The Effect of Aging and Rapid Saline Infusion on Compensatory Reserve during Whole‐Body Passive Heat Stress
Abstract
The compensatory reserve is defined as the physiological capacity to compensate for reductions in central blood volume. It is measured by a machine learning algorithm, called CRI, which analyzes continuous changes in the features of a photoplethysmographic signal obtained by finger pulse oximetry. The purpose of this study was 2‐fold. First, we examined the effect of healthy aging on compensatory reserve during normothermic and heat stress conditions. Second, we examined the effect of rapid saline infusion during heat stress on compensatory reserve. Eleven young (6 males/5 females; mean ± SD: age, 25 ± 4 years; height, 165 ± 6 cm; weight, 63 ± 9 kg) and ten aged (4 males/6 females; age, 69 ± 4 years; height, 165 ± 9 cm; weight, 68 ± 9 kg) adults were exposed to central hypovolemia via 15 and 30 mmHg of lower‐body negative pressure (LBNP) under normothermic and heat stress (increase in core temperature of 1.5°C) conditions. Approximately 10 min after the heat stress LBNP challenge, warm saline was rapidly infused (15 ml/kg in ~6 min) while subjects remained hyperthermic. Absolute CRI values (Table) range between 0 and 1, where 0 represents little to no reserve for cardiovascular compensation and 1 represents maximal physiological reserve to compensate for central hypovolemia. Under normothermic conditions, an age × LBNP level interaction was observed (PPP=0.21) adults. During 30 mmHg LBNP, CRI was reduced in both groups (P≤0.01). During whole‐body passive heat stress, CRI was lower relative to normothermic baseline in both groups (PPP=0.06), but not at 15mmHg (P=0.27). Relative to heat stress, rapid saline infusion did not affect CRI in young (P=0.47) or aged (P=0.99) adults. These results demonstrate that CRI responses at low levels of central hypovolemia (i.e. 15 mmHg ≈ 250 ml) differ between young and aged adults under normothermic and heat stress conditions. Furthermore, CRI is unaffected by rapid saline infusion performed under heat stress conditions in both young and aged adults.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Apr 01, 2017
- Source ID
- 10.1096/fasebj.31.1_supplement.1085.4
Entities
People
- Craig G Crandall
- Daniel Gagnon
- Hai Ngo
- Paula Y.s. Poh
- Steven A Romero
- Victor A Convertino
Organizations
- United States Army Institute of Surgical Research
- United States Department of Defense
- University of Texas at Austin
- Université de Montréal