Date of Award
1993
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
This thesis examined age-related changes in the ventilatory response to exercise and in the ventilatory response to inhaled carbon dioxide (CO{dollar}\sb2{dollar}) at rest. Specifically, the purposes were to: (1) examine the ventilatory response to CO{dollar}\sb2{dollar} production (VCO{dollar}\sb2{dollar}) during graded exercise below the ventilation threshold (T{dollar}\sb{lcub}\rm \.VE{rcub}{dollar}) in men and women aged 55 to 86 yrs, (2) determine the ventilatory response to CO{dollar}\sb2{dollar} at rest and evaluate the CO{dollar}\sb2{dollar} sensitivity of the central and peripheral chemoreceptors in young (YS, n = 7, 28.3 yrs) and old (OS, n = 11, 76.1 yrs) humans, and (3) determine the temporal parameters of the ventilatory response to CO{dollar}\sb2{dollar} in young (YS, n = 4, 27.0 yrs) and old (OS, n = 5, 74.2 yrs) men.;The first study showed significant positive relationship between the ventilatory response to VCO{dollar}\sb2{dollar}, referred to as {dollar}\Delta{dollar}V{dollar}\sb{lcub}\rm E{rcub}/\Delta{dollar}VCO{dollar}\sb2{dollar}, and advancing age, increasing by 0.29/yr for men and by 0.20/yr for women. At a common metabolic demand (VCO{dollar}\sb2{dollar} = 1.0 {dollar}\ell{dollar} min{dollar}\sp{lcub}-1{rcub}{dollar}), V{dollar}\sb{lcub}\rm E{rcub}{dollar} was 14% higher in men aged 80-86 yrs compared to men aged 55-64 yrs while for women, there were no differences between age groupings. The men aged 75 to 86 yrs appear to have reached the appropriate exercise V{dollar}\sb{lcub}\rm E{rcub}{dollar} primarily by an increase in breathing frequency (f{dollar}\sb{lcub}\rm b{rcub}{dollar}) with a levelling off of V{dollar}\sb{lcub}\rm T{rcub}{dollar}. The increased ventilatory response to VCO{dollar}\sb2{dollar} with advancing age may be related to an age-dependent increase in dead-space ventilation (V{dollar}\sb{lcub}\rm D{rcub}{dollar}) and to a greater non-uniformity of ventilation-perfusion ratio.;In the second study, the ventilatory responses to CO{dollar}\sb2{dollar} (eucapnia and hypercapnia) were determined in hyperoxia and hypoxia and, for each subject, the ventilatory responses were fitted to the Lloyd equation, V{dollar}\sb{lcub}\rm E{rcub}{dollar} = S(P{dollar}\sb{lcub}\rm ET{rcub}{dollar}CO{dollar}\sb2{dollar} - B) for the determination of the CO{dollar}\sb2{dollar} sensitivity (S). In hypercapnia, hypoxic V{dollar}\sb{lcub}\rm E{rcub}{dollar} was 24% lower in OS (39.9 {dollar}\pm{dollar} 2.7 (SE), {dollar}\ell\cdot{dollar}min{dollar}\sp{lcub}-1{rcub}){dollar} compared to YS (52.2 {dollar}\pm{dollar} 3.2) while there were no age differences in hyperoxic V{dollar}\sb{lcub}\rm E{rcub}{dollar}. In hypoxia, S was significantly lower in OS (3.25 {dollar}\pm{dollar} 0.38 {dollar}\ell\cdot{dollar}min{dollar}\sp{lcub}-1{rcub}\cdot{dollar} Torr{dollar}\sp{lcub}-1{rcub}{dollar}) compared to YS (4.76 {dollar}\pm{dollar} 0.37) and appeared to have resulted from a lower peripheral chemoreflex CO{dollar}\sb2{dollar} sensitivity (OS, 0.86 {dollar}\pm{dollar} 0.21 {dollar}\ell\cdot{dollar}min{dollar}\sp{lcub}-1{rcub}\cdot{dollar}Torr{dollar}\sp{lcub}-1{rcub}{dollar}; YS, 2.16 {dollar}\pm{dollar} 0.43).;Finally, the third study determined the ventilatory response to CO{dollar}\sb2{dollar} in euoxia, hyperoxia, and mild hypoxia. A double component exponential model was used to estimate the central and peripheral chemoreflex gains (g{dollar}\sb{lcub}\rm c{rcub}{dollar},g{dollar}\sb{lcub}\rm p{rcub}{dollar}), time constants of the responses ({dollar}\tau\sb{lcub}\rm c{rcub}{dollar},{dollar}\tau\sb{lcub}\rm p{rcub}{dollar}), and time delays (T{dollar}\sb{lcub}\rm c{rcub}{dollar},T{dollar}\sb{lcub}\rm p{rcub}{dollar}). YS and OS showed similar characteristics for T{dollar}\sb{lcub}\rm c{rcub}{dollar}, T{dollar}\sb{lcub}\rm p{rcub}{dollar}, {dollar}\tau\sb{lcub}\rm c{rcub}{dollar}, and {dollar}\tau\sb{lcub}\rm p{rcub}{dollar}. In hypoxia, g{dollar}\sb{lcub}\rm c{rcub}{dollar} and g{dollar}\sb{lcub}\rm p{rcub}{dollar} were significantly smaller for OS (g{dollar}\sb{lcub}\rm c{rcub}{dollar}, OS = 1.27 {dollar}\pm{dollar} 0.10 {dollar}\ell\cdot{dollar}min{dollar}\sp{lcub}-1{rcub}\cdot{dollar}Torr{dollar}\sp{lcub}-1{rcub}{dollar} and YS = 2.07 {dollar}\pm{dollar} 0.23, p = 0.0104; g{dollar}\sb{lcub}\rm p{rcub}{dollar}, OS = 0.91 {dollar}\pm{dollar} 0.08 and YS = 1.28 {dollar}\pm{dollar} 0.14, p = 0.0481). This study demonstrated that the ventilatory responses to CO{dollar}\sb2{dollar} in euoxia and hyperoxia are similar for young and older men while in hypoxia, the response in older men is characterized by lower gains for the central and peripheral chemoreflex loops.;These studies have determined the ventilatory response to VCO{dollar}\sb2{dollar} during exercise and the ventilatory response to inhaled CO{dollar}\sb2{dollar} at rest and suggest possible age-related alterations in the mechanisms that control these responses in the elderly.
Recommended Citation
Poulin, Marc Jean, "Ventilatory Response To Carbon Dioxide Stimuli In Aged Humans" (1993). Digitized Theses. 2215.
https://ir.lib.uwo.ca/digitizedtheses/2215