Received March 7, 2004
Revised April 14, 2004
Accepted after revision July 14, 2004

¹ The University of Western Ontario
² Countess of Chester Hospital
³ The Universtity of Western Ontario

^* To whom correspondence should be addressed. E-mail: avovk{at}hsph.harvard.edu.

	Abstract

The rate and duration of peripheral chemoreceptor resensitization following sustained hypoxia was characterized in young and older (74 yrs.) adults. In addition cerebral blood velocity (CBV) was measured in young subjects during and following the relief from sustained hypoxia. Following 20 min of sustained eucapnic hypoxia (50 mmHg), subjects were re-exposed to brief (1.5 min) hypoxic pulses (50 mmHg), and the magnitude of the ventilatory response was used to gauge peripheral chemosensitivity. Five minutes after the relief from sustained hypoxia, ventilation (VE) increased to 40.3 ± 4.5% of the initial hypoxic ventilatory response, and by 36 min VE increased to 100%, indicating that peripheral chemosensitivity to hypoxia was restored. The VE response magnitude vs. time demonstrated that VE, hence peripheral chemosensitivity, was restored at a rate of 1.9% per min. Cerebral blood flow (CBF, inferred from CBV) remained constant during sustained hypoxia and increased by the same magnitude during the hypoxic pulses suggesting that CBF has a small, if any, impact on the decline in VE during hypoxia and its subsequent recovery. To address the issue of whether hypoxic pulses affect subsequent challenges, series (continuous hypoxic pulses at various recovery intervals) and parallel (only one pulse per trial) methods were used. There were no differences in the ventilatory responses between the series and parallel methods. Older adults demonstrated a similar rate of recovery as in the young, suggesting that ageing in active older adults does not affect the peripheral chemoreceptor response.

Key Words: Chemoreceptor, Respiratory control, Ventilation