Date of Award


Degree Type


Degree Name

Doctor of Philosophy


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.



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