The progressive effects of ageing on chemosensitivity in healthy subjects

Summary 

The aim of this study was to compare the central inspiratory drive (P_0.1) response to hypoxia and hypercapnia between different age groups of elderly, nonsmoker, healthy subjects and young healthy controls.

A random sample, proportionally stratified by age (65–69, 70–74, 75–79 and 80–84yrs) from a sample of nonsmoker elderly subjects representative of a general population and 47 healthy subjects aged 20–40 were selected. Arterial blood gas, lung volumes, diffusing capacity, maximal respiratory pressure and oxygen uptake measurements were performed. Breathing pattern and mouth occlusion pressure, as well as P_0.1 responses to hyperoxic progressive hypercapnia and isocapnic progressive hypoxia were evaluated.

The elderly subjects had lower P0.1 responses to hypoxia (0.017±0.006 vs. 0.031±0.008kPa/%, P<0.001) and hypercapnia (0.042±0.018 vs. 0.051±0.030kPa/mmHg, P=0.047) than the young healthy controls.

Hypoxic sensitivity gradually decreased as age increased to 70–74 and remained unchanged from 75 years of age onward. CO₂ threshold was lower in the elderly groups than in young healthy controls. Lung volumes, inspiratory muscle strength and baseline metabolic rate were the principal determinants of hypoxic sensitivity.

In summary, during old age, a progressive decline in hypoxic sensitivity and a decrease in the CO₂ threshold are experienced. These alterations remain stable from the age of 75 onward.

Keywords: Ventilation control, Chemical sensitivity, Carotid bodies, Elderly medicine, Hypoxic ventilatory responses