinge uit Hoofstuk 2 dui aan dat ons gemodifiseerde asemhalingsbaan
HVR effektief meet terwyl isokapniese toestande gehantaaf word. Die ventilatoriese
veranderlikes gemeet, het betekenisvol verskil met herhaalde korttermyn blootstelling aan
hipoksie in a 30-minuut periode, en die binne- en tussen-daagse afwykbaarheid het nie
betekenisvol verskil nie. Verder het die afwykbaarheid van die HVR reaksie (soos bepaal
deur die koëffisiënt van variasie (KV)) ongeveer 27 % beloop tussen toetse van beide
parameters. Herhaalde metings word vir toekomstige bepalings van die HVR voorgestel.
In Hoofstuk 3 was die hoofbevindinge dat hipoksiese sensitiwiteit nie verskil tussen
Kaukasiese- en Xhosa- seevlak populasies in Suid-Afrika nie, en dat ventilatoriese
komponente in beide normoksie en hipoksie verskillend was tussen hierdie twee
populasies. Twee definitiewe asemhalingspatrone was duidelik merkbaar: vlak, vinnige
asemhaling in Xhosa proefpersone, en dieper, stadiger asemhaling in Kaukasiërs. Verder
het laer arteriële suurstof versadigingsvlakke gedurende hipoksie in Xhosa proefpersone
daarop gedui dat hierdie twee asemhalingspatrone moontlik verskil in hul effektiwiteit
om die bloed met suurstof te verryk.
Inter-individuele variasie in HVR binne elke populasie was van dieselfde groot omvang
as wat in die literatuur gerapporteer word (Beall et al., 1997), wat die gebruik van
herhaalde metings in toekomstige studies verder ondersteun.
Soos voorheen gerapporteer (Sahn et al., 1977, Reeves et al., 1993), dokumenteer ek in
Hoofstuk 3 'n merkbare korrelasie tussen HVR en parsiële druk van eind-tidale CO2
(PET CO2
). Verdere HVR studies behoort PET CO2 as a kovariant te beskou, ten spyte van
die feit dat my analise van kovariansie (ANCOV A) geen inter-populasie verskille in
HVR getoon het nie.
In Hoofstuk 4 rapporteer ek dat regressie analise bewys dat die HVR van ouers nie 'n
voorspeller van dié van hul kinders is nie. Geen betekenisvolle oorerflikheid was duidelik
vir enige van die addisionele sleutelveranderlikes van hipoksiese VE ,hipoksiese Sa02, of
die KV van HVR nie, maar 'n vorige analise het getoon dat ek te min proefpersone
getoets het om oorerflikheid (of die gebrek daaraan) m.b.v. regressie analises te kan
demonstreer. Dit is belangrik dat intra-populasie herhaalbaarheidsskattings (86 %) getoon
het dat ten spyte van sy hoë afwykbaarheid, die HVR hoogs herhaalbaar is, en daarom 'n
nuttige vergelykende navorsingshulpmiddel is vir studies rakende menslike aanpassing by
hipoksie.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/70079 |
| Date | 03 1900 |
| Creators | Terblanche, Jonathan Steed |
| Contributors | Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 195 p. : ill. |
| Rights | Stellenbosch University |
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